Entire Report - September 2011


National Overview

NCDC transitioned to the nClimDiv dataset on Thursday, March 13, 2014. This was coincident with the release of the February 2014 monthly monitoring report. For details on this transition, please visit our public FTP site and our U.S. Climate Divisional Database site.

Maps and Graphics

Temperature and Precipitation Ranks
U.S. Percentage Areas
More Information

National Overview:



September Extreme Weather/Climate Events
  • Climate Highlights — September
  • During September, a persistent upper-level weather pattern brought above-average temperatures to the western third of the country, below-average temperatures to the central United States, and above-normal temperatures to the Northeast. The remnants of Tropical Storm Lee brought significant rainfall from the Gulf Coast into the Northeast, causing above-normal precipitation for most of the eastern United States, and alleviating drought across parts of the Gulf Coast. Dry conditions prevailed across the Plains and into the Northwest, with the national precipitation average near normal.
  • The average U.S. temperature in September was 66.9 degrees F (19.4 degrees C), which is 1.5 degrees F (0.8 degrees C) above the long-term (1901-2000) average. Precipitation, averaged across the nation, was 2.43 inches (61.7 2 mm). This was 0.10 inch (1.15 mm) below the long-term average, with large variability between regions. This monthly analysis is based on records dating back to 1895.
  • Above-normal temperatures dominated the western United States, with five states — California, Idaho, Nevada, Oregon, and Washington — having one of their ten warmest Septembers on record.
  • A persistent upper-level low pressure system was associated with 14 states having below-normal September temperatures across the central United States. Mississippi tied its ninth coolest September on record.
  • Eight states in the Northeast had September temperatures among their ten warmest — Connecticut, New Hampshire, New Jersey, New York, Maine, Massachusetts, Rhode Island, and Vermont
  • Precipitation averaged across the Nation during September was near normal, with most of the rainfall during the month coming from Tropical Storm Lee. Lee made landfall along the Louisiana coast on September 4th, and moved along a frontal boundary into the Ohio Valley and eventually into the Northeast. Rainfall totals over 10 inches (254 mm) were widespread along the track of the storm.
  • A string of eleven adjacent states from Louisiana to New York had a top ten wet September, partially attributable to Tropical Storm Lee. Across Pennsylvania, 9.71 inches (246.63 mm) of rain fell during the month, 6.25 inches (158.64 mm) above average, marking the wettest September on record for the state. The Northeast climate region had its second wettest September on record, with 6.70 inches (170.18 mm). This total is shy of the record of 8.04 inches (204.22 mm) from 1999 when Hurricane Floyd impacted the region.
  • Dry conditions prevailed across the Plains states. Kansas, Minnesota, Montana, South Dakota, and Texas had precipitation totals during September rank among their ten driest since 1895. Nine other states from the Plains to the Northwest also had below-normal precipitation totals during the month.
  • Record breaking drought, combined with strong winds, created ideal wildfire conditions across eastern Texas the first half of the month. Three large wildfires burned approximately 94,000 acres (38,040 hectares) and destroyed over 1,600 homes during September.
  • At the end of September, about a tenth of the United States remained in the worst category of drought, called D4 or exceptional drought, which has remained fairly constant since early summer 2011. Nearly all (97%) of Texas was in extreme to exceptional (D3-D4) drought, which is a record, and nearly four-fifths (79%) of Oklahoma was in extreme to exceptional drought.
  • Two areas of the southern U.S. experienced the most severe drought in the 1900-present record, according to the Palmer Hydrological Drought Index (PHDI). The two regions having the most severe PHDI on record are eastern New Mexico into western Texas and southwest Oklahoma, and northwestern Louisiana into adjacent eastern Texas. These two regions account for 4.2 percent of the area of the contiguous U.S.
  • A list of select September temperature and precipitation records can be found here.
  • Climate Highlights — July-September (3-month period) and Year-to-Date period
  • During the July-September period, the United States as a whole experienced much above normal temperatures. The nationally averaged temperature of 73.4 degrees F (23.0 degrees C) ranks as the second warmest July-September on record.
  • New Mexico and Texas had record warm temperatures during the three month period, with temperatures of 3.5 degrees F (2.0 degrees C) and 4.2 degrees F (2.3 degrees C) above average, respectively. Twenty-two additional states had three-month average temperatures in the top third of their historical record. Six states across the central and southeastern United States had near-normal temperatures during the period, while no state had below-normal temperatures.
  • July-September precipitation for the United States was 0.72 inch (18.40 mm) below normal, but with significant regional variability. Below-normal precipitation was widespread across the central and northwestern United States while wetter-than-normal conditions were prevalent across the Northeast. Vermont, New Jersey, and Maryland had a record wet July-September. The Northeast climate region was also record wet during the period, with 17.62 inches (447.55 mm) of precipitation.
  • For the first nine months of 2011, the U.S. average temperature was 1.0 degree F (0.6 degrees C) above average. Above-normal temperatures were anchored across the Southern Plains and along the Eastern Seaboard, while parts of the Northern Plains and Northwest were cooler than average. The Texas statewide average temperature for January-September tied as record warm at 70.8 degrees F (21.6 degrees C), 2.9 degrees F (1.6 degrees C) above average.
  • Precipitation totals were mixed for January-September 2011, and the nationally averaged value was 0.54 inch (13.76 mm) below average. Above-normal precipitation was widespread across the northern tier of the country, particularly the Northeast, while below-normal precipitation was reported across the southern tier.
  • New Mexico and Texas, as well as the South climate region, all experienced record dry conditions during January-September. Conversely, Vermont, New York, New Jersey, Pennsylvania, Ohio, and the Northeast climate region were record wet during the nine-month period.
  • The Regional Climate Extremes Index, which is sensitive to extremes in temperature, rainfall, dry streaks, drought, and tropical cyclones, indicated that for the Northeast climate region an area nearly three times the average value was affected by extreme climate conditions for the year-to-date period. For the South climate region, the Regional Climate Extremes Index was over twice the average value. The values both represented the second highest values for the January-September period. For the Northeast, contributing factors included a large area of warm minimum temperatures, wet PDSI, 1-day precipitation totals, and days with precipitation. For the South, contributing factors included a large area experiencing warm minimum and maximum temperatures, dry PDSI, and days without precipitation.
  • The warm season (April-September) 2011 Residential Energy Demand Temperature Index (REDTI) is 100.0, which is the highest warm season value in 117 years. (The period of record mean is 52.0). The REDTI model indicates that the national residential energy consumption was 10.3 percent above the mean for the period of record. The correlation between energy usage and the REDIT is 0.51.
  • Updated information on the U.S. Billion Dollar Weather/Climate Disasters during 2011.

Alaska Temperature and Precipitation:

  • Alaska had its 24th warmest September on record, with a temperature 1.3°F (0.76°C) above the 1971–2000 average.
  • Alaska had its 47th warmest July-September on record, with a temperature 0.3°F (0.17°C) below the 1971–2000 average.
  • Alaska had its 38th warmest year-to-date period on record, with a temperature near the 1971–2000 average.
  • Alaska had its 26th driest September since records began in 1918, with an anomaly that was 19.0 percent below the 1971–2000 average.
  • Alaska had its 29th wettest July-September on record, with an anomaly that was 10.8 percent above the 1971–2000 average.
  • Alaska had its 37th driest year-to-date period on record, with an anomaly that was 0.8 percent above the 1971–2000 average.

For additional details about recent temperatures and precipitation across the U.S., see the Regional Highlights section below. For information on local temperature and precipitation records during the month, please visit NCDC's Records page. For details and graphics on weather events across the U.S. and the globe please visit NCDC's Global Hazards page.


Regional Highlights:

These regional summaries were provided by the six Regional Climate Centers and reflect conditions in their respective regions. These six regions differ spatially from the nine climatic regions of the National Climatic Data Center.

  • Northeast Region: (Information provided by the Northeast Regional Climate Center)
  • September was the sixth consecutive month with above normal temperatures in the Northeast. The mean of 63.7 degrees F (17.6 degrees C) was 2.9 degrees F (1.6 degrees C) above normal. It was the Northeast’s 11th warmest September since 1895. Each of the states had means that were above normal for the third month in a row, with departures in the north a few degrees greater than in the southern states. Vermont’s average of 62.0 degrees F (16.7 degrees C) was 4.8 degrees F (2.7 degrees C) warmer than normal, while West Virginia’s average of 65.1 degrees F (18.4 degrees C) was only 1.1 degrees F (0.6 degrees C) above normal. It was the 2nd warmest September since 1895 in Connecticut, the 3rd warmest in New Hampshire and Vermont, and the 4th warmest in Massachusetts.
  • September was a wet month in the Northeast, with measurable rain falling somewhere in the region on all but a few days. Overall, the Northeast averaged 6.66 inches (169 mm), which was 170 percent of normal. It was the 2nd wettest September in the Northeast since record keeping began in 1895. Eleven states had totals that were above normal. Pennsylvania’s total of 9.71 inches (247 mm) was 239 percent of normal and Maryland’s total of 9.55 inches (243 mm) was 232 percent of normal. It was the wettest September in 117 years in Pennsylvania and the 2nd wettest in Maryland. Maine, at 88 percent, was the only state with below normal rainfall. September was one of six months with above normal precipitation in 2011; three of those months, April, August and September, placed 2nd wettest since 1895. When totals from August and September were combined, Maryland, New Jersey, New York, Pennsylvania, Vermont, and the Northeast saw their wettest August-September in 117 years. When January through September precipitation totals were combined, it was the wettest period on record in the Northeast, New Jersey, New York, Pennsylvania, and Vermont. Many new precipitation records were established, including the August through September total of 29.58 inches (75.1 cm) at Philadelphia. Their previous record for the same period was 18.49 inches (47.0 cm) in 1882. January through September totals at Binghamton, NY (52.70 inches, 133.9 cm) and Harrisburg, PA (61.82 inches, 157.0 cm) have already topped their all-time yearly totals.
  • The ground was already saturated from abundant rainfall in August when the remnants of Tropical Storm Lee merged with a stalled front on September 5th. The front stretched from New England to the Gulf Coast and had produced heavy rain before the tropical influence. As the storm moved along the front from the 5th to the 8th, rainfall totals of 6-9 inches (152-229 mm) fell throughout the Susquehanna and Delaware River Basins. A narrow band from central Pennsylvania to the southern tier of New York saw up to, and, in a few locations, over 12 inches (305 mm) from this event. The ensuing flooding along the Susquehanna River and its tributaries reached historic proportions. Floodwaters in Binghamton, and Owego, NY, and Waverly and Wilkes-Barre, PA crested above the record levels set in June 2006. The Swatara Creek at Hershey, PA crested at 26.8 feet (8.2 m), topping the previous record by more than 10 feet (3.0 m). In anticipation of the flooding, over 100,000 Northeast residents were evacuated in Binghamton, Wilkes-Barre and other affected communities, including 1,000 Maryland residents near the Conowingo Dam. Operators there opened its spill gates to lessen the pressure on the dam. Cities, towns, suburbs, roads and fields were under water. At the height of the event, major highways and minor roads, eroded by rushing water or blocked by mudslides, were closed; one hundred roads and 30 bridges in Pennsylvania remained closed at the end of the month. While the main impact from this event was felt in Pennsylvania and New York, parts of New Jersey and Connecticut that were flooded during Irene’s visit in August saw flooding once again from Lee’s rainfall. Fifteen counties in New York and 42 counties in Pennsylvania were declared disaster areas, making them eligible for federal aid. On September 17th, New York’s governor announced additional assistance for flood victims, including $2.4 million to farms affected by Irene and Lee and up to $16 million for a program to provide temporary work to unemployed New Yorkers to assist in rebuilding and reconstruction efforts. The total cost of the damage caused by the flooding has not been determined, but one initial estimate, from Dauphin County, PA, home to Harrisburg, was $151 million. In that county, 294 homes or businesses were destroyed, more than 1000 homes/businesses had major damage, and more than 1200 buildings suffered minor damage. In Anne Arundel County, MD, road damage alone was estimated at $1.5 million.
  • For more information, please go to the Northeast Regional Climate Center Home Page.
  • Midwest Region: (Information provided by the Midwest Regional Climate Center)
  • September 2011 started off where summer left off - hot. A heat wave the first three days of the month set record maximum temperatures across the region, with a number of locations reaching maximums in excess of 100 degrees F (38 degrees C). Temperatures the first three days of September were well above normal across the entire Midwest, with departures from 9 degrees F to 14 degrees F (5 degrees C to 7.8 degrees C) above normal from Missouri east-northeast to Ohio. However, that was the last of the unseasonably warm weather for most of the region. Temperatures the remainder of September were 4 degrees F to 5 degrees F (2.2 degrees C to 2.8 degrees C) below normal across the central Midwest, dropping to near normal on the periphery of the region from northern Minnesota around to eastern Ohio. This same pattern was reflected at the end of the month, with average daily temperatures for September ranging from 2 degrees F to 4 degrees F (1.1 degrees C to 2.2 degrees C) below normal in the central Midwest, and near normal across most of Minnesota, northern Wisconsin, Michigan, and Ohio.
  • For most of September it was dry across the Midwest, with the exception of along and south of the Ohio River. That changed the last ten days of the month, when an upper level low stalled over the southern Great Lakes and brought frequent and sometimes heavy rain to the eastern half of the region. Precipitation the last ten days of the month was 200 to more than 400 percent of normal from Wisconsin and Illinois eastward. West of the Mississippi River, however, rainfall was well below normal and existing areas of drought saw little relief. For the entire month, precipitation was normal to 300 percent of normal from eastern Wisconsin and Illinois east through Ohio and Kentucky. Most of Minnesota, Iowa, and northern Missouri received less than 50 percent of normal precipitation.
  • Smoke from a wildfire in northern Minnesota was transported south into Wisconsin, Illinois, and Indiana on September 13th by strong northwest surface winds. The smoke reduced visibility in northern Illinois and was easily detected as far south as central Illinois and Indiana. The upper level low over the central U.S. at the end of the month generated some unusual weather. On September 24th there were numerous reports of waterspouts over Lake Michigan from Milwaukee south to Chicago. Thunderstorms produced a few weak tornadoes in Indiana, Kentucky, and Michigan during the week. On September 29th, a strong cold front swept through the Midwest and was followed by very windy, cool weather. Winds gusted to between 50 and 60 mph across the northern half of the region, and there were numerous power outages and reports tree damage from the winds. A wind gust of 68 mph was reported at a crib in southern Lake Michigan. The strong north-northwest winds combined with a 200 mile fetch over the lake to generate waves to 25 feet over southern Lake Michigan. In northwestern Iowa, firefighters had difficulty responding to the many field fires resulting from very dry conditions and the strong winds.
  • At the end of September freezing temperatures had generally been recorded as far south as central Iowa, Wisconsin, and the northern half of Lower Michigan. There were scattered occurrences south through central Illinois, and through Indiana to the Ohio River. A hard freeze (28 degrees F (-2.2 degrees C)) had occurred in northeastern Minnesota, northern Wisconsin, and northern Lower Michigan.
  • For details on the weather and climate events of the Midwest, see the weekly summaries in the MRCC Midwest Climate Watch page.
  • Southeast Region: (Information provided by the Southeast Regional Climate Center)
  • Mean temperatures in September ranged from 1-4 degrees F (0.5-2.2 degrees C) below average across Alabama, Georgia, and the Florida Panhandle to 1-3 degrees F (0.5-1.6 degrees C) above average across Virginia, the Carolinas, and the Florida Peninsula. Monthly temperatures were below average across Puerto Rico and the U.S. Virgin Islands. Miami, FL recorded its third warmest September in a record extending back to 1895. September 5th marked the end of an impressive streak of 109 consecutive days of 90 degrees F (32.2 degrees C) or higher temperatures at the station on the University of South Carolina campus in Columbia. This shattered the previous record of 63 consecutive days set back in 1986. A stretch of unseasonably cool weather was observed from the 6th to the 10th of the month in the wake of Tropical Storm Lee. During this period over 150 daily minimum and 200 daily low maximum temperature records were either tied or broken across southern portions of Alabama and Georgia and across the Florida Panhandle. Another stretch of cool weather was observed more broadly across the region from the 16th to the 19th of the month following the passage of a cold front.
  • As in August, monthly precipitation was generally below normal across the Southeast, except in areas affected by tropical cyclone activity. Tropical Storm Lee dropped between 8-13 inches (203.2-330.2 mm) of rain across central Alabama, northwest Georgia, western North Carolina, and much of Virginia from the 3rd to the 9th of the month. Major flooding was reported along several rivers and creeks across central and southern Alabama, forcing numerous high water rescues. Significant flash flooding was also reported in Birmingham, AL, which recorded its second wettest September on record with 12.14 inches (308.4 mm) of precipitation. Nearby Tuscaloosa recorded its wettest September on record and came within 0.01 inches of tying its all-time 24-hour rainfall total of 6.44 inches (163.6 mm) on the 5th of the month in a record extending back to 1948. The heavy rain from Lee coupled with the rainfall from Hurricane Irene last month contributed to an estimated $10 million in damage to roads and bridges across northern Virginia. On the 12th and 13th of the month, Hurricane Maria dropped up to 10 inches (254.0 mm) of rain across Puerto Rico, triggering several landslides along the eastern slopes of the island. Cape Hatteras, NC recorded 14.23 inches (361.4 mm) of rain for the month, making it the fifth wettest September on record. Most of this rainfall was associated with thunderstorms in the middle of the month. On the 25th, nearly 3 inches (76.2 mm) of rain fell in just 30 minutes in downtown Columbia, SC, resulting in major urban flooding and property damage. The driest locations across the Southeast (less than 50 percent of normal) were found across eastern North Carolina, southern Georgia, and portions of northern Florida.
  • There were 331 reports of severe weather across the Southeast in September, including 11 confirmed tornadoes. These tornadoes were weak (EF-0 to EF-1) and nearly all were associated with Tropical Storm Lee. Some notable events, all occurring on the 5th of the month, included an EF-1 that damaged more than 600 homes across Cherokee County, GA; an EF-1 in Wilkes County, NC that damaged several outbuildings in Stone Mountain State Park; and an EF-1 in Carroll County, VA that resulted in two injuries when several gas pumps blew into a local gas station. On the 29th of the month, a man was injured in Tyrell County, NC when an EF-1 tornado lifted his mobile home off its foundation. Storm surge and high winds from Tropical Storm Lee also caused structural damage along the Alabama coast and contributed to at least one drowning death.
  • The beneficial rain from Tropical Storm Lee helped eliminate several areas of drought across the western and northern fringes of the region. In particular, areas of severe drought (D2) were eliminated across southern Alabama and northwest Georgia. Conversely, the region of extreme drought (D3) expanded into parts of northern South Carolina. Reservoir levels continued to fall across parts of Georgia, where rainfall deficits have been the greatest, and water restrictions were implemented in several more communities in the southern part of the state. For the second time this year, a locally-acquired case of dengue fever was confirmed in Miami-Dade County, FL in September. This disease, which is carried by mosquitoes and thrives in warm and wet conditions, is now endemic in the county.
  • For more information, please go to the Southeast Regional Climate Center Home Page.
  • High Plains Region: (Information provided by the High Plains Regional Climate Center)
  • September 2011 temperatures were generally below normal in the eastern portion of the High Plains Region and above normal in the western and northern areas of the Region. Temperature departures were up to 6.0 degrees F (3.3 degrees C) below normal in Kansas, Nebraska, and South Dakota. The cooler than normal temperatures allowed many locations across eastern Nebraska to be ranked in the top 10 coolest Septembers on record. Lincoln, Nebraska had its 6th coolest September with an average temperature of 61.5 degrees F (16.4 degrees C) which was 4.5 degrees F (2.5 degrees C) below normal (period of record 1887-2011). Lincoln’s coolest September occurred in 1993 with an average temperature of 59.9 degrees F (15.5 degrees C). Meanwhile, Colorado, Wyoming, North Dakota, and pockets of western South Dakota and the panhandle of Nebraska had temperature departures which were up to 6.0 degrees F (3.3 degrees C) above normal. Some locations in Wyoming ranked in the top 10 warmest Septembers on record. For instance, Yellowstone National Park, Wyoming tied for its 6th warmest September on record with an average temperature of 57.0 degrees F (13.9 degrees C) (period of record 1894-2011). The warmest September occurred in 1990 with an average temperature of 58.9 degrees F (14.9 degrees C).
  • September was a quiet month for the High Plains Region. Severe weather was reported on only a few days this month and the majority of the Region was dry. Much of Kansas, Nebraska, South Dakota, North Dakota, and Wyoming received only 50 percent of normal precipitation and many areas received less than 25 percent of normal precipitation. Several of these locations ranked in the top 10 driest Septembers on record and a few even broke records. For instance, Sioux Falls, South Dakota had its driest September on record with only 0.20 inches (5 mm) of precipitation (period of record 1893-2011). The old long-standing record of 0.21 inches (5 mm) occurred in 1899. Boysen Dam, Wyoming, which is located in the central part of the state, received no precipitation this month and tied for its driest September (period of record 1948-2011). Interestingly, the other driest September occurred just last year (2010) which makes two Septembers in a row without precipitation. Pockets of Colorado and North Dakota had precipitation which was more than 150 percent of normal. This month’s wet location was Colorado Springs, Colorado. Colorado Springs had its wettest September on record with 5.91 inches (150 mm) of precipitation (period of record 1894-2011). The old record occurred in 2008 with 4.97 inches (126 mm). An impressive 4.50 inches (114 mm) of the monthly total fell in one day, September 14th. Not only did this set a record for the day, the September 14 precipitation set a new record for the highest one-day precipitation total on record (for any day of any month)! The old record of 4.29 inches (109 mm) occurred on September 11, 2008.
  • There were many changes to the U.S. Drought Monitor this month. Areas of improvement include northeastern Colorado and the Black Hills region of South Dakota where abnormally dry conditions (D0) were erased. East central Kansas had a one category improvement from extreme drought (D3) to severe drought (D2) while a pocket of exceptional drought (D4) in south-central Colorado was downgraded to D3. D0 expanded to include much of eastern South Dakota and two pockets of moderate drought (D1) expanded there as well. In addition, an area of D0 expanded through parts of central Nebraska and the panhandle. Meanwhile, the ongoing drought in eastern Colorado and western Kansas remained largely unchanged. According to the U.S. Seasonal Drought Outlook drought conditions in western Kansas and eastern Colorado were expected to improve somewhat. The drought conditions in central Colorado, western Kansas, and eastern South Dakota were expected to persist, while drought conditions in western Colorado were expected to develop
  • For more information, please go to the High Plains Regional Climate Center Home Page.
  • Southern Region: (Information provided by the Southern Regional Climate Center)
  • With the exception of Texas, fall in the Southern Region began as a contrast to the past several months, in that most of the region experienced cooler than normal temperatures. The state average September temperature in Texas was 77.80 degrees F ( 25.44 degrees C), or the nineteenth warmest on record (1895-2011). Stations in the southern half of the state averaged between 2 to 5 degrees F (1.11 to 2.78 degrees C) above normal, while stations in the northern half of the state averaged between 0 to 3 degrees F (0 to 1.67 degrees C) above normal. The highest negative temperature anomalies were observed in northern Arkansas, where many stations averaged between 2 and 5 degrees F ( 1.11 to 2.78 degrees C) below monthly expected values. This was also the case in central Mississippi and in northeastern Oklahoma. Elsewhere, temperatures were only slightly cooler than normal. For Arkansas, it was the twentieth coolest September on record (1895-2011) with a state average temperature for the month of 70.30 degrees F (21.28 degrees C). In Mississippi, it was the ninth coolest September on record (1895-2011), with a state average temperature of 72.30 degrees F (22.39 degrees C). Tennessee and Louisiana reported state average temperatures of 68.30 degrees F (20.17 degrees C) and 75.90 degrees F (24.39 degrees C), respectively. Oklahoma recorded a state average temperature of 71.4 degrees F (21.89 degrees C). State rankings for Oklahoma, Tennessee and Louisiana are as follows: thirty-sixth coolest on record (1895-2011) for Oklahoma, thirtieth coolest on record (1895-2011) for Tennessee, and thirty-second coolest on record (1895-2011) for Louisiana.
  • September precipitation totals in the Southern Region varied dramatically from west to east. Conditions were quite dry in Texas, Oklahoma and Arkansas, with most stations reporting only between 5 to 50 percent of normal. By contrast, conditions were quite wet in Tennessee, Mississippi, and Louisiana, with a bulk of stations reporting between 150 to 200 percent of normal precipitation. This was primarily due to Tropical Storm Lee, which stalled off the Gulf Coast in the early part of the month and eventually made its way inland across the eastern half of the Southern Region. The storm dumped copious amounts of rainfall. Areas within the Florida parishes of Louisiana reported up to 10 inches (254.00 mm) of rainfall, however, most of the values reported in the Southern Region varied from 3 to 7 inches (76.20 to 177.80 mm). By month's end, Louisiana recorded a state average precipitation value of 6.93 inches (176.60 mm). This equates to the tenth wettest September for the state on record (1895-2011). Both Mississippi and Tennessee reported their seventh wettest September on record (1895-2011). Mississippi averaged 7.67 inches (194.82 mm) for the month, while Tennessee averaged 6.73 inches (170.94 mm) for the month. Drought ridden Texas remained dry for the month. The state averaged 1.08 inches (27.43 mm), which is the first time since May that the state averaged more than an inch of precipitation. However, it was still the seventh driest September on record (1895-2011) for the state. For Oklahoma, it was the twentieth driest September on record (1895-2011) with a state average precipitation value of 1.72 inches (43.69 mm). Arkansas experienced its thirty-seventh driest September on record (1895-2011) with a state average precipitation value of 2.63 inches (66.81 mm).
  • Due to dry conditions in Arkansas, Oklahoma and Texas, drought conditions have changed very little over the western half of the Southern Region in the past month. Approximately 53 percent of the Region remains in exceptional drought, most of which is Texas and western and central Oklahoma. Exceptional drought is also still persisting in northwestern Louisiana. Drought conditions did, however; improve in Tennessee, Mississippi and southern/southeastern Louisiana. In the case of the latter, southern and southeastern Louisiana is now drought free. This is also the case for most of Mississippi. In Tennessee, a small area of moderate drought remains in the northwestern corner of the state.
  • Several tornadoes touched down on September 3 and 4, in southern Louisiana and southern Mississippi. There were no reported injuries or fatalities, and damage was mostly limited to power lines and trees. One mobile home was turned over in Hancock County, Mississippi.
  • According to the Star-Telegram, drought is having a big impact on tree health in northern Texas. It is reported that many trees in Trinity Park, are losing leaves and turning brown. It is further reported that in Houston, approximately ten percent of the trees are expected to die. A high mortality rate is also being seen in Hill County.
  • On September 1, 2011, Tropical Storm Lee formed just off the southern coast of central Louisiana. The storm moved very slowly toward the coast. On September 3, 2011, the storm stalled just before landfall. The stalling of the storm allowed for some minor intensification, but more importantly, the stalled caused rainfall amounts to be quite high in the southeastern portion of the state. The storm finally made landfall in south central Louisiana on September 4, 2011. Lee continued to move slowly, moving north east. Shortly after landfall, Lee was downgraded to a tropical depression, but the rains did not let up. The storm passed through southern and central Mississippi, and then through eastern Tennessee. By the time the storm had moved out of the Southern Region, the storm had dumped up to 10 inches (254.00 mm) of rainfall in southeastern Louisiana, 3 to 10 inches (76.20 to 254.00 mm) of rainfall in central and southern Mississippi, and approximately 3 to 7 inches (76.20 to 177.80 mm) of rainfall in central and eastern Tennessee. Storm surges from Lee caused several homes to be flooded in parts of Slidell, Louisiana. Lee also caused major power outages in New Orleans, with approximately 38,000 customers losing power. Widespread flooding was also reported in Mississippi, in particular, in Hancock and Jackson Counties.
  • For more information, please go to the Southern Regional Climate Center Home Page.
  • Western Region: (Information provided by the Western Regional Climate Center)
  • September was generally dry in the West with isolated pockets of high precipitation in the southern part of the region due to a strong mid-month monsoon surge. Temperatures ranged from near normal and slightly below normal on the coast and in the Southwest to record breaking in the Northwest.
  • Temperatures along the California and southern Oregon coast remained below normal as has been the case all summer. The Santa Barbara, California airport had one of the greatest negative temperature departures from normal this month in the West. Average temperature was 62.9 F (17.2 C), the 8th coolest September temperature in the record beginning in 1941.
  • Many high temperature records were set throughout the Northwest, especially along the Oregon-Washington border, Northern California, Idaho and Wyoming. Northern Nevada and Montana also saw several high temperature ties and records. Seattle-Tacoma Airport experienced a streak of nine consecutive 80 F (26.6 C) and greater days ending September 11, breaking a record of eight consecutive days in 1989. The average temperature for the month at Seattle-Tacoma was 64.0 F (17.8 C), the 5th warmest September on record since 1948. Pullman, Washington had a monthly average of 62.7 F (17 C), the 4th warmest September on a record beginning in 1941. Nearby Lewiston, Idaho experienced its 3rd warmest September on record with a monthly average of 69.4 F (20.7 C). Phoenix saw several high temperatures tied, as did Las Vegas; though near and slightly above normal temperatures prevailed in Arizona, New Mexico, southern Nevada, Utah and Colorado.
  • The Southwest monsoon season is typically taken as ending September 30, allowing rainfall totals for the season to be compared to previous years. The monsoon activity was slow for most of the season (since June 15). A final burst in mid-September brought record rainfall to Tucson, Arizona as well as significant precipitation to the Four Corners region into central Colorado. September 15 saw 2.83 in (71.9 mm) at the Tucson Airport, breaking a daily record of 1.18 in (29.9 mm) set in 1944. The same station received 5.6 in (142.2 mm) of precipitation for the month, the wettest September on record. The monsoon season total for Tucson, 8.62 in (218.9 mm), ranks as the 10th wettest in a record dating back to 1895.
  • Colorado Springs also experienced intense precipitation due to the monsoon surge. On September 14, Colorado Springs received a daily record 4.5 in (114.3 mm), shattering the previous record of 0.46 in (11.68 mm) set in 1967. Their September was 5.91 in (150.1 mm), surpassing the previous 1984 record of 5.01 in (127.2 mm) in a record dating from 1948.
  • The Northwest, northern Nevada, and California remained generally dry and at below average precipitation values due to persistent upper level high pressure throughout the month that held precipitation to the north. Salem, Oregon received 0.35 in (8.9 mm) of total precipitation, the 9th driest September since records began at that location in 1893. Very few locations in the Northwest received above average precipitation. One such station, Quillayute on Washington’s Olympic Peninsula, received a total of 7.68 in (195 mm) for the month, the 9th wettest September at this location and 167% of the average rainfall of 4.59 in (116.6 mm).
  • September (all month) Northwest Wildfires: Large acreages of lightning caused fires burned throughout the month in Montana, Oregon, and Idaho. In some areas, especially Missoula, MT, extensive smoke and haze to populated areas and reducing air quality and visibility.
  • September (all month), Severe drought: The Southwest experienced moderate to exceptional drought during the month of September, with only little relief provided by monsoon rains in the first half of the month. The severity of the drought was reduced in parts of Arizona and southern Colorado by the end of the month; severe drought conditions persist in New Mexico.

See NCDC's Monthly Records web-page for weather and climate records for the most recent month. For additional national, regional, and statewide data and graphics from 1895-present, for any period, please visit the Climate at a Glance page.


PLEASE NOTE: All of the temperature and precipitation ranks and values are based on preliminary data. The ranks will change when the final data are processed, but will not be replaced on these pages. Graphics based on final data are provided on the Temperature and Precipitation Maps page and the Climate at a Glance page as they become available.

Global Analysis

Contents of this Section:


September 2011 Selected Climate Anomalies and Events MapSeptember 2011 Selected Climate
Anomalies and Events Map

Global Highlights

  • The combined global land and ocean average surface temperature for September 2011 was the eighth warmest on record at 15.53°C (59.95°F), which is (0.53°C) 0.95°F above the 20th century average of 15.0°C (59.0°F). The margin of error associated with this temperature is +/- 0.11°C (0.20°F).
  • Separately, the global land surface temperature was 0.87°C (1.57°F) above the 20th century average of 12.0°C (53.6°F), making this the fourth warmest September on record. The margin of error is +/- 0.24°C (0.43°F). Warmer-than-average conditions occurred across Europe, northern and western Africa, the Middle East, western Russia, the western and northeastern United States, and Mexico. Cooler-than-average regions included much of eastern Asia, western Canada and southeastern Alaska, and part of the central United States.
  • Separately, the global land surface temperature was 0.87°C (1.57°F) above the 20th century average of 12.0°C (53.6°F), making this the fourth warmest September on record. The margin of error is +/- 0.24°C (0.43°F).
  • The September global ocean surface temperature was 0.40°C (0.72°F) above the 20th century average of 16.2°C (61.1°F), making it the 14th warmest September on record. The margin of error is +/- 0.04°C (0.07°F). The warmth was most pronounced across the north central and northwest Pacific Ocean and within about the 30°N–40°N latitude belt across the Atlantic.
  • The September global ocean surface temperature was 0.40°C (0.72°F) above the 20th century average of 16.2°C (61.1°F), making it the 14th warmest September on record. The margin of error is +/- 0.04°C (0.07°F).
  • The United Kingdom marked its warmest September since 2006 and sixth warmest in the last 100 years, at 1.5°C (2.7°F) above the 1971–2000 average.
  • Spain had its warmest September since 1990 for the and fifth warmest over the past 50 years, at 1.8°C (3.2°F).
  • The combined global land and ocean average surface temperature for the January – September period was 0.51°C (0.92°F) above the 20th century average of 14.1°C (57.5°F), making it the 11th warmest such period on record. The margin of error is +/- 0.10°C (0.18°F).
  • The January – September worldwide land surface temperature was 0.80°C (1.44°F) above the 20th century average — the 7th warmest such period on record. The margin of error is +/- 0.20°C (0.36°F). The global ocean surface temperature for the year to date was 0.41°C (0.74°F) above the 20th century average and was the 12th warmest such period on record. The margin of error is +/- 0.04°C (0.07°F).
  • La Niña conditions strengthened during September 2011. According to NOAA's Climate Prediction Center, La Niña is expected to gradually strengthen further and continue into the Northern Hemisphere winter 2011/12.
  • Arctic sea ice reached its annual minimum extent on September 9th at 4.33 million square km (1.67 million square miles), marking the second smallest extent on record. In September 2007, the sea ice extent dipped to 4.17 million square km (1.61 million square miles). According to the University of Washington's Polar Science Center, Arctic sea ice volume, which depends on ice thickness and extent, dropped to 4,000 cubic km (960 cubic miles) on September 10th, the smallest volume on record.
  • The average Arctic sea ice extent during September was 34.5 percent below average, ranking as the second smallest September extent since satellite records began in 1979. The extent was 2.43 million square kilometers (938,000 square miles) below average and 310,000 square kilometers (120,000 square miles) above the record low September extent set in 2007.
  • On the opposite pole, sea ice extent typically reaches its annual maximum extent during September, but environmental conditions extended the ice growth season into October. The September Antarctic monthly average extent was 0.9 percent above the 1979–2000 average, the 14th largest on record.

Please Note: The data presented in this report are preliminary. Ranks and anomalies may change as more complete data are received and processed. Effective with the September 2009 State of the Climate Report, NCDC transitioned to the new version (version 3b) of the extended reconstructed sea surface temperature (ERSST) dataset. ERSST.v3b is an improved extended SST reconstruction over version 2. For more information about the differences between ERSST.v3b and ERSST.v2 and to access the most current data, please visit NCDC's Global Surface Temperature Anomalies page.

==global-temps-errata==

Introduction

Temperature anomalies for September 2011 are shown on the dot maps below. The dot map on the left provides a spatial representation of anomalies calculated from the Global Historical Climatology Network-Monthly (GHCN-M) version 3 dataset of land surface stations using a 1961–1990 base period. The dot map on the right is a product of a merged land surface and sea surface temperature (SST) anomaly analysis developed by Smith et al. (2008). For the merged land surface and SST analysis, temperature anomalies with respect to the 1971–2000 average for land and ocean are analyzed separately and then merged to form the global analysis. For more information, please visit NCDC's Global Surface Temperature Anomalies page.


September

The return of La Niña conditions in the central equatorial Pacific Ocean in August brought slightly cooler temperature anomalies than in previous months where ENSO-neutral conditions prevailed. As would be expected for such conditions, temperature anomalies were lower across the globe—although still well above the 20th century average—compared with recent months. According to NOAA's Climate Prediction Center, La Niña conditions strengthened across the eastern half of the equatorial Pacific during September and are predicted to gradually continue to strengthen through the Northern Hemisphere winter 2011/12.

The global monthly averaged land surface temperature was 0.87°C (1.57°C) above average, the fourth warmest September on record. This positive anomaly was the smallest for any month since May 2011, when the previous La Niña ended. The Northern Hemisphere land temperature, where the majority of land mass is located, had its third warmest September on record and the Southern Hemisphere tied with 1995 as the third warmest. Europe, northern and western Africa, western Russia, the western and northeastern United States, Canada, and Mexico observed the warmest anomalies, while it was cooler than average across much of eastern Asia, and parts of the central United States.

In Western Europe, the United Kingdom marked its warmest September since 2006 and sixth warmest in the last 100 years, at 1.5°C (2.7°F) above the 1971–2000 average, according to the UK Met Office.

It was also warmer than average in Southern Europe. AEMet, Spain's Meteorological Agency, reported that it was the warmest September since 1990 for the country and fifth warmest in the past 50 years, at 1.8°C (3.2°F) above the 1971–2000 average.

In the Southern Hemisphere, although not possible to decipher from these dot maps, Australia experienced a wider range of daily temperatures than normal. According to the country's Bureau of Meteorology (BoM), the average maximum temperature for September across Australia was 0.92°C (1.65°F) warmer than normal. However, the average minimum temperature was 0.57°C cooler than normal, which was the lowest minimum temperature since 1985.

The monthly averaged global ocean temperature was 0.40°C (0.72°F) above the 20th century average, the 14th warmest September in the 132-year period of record but the coolest since 1999. Monthly sea surface temperature anomalies were similar in both the Northern and Southern Hemispheres, ranking 13th and 14th warmest, respectively. Across the globe, the coolest anomalies occurred across the central and eastern equatorial Pacific (the region where ENSO conditions are measured), the northeastern Pacific, the southeastern Atlantic, and the parts of southern oceans. The warmest anomalies were observed in the north central and northwest Pacific Ocean and within about the 30°N–40°N latitude belt across the Atlantic.

Combined, the monthly averaged global land and ocean temperature was the eighth warmest September on record, at 0.53°C (0.95°F) above the 20th century average. The Northern Hemisphere had its sixth warmest September and the Southern Hemisphere, which is comprised of nearly 80 percent ocean and almost 20 percent land, had its ninth warmest September on record.

Year-to-date (January–September)

La Niña conditions have been present during all months to-date in 2011, with the exception of May, June, and July, when ENSO-neutral conditions briefly returned. These conditions impacted temperatures around the globe, making the January–September combined global land and ocean temperature the 11th warmest such period on record and the coolest since 2008, at 0.51°C (0.92°F) above average. The January-September 2011 Blended Land and Ocean Surface Temperature Anomalies in degree CelsiusJanuary–September 2011 map of temperature anomalies shows regions with anomalously warm and anomalously cool temperatures. Overall, the global land surface temperature anomaly (0.80°C / 1.44°F) was nearly twice as high as the global sea surface temperature anomaly (0.41°C / 0.74°F) for this period, ranking as 7th warmest and 12th warmest, respectively.

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The average position of the upper-level ridges of high pressure and troughs of low pressure (depicted by positive and negative 500-millibar height anomalies on the September 2011 height and anomaly mapSeptember 2011 map, respectively) are generally reflected by areas of positive and negative temperature anomalies at the surface, respectively. For other Global products, please see the Climate Monitoring Global Products page.

Images of sea surface temperature anomalies are available for each week from 2004 to present on the weekly SST page.


Temperature Rankings and Graphics

Current Month | Year-to-date

September Anomaly Rank
(out of 132 years)
Records
°C °F Year(s) °C °F
Global
Land +0.87 ± 0.24 +1.57 ± 0.43 Warmest 4th 2005 +1.00 +1.80
Coolest 129th 1912 -0.78 -1.40
Ocean +0.40 ± 0.04 +0.72 ± 0.07 Warmest 14th 2003 +0.57 +1.03
Coolest 119th 1912 -0.45 -0.81
Land and Ocean +0.53 ± 0.11 +0.95 ± 0.20 Warmest 8th 2005 +0.66 +1.19
Coolest 125th 1912 -0.54 -0.97
Northern Hemisphere
Land +0.88 ± 0.25 +1.58 ± 0.45 Warmest 3rd 2005 +1.16 +2.09
Coolest 130th 1912 -0.91 -1.64
Ocean +0.43 ± 0.04 +0.77 ± 0.07 Warmest 13th 2003 +0.66 +1.19
Coolest 120th 1912 -0.56 -1.01
Land and Ocean +0.60 ± 0.15 +1.08 ± 0.27 Warmest 6th 2005 +0.82 +1.48
Coolest 127th 1912 -0.69 -1.24
Southern Hemisphere
Land +0.85 ± 0.15 +1.53 ± 0.27 Warmest 3rd 1997 +1.07 +1.93
Coolest 130th 1894 -0.81 -1.46
Ocean +0.39 ± 0.04 +0.70 ± 0.07 Warmest 14th 1997 +0.57 +1.03
Coolest 119th 1911 -0.51 -0.92
Land and Ocean +0.46 ± 0.07 +0.83 ± 0.13 Warmest 9th 1997 +0.65 +1.17
Coolest 124th 1911 -0.54 -0.97
Ties: 2000, 2001, 2004

January–September Anomaly Rank
(out of 132 years)
Records
°C °F Year(s) °C °F
Global
Land +0.80 ± 0.20 +1.44 ± 0.36 Warmest 7th 2007 +1.04 +1.87
Coolest 126th 1893 -0.62 -1.12
Ocean +0.41 ± 0.04 +0.74 ± 0.07 Warmest 12th 1998 +0.55 +0.99
Coolest 121st 1911 -0.49 -0.88
Land and Ocean +0.51 ± 0.10 +0.92 ± 0.18 Warmest 11th 1998, 2010 +0.66 +1.19
Coolest 122nd 1911 -0.47 -0.85
Northern Hemisphere
Land +0.91 ± 0.21 +1.64 ± 0.38 Warmest 6th 2007 +1.19 +2.14
Coolest 127th 1893 -0.68 -1.22
Ocean +0.40 ± 0.04 +0.72 ± 0.07 Warmest 12th 2005, 2010 +0.56 +1.01
Coolest 121st -0.48 -0.86 0.05
Land and Ocean +0.59 ± 0.14 +1.06 ± 0.25 Warmest 10th 2010 +0.75 +1.35
Coolest 123rd -0.48 -0.86 0.06
Southern Hemisphere
Land +0.51 ± 0.14 +0.92 ± 0.25 Warmest 13th 2005 +0.90 +1.62
Coolest 120th 1917 -0.71 -1.28
Ties: 1992, 1995
Ocean +0.43 ± 0.04 +0.77 ± 0.07 Warmest 11th 1998 +0.58 +1.04
Coolest 122nd 1911 -0.52 -0.94
Land and Ocean +0.44 ± 0.07 +0.79 ± 0.13 Warmest 12th 1998 +0.63 +1.13
Coolest 121st 1911 -0.53 -0.95

The most current data may be accessed via the Global Surface Temperature Anomalies page.

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Precipitation

The maps below represent anomaly values based on the GHCN-M version 2 dataset of land surface stations using a base period of 1961–1990. Precipitation anomalies on a month-to-month basis are often highly variable across the globe and even within regions.

September brought a mix of wet and dry conditions around the globe. Tropical cyclones Talas and Roke impacted Japan and nearby regions with intense precipitation; Nesat brought extremely heavy rainfall to the Philippines; and Irene and Lee drenched the northeastern United States. Irene also dumped heavy rain over the Dominican Republic. The southwest Asian monsoon brought heavy precipitation to Pakistan and eastern India. Other regions with much higher-than-normal precipitation included Colombia in South America and part of southeastern Africa around Mozambique, Zimbabwe, and Tanzania. Below-average precipitation anomalies across the southern tier of the United States are indicative of ongoing major drought conditions. It was also exceptionally dry across the western United States, much of eastern and southern South America, particularly eastern Brazil, much of central Asia, including nearly all of Mongolia, and much of Australia.

The Bureau of Meteorology reported that Australia as a whole experienced 26 percent below-average rainfall for the month, with the two driest regions in separate parts of the country: the Northern Territory in the north (78 percent below average) and South Australia in the south (50 percent below average). New South Wales was the only state with above-average rainfall.

According to AEMet, it was much drier than normal in Spain, with average rainfall across the country (16 mm / 0.63 in) about one-third of normal, making this month the driest September since 1988.

Details on major flooding and drought events around the world are available in the September 2011 Global Hazards report.

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References

Peterson, T.C. and R.S. Vose, 1997: An Overview of the Global Historical Climatology Network Database. Bull. Amer. Meteorol. Soc., 78, 2837-2849.

Quayle, R.G., T.C. Peterson, A.N. Basist, and C. S. Godfrey, 1999: An operational near-real-time global temperature index. Geophys. Res. Lett., 26, 333-335.

Smith, T.M., and R.W. Reynolds (2005), A global merged land air and sea surface temperature reconstruction based on historical observations (1880-1997), J. Clim., 18, 2021-2036.

Smith, et al (2008), Improvements to NOAA's Historical Merged Land-Ocean Surface Temperature Analysis (1880-2006), J. Climate., 21, 2283-2293.

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Global Hazards

Please note: Material provided in this report is chosen subjectively and included at the discretion of the National Climatic Data Center (NCDC). The ability to report on a given event is limited by the amount of information available to NCDC at the time of publication. Inclusion of a particular event does not constitute a greater importance in comparison with an event that has not been incorporated into the discussion. Data included in this report are preliminary unless otherwise stated. Links to supporting information are valid at the time of publication, but they are not maintained or changed after publication.


Updated 5 October 2011


Early SeptemberDozens of wildfires burn in Texas read more Early SeptemberRecord high temperatures continue Texas and Oklahoma read more Early to mid-SeptemberMonsoon floods devastate Sindh province in Pakistan read more September 1st–11thTropical Storm Lee dumps very heavy rain in the from Louisiana to New York read more SeptemberFlooding in Thailand since late July kills at least 112 people read more mid-SeptemberSichuan province in China sees worst floods since 1847 read more September 2ndTropical Storm Talas strikes Japan read more September 12thPost Tropical Cyclone Katia hits northern UK read more September 21stTyphoon Roke makes landfall in Japan read more September 27thTyphoon Nesat roars ashore over the main Philippine island of Luzon read more SeptemberThousands of walruses documented on shore near Point Lay, Alaska read more



Drought conditions

Daily Fire Danger Map for Texas
Texas Daily Fire Danger Map
5 September 2011
Image Credit:
Texas Forest Service

Strong winds from Tropical Storm Lee, combined with record heat, drought, low humidity, and continued lack of rain, sparked numerous wildfires in Texas during the beginning of September. Dozens of fires burned across the state, including the most destructive fire in the state's history. The Bastrop County Fire burned over 34,000 acres (13,760 hectares) and destroyed almost 1,600 homes, dwarfing the now second most destructive fire that occurred this past April near Possum Kingdom Lake, which charred 168 homes. The Bastrop County Fire covered an area of 24 miles by 20 miles (39 kilometers by 32 kilometers). Two people were killed in that blaze on September 5th. Since November 2010, more than 3.6 million acres (1.46 million hectares) have been burned across Texas, including over 135,000 acres (54,600 hectares) during the first week in September. All but 3 of the 254 counties in Texas reported burn bans during the month.

Please visit NCDC's Drought and Wildfire pages for more detailed information.

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Extreme Temperatures

The sweltering heat that gripped the southern United States throughout the summer continued to set records into the first half of September. On the 13th, Wichita Falls, Texas recorded its 100th day of 100°F (37.8°C) temperatures in 2011, shattering the old record of 79 days set in 1980. This is the first time in recorded history that any Texas locale has achieved this distinction. That same day, Dallas/Fort Worth, Texas recorded its most 100°F days in a calendar year, 70, breaking the previous record set in 1980. It is interesting to note how that record was broken—the temperature reached 107°F (41.7°C) on the 70th day, surpassing the previous daily record set in 1965 by a full 7°F (4°C). For the summer (June through August), the state of Texas recorded the hottest summer for any state since records began in 1895. Neighboring Oklahoma had the second hottest summer for any state on record. At least 46 deaths in Texas and 20 deaths in Oklahoma were attributed to the heat.

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Heavy rainfall and flooding

Seasonal monsoon rains led to major flooding in southern Pakistan's Sindh province in early to mid-September. The districts of Badin, Tandoallahyar, Sakrand, and Ghotki were among the hardest hit. From August 10th through mid-September, floods killed an estimated 347 people, according to Pakistan's disaster authority, and destroyed or damaged almost one million homes. More than 7.5 million people were impacted. Additionally, 4.2 million acres (1.7 million hectares) of land have been affected by the floods, including 1.6 million acres (647,000 hectares) of cropland. Catastrophic flooding also occurred in Pakistan in 2010, due concentrated rains in the north flowing southward along the Indus River and its tributaries. This year, the flooding occurred due to widespread heavy rainfall across the region. In India, more than a week of heavy rains in mid-September impacted about 2,600 villages in the eastern state of Orissa, leaving 16 people dead and 61,000 residents forced to evacuate their homes. Since the beginning of the South Asian Monsoon season this year, at least 335 people were killed across five states by the end of September.


Rainfall measurements (inches) and storm track for Tropical Storm Lee over the eastern United States.
Tropical Storm Lee
1–11 September 2011
Image Credit: NOAA's
Hydrometeorological Prediction Center

During September 1st–11th, slow moving Tropical Storm Lee made landfall in southern Louisiana and dropped copious amounts of rain over parts of Louisiana, Mississippi, Alabama, and Tennessee as it weakened and tracked up into the northeastern U.S. Lee brought more rain to regions are already waterlogged and still recovering from the effects of Hurricane Irene. New Orleans, Louisiana received more than a foot of rain. According to NOAA's Storm Prediction Center, there were 54 preliminary tornado reports related to the storm across eight states from the 3rd through the 7th. The tornadoes damaged hundreds of homes and hundreds of thousands of residents lost power. After recording its all-time driest month in August with just 0.01 inches (0.25 mm) of precipitation, Chattanooga, Tennessee received 9.49 inches (241.0 mm) of rain on September 5th, breaking the previous daily record of 1.59 inches (40.4 mm) set in 1959. In the Northeast, river and streams burst their banks, leading to major flooding. More than 100,000 people living along the Susquehanna River in northeastern Pennsylvania were evacuated as the river rose to record levels. In Wilkes-Barre, the river crested at almost 42.7 feet (13.0 meters), higher than the previous record level of 40.9 feet (12.5 meters) set in 1972 due to Hurricane Agnes. In total, 14 people were killed due to effects of the storm.

In northern and northeastern Thailand, monsoon rains and related flooding and landslides led to at least 224 deaths since late July when Tropical Storm Nock-Ten hit the country. More than 300,000 homes were either damaged or destroyed across 29 provinces and 3 million acres (1.2 million hectares) of cropland were submerged. The monsoon season lasts from August to October in Thailand.

In China, more than a week of heavy rains during mid-September led to at least 57 deaths and affected 12.3 million residents in the southwestern and central provinces of Sichuan, Henan, and Shaanxi. According to Xinhua, the floods were expected to be the worst in Sichuan since records began in 1847. More than 120,000 houses were destroyed and economic losses were initially estimated to be $2.7 billion U.S. dollars.

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Tropical Cyclones

Tropical Storm Talas nearing Japan on 2 September 2011
Tropical Storm Talas
2 September 2011
Image Credit:
NASA Earth Observatory

Typhoon Talas, the deadliest cyclone to hit Japan since 2004, was a slow moving system that dumped copious rainfall across western Japan on September 2nd. Wakayama and Nara prefectures sustained much of the damage. At least 59 people were killed and about 50 remained missing with thousands more stranded by the storm. A U.S.-based catastrophe modeling company estimated that damages may range from $150–600 million U.S. dollars. Talas was the 12th named storm and 5th typhoon of the Pacific typhoon season.


Post Tropical Storm Katia moving across northern United Kingdom.
Post Tropical Storm Katia
12 September 2011
Image Credit: NOAA
Environmental Visualization Laboratory

In the North Atlantic, Hurricane Katia avoided North America and instead impacted the northern United Kingdom on September 12th, with winds gusting higher than 80 mph (129 km/hr) across Scotland, Northern Ireland, northern England, part of Wales, and the Republic of Ireland. One person was killed in Northern Ireland due to the effects of the storm. The winds were the highest recorded in the region since Hurricane Lili tore through in 1996.

Typhoon Roke struck Japan near the city of Hamamatsu on September 21stand made its way northeastward past Tokyo. The storm exited the northern island of Hokkaido on the 24th but not before dropping up to 17 inches (420 mm) of rain in some areas. The torrential rains triggered flooding and mudslides that left at least 16 people dead or missing. There was fear that the storm would hit the Fukushima nuclear site, which was damaged in March 2011, but fortunately the storm was of little consequence in that area.


Rainfall totals (mm) for Typhoon Nesat as it crosses over the northern Philippine island of Luzon
Post Typhoon Nesat Rainfall Totals
27 September 2011
Image Credit: NASA TRMM

Typhoon Nesat (locally referred to as Pedring) made landfall on the northern Philippine island of Luzon on September 27th. Just prior to striking the island, Nesat was equivalent to a Category 3 storm on the Saffir-Simpson scale, with sustained winds of 121 mph (195 km/hr). According to NASA TRMM satellite analysis, the highest rainfall amounts of about 14.8 inches (375 mm) occurred over the central eastern Luzon coast. Large portions of the island recieved more than 5.9 inches (150 mm) of precipitation. Water was waist high in the streets of Manila, the nation's captial. At least 39 people were killed and more than 100,000 families were affected. Preliminary crop and infrastructure damage was estimated at $76.8 million U.S. dollars. The storm then moved into the South China Sea and headed toward the southern Chinese island province of Hainan. On September 29th, Nesat made a second landfall on the island's eastern tip, with wind speeds up to 94 mph (150 km/hr). Little damage was reported. The storm made a third and final landfall over Vietnam, where 4,000 residents were evacuated and the storm quickly weakened. Nesat lost all tropical storm status on September 30th.

Please visit NCDC's Hurricanes & Tropical Storms page for more detailed tropical cyclone statistics.

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Ecosystems Impacts

Aerial photo of walruses beached near Point Lay, Alaske in September 2011
Walruses near Point Lay, Alaska
September 2011
Image Credit: NOAA's
National Marine Mammal Laboratory

Preliminary data from the National Snow & Ice Data Center indicate that on September 9th Arctic sea ice extent reached its second lowest value on record, behind 2007. This year continues a trend of declining sea ice, with satellite records dating back to 1979. In late summer, an estimated 20,000 walruses were documented on the coastal shores near Point Lay in northwestern Alaska by the U.S. Geological Survey's Alaska Science Center. Walruses typically spend the warm summer months far offshore, foraging for food on the shallow continental shelf of the Chiukchi Sea and resting on ice floats. However, these ice floats are melting, forcing the walruses to come ashore in search of food (they require about 100 lbs per day). This poses a problem because, with so many animals crowded together, the young calves can be trampled to death. This is the fourth year (also 2007, 2009, and 2010) this phenomenon has been observed in recent times. Walruses are currently being considered for inclusion on the endangered species list.

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Synoptic Discussion

Note: This Synoptic Discussion describes recent weather events and climate anomalies in relation to the phenomena that cause the weather. These phenomena include the jet stream, fronts and low pressure systems that bring precipitation, high pressure systems that bring dry weather, and the mechanisms which control these features — such as El Niño, La Niña, and other oceanic and atmospheric drivers (PNA, NAO, AO, and others). The report may contain more technical language than other components of the State of the Climate series.


NCDC transitioned to the nClimDiv dataset on Thursday, March 13, 2014. This was coincident with the release of the February 2014 monthly monitoring report. For details on this transition, please visit our public FTP site and our U.S. Climate Divisional Database site.


Synoptic Discussion

Upper-level circulation pattern and anomalies for September 2011
Upper-level circulation pattern and anomalies for September 2011.

The weather patternweather pattern over the contiguous United States during September 2011 was a battle between an upper-level high pressure ridge (which dominated the country during the summer) and strong upper-level low pressure systems moving in the seasonally-reinvigorated jet stream flow. The month began with warm high pressure pervasive across most of the country. A strong upper-level low pressure trough plunged into the Southeast early in the month, bringing cooler-than-normal weather in its wake, while warm high pressure built up in the West. This was followed by another ridge-West/trough-East pattern during the last third of the month (weeks 4 and 5). This west-east pattern dominated the upper-level circulation for the month and contributed to the third warmest September in the 117-year record in Oregon. Early in the month, heavy rains resulted when Tropical Storm Lee joined with the upper-level trough, cutting a wet swath from the mid-Gulf Coast to the Northeast. Pennsylvania had the wettest September on record with Maryland ranking second wettest and Ohio third wettest. The rains from Lee were compounded by moisture from Hurricane Irene the previous month, resulting in widespread flooding across Pennsylvania, Maryland, and Virginia. Over four dozen preliminary tornado reports were generated by Lee, contributing to a near-normal month for tornado activity. Rain-producing systems mostly missed the central and western regions, with five states in the Great Plains ranking in the top ten driest category for September.

September 2011 temperature anomalies
September 2011 temperature anomalies.

Numerous temperature extremes at both ends of the scale occurred. More than 2300 daily high temperature records were tied or broken in September 2011 compared to over 2100 reports of daily high temperatures that were coldest on record. September had 151 reports of the hottest monthly maximum temperature on record and 5 reports of the coldest monthly maximum temperature on record. There were nearly 1950 reports of record warm daily minimum temperatures and roughly 1400 reports of record cold daily minimum temperatures. All-time record temperatures occurred as well, with 11 hottest maximums but no coldest minimums reported. The mixture of hot and cold temperature anomalies gave the Residential Energy Demand Temperature Index (REDTI) a value near the middle of the historical distribution, indicating that the national residential energy consumption was about average for September 2011. However, the April-September 2011 REDTI was the highest value for this season in the 117-year record, indicating that the national residential energy consumption was about 10.3 percent above the long-term average for the warm season.

Palmer Hydrological Drought Index for Rio Grande River Basin, January 1900-September 2011
Palmer Hydrological Drought Index for Rio Grande River Basin, January 1900-September 2011.

The circulation pattern, with its numerous cold fronts that swept across the nation, brought rain to some areas, but most areas outside the influence of Tropical Storm Lee were drier than normal. Minnesota (5th driest), Montana and Texas (both 7th driest), and Kansas and South Dakota (both 9th driest) ranked in the top ten driest category for September 2011. The dryness has persisted for the last twelve months, with Texas ranking driest on record and New Mexico and Oklahoma second driest for October 2010-September 2011. Strong winds associated with Tropical Storm Lee fanned wildfires across Texas, but national wildfire statistics for September were near average. Moderate to exceptional drought covered about 29 percent of the contiguous U.S. (24 percent of the U.S. including Alaska and Hawaii) at the end of September, with two core areas being the Southern Plains (76 percent coverage) and Southeast (42 percent coverage). Nearly all (97 percent) of the Lone Star State was in extreme to exceptional drought (the worst categories), which is a record in the eleven years of the U.S. Drought Monitor, and four-fifths (79 percent) of Oklahoma was in extreme to exceptional drought. Two areas of the southern U.S. experienced the most severe drought in the 1900-present record, according to the Palmer Hydrological Drought Index (PHDI). The two regions having the most severe PHDI on record were eastern New Mexico into western Texas and southwest Oklahoma, and northwestern Louisiana into adjacent eastern Texas.

Northeast region Climate Extremes Index, April-September, 1910-2011
Northeast region Climate Extremes Index, April-September, 1910-2011.

When averaged together, the mixture of temperature and precipitation extremes gave the U.S. the 11th warmest and 50th driest September in the 117-year record. Averaging extremes tends to cancel them out. But when extremes are combined cumulatively, like in the U.S. Climate Extremes Index (CEI), they tell a different story. The large total area of hot daytime temperatures, warm nighttime temperatures, and very wet or very dry conditions gave the U.S. the second highest July-September and April-September CEI, seventh highest January-September CEI, and tenth highest September CEI in the 1910-2011 record. On a regional basis, the CEI was record high for the Northeast region (September, July-September, and the warm season [April-September]) and South region (July-September and the warm season). The warm season was much more extreme than previous years for the Northeast and South regions, but for different reasons. Both the Northeast and South had very warm temperatures for April-September 2011, but the precipitation patterns were opposite — the Northeast was record wet while the South was second driest.

Sea surface temperature (SST) anomalies for four La Niña/El Niño regions
Sea surface temperature (SST) anomalies for four La Niña/El Niño regions.

Cold fronts and low pressure systems moving in the storm track flow are influenced by the broadscale atmospheric circulation. Four such large-scale atmospheric circulation drivers were potentially influential during September. Ocean temperatures and atmospheric circulation anomalies indicated that the equatorial Pacific was in a weak, but strengthening, La Niña state. La Niña this time of year (July-September) is weakly associated with temperature and precipitation anomalies across the U.S. — temperatures are typically warmer than normal in the central U.S. and cooler than normal in the West, with drier than normal conditions dominating across the central regions and wet conditions in the Southeast to Mid-Atlantic. The Pacific/North American (PNA) pattern was negative early in September and again during the last third of the month (corresponding to the times when strong upper-level low pressure troughs dominated the eastern U.S.), and positive at mid-month. The PNA during this transitional time of year (between the times represented by July and October on the PNA teleconnection maps) typically has a weak relationship with temperature and precipitation throughout the Lower 48 States. The North Atlantic Oscillation (NAO) pattern was neutral to slightly positive for September. Like the PNA, the NAO during this transitional time of year (between the times represented by July and October on the NAO teleconnection maps) typically has a weak relationship with temperature and precipitation throughout the Lower 48 States. The Arctic Oscillation (AO) pattern was also slightly positive for September. A positive AO this time of year (July-September) is typically associated with warmer-than-normal temperatures in the Northern Plains, dryness from the Southern Plains to the Great Lakes and New England, and anomalous wetness in the Southeast.

The pattern of observed temperature anomalies for September 2011 and the last three months (July-September) corresponds slightly to the NAO pattern for July (warmer than normal in the Northwest, cooler than normal in the Southeast) and to the AO pattern for July-September (warmer than normal in the Northern Plains). The September 2011 and July-September 2011 precipitation patterns are a reasonable match for the La Niña and NAO patterns, especially from the Great Plains to Mid-Atlantic (La Niña) and Ohio Valley (NAO).

Tornadoes

NCDC transitioned to the nClimDiv dataset on Thursday, March 13, 2014. This was coincident with the release of the February 2014 monthly monitoring report. For details on this transition, please visit our public FTP site and our U.S. Climate Divisional Database site.


Track of Tropical Storm Lee
Track of Tropical Storm Lee
Source: NOAA's HPC

September marked the end of the warm season for the United States and the tornado activity continued its annual decline. According to preliminary data from the Storm Prediction Center, during September there were 62 preliminary tornado reports across the country, which was slightly below average. The majority of the tornadoes reported during the month occurred along the path of tropical storm Lee. The tropical system quickly became extra-tropical after making landfall in Louisiana on September 3rd. The system interacted with a frontal system moving across the country, spawning severe weather from Louisiana into the Northeast. There were no reported tornado fatalities during September.

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Hurricanes & Tropical Storms

NCDC transitioned to the nClimDiv dataset on Thursday, March 13, 2014. This was coincident with the release of the February 2014 monthly monitoring report. For details on this transition, please visit our public FTP site and our U.S. Climate Divisional Database site.


Note: This report catalogs recent tropical cyclones and places each basin's tropical cyclone activity in a climate-scale context. It is not updated in real time. Users seeking real time status and forecasts of tropical cyclones should visit The National Hurricane Center.

Atlantic Basin


Lee formed on September 2 from a broad but disorganized tropical wave that entered the Western Caribbean in late August. While the core of the storm meandered inland on September 4 roughly 50 miles (80 km) southwest of Lafayette, LA, its squalls impacted the Gulf Coast as early as the day prior. Lee’s high moisture content and slow speed promoted 24-hour rainfall totals in excess of 5 inches (127 mm) in most locations, including New Orleans Airport and Holden, LA where 11.05 inches (281 mm) and 15.43 inches (393 mm) fell, respectively. Because the storm traversed moderate to severe drought-stricken areas of the Gulf States, existing conditions actually worked to mitigate flood damages. (Lee offered minimal relief to arid Texas; consequently, the storm’s gusts assisted in fueling the Bastrop wildfires.) After becoming post-tropical on September 5, Lee’s remnants traveled northeast, drenching regions along the axis of the Appalachian Mountain range. Several locations set new 24-hour rainfall records, including Jackson, MS whose 11.68 inches (297 mm) of rain broke the city’s previous record of 8.54 inches (217 mm) set in 1979; and Chattanooga, TN which received 9.85 inches (250 mm) of rainfall besting its previous 7.61 inches (193 mm) set in 1886. In the northeastern U.S., Binghamton, NY and Hershey, Pennsylvania both experienced flooding of historic proportions as the Susquehanna River and Swatara Creek crested at 25.69 feet (7.83 m) and 27.2 feet (8.3 m), respectively–their highest levels on record. Binghamton, NY itself received a total of 9.02 inches (229.1 mm) of rain, setting an all-time rain event for the city. Lee is responsible for 21 fatalities and over $250 million in damages. In addition, Lee spawned several weak (EF-0 and EF-1) tornadoes–of which there were more than 40 total reports.

Lee
Tropical Storm Lee Satellite Image
Lee Track
Tropical Storm Lee Forecast Track


Safir Simpson Color Legend for Track Map from Unisys
Saffir-Simpson Scale Color Legend
Tropical Cyclone Summary
Tropical Cyclone Lee
Cyclogenesis Date 09/02
Cyclolysis Date 09/05
Highest Saffir-Simpson Category TS
Maximum 6-hr Sustained Wind 58 mph (50 kt or 93 km/h)
Min Pressure 986 mbar
Accumulated Cyclone Energy (ACE*) Index (kt2) 2.1575 x 104
Landfall Information (date, location and sustained winds) 09/04 –Lafayette, Louisiana (40 kt or 72 km /h)
Deaths 17
*The (ACE) Index calculations are based on preliminary data.


Originating from a steadily organizing east African wave, Maria spun into a tropical storm the morning of September 7. As it tracked westward toward the islands of the Caribbean, the storm endured a several-day bout with high wind shear. Despite being disorganized, Maria brought heavy rain and gusty winds to the islands, including a 24-hour rainfall total of 10.71 inches (272 mm) along Puerto Rico’s east coast–a region affected by Hurricane Irene weeks before. From there, Maria tracked north-northwest at a rapid speed of 45 mph (72 km/h). The storm reached hurricane intensity mid-September and maintained this intensity as it made landfall on September 16 in Newfoundland, Canada. Due to Maria’s swift crossing, less than an inch (20 mm) of precipitation was reported in locations such as St. John’s, Newfoundland. The storm transitioned into a post-tropical cyclone later that evening. Maria’s naming on September 7 represents the second earliest arrival of a 13th named storm. (Hurricane Maria of the 2005 season ranks first with a formation date of September 2.) In addition to being the 13th named storm, Maria is also the 13th hurricane to make landfall in Newfoundland since records began in 1851. Together with hurricane Igor of the 2010 season, Maria makes 2011 the second consecutive year during which a landfalling hurricane has occurred within the Canadian island; this event has never before been recorded.

Maria
Tropical Storm Maria Satellite Image
Maria Track
Tropical Storm Maria Forecast Track


Safir Simpson Color Legend for Track Map from Unisys
Saffir-Simpson Scale Color Legend
Tropical Cyclone Summary
Tropical Cyclone Maria
Cyclogenesis Date 09/07
Cyclolysis Date 09/16
Highest Saffir-Simpson Category Cat 1
Maximum 6-hr Sustained Wind 81 mph (70 kt or 130 km/h)
Min Pressure 979 mbar
Accumulated Cyclone Energy (ACE*) Index (kt2) 9.9225 x 104
Landfall Information (date, location and sustained winds) 09/16 – Avalon Peninsula, Newfoundland (56 kt or 103 km /h)
Deaths 0
*The (ACE) Index calculations are based on preliminary data.


On September 7, Tropical Storm Nate churned into existence in Mexico’s Bay of Campeche. After stalling for several days, the compact storm, whose intensity flirted with, yet remained shy of hurricane strength, finally advanced inland just north of Barra de Nautla in the Mexican state of Veracruz on September 11. A short thirteen hours later, Nate dissipated into a remnant low over central Mexico. A total of 5 fatalities were reported.

Nate
Tropical Storm Nate Satellite Image
Nate Track
Tropical Storm Nate Forecast Track


Safir Simpson Color Legend for Track Map from Unisys
Saffir-Simpson Scale Color Legend
Tropical Cyclone Summary
Tropical Cyclone Nate
Cyclogenesis Date 09/08
Cyclolysis Date 09/11
Highest Saffir-Simpson Category TS
Maximum 6-hr Sustained Wind 63 mph (55 kt or 102 km/h)
Min Pressure 994 mbar
Accumulated Cyclone Energy (ACE*) Index (kt2) 3.8900 x 104
Landfall Information (date, location and sustained winds) 09/11 – Veracruz, Mexico (39 kt or 72 km /h)
Deaths 4
*The (ACE) Index calculations are based on preliminary data.


Since its inception as a weak tropical storm on September 20 high wind shear acted as an impediment to Ophelia’s development. By September 25, dry air and wind shear values of 20-25 knots had denatured Ophelia, and the storm dissipated east of the northern Lesser Antilles. Against all odds, the remnants of Ophelia regenerated into a tropical depression the evening of September 27. In the days to follow, Ophelia underwent rapid cyclogenesis, attaining hurricane strength on the evening of September 29 and major hurricane intensity by the next morning. The storm tracked over the open Atlantic intensifying to a Category 4 hurricane (the 2nd of the season) east of Bermuda on October 1. The following day, Ophelia progressively weakened back to a Category 1 hurricane and passed over Newfoundland’s Avalon Peninsula as a tropical storm, on the morning of October 3. The storm was declared post-tropical north of Cape Race, Newfoundland that same day.

Ophelia
Tropical Storm Ophelia Satellite Image
Ophelia Track
Tropical Storm Ophelia Forecast Track


Safir Simpson Color Legend for Track Map from Unisys
Saffir-Simpson Scale Color Legend
Tropical Cyclone Summary
Tropical Cyclone Ophelia
Cyclogenesis Date 09/21
Cyclolysis Date 10/03
Highest Saffir-Simpson Category Cat 4
Maximum 6-hr Sustained Wind 138 mph (120 kt or 222 km/h)
Min Pressure 940 mbar
Accumulated Cyclone Energy (ACE*) Index (kt2) 18.7475 x 104
Landfall Information (date, location and sustained winds)
Deaths 0
*The (ACE) Index value preliminary data for Ophelia was recalculated to include a N-day regeneration on Sep 28-Oct 3.


Philippe was designated a tropical storm on September 24, 12 hours after entering the eastern Atlantic as a tropical wave. Strong shear, which affected the system as early as late September, seemed to signal Philippe’s dissipation; however, after lingering in the middle Atlantic for 12 days, the storm entered into a relaxed shear environment and briefly strengthened into the 5th hurricane of the Atlantic season on October 6. Hours after reaching peak winds of 90 mph (150km/h), Philippe began to progressively weaken. The storm became post-tropical just west of the Azores on October 8. No hazard was posed to land areas. Philippe’s naming on September 24 represents the second earliest arrival of a 16th named storm. (Hurricane Philippe of the 2005 season ranks first with a formation date of September 17.) Lasting a total of 15 days, it is the longest-lived tropical cyclone in the Atlantic since hurricane Bertha of 2008.

Philippe
Tropical Storm Philippe Satellite Image
Philippe Track
Tropical Storm Philippe Forecast Track


Safir Simpson Color Legend for Track Map from Unisys
Saffir-Simpson Scale Color Legend
Tropical Cyclone Summary
Tropical Cyclone Philippe
Cyclogenesis Date 09/24
Cyclolysis Date 10/09
Highest Saffir-Simpson Category TS
Maximum 6-hr Sustained Wind 92 mph (80 kt or 148 km/h)
Min Pressure 976 mbar
Accumulated Cyclone Energy (ACE*) Index (kt2) 14.8425 x 104
Landfall Information (date, location and sustained winds)
Deaths 0
*The (ACE) Index calculations are based on preliminary data.


West North Pacific Basin

Noru
Tropical Storm Noru Satellite Image
Noru Track
Tropical Storm Noru Forecast Track


Safir Simpson Color Legend for Track Map from Unisys
Saffir-Simpson Scale Color Legend
Tropical Cyclone Summary
Tropical Cyclone Noru
Cyclogenesis Date 09/03
Cyclolysis Date 09/06
Highest Saffir-Simpson Category TS
Maximum 6-hr Sustained Wind 52 mph (45 kt or 83 km/h)
Min Pressure 990 mbar
Accumulated Cyclone Energy (ACE*) Index (kt2) 1.4600 x 104
Landfall Information (date, location and sustained winds) N/A
Deaths 0
*The (ACE) Index calculations are based on preliminary data.

Kulap
Tropical Storm Kulap Satellite Image
Kulap Track
Tropical Storm Kulap Forecast Track


Safir Simpson Color Legend for Track Map from Unisys
Saffir-Simpson Scale Color Legend
Tropical Cyclone Summary
Tropical Cyclone Kulap(Nonoy)
Cyclogenesis Date 09/07
Cyclolysis Date 09/08
Highest Saffir-Simpson Category TS
Maximum 6-hr Sustained Wind 52 mph (45 kt or 83 km/h)
Min Pressure 1000 mbar
Accumulated Cyclone Energy (ACE*) Index (kt2) .9700 x 104
Landfall Information (date, location and sustained winds) N/A
Deaths 0
*The (ACE) Index calculations are based on preliminary data.

Roke
Tropical Storm Roke Satellite Image
Roke Track
Tropical Storm Roke Forecast Track


Safir Simpson Color Legend for Track Map from Unisys
Saffir-Simpson Scale Color Legend
Tropical Cyclone Summary
Tropical Cyclone Roke(Onyok)
Cyclogenesis Date 09/13
Cyclolysis Date 09/22
Highest Saffir-Simpson Category Cat 4
Maximum 6-hr Sustained Wind 131 mph (115 kt or 211 km/h)
Min Pressure 940 mbar
Accumulated Cyclone Energy (ACE*) Index (kt2) 12.5700 x 104
Landfall Information (date, location and sustained winds) N/A
Deaths 0
*The (ACE) Index calculations are based on preliminary data.

Sonca
Tropical Storm Sonca Satellite Image
Sonca Track
Tropical Storm Sonca Forecast Track


Safir Simpson Color Legend for Track Map from Unisys
Saffir-Simpson Scale Color Legend
Tropical Cyclone Summary
Tropical Cyclone Sonca
Cyclogenesis Date 09/15
Cyclolysis Date 09/20
Highest Saffir-Simpson Category Cat 2
Maximum 6-hr Sustained Wind 98 mph (85 kt or 157 km/h)
Min Pressure 970 mbar
Accumulated Cyclone Energy (ACE*) Index (kt2) 8.5500 x 104
Landfall Information (date, location and sustained winds) N/A
Deaths 0
*The (ACE) Index calculations are based on preliminary data.

Nesat
Tropical Storm Nesat Satellite Image
Nesat Track
Tropical Storm Nesat Forecast Track


Safir Simpson Color Legend for Track Map from Unisys
Saffir-Simpson Scale Color Legend
Tropical Cyclone Summary
Tropical Cyclone Nesat(Pedring)
Cyclogenesis Date 09/23
Cyclolysis Date 09/30
Highest Saffir-Simpson Category Cat 3
Maximum 6-hr Sustained Wind 121 mph (105 kt or 194 km/h)
Min Pressure 950 mbar
Accumulated Cyclone Energy (ACE*) Index (kt2) 12.9350 x 104
Landfall Information (date, location and sustained winds) 09/27– Luzon, Philippines (95 kt or 176 km /h)
09/29– Hainan, China (65 kt or 120 km /h)
09/30– northen Vietnam (55 kt or 102 km /h)
Deaths 61
*The (ACE) Index calculations are based on preliminary data.

Nalgae
Tropical Storm Nalgae Satellite Image
Nalgae Track
Tropical Storm Nalgae Forecast Track


Safir Simpson Color Legend for Track Map from Unisys
Saffir-Simpson Scale Color Legend
Tropical Cyclone Summary
Tropical Cyclone Nalgae(Quiel)
Cyclogenesis Date 09/28
Cyclolysis Date 10/04
Highest Saffir-Simpson Category Cat 4
Maximum 6-hr Sustained Wind 150 mph (130 kt or 241 km/h)
Min Pressure 935 mbar
Accumulated Cyclone Energy (ACE*) Index (kt2) 13.5475 x 104
Landfall Information (date, location and sustained winds) 10/01– Luzon, Philippines (86 kt or 160 km /h)
Deaths 10
*The (ACE) Index calculations are based on preliminary data.


East North Pacific Basin

Hurricane Hilary initially formed in the southeast Gulf of Tehuantepec near mid-September. On September 21, the disturbance was declared a tropical depression, six hours after which Tropical Storm Hilary was named. The following day, Hilary intensified into the 7th hurricane of the Eastern Pacific season as well as a major hurricane. Bounded by easterlies to the south and a mid-level subtropical ridge to the north, Hilary steered west-northwestward which kept its core offshore. At its closest, the small storm passed 75 miles (120 km) parallel to the southwest coastline of Mexico, where its outer bands produced 24-hour rains accumulating to 8.58 inches (218 mm) in the state of Tabasco. In the Mexican state of Colima, wave heights reached 9-15 feet (2.7-4.6 m). Continuing its rapid intensification, Hilary became a Category 4 hurricane over the open Pacific the morning of September 23. During this time, the Tropical Rainfall Measuring Mission (TRMM) recorded cloud top temperatures of -63 degrees F (-52 degrees C), cloud heights which extended 8.6 miles (14 km) vertically around the eye wall, and bands of precipitation capable of producing 2 inches (50 mm) of rainfall per hour. As it departed the basin’s warmest waters, Hilary began to steadily weaken and had lost all tropical characteristics by September 30. The storm never made landfall. Hilary is the Eastern Pacific’s fourth Category 4 hurricane this season, and with maximum sustained winds of 145 mph (230 km/h), it is the second strongest behind Hurricane Dora of July.

Hilary
Tropical Storm Hilary Satellite Image
Hilary Track
Tropical Storm Hilary Forecast Track


Safir Simpson Color Legend for Track Map from Unisys
Saffir-Simpson Scale Color Legend
Tropical Cyclone Summary
Tropical Cyclone Hilary
Cyclogenesis Date 09/21
Cyclolysis Date 09/30
Highest Saffir-Simpson Category Cat 4
Maximum 6-hr Sustained Wind 144 mph (125 kt or 232 km/h)
Min Pressure 944 mbar
Accumulated Cyclone Energy (ACE*) Index (kt2) N/A
Landfall Information (date, location and sustained winds)
Deaths 0
*The (ACE) Index calculations are based on preliminary data.

Drought

NCDC transitioned to the nClimDiv dataset on Thursday, March 13, 2014. This was coincident with the release of the February 2014 monthly monitoring report. For details on this transition, please visit our public FTP site and our U.S. Climate Divisional Database site.

Issued 13 October 2011
Contents Of This Report:
Map showing Palmer Z Index

National Drought Overview

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Detailed Drought Discussion

Overview

September 2011 was a warm month with near-average precipitation (eleventh warmest and 50th driest, based on data back to 1895) when weather conditions are averaged across the country. But this reflected regional extremes (in both monthly temperature and precipitation) which resulted from persistent weekly regional patterns of temperature anomalies (weeks 1, 2, 3, 4, 5) and variable weekly regional patterns of extreme precipitation anomalies (weeks 1, 2, 3, 4, 5). Heavy rain from Tropical Storm Lee early in the month cut a swath from the Central Gulf Coast to the Northeast, severing the Southeast drought area from the Southern Plains drought area and improving conditions along the edge of the rain shield. The percent area in moderate to exceptional drought (D1-D4) dropped from 55 percent at the end of August to 42 percent at the end of September for the Southeast, and from 86 percent to 76 percent for the South. But little change occurred in the extreme to exceptional (D3-D4) drought categories: the South coverage was 64 percent at the end of September and the Southeast coverage was 23 percent. Very little change occurred in drought coverage of the Southwest (Arizona, New Mexico, and Colorado), where moderate-to-exceptional drought coverage remained about 65 percent, with extreme to exceptional coverage at a steady 31 percent. In Hawaii, moderate to exceptional drought coverage hovered around 45 percent, but severe to exceptional (D2-D4) drought coverage jumped from 5 percent at the end of August to 15 percent at the end of September. Nationally, the moderate-to-exceptional drought footprint covered about a fourth of the country, but about a tenth of the U.S. remained in the worst category (D4, exceptional drought), which has been fairly constant since early summer. Two areas of the southern U.S. experienced the most severe drought in the 1900-present record, according to the Palmer Hydrological Drought Index (PHDI). The two regions having the most severe PHDI on record are eastern New Mexico into western Texas and southwest Oklahoma, and northwestern Louisiana into adjacent eastern Texas. These two regions accounted for 4.2 percent, by area, of the country.

U.S. Drought Monitor map from September 27, 2011
The U.S. Drought Monitor drought map valid September 27, 2011.

By the end of the month, the core drought areas in the U.S. included:

  • a large area of moderate (D1) to exceptional (D4) drought across the Southwest, Southern and Central Plains;
  • areas of moderate to extreme drought in the Southeast;
  • areas of moderate to severe (D2) drought in the Midwest; and
  • parts of Hawaii, where moderate to severe drought persisted.

Palmer Drought Index

The Palmer drought indices measure the balance between moisture demand (evapotranspiration driven by temperature) and moisture supply (precipitation). The Palmer Z Index depicts moisture conditions for the current month, while the Palmer Hydrological Drought Index (PHDI) and Palmer Drought Severity Index (PDSI) depict the current month's cumulative moisture conditions integrated over the last several months.

Palmer Z Index map Palmer Hydrological Drought Index map

As seen on the September 2011 Palmer Z Index map, low precipitation and above-normal evapotranspiration due to above-normal temperatures led to short-term drought across the Southern Plains, southern Florida, and the Northwest to Northern Rockies this month. Temperatures were not a factor in the Central Plains to Upper Mississippi Valley, but below-normal precipitation resulted in short-term dryness there. Wet conditions are evident on the Z Index map over a large area from the Mid-Gulf Coast to the Northeast where moisture from Tropical Storm Lee fell. Compared with the August 2011 PHDI map, the September 2011 PHDI map indicates that drought conditions intensified in the Southern Plains; drought conditions improved in the Mid-Gulf Coast States; moist conditions decreased in the Pacific Northwest and parts of the Midwest to western Great Lakes; and moist conditions increased in the Ohio Valley to Northeast. The September 2011 PHDI map also reflects the long-term nature of the drought conditions. The Z Index and PHDI maps in combination show that tropical rains brought relief to the Mid-Gulf Coast drought areas, and dry weather dried out parts of the Northwest, Northern Rockies, and Midwest, but for the Southern Plains and Northeast — it rained where it was already wet and was drier than normal over the existing drought areas.


Standardized Precipitation Index

The Standardized Precipitation Index (SPI) measures moisture supply. The SPI maps here show the spatial extent of anomalously wet and dry areas at time scales ranging from 1 month to 24 months.

1-month Standardized Precipitation Index 2-month Standardized Precipitation Index 3-month Standardized Precipitation Index

Dryness is evident across much of the Great Plains to western Great Lakes during September (1 month map), and across the Northwest to Northern High Plains and parts of the Midwest at 1 to 3 months. The Southwest, Southern Plains, and Southeast dryness can be seen at all time scales from 2 to 24 months, but is most severe at 6, 9, and 12 months. Wet conditions caused by Tropical Storm Lee moisture can be seen at 1 month, and the flooding spring rains in the Midwest and Northern Plains show up at 6 and 9 months. In addition to the Northern Plains and Midwest to Northeast wetness, the usually wet conditions from last winter across much of the West are evident in the 12- and 24-month time scales. This illustrates the persistence of the dry and wet areas.


6-month Standardized Precipitation Index 12-month Standardized Precipitation Index 24-month Standardized Precipitation Index

Agricultural and Hydrological Indices and Impacts

Leaky Bucket model soil moisture percentiles
Leaky Bucket model soil moisture percentiles
USGS monthly streamflow percentiles
USGS monthly streamflow percentiles

Drought conditions were reflected in numerous agricultural, hydrological, and other meteorological indicators, both observed and modeled. Across the drought areas of the Southwest, Southern Plains, and Southeast, streamflows were low, some groundwater well stations were at or near record low levels for this time of year, soil moisture was depleted, water restrictions were implemented in many communities, and pastures, rangeland, crops, and natural vegetation were ravaged. Dry soils were widespread across the Great Plains and Rockies States and into the Northwest. Low soil moisture and stream levels and stressed vegetation were observed across parts of the western Great Lakes. Much of the Far West, Great Plains, and Northern Rockies had few, if any, days with rain in September. A large area of dry soils was indicated for Mexico connected to the Southern Plains dryness, and dry soils in the western Great Lakes extended into Canada. Above-normal temperatures coupled with the subnormal precipitation placed additional stress on vegetation in the West and Southern Plains. This summary is based on the following observed and modeled indicators:

hydrological:

USGS groundwater map
USGS groundwater map.

agricultural:

VegDRI (Vegetation Drought Response Index) map
VegDRI (Vegetation Drought Response Index) map.

meteorological:

Map of maximum consecutive dry days
Map of maximum consecutive dry days.

Regional Discussion

September 2011 was a drier-than-normal month for most of the stations in the Hawaiian Islands. About 45 percent of the state was classified in the moderate to exceptional drought categories at the end of September, about the same as at the end of August. However, severe to exceptional (D2-D4) drought coverage jumped from 5 percent at the end of August to 15 percent at the end of September, and virtually all of the state (95 percent) was classified in the D0-D4 categories (abnormally dry to exceptional drought) at the end of September compared to 75 percent at the end of August. Streamflow was below normal and long-term rainfall deficits remained at most time scales (last 2, 3, 6, 12, 24, 36 months), especially for the southern islands.

Many stations in southern Alaska (except the panhandle) were drier than normal during September, and dryness remained at longer time scales (2, 3, 6, 12, 24, 36 months). The September 30th snow water content was below normal, but this is early in the season and the snow depth amounts this time of year are typically low. Although September 2011 ranked as the 26th driest September in the 1918-2011 record, July-September 2011 ranked 29th wettest, so there was no drought or abnormal dryness indicated on the September 27th USDM.

The precipitation pattern for Puerto Rico was mixed during September. Above-normal rainfall dominated at longer time scales (2, 3, and 6 months, year to date, and water year [October-September]), and streamflow was above average, so the September 27th USDM map had no drought or abnormally dry areas on the island.

State precipitation ranks, September 2011 State precipitation ranks, October 2010-September 2011

On a statewide basis, September 2011 ranked in the top ten driest Septembers for five states in the Great Plains and Northern Rockies, top ten wettest for eleven states from the Gulf Coast to Northeast, and wettest on record for Pennsylvania. Nine other states (in the northwestern and central parts of the country) ranked in the dry third of the historical record for September. July-September 2011 ranked in the top ten driest category for seven states in the Northwest, Southern Plains, and Southeast. Record to near-record dryness occurred for Texas, Oklahoma, and New Mexico at several other time scales (April-September; year-to-date [January-September]; and last 12 months [October 2010-September 2011]). For Texas, every time period from the last four months to last twelve months (June-September 2011 back to October 2010-September 2011) ranked driest on record, while Oklahoma ranked first or second driest and New Mexico first to fourth driest for those time periods. Louisiana had the driest December-September in the 117-year record and Florida, Georgia, and South Carolina each ranked fourth driest for October-September. Widespread dryness in the Rio Grande and Texas Gulf Coast basins has resulted in the driest water year (October-September) for those river basins, with the Arkansas-White-Red Basin ranking second driest and South Atlantic-Gulf Basin ranking tenth driest. In contrast, the Mid-Atlantic and New England basins ranked third wettest for October 2010-September 2011, with the last eight to nine years consistently much wetter than normal. The record dryness in the Southern Plains was accompanied by record heat statewide for Texas, Oklahoma, and New Mexico (July-September, April-September, and January-September).

Rio Grande River Basin Precipitation, October-September, 1895-2011 Texas Gulf Coast Basin Precipitation, October-September, 1895-2011

Percent area South region in moderate to exceptional drought, 2000-2011

During September, exceptional drought (the worst USDM category) expanded to 55 percent of the South region, which is the largest such extent in the 11-year history of the USDM. Exceptional drought afflicted 88 percent of Texas and 69 percent of Oklahoma in September, also USDM records. The number held steady at a record 11 to 12 percent for the contiguous United States.

On a more localized basis, record dryness has occurred for at least one climate division in the Southwest, Southern Plains, Southeast, or Northwest at every time scale from September 2011 through the 12-month period, October 2010-September 2011. Record warm temperatures have occurred for at least one climate division during all of the last 12 time periods or "seasons" (September 2011 back through October 2010-September 2011), especially in the Southern Plains during the spring and summer:

Precipitation anomaly maps:
Temperature anomaly maps:

The prolonged and intense drought conditions have caused a rapid intensification of the PHDI, with the September 2011 PHDI at record low values for several climate divisions in the Southwest to Lower Mississippi Valley (reliable PHDI records go back to January 1900). There were two epicenters of record low PHDI values — one from eastern New Mexico into western Texas and southwest Oklahoma, and the other from northwestern and central Louisiana into adjacent eastern Texas. The climate divisions with record low PHDI values include:

New Mexico-Texas-Oklahoma region:
Louisiana-Texas region:

The PHDI reached record intensity during 2011 in Louisiana climate divisions 2 and 4, New Mexico climate divisions 6 and 7, Texas climate division 1, on a statewide basis in Texas, and in the Rio Grande and Texas Gulf Coast river basins. In all of these cases, even though the intensity of the current drought is record or near-record, the duration of earlier droughts exceeds the duration of the current drought.

Oklahoma Division 7 PHDI, January 1900-September 2011 Louisiana Division 1 PHDI, January 1900-September 2011

Rio Grande River Basin PHDI, January 1900-September 2011 Texas Division 2 PHDI, January 1900-September 2011

Percent area of the Western U.S. in moderate to extreme drought, based on the Palmer Drought Index
Percent area of the Western U.S. in moderate to extreme drought, based on the Palmer Drought Index.

The West was generally drier than normal in September, but a few areas were wetter than average. This did little to change the overall pattern for the water year (October-September) — extremely dry conditions have been persistent from Arizona and New Mexico into southern Colorado, but abundant precipitation has fallen across the rest of the West. This is evident in both the low elevation station precipitation as well as the high elevation (SNOTEL) station precipitation, modeled soil moisture, and PHDI. An analysis of early data by the USDA indicated that reservoir levels were, on average, above normal in most western states. September 30th snow water content at the higher elevation SNOTEL stations was much above normal, but this is early in the snow season when snow cover is just becoming established and normals are low. According to the USDM, 19 percent of the West was experiencing moderate to exceptional drought at the end of September, about the same as August, while the Palmer Drought Index statistic was about 16 percent, an increase of about 2 percent. When the statistics for the Arizona-New Mexico-Colorado drought area (the Southwest drought area) are aggregated, the percent area in moderate to exceptional (USDM categories) drought has fluctuated between 60 and 70 percent for the last seven months. The percent area in the exceptional and extreme to exceptional categories steadily increased from March to June then leveled off with monsoon showers in July, then decreased slightly in August, holding steady at about 31 percent in extreme to exceptional drought at the end of this month.

A more detailed drought discussion, provided by the NOAA Regional Climate Centers and others, can be found below.

SoutheastSouthMidwestNortheastHigh Plains
WestUpper Colorado River BasinPacific Islands

As noted by the Southeast Regional Climate Center, as in August, monthly precipitation during September 2011 was generally below normal across the Southeast, except in areas affected by tropical cyclone activity. Tropical Storm Lee dropped between 8 and 13 inches (203.2-330.2 mm) of rain across central Alabama, northwest Georgia, western North Carolina, and much of Virginia from the 3rd to the 9th of the month. Major flooding was reported along several rivers and creeks across central and southern Alabama. On the 12th and 13th of the month, Hurricane Maria dropped up to 10 inches (254.0 mm) of rain across Puerto Rico, triggering several landslides along the eastern slopes of the island. The driest locations across the Southeast (less than 50 percent of normal) were found across eastern North Carolina, southern Georgia, and portions of northern Florida. Mean temperatures in September ranged from 1-4 degrees F (0.5-2.2 degrees C) below average across Alabama, Georgia, and the Florida Panhandle to 1-3 degrees F (0.5-1.6 degrees C) above average across Virginia, the Carolinas, and the Florida Peninsula. Monthly temperatures were below average across Puerto Rico and the U.S. Virgin Islands.

The beneficial rain from Tropical Storm Lee helped eliminate several areas of drought across the western and northern fringes of the region. In particular, areas of severe drought (D2) were eliminated across southern Alabama and northwest Georgia. Conversely, the region of extreme drought (D3) expanded into parts of northern South Carolina. Reservoir levels continued to fall across parts of Georgia, where rainfall deficits have been the greatest, and water restrictions were implemented in several more communities in the southern part of the state.

As explained by the Southern Regional Climate Center, September precipitation totals in the Southern region varied dramatically from west to east. Conditions were quite dry in Texas, Oklahoma and Arkansas, with most stations reporting only between 5 to 50 percent of normal. By contrast, conditions were quite wet in Tennessee, Mississippi, and Louisiana, with a bulk of stations reporting between 150 to 200 percent of normal precipitation. This was primarily due to Tropical Storm Lee, which stalled off the Gulf Coast in the early part of the month and eventually made its way inland across the eastern half of the Southern region. The storm dumped copious amounts of rainfall. Areas within the Florida parishes of Louisiana reported up to 10 inches (254.00 mm) of rainfall, however, most of the values reported in the Southern region varied from 3 to 7 inches (76.20 to 177.80 mm). By month's end, Louisiana recorded a state average precipitation value of 6.93 inches (176.60 mm). This equates to the tenth wettest September for the state on record (1895-2011). Both Mississippi and Tennessee reported their seventh wettest September on record (1895-2011). Mississippi averaged 7.67 inches (194.82 mm) for the month, while Tennessee averaged 6.73 inches (170.94 mm) for the month. Drought ridden Texas remained dry for the month. The state averaged 1.08 inches (27.43 mm), which is the first time since May that the state averaged more than an inch of precipitation. However, it was still the seventh driest September on record (1895-2011) for the state. For Oklahoma, it was the twentieth driest September on record (1895-2011) with a state average precipitation value of 1.72 inches (43.69 mm). Arkansas experienced its 37th driest September on record (1895-2011) with a state average precipitation value of 2.63 inches (66.81 mm). With the exception of Texas, fall in the Southern region began as a contrast to the past several months, in that most of the region experienced cooler than normal temperatures.

Due to dry conditions in Arkansas, Oklahoma and Texas, drought conditions changed very little over the western half of the Southern region in the past month. Approximately 53 percent of the region remained in exceptional drought, most of which was Texas and western and central Oklahoma. Exceptional drought also persisted in northwestern Louisiana. Drought conditions did, however, improve in Tennessee, Mississippi and southern/southeastern Louisiana, with the latter (Mississippi and southern/southeastern Louisiana) drought free at the end of September. In Tennessee, a small area of moderate drought remained in the northwestern corner of the state. According to the Star-Telegram, drought has had a big impact on tree health in northern Texas. It was reported that many trees in Trinity Park, were losing leaves and turning brown. It was further reported that in Houston, approximately ten percent of the trees were expected to die. A high mortality rate was also being seen in Hill County.

As summarized by the Midwest Regional Climate Center, for most of September it was dry across the Midwest, with the exception of along and south of the Ohio River. That changed the last ten days of the month, when an upper level low stalled over the southern Great Lakes and brought frequent and sometimes heavy rain to the eastern half of the region. Precipitation the last ten days of the month was 200 to more than 400 percent of normal from Wisconsin and Illinois eastward. West of the Mississippi River, however, rainfall was well below normal and existing areas of drought saw little relief. For the entire month, precipitation was normal to 300 percent of normal from eastern Wisconsin and Illinois east through Ohio and Kentucky. Most of Minnesota, Iowa, and northern Missouri received less than 50 percent of normal precipitation. September 2011 started off where summer left off — hot. A heat wave the first three days of the month set record maximum temperatures across the region, with a number of locations reaching maximums in excess of 100 degrees F (38 degrees C). However, that was the last of the unseasonably warm weather for most of the region. Temperatures the remainder of September were 4 degrees F to 5 degrees F (2.2 degrees C to 2.8 degrees C) below normal across the central Midwest, dropping to near normal on the periphery of the region from northern Minnesota around to eastern Ohio. This same pattern was reflected at the end of the month, with average daily temperatures for September ranging from 2 degrees F to 4 degrees F (1.1 degrees C to 2.2 degrees C) below normal in the central Midwest, and near normal across most of Minnesota, northern Wisconsin, Michigan, and Ohio.

As noted by the Northeast Regional Climate Center, September 2011 was a wet month in the Northeast, with measurable rain falling somewhere in the region on all but a few days. Overall, the Northeast averaged 6.66 inches (169 mm), which was 170 percent of normal. It was the second wettest September in the Northeast since record keeping began in 1895. September was the ninth consecutive month with above-normal temperatures in the Northeast. The mean of 63.7 degrees F (17.6 degrees C) was 2.9 degrees F (1.6 degrees C) above normal. It was the Northeast's eleventh warmest September since 1895.

As explained by the High Plains Regional Climate Center, September 2011 was a quiet month for the High Plains region. Severe weather was reported on only a few days this month and the majority of the region was dry. Much of Kansas, Nebraska, South Dakota, North Dakota, and Wyoming received only 50 percent of normal precipitation and many areas received less than 25 percent of normal precipitation. Several of these locations ranked in the top 10 driest Septembers on record and a few even broke records. For instance, Sioux Falls, South Dakota had its driest September on record with only 0.20 inch (5 mm) of precipitation (period of record 1893-2011). The old long-standing record of 0.21 inch (5 mm) occurred in 1899. Boysen Dam, Wyoming, which is located in the central part of the state, received no precipitation this month and tied for its driest September (period of record 1948-2011). Interestingly, the other driest September occurred just last year (2010) which makes two Septembers in a row without precipitation. Pockets of Colorado and North Dakota had precipitation which was more than 150 percent of normal. Temperatures were generally below normal in the eastern portion of the High Plains region and above normal in the western and northern areas of the region.

There were many changes to the USDM this month. Areas of improvement include northeastern Colorado and the Black Hills region of South Dakota where abnormally dry conditions (D0) were erased. East central Kansas had a one category improvement from extreme drought (D3) to severe drought (D2) while a pocket of exceptional drought (D4) in south-central Colorado was downgraded to D3. D0 expanded to include much of eastern South Dakota and two pockets of moderate drought (D1) expanded there as well. In addition, an area of D0 expanded through parts of central Nebraska and the panhandle. Meanwhile, the ongoing drought in eastern Colorado and western Kansas remained largely unchanged.

As summarized by the Western Regional Climate Center, September was generally dry in the West with isolated pockets of high precipitation in the southern part of the region due to a strong mid-month monsoon surge. Temperatures ranged from near normal and slightly below normal on the coast and in the Southwest to record breaking in the Northwest.

The Southwest monsoon season is typically taken as ending September 30, allowing rainfall totals for the season to be compared to previous years. The monsoon activity was slow for most of the season (since June 15). A final burst in mid-September brought record rainfall to Tucson, Arizona as well as significant precipitation to the Four Corners region into central Colorado. Other Southwest locations did not fare as well as Tucson and saw lower than average monsoon precipitation for the month and season. The scattered nature of September's precipitation in the Southwest allowed for drought conditions to persist in Arizona, New Mexico, and southern Colorado, with only slight improvements in southern Arizona and Colorado. The Northwest, northern Nevada, and California remained generally dry and at below-average precipitation values due to persistent upper-level high pressure throughout the month that held precipitation to the north. Salem, Oregon received 0.35 in (8.9 mm) of total precipitation, the 9th driest September since records began at that location in 1893. Very few locations in the Northwest received above average precipitation.

Many high temperature records were set throughout the Northwest, especially along the Oregon-Washington border, Northern California, Idaho and Wyoming. Northern Nevada and Montana also saw several high temperature ties and records.

Upper Colorado River Basin: As reported by the Colorado Climate Center, the September 20th NIDIS (National Integrated Drought Information System) assessment for the Upper Colorado River Basin (UCRB) indicated that, 100 percent of the USGS streamgages in the UCRB recorded normal (25th - 75th percentile) or above normal 7-day average streamflows, with 56 percent of the gages recording flows above the 75th percentile and no gages recording below normal flows. All the major reservoirs' storage volumes in the UCRB continued decreasing in September, with Flaming Gorge and Lake Powell seeing only minor decreases. All of the major reservoirs above Lake Powell were near or above their average September levels. Only Navajo Reservoir was below last year's levels. Lake Powell's volume was 89 percent of average and 73 percent of capacity, compared to 63 percent of capacity last year at this time. Cooler temperatures combined with ample precipitation helped to ease water demands and lower reference evapotranspiration (refET) throughout much of the basin. The VIC model showed improved soil moisture conditions for the San Luis Valley, the Four Corners and also for northeast Colorado. Poor soil moisture conditions were still prevalent throughout much of southeast Colorado. Southern Wyoming and parts of eastern Utah were showing slightly dry soils, while the Wasatch mountains in Utah and the northern mountains of Colorado were showing wet soils. Satellite imagery of vegetation conditions showed very dry vegetation in the Four Corners region, the San Luis Valley, and southeast Colorado. Vegetation conditions were moist for the northern portion of the UCRB and slightly drier than average for northeast Colorado.

Pacific Islands: According to reports from National Weather Service offices, the Pacific ENSO Applications Climate Center (PEAC), and partners, conditions varied across the Pacific Islands.

As noted by the National Weather Service office in Honolulu, well below-normal rainfall during the warmest time of the year combined to increase drought intensity over the leeward areas of the state. The greatest changes occurred on the Big Island where extreme drought, or D3 category conditions on the USDM map, once again started. The coverage of D3 was currently along the lower elevations of the south Kohala district, leeward north Kohala district and the southern end of the Kau district. Severe drought, or D2 category conditions, continued to encompass most of the north Kona district, the Pohakuloa region of the Hamakua district and the eastern portion of the Kau district. Leeward Big Island areas not under D2 conditions were considered to be under D1, or moderate drought. Maui County remained under severe drought over the leeward Haleakala slopes from Kamaole to Ulupalakua, and the upcountry and Kaupo sections remained under moderate drought. Lanai and the western third of Molokai also remained under moderate drought conditions. Significant dryness over leeward Oahu resulted in the initiation of moderate drought over the Waianae slopes from Makaha to Ewa. Severe drought has affected portions of the state of Hawaii continuously since June 2008.

Some drought impacts in Hawaii include the following:

  • On Oahu, the water supply in the Waimanalo reservoir has been rapidly decreasing and has dropped over 25 feet since early in the year. The State of Hawaii Department of Agriculture was maintaining a voluntary 10 percent cutback in irrigation water use but may shift to mandatory restrictions if water levels fail to recover soon.
  • On Molokai, the State of Hawaii Department of Agriculture has kept in place the mandatory 30 percent cutback in irrigation water consumption for the Kualapuu reservoir system.
  • On Lanai, pastures and general vegetation conditions were in a degraded state.
  • On Maui, pastures and general vegetation conditions have declined along the leeward slopes of Haleakala and have been impacting ranching operations. Water supply levels for upcountry Maui continued to decline with recent ditch flows from east Maui averaging less than 30 percent of capacity. The Maui County Department of Water Supply has maintained their call for a 5 percent reduction in water use. The request for a 10 percent reduction in water use by central and south Maui residents also remained in effect.
  • On the Big Island, drought impacts over the leeward areas of the island have worsened over the past month. Pastures and general vegetation from Kawaihae to north Kona were in very poor condition and brush fires were becoming a bigger issue as the dry conditions continued. Pastures in the southern portion of the Kau district were also deteriorating. The USDA Farm Service Agency reported that various areas of the island had 30 to 100 percent loss of forage for livestock. Many ranchers have already destocked cattle and water hauling operations have been ongoing for several months. Coupled with higher feed prices, the impact on ranching operations has been significant. In other areas of agriculture, yields for tangerines, oranges, and pummelos were down about an average of 50 percent.

SPI values for seven time periods for Hawaiian Island stations, computed by the Honolulu NWS office.
SPI values for seven time periods for Hawaiian Island stations

On other Pacific Islands, there have been reports from American Samoa of streams drying up and wildfires breaking out. In September, rainfall was well-below normal in American Samoa, below normal in Saipan, slightly below normal in Kosrae, and above to well-above normal at most other locations.

Pacific Island Percent of Normal* Precipitation
Station Name Oct 2010 Nov 2010 Dec 2010 Jan 2011 Feb 2011 Mar 2011 Apr 2011 May 2011 Jun 2011 Jul 2011 Aug 2011 Sep 2011 Oct 2010-Sep 2011
Chuuk 113% 66% 85% 76% 137% 156% 109% 66% 218% 124% 147% 120% 117%
Guam IAP 112% 53% 76% 205% 166% 138% 142% 95% 96% 195% 109% 121% 122%
Kapingamarangi 26% 25% 9% 22% 2% 61% 74% 69% 247% 199% 214% 181% 86%
Koror 89% 94% 75% 163% 145% 170% 130% 180% 129% 166% 145% 184% 138%
Kosrae 85% 74% 76% 82% 67% 51% 74% 151% 114% 76% 105% 86% 87%
Kwajalein 162% 158% 37% 119% 316% 277% 49% 91% 121% 100% 135% 101% 125%
Majuro 96% 142% 95% 100% 190% 188% 28% 109% 97% 118% 106% 108% 111%
Pago Pago 153% 82% 92% 183% 110% 52% 36% 35% 132% 40% 60% 26% 88%
Pohnpei 75% 97% 75% 98% 125% 148% 47% 95% 128% 85% 120% 97% 97%
Saipan 40% 82% 43% 182% 124% 164% 209% 154% 174% 110% 108% 64% 100%
Yap 141% 98% 69% 164% 123% 171% 129% 169% 113% 157% 133% 155% 135%
* 1971-2000 Normals

SPI values for seven time periods for Pacific Islands, computed by the Honolulu NWS office.
SPI values for seven time periods for Pacific Islands

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State/Regional/National Moisture Status
A detailed review of drought and moisture conditions is available for all contiguous U.S. states, the nine standard regions, and the nation (contiguous U.S.):

States
alabama arizona arkansas california colorado connecticut
delaware florida georgia idaho illinois indiana
iowa kansas kentucky louisiana maine maryland
massachusetts michigan minnesota mississippi missouri montana
nebraska nevada new hampshire new jersey new mexico new york
north carolina north dakota ohio oklahoma oregon pennsylvania
rhode island south carolina south dakota tennessee texas utah
vermont virginia washington west virginia wisconsin wyoming

Regional
northeast u. s. east north central u. s. central u. s.
southeast u. s. west north central u. s. south u. s.
southwest u. s. northwest u. s. west u. s.

National
Contiguous United States

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Drought Indicators
The following indicators illustrate the drought conditions this month:

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Contacts & Questions
For additional, or more localized, drought information, please visit:

Global Snow & Ice

Sea Ice Extent

According to the National Snow and Ice Data Center (NSIDC), the Northern Hemisphere sea ice extent which is measured from passive microwave instruments onboard NOAA satellites averaged for September 2011, was 4.61 million square km (1.78 million square miles), 34.5 percent below the 1979-2000 average. This is the second smallest September extent since records began in 1979. The September sea ice extent was 310,000 square kilometers (120,000 square miles) larger than the monthly average for September 2007, when the smallest monthly extent in the satellite record occurred. Below-average ice extent was observed across all regions of the Arctic with the exception of the East Greenland Sea, where near-normal ice extent was observed. September 2011 marks the 15th consecutive September and 124th consecutive month with below average Arctic sea ice extent. September Arctic sea ice extent has decreased at an average rate of 12 percent per decade.

September's PIOMAS Arctic Ice Anomaly
Sea Ice Volume Anomaly
Source: UW's Polar Ice Center

On September 9th, the Arctic sea ice reached its annual minimum extent, marking the end of the melt season. According to NSIDC, the minimum extent of 4.33 million square km (1.67 million square miles) was the second smallest extent in the satellite record, slightly larger than the 4.17 million square km (1.61 million square miles) that occurred in September 2007. According to the Polar Science Center, at the University of Washington, the second smallest extent was accompanied by record small sea ice volume across the Arctic. On September 10th the sea ice volume dropped to 4,000 cubic km (960 cubic miles), the smallest single day Arctic sea ice volume in its record. Also, the monthly averaged ice volume for September 2011 was record low at 4,200 cubic km (1,007 cubic miles) — 66 percent lower than the mean over this period and 75 percent lower than the September maximum in 1979.

The September 2011 Southern Hemisphere sea ice extent was 0.9 percent above the 1979-2000 average. This tied with September 1981 as the 14th largest (19th smallest) monthly Southern Hemisphere sea ice extent on record. The Southern Hemisphere sea ice extent typically reaches its annual maximum during the month of September. This year, environmental conditions allowed the growth season to continue well into October. September Southern sea ice has increased at a rate of 0.7 percent per decade.

For further information on the Northern and Southern Hemisphere snow and ice conditions, please visit the NSIDC News page.

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Upper Air

Contents of this Section:


Note: Beginning in December 2010, all data are reported here with respect to the 1981–2010 base period. Prior to December 2010, radiosonde data were reported with respect to the 1961–1990 base period and satellite data were reported with respect to the 1979–1998 base period. Remote Sensing Systems continues to provide data to NCDC with respect to the 1979–1998 base period; however, NCDC readjusts the data to the 1981–2010 base period so that the satellite measurements are comparable. This change provides a more consistent comparison between the various datasets.


Note: Effective with the January 2011 report, Remote Sensing Systems (RSS) transitioned to a new version (3.3) of the RSS MSU/AMSU atmospheric temperature datasets. Information about the differences between version 3.2 and 3.3 is available.



Troposphere

Temperatures above the Earth's surface are measured within the lower troposphere, middle troposphere, and stratosphere using in-situ balloon-borne instruments (radiosondes) and polar-orbiting satellites (NOAA's TIROS-N). The radiosonde and satellite records have been adjusted to remove time-dependent biases (artificialities caused by changes in radiosonde instruments and measurement practices as well as changes in satellite instruments and orbital features through time). Global averages from radiosonde data are available from 1958 to present, while satellite measurements date back to 1979.

Lower Troposphere

Current Month | Year-to-date

These temperatures are for the lowest eight kilometers (five miles) of the atmosphere. Information on the University of Alabama in Huntsville (UAH) and Remote Sensing Systems (RSS) sources of troposphere data is available.

September Lower Troposphere
September Anomaly Rank
(out of 33 years)
Record Years Decadal Trend
°C °F Year °C °F °C °F
UAH +0.29 +0.52 Coolest 29th 1984 -0.61 -1.10 +0.18 +0.33
Warmest 5th 2010 +0.48 +0.86
RSS +0.18 +0.32 Coolest 25th 1984 -0.57 -1.03 +0.18 +0.32
Warmest 8th 2010 +0.40 +0.72
Year-to-Date Lower Troposphere
January–
September
Anomaly Rank
(out of 33 years)
Record Years Decadal Trend
°C °F Year °C °F °C °F
UAH +0.16 +0.29 Coolest 26th 1984 -0.32 -0.58 +0.13 +0.24
Warmest 6th 1998 +0.51 +0.92
RSS +0.07 +0.13 Coolest 22nd 1985 -0.38 -0.68 +0.14 +0.26
Warmest 11th 1998 +0.52 +0.94

Mid-troposphere

Current Month | Year-to-date

These temperatures are for the atmospheric layer centered in the mid-troposphere (approximately 3–10 km [2–6 miles] above the Earth's surface), which also includes a portion of the lower stratosphere. (The Microwave Sounding Unit [MSU] channel used to measure mid-tropospheric temperatures receives about 25 percent of its signal above 10 km [6 miles].) Because the stratosphere has cooled due to increasing greenhouse gases in the troposphere and losses of ozone in the stratosphere, the stratospheric contribution to the tropospheric average, as measured from satellites, September create an artificial component of cooling to the mid-troposphere temperatures. The University of Washington (UW) versions of the UAH and RSS analyses attempt to remove the stratospheric influence from the mid-troposphere measurements, and as a result the UW versions tend to have a larger warming trend than either the UAH or RSS versions. For additional information, please see NCDC's Microwave Sounding Unit page.

The radiosonde data used in this global analysis were developed using the Lanzante, Klein, Seidel (2003) ("LKS") bias-adjusted dataset and the First Difference Method (Free et al. 2004) (RATPAC). Additional details are available. Satellite data have been adjusted by the Global Hydrology and Climate Center at the University of Alabama in Huntsville (UAH). An independent analysis is also performed by Remote Sensing Systems (RSS) and a third analysis has been performed by Dr. Qiang Fu of the University of Washington (UW) (Fu et al. 2004)** to remove the influence of the stratosphere on the mid-troposphere value. Global averages from radiosonde data are available from 1958 to present, while satellite measurements began in 1979.

Radiosonde measurements indicate that, for the January–September year-to-date period, temperatures in the mid-troposphere were 0.17°C (0.31°F) above average, resulting in the ninth warmest January–September period (out of 54 years). Satellite analyses of the January–September year-to-date period for the middle troposphere was the 8th to 15th warmest in the 33-year satellite record, depending on the data source.

The global mid-troposphere temperatures were well above average during September 2011. As shown in the table below, satellite measurements for September 2011 ranked fifth to ninth warmest on record, depending on the data source.

September Mid-troposphere
September Anomaly Rank
(out of 33 years)
Record Years Decadal Trend
°C °F Year °C °F °C °F
UAH +0.17 +0.31 Coolest 27th 1984 -0.56 -1.01 +0.12 +0.21
Warmest 6th 2010 +0.42 +0.76
RSS +0.14 +0.25 Coolest 25th 1984 -0.56 -1.01 +0.14 +0.25
Warmest 9th 2010, 1998 +0.40 +0.72
UW-UAH +0.28 +0.50 Coolest 29th 1984 -0.67 -1.21 +0.19 +0.34
Warmest 5th 2010 +0.52 +0.94
UW-RSS +0.24 +0.43 Coolest 28th 1984 -0.63 -1.13 +0.19 +0.35
Warmest 5th 1998 +0.50 +0.90
Year-to-Date Mid-troposphere
January–
September
Anomaly Rank
(out of 33 years*)
Record Years Decadal Trend
°C °F Year °C °F °C °F
UAH +0.02 +0.04 Coolest 17th 1993, 1989, 1984 -0.25 -0.45 +0.05 +0.09
Warmest 15th 1998 +0.51 +0.92
RSS +0.02 +0.04 Coolest 18th 1985 -0.28 -0.50 +0.09 +0.16
Warmest 15th 1998 +0.52 +0.94
UW-UAH +0.10 +0.18 Coolest 26th 1984 -0.32 -0.58 +0.11 +0.20
Warmest 8th 1998 +0.61 +1.10
UW-RSS +0.09 +0.16 Coolest 23rd 1984 -0.33 -0.59 +0.14 +0.26
Warmest 11th 1998 +0.60 +1.08
RATPAC* +0.17 +0.31 Coolest 46th 1965 -0.85 -1.53 +0.15 +0.28
Warmest 9th 2010 +0.57 +1.03

*RATPAC rank is based on 54 years of data

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Stratosphere

Current Month

The table below summarizes stratospheric conditions for September 2011. On average, the stratosphere is located approximately 16–23 kilometers (10–14 miles) above the Earth's surface. Over the last decade, stratospheric temperatures have been below average in part due to the depletion of ozone. The large positive anomaly in 1982 was caused by the volcanic eruption of El Chichon in Mexico, and the sharp jump in temperature in 1991 was a result of the eruption of Mt. Pinatubo in the Philippines. In both cases the temperatures returned to pre-eruption levels within two years.

September Stratosphere
September Anomaly Rank
(out of 33 years)
Record Years Decadal Trend
°C °F Year °C °F °C °F
UAH -0.43 -0.77 Coolest 8th 1996 -0.61 -1.10 -0.42 -0.75
Warmest 26th 1991 +1.64 +2.95
RSS -0.35 -0.63 Coolest 7th 1996 -0.53 -0.95 -0.30 -0.54
Warmest 27th 1991 +1.51 +2.72
Year-to-Date Stratosphere
January–
September
Anomaly Rank
(out of 33 years)
Record Years Decadal Trend
°C °F Year °C °F °C °F
UAH -0.40 -0.72 Coolest 3rd 1996 -0.47 -0.85 -0.36 -0.65
Warmest 31st 1992, 1983 +1.01 +1.82
RSS -0.35 -0.63 Coolest 3rd 1996 -0.40 -0.72 -0.29 -0.52
Warmest 31st 1992 +0.99 +1.78

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References

Christy, John R., R.W. Spencer, and W.D. Braswell, 2000: MSU tropospheric Temperatures: Dataset Construction and Radiosonde Comparisons. J. of Atmos. and Oceanic Technology, 17, 1153-1170.

Free, M., D.J. Seidel, J.K. Angell, J. Lanzante, I. Durre and T.C. Peterson (2005) Radiosonde Atmospheric Temperature Products for Assessing Climate (RATPAC): A new dataset of large-area anomaly time series, J. Geophys. Res., 10.1029/2005JD006169.

Free, M., J.K. Angell, I. Durre, J. Lanzante, T.C. Peterson and D.J. Seidel(2004), Using first differences to reduce inhomogeneity in radiosonde temperature datasets, J. Climate, 21, 4171-4179.

Fu, Q., C.M. Johanson, S.G. Warren, and D.J. Seidel, 2004: Contribution of stratospheric cooling to satellite-inferred tropospheric temperature trends. Nature, 429, 55-58.

Lanzante, J.R., S.A. Klein, and D.J. Seidel (2003a), Temporal homogenization of monthly radiosonde temperature data. Part I: Methodology, J. Climate, 16, 224-240.

Lanzante, J.R., S.A. Klein, and D.J. Seidel (2003b), Temporal homogenization of monthly radiosonde temperature data. Part II: trends, sensitivities, and MSU comparison, J. Climate, 16, 241 262.

Mears, Carl A., M.C. Schabel, F.J. Wentz, 2003: A Reanalysis of the MSU Channel 2 tropospheric Temperature Record. J. Clim, 16, 3650-3664.

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Wildfires

Updated: 6 October 2011


Overview

During September 2011, approximately 765,500 acres (309,500 hectares) burned across the country, slightly higher than the 10-year average of 614,300 acres (348,500 hectares) but less than the September record of 1.47 million acres (595,000 hectares), which burned in 2006. During the January-September period, 7.72 million acres (3.12 million hectares) burned across the U.S. — the 5th most in the 12-year period of record. The most acres burned during the January-September period occurred in 2006 when 9.1 million acres (3.68 million hectares) burned nationwide.

September Wildfire Statistics*

September 2011 2001-2010 Average (10-years) Rank (of 12 years) Record (year)
Area Burned 765,417 acres 614,273 acres 4thlargest (9thsmallest) 1,474,795 acres (2006)
Number of Fires 6,552 6,623 5thmost (7thleast) 13,598 (2010)
Area Burned
per Fire
116.8 acres 99.7 acres 3rdlargest (10thsmallest) 307.0 acres (2006)

Year-to-Date Wildfire Statistics*

Year-to-Date
as of September 30th 2011
2001-2010 Average (10-years) Rank (of 12 years) Record (year)
Area Burned 7,721,459 acres 5,948,948 acres 5th largest (8thsmallest) 9,074,358 acres (2006)
Number of Fires 60,422 64,563 4thleast (9thmost) 83,752 (2006)
Area Burned
per Fire
127.8 acres 91.7 acres 2nd largest (11thsmallest) 153.5 acres(2005)

*Data Source: The National Interagency Fire Center (NIFC) Situation Report.


Significant Events

Texas Wildfires 6 September 2011
Texas Wildfires 6 September 2011
Source: NASA

During the first week of September, three large wildfires raged across eastern Texas. As Tropical Storm Lee made landfall along the Louisiana coast, the storm caused strong winds to whip up across the state. The strong winds, combined with the ongoing drought, created ideal wildfire conditions. The Bastrop fire was ignited on September 4th, just east of Austin, Texas. The fire burned rapidly out of control with extremely low 10-hour and 100-hour fuel moistures reported. By the end of the month, the fire had burned over 34,000 acres (13,800 hectares) and destroyed over 1,600 homes. According to media reports, the fire broke the record for the number of homes lost due to a single fire in Texas history. The Riley Road fire burned northwest of Houston, and charred nearly 19,000 acres (7,700 hectares) before being fully contained on the 14th. The fire destroyed 76 structures in its path. The Bear Creek fire burned near Linden, Texas and covered over 40,000 acres (16,200 hectares) before containment on the 18th. For 2011 through the end of September, over 3.7 million acres (1.5 million hectares) have burned across the state of Texas.

Minnesota Wildfires 12 September 2011
Minnesota Pagami Creek Wildfire
12 September 2011
Source: NASA

The Pagami Creek fire burned approximately 93,000 acres (37,600 hectares) in the Superior National Forest in northern Minnesota by the end of September and was only 60 percent contained on the 30th. The fire was ignited on August 18th by a lightning strike. The fire was not initially suppressed to allow natural processes to take place in the forest. The fire had only grown to 13 acres (5 hectares) by September 12th. But after the 12th, strong winds and dry conditions caused the fire to grow rapidly out of control. The acreage burned is the tenth most by a single fire in Minnesota history, and the largest fire to affect the state since the Cloquet-Moose Lake Fire in 1918. By the end of September over 5.7 million dollars had been spent to control the wildfire.


Discussion

During September, dry conditions persisted for most of the country, with the exception of the track of Tropical Storm Lee and the Northeast. Above-normal temperatures dominated the western third of the country, in contrast to the summer period which was cooler than normal for the region. Above-normal temperatures were also present along the U.S.-Canadian Border, the Northeast, and Texas. Below-normal temperatures were present along the Gulf Coast, stretching into the Central Plains. See the U.S. Temperature and Precipitation discussion for more information. According to the U.S. Drought Monitor, the overall size of the drought footprint shrank slightly across the contiguous U.S. during September. Tropical Storm Lee, which made landfall along the Louisiana coast, moved northeastward and interacted with a frontal system, bringing heavy rainfall from the Gulf Coast, to Northeast, eliminating drought conditions for parts of the Lower Mississippi, Ohio, and Tennessee Valleys. Extreme drought (D3) persisted across Georgia, which did not receive any rainfall from Tropical Storm Lee. Exceptional drought (D4) continued across most of the Southern Plains, stretching into the Southwest. Severe drought (D2) conditions continued across parts of Iowa and Illinois, as well as extreme northern Minnesota. Abnormally dry conditions developed across the Northern Rockies and the central Great Basin.

Wildfire information and environmental conditions are provided by the National Interagency Fire Center (NIFC) and the U.S. Forest Service (USFS) Wildland Fire Assessment System (WFAS).

On September 1st, there were 58 large wildfires burning nationwide. The majority of the large wildfires were active across the northwestern quadrant of the country, with nine fires burning in Oregon, three in Washington, five in Idaho, four in Montana, and three in Wyoming. Dry conditions the second half of August increased the fire danger across the region, as well as the Keetch–Byram Drought Index (KBDI) values across the higher elevations. Extremely low 10-hour fuel moistures were widespread, with moderately low 100-hour and 1,000-hour fuel moistures. Twelve large wildfires were burning across the Southwest in California (4), Arizona (4), Nevada (2), New Mexico (1), and Colorado (1). During the second half of August, the monsoonal rain showers across the Southwest slowed significantly, and the heat across the region created ideal wildfire conditions. Very high fire danger was observed across portions of the Southwest, stretching across the Great Basin. Small fuels (10-hour fuel moistures) were extremely dry, while larger fuels (100-hour and 1,000-hour fuel moistures) were moderately dry across the region. KBDI values were relatively low. Across the Southern Plains, there were 15 large wildfires burning in Texas, as well as two in Arkansas and one in Oklahoma. Continued dryness and warm temperatures caused 10-hour fuel moistures to plummet and the fire danger to increase. KBDI were very high across the area. Single large wildfires were also active in Alabama, Minnesota, and in North Carolina.

By mid-September, there were 44 large wildfires burning across the country. There were 16 fires active across Washington (2), Oregon (8), Idaho (4), and Montana (2). Across the region, temperatures were above average and precipitation was below average during the first half of the month, which lowered fuel moistures of all sizes (10-hour, 100-hour, and 1,000-hour fuel moistures) and increased the fire danger and KBDI values. Five large fires were active across central California, where 10-hour and 100-hour fuel moistures were extremely low. Below-average precipitation during the first two weeks of the month increased KBDI values. Across the South, 22 large wildfires were active in Texas (14), Louisiana (2), Oklahoma (5), and Arkansas (1). Dry and windy conditions were widespread the first half of September across the region causing high fire danger and KBDI values and extremely low 10-hour and 100-hour fuel moistures. One additional fire was active across northern Minnesota, where low 10-hour fuel moistures were observed.

By the end of September, large fire activity across the U.S. had slowed significantly, with 11 large fires actively burning. There were five large wildfires active across Idaho (3), Montana (1), and Oregon (1) in the Pacific Northwest. At the end of the month, the low elevations of the region were experiencing high fire danger. Extremely low 10-hour fuel moistures were also widespread, with the exception of the coastal regions, and 100-hour and 1,000-hour fuel moistures were moderately dry across the region. In Texas, four large wildfires remained active on September 30th. Continued dryness caused the fire danger to be extremely high across the eastern and northern portions of the state. Extremely low 10-hour fuel moistures and moderately dry 100-hour and 1,000-hour fuel moistures were associated with the ideal wildfire conditions. Extremely high KBDI values across the state were attributable to the ongoing exceptional drought. There was also a single large wildfire burning in north central Florida, where high KBDI values were observed. The Pagami Creek wildfire in Minnesota continued to burn in the Superior National Forest.


All Fire Related Maps


Citing This Report

NOAA National Climatic Data Center, State of the Climate for September 2011, published online October 2011, retrieved on October 24, 2014 from http://www.ncdc.noaa.gov/sotc/2011/9.