Drought - September 2020
Issued 13 October 2020
Please note that the values presented in this report are based on preliminary data. They will change when the final data are processed, but will not be replaced on these pages
National Drought Highlights
- Based on the Palmer Drought Index, severe to extreme drought affected about 22% of the contiguous United States as of the end of September 2020, an increase of about 3% from last month. About 16% of the contiguous U.S. fell in the severely to extremely wet categories.
- About 36% of the contiguous U.S. fell in the moderate to extreme drought categories (based on the Palmer Drought Index) at the end of September
- On a broad scale, the 1980s and 1990s were characterized by unusual wetness with short periods of extensive droughts, the 1930s and 1950s were characterized by prolonged periods of extensive droughts with little wetness, and the first two decades of the 2000s saw extensive drought and extensive wetness (moderate to extreme drought graphic, severe to extreme drought graphic).
- A file containing the national monthly percent area severely dry and wet from 1900 to present is available for the severe to extreme and moderate to extreme categories.
- Historical temperature, precipitation, and Palmer drought data from 1895 to present for climate divisions, states, and regions in the contiguous U.S. are available at the Climate Division: Temperature-Precipitation-Drought Data page. These filenames begin with "climdiv".
According to the weekly U.S. Drought Monitor (USDM), as of September 29, 2020, 42.59% of the contiguous U.S. (CONUS) (35.78% of the U.S. including Alaska, Hawaii, and Puerto Rico) was classified as experiencing moderate to exceptional (D1-D4) drought.
Detailed Drought Overview
The atmospheric circulation over North America during September 2020, like last month, consisted of sub-tropical high pressure across the southern states with a storm track that was deflected to the northern states and across the U.S.-Canadian border. Upper-level troughs moving in the jet stream flow occasionally pushed south into the ridge, sending cold fronts plunging across the Plains into the Deep South. Several Atlantic tropical systems were steered into the southern and southeastern CONUS, also weakening the subtropical ridge. These included Hurricane Sally and Tropical Storm Beta. When averaged across the month, the upper-level circulation pattern consisted of an anomalously strong ridge over the western CONUS which extended north along the North American coast to Alaska, and south into the Gulf of Mexico, and a weak trough which extended from the Great Lakes to Gulf Coast. The ridge kept temperatures warmer than normal across the West into southeast Alaska, with record heat widespread across the West Coast. The western ridge and an associated northwesterly flow over central parts of North America kept the West and most of the Great Plains and Northeast drier than normal. Hurricane Sally drenched the Southeast with heavy rain, and Tropical Storm Beta soaked Texas before giving the Southeast to Mid-Atlantic another round of heavy rain. Above-normal precipitation fell across parts of the Mississippi Valley from frontal rains, and Pacific fronts brushed the coastal Northwest with above-normal precipitation. The fronts and tropical systems helped keep monthly temperatures near to cooler than normal across much of the country east of the Rockies.
The extremely hot temperatures, especially in the West and parts of the Northeast, increased evapotranspiration (ET) (as seen by such indices as the ESI and EDDI). The high ET in these regions exacerbated drought conditions for the areas that had below-normal rainfall (as seen, for example, by the Palmer Z Index and SPEI). The high ET and low precipitation further dried soils (as seen in satellite observations of soil moisture [SMOS; SPoRT LIS 0-10 cm depth, 0-40 cm depth, 0-100 cm depth, 0-200 cm depth, RSM], field reports [USDA NASS reports], and models [VIC, CPC, NLDAS, NASA GRACE surface soil moisture and root zone soil moisture, and Leaky Bucket]) and stressed vegetation (VegDRI, QuickDRI, VHI, NESDIS stressed and healthy vegetation). This was especially true in the Southwest, Northeast, much of the central and northern Plains, and parts of the Midwest. Many of the streams and groundwater levels (GRACE satellite estimates, USGS observations) were low in these areas, with record low streamflow in the Northeast. Dozens of large wildfires raged across the West and Plains (wildfire maps for September 1, 7, 10, 11, 13, 16, 21, 24, 28, 30), with 7.5 million acres burned nationwide so far this year, nearly double the value from a month ago, according to a September 30 National Interagency Coordination Center report. Reports received from the CoCoRaHS Condition Monitoring Resource (for September 8-14, 15-21, 22-28) included crop and livestock issues (reduced yields and pasture/forage, plant/animal stress, and drying ponds, lakes, and streams), fire impacts, air quality problems, dry landscaping, and wildlife concerns, plus low wells in the Northeast.
As a result of these conditions, drought or abnormal dryness expanded or intensified across much of the West, central to northern Plains, Northeast, and Hawaii, and parts of the Midwest. Drought or abnormal dryness contracted in parts of the southern Plains and other parts of the Midwest, as well as parts of Alaska and Hawaii. Drought expansion exceeded contraction with the USDM-based national moderate-to-exceptional drought footprint across the CONUS rising from 39.4 percent at the end of August to 42.6 percent at the end of September (from 33.3 percent to 35.8 percent for the 50 States and Puerto Rico). According to the Palmer Drought Index, which goes back to the beginning of the 20th century, about 35.7 percent of the CONUS was in moderate to extreme drought at the end of September, an increase compared to the end of August.
Drought conditions at the end of September, as depicted on the September 29, 2020 USDM map, included the following core drought and abnormally dry areas:
- Moderate (D1) to extreme (D3) drought, with a few spots of exceptional (D4) drought, extended from the West Coast to Rocky Mountains and into the adjacent High Plains. The percent area of the West experiencing moderate to exceptional drought, according to USDM statistics, increased from 67.6 percent at the end of August to 76.1 percent at the end of September. The percent area of the West (from the Rockies to the West Coast) in moderate to extreme drought (based on the Palmer Drought Index) continued its increase to about 72.0 percent. The Oregon and Washington coasts, and a few areas in the Rockies, were wetter than normal, but most of the West was drier than normal for September with some areas record dry. The short-term dryness (September, August-September, July-September) just added to longer-term dryness (last 6, 9, 12, 24 months), making matters worse. Arizona or Utah had the driest July-September, April-September, and January-September. The excessive heat in the Far West broke records and exacerbated the drought (September 2020 SPEI compared to SPI).
- Drought has expanded rapidly in the Plains during the last couple months. Abnormal dryness to severe drought (D2) covered most of the central to northern Plains at the end of September, with areas of extreme drought, while moderate to exceptional drought persisted in western portions of the southern Plains.
- In the Midwest, moderate to severe drought from the central Plains extended into western Iowa, moderate to severe drought expanded in southwest Missouri, and abnormal dryness with areas of moderate drought persisted across much of the Ohio Valley.
- In the Northeast, very dry to record dry conditions expanded moderate to severe drought and led to extreme drought developing. Maine had the driest September, and Rhode Island had the driest July-September, in the 1895-2020 record. Drought expanded from 28.0 percent last month to cover 45.3 percent of the Northeast by the end of September. Extreme drought spread into Rhode Island during September, covering 99 percent of the state by the end of the month. If the period August 30-October 4, 2016, when extreme drought sat on the state line and touched 0.01 percent of the state, is excluded, this September is the first time in the USDM's history that Rhode Island has experienced extreme drought.
- In Hawaii, moderate drought contracted on the Big Island, but abnormal dryness to extreme drought expanded on the other islands.
- Pockets of abnormal dryness and moderate drought persisted in Alaska.
- In the Caribbean, abnormal dryness continued in southern Puerto Rico and in the U.S. Virgin Islands.
- In the U.S.-Affiliated Pacific Islands (USAPI), abnormal dryness disappeared in the Marianas and shrank in the Marshall Islands, severe drought continued in the Marshalls at Wotje, and conditions worsened to extreme drought in southern Micronesia at Kapingamarangi.
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. While both the PDSI and PHDI indices show long-term moisture conditions, the PDSI depicts meteorological drought while the PHDI depicts hydrological drought. The PDSI map may show less severe and extensive drought (as well as wet spell conditions) in some parts of the country than the PHDI map because the meteorological conditions that produce drought and wet spell conditions are not as long-lasting as the hydrological impacts.
Used together, the Palmer Z Index and PHDI maps show that short-term drought occurred across much of the West and Northeast, expanding and intensifying long-term dry conditions, and across much of the central to northern Plains and Upper Mississippi Valley, contracting long-term wet conditions (PHDI maps for September compared to August). Short-term wet conditions in eastern Texas to the Lower Mississippi, and in the Southeast, intensified or expanded long-term wet conditions in those regions.
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.
The SPI maps illustrate how moisture conditions have varied considerably through time and space over the last two years. Dry conditions are evident across large parts of the West at the 1- to 12-month time scales. Parts of the Pacific Northwest and southern to central Rockies are dry at 24 months. Parts of the central to northern Plains are dry at 1-12 months. The southern High Plains (west Texas) to central High Plains (eastern Colorado and eastern Wyoming) are dry at the 1-12 month time scales. The Mid-Mississippi Valley (Iowa to Illinois) are dry at 2 to 3 months, with dryness persisting into the 6- to 12-month time scales in western Iowa and eastern Nebraska. Parts of the Ohio Valley are dry at the 1-month time scale, and parts of the southern Great Lakes are dry at 2 to 6 months. Much of the Northeast is dry at 1 to 9 months. Most of the country east of the Rockies is wet at 24 months; wet conditions dominate from the Great Lakes to Gulf of Mexico coast at 9 to 12 months; parts of the Great Lakes are wet at 3 to 6 months; and the Lower Mississippi Valley, Southeast, and Mid-Atlantic region are mostly wet at 1 to 6 months.
Standardized Precipitation Evapotranspiration Index
The SPI measures water supply (precipitation), while the SPEI (Standardized Precipitation Evapotranspiration Index) measures the combination of water supply (precipitation) and water demand (evapotranspiration as computed from temperature). Warmer temperatures tend to increase evapotranspiration, which generally makes droughts more intense.
September 2020 continued a trend of very warm temperatures across the West. Record heat occurred in the Far West with several states having a record hot September, including California and Oregon. The September heat, when combined with record warmth in August and July, and a much warmer-than-normal June and May, gave parts of the Southwest a record warm July-September and April-September. States having a record warm July-September include California, Nevada, and Arizona. States having a record warm April-September include California and Arizona. Precipitation for September, July-September, and April-September was below normal to record dry in these areas. The combination of hot and dry conditions resulted in a much more severe SPEI than SPI for September across the West, and for July-September (SPEI vs. SPI) for much of the West.
Arizona had a record dry SPEI for the last 2 to 6 months (SPEI for August-September, July-September, June-September, May-September, April-September). The SPI was also record dry for those periods. But at the 9-month time scale, Arizona's SPEI was record dry while the SPI was not record dry. The SPEI in California was record dry and far exceeded the SPI for the last 1 to 4 months (SPEI for September, SPEI for August-September, SPEI for July-September, SPEI for June-September). Colorado's August-September SPEI was at record dry levels and far exceeded the SPI which was not at record dry levels.
New Mexico had a record dry SPEI for the last 2, 4, 5, and 6 months while the SPI was not record dry for those time periods. The SPEI for Nevada was record dry for August-September, July-September, and April-September, while the corresponding SPI values were not record dry. In Utah, the SPEI was record dry for August-September, July-September, May-September, and April-September. The corresponding SPI was record dry for August-September and April-September, but not for July-September and May-September.
In the Northeast, Maine had a record dry SPEI for September as well as a record dry SPI. The SPEI for Rhode Island was record dry for August-September, July-September, and June-September, while the corresponding SPI values were not.
Much of the West has experienced persistent warmer-than-normal temperatures for most of the last nine years. The unusual warmth has made the SPEI more extreme than the SPI for those dry areas in the West at the longer time scales (SPEI maps for last 12, 24, 36, 48, 60, 72 months) (SPI maps for last 12, 24, 36, 48, 60, 72 months). The data also reveal a significant warming trend across the region over the last 40 years.
Most of Hawaii was drier than normal for the last one to 4 months. Dryness persisted on Oahu and the Big Island at the 6-month time scale and all of the main islands except Kauai at 9 to 24 months. Wet conditions dominated at 36 months with a mixed anomaly pattern at longer time scales (last 1, 2, 3, 4, 6, 9, 12, 24, 36, 48, 60 months) (climate engine model percent of normal precipitation map for the last month). Streamflow was mostly below normal on the islands from Oahu to the Maui, near normal on the Big Island, and had a mixed anomaly pattern on Kauai. Drought and abnormal dryness contracted across parts of the Big Island but expanded on the other main islands with extreme drought added to Molokai and Maui. The statewide moderate to extreme drought area shrank to 39.7 percent by the end of the month.
September 2020 was drier than normal across western and southern coastal Alaska and in the panhandle, and wetter than normal in interior to northern coastal and eastern interior regions. At the 2- to 3-month time scales, the western half of the state was drier than normal with a mixed anomaly pattern to the south and wetter than normal towards the eastern interior. At 4 to 6 months, drier-than-normal conditions were entrenched along the southern and western coastal areas, with mostly wetter-than-normal conditions along the panhandle to eastern interior region. The dryness continued along the southern coastal areas at 9 months before abating and a mixed to wetter-than-normal pattern became dominant at 12 to 24 months. Dry conditions from the panhandle to Cook Inlet became evident again at longer time scales (low elevation station precipitation anomaly maps for the last 1, 2, 3, 4, 6, 9, 12, 24, 36, 48, 60 months) (high elevation SNOTEL station precipitation maps for last 1 and 12 months, and SNOTEL basin maps for last 12 months) (gridded precipitation percentile maps for the last 1, 3, and 9 months) (climate division precipitation rank maps for the last 1, 3, 6, 9, 12 months) (station percent of normal maps from ACCAP for the last 1 month) (Leaky Bucket model precipitation percentile map). September was near to warmer than normal across the state. By 3 months, warmer-than-normal temperatures spread across western and southern portions of Alaska with near to cooler-than-normal areas in the east and in the panhandle. Warmer-than-normal conditions dominated the state at 6 months, with near to cooler-than-normal conditions taking over by 9 months. At 12 months, cooler-than-normal temperatures were limited to the interior to eastern sections with warmer-than-normal conditions to the north, west, and south (low elevation station temperature maps for the last 1, 2, 3, 4, 9, 12 months) (gridded temperature percentile maps for the last 1, 3, and 9 months) (climate division temperature rank maps for the last 1, 3, 6, 9, 12 months) (Leaky Bucket model temperature percentile map). Modeled soil moisture and satellite-based soil moisture estimates showed drier-than-normal conditions in southern coastal, western coastal, and northeastern areas, while streamflow was mostly near normal. A few large wildfires lingered in the southwest and northeast areas, but they were mostly gone by mid-month (wildfire maps for September 1, 7, 10, 13, 16). According to the National Interagency Fire Center's (NIFC) National Interagency Coordination Center, as of September 30th, 181,234 acres have been burned in Alaska so far this year. Abnormal dryness continued in the northwest and south central coastal areas; moderate drought disappeared from Kodiak Island but continued in the northwest. Moderate drought held onto 0.8 percent of the state with abnormal dryness and moderate drought shrinking to cover 22.2 percent of the state on the September 29th USDM map.
Puerto Rico and U.S. Virgin Islands
September 2020 had a mixed precipitation anomaly pattern across Puerto Rico and the U.S. Virgin Islands (USVI). It was drier than normal across eastern and southern Puerto Rico and the USVI (except eastern St. Croix), and wetter than normal over northwest Puerto Rico, for September and August-September. Wetter-than-normal conditions dominated Puerto Rico at the 3-month time scale while the USVI had a mixed anomaly pattern. Starting at the 4-month time scale and going to 6 months, wetter-than-normal conditions were confined to western portions of Puerto Rico while the USVI and eastern Puerto Rico were drier than normal. The USVI were drier than normal at longer time scales. Puerto Rico was drier than normal in the southeast at 9 to 12 months, dryness dominated at 24 to 36 months, and wet conditions dominated at 48 to 60 months (radar-based precipitation anomaly estimates for the last 1, 2, 3, 6, 9, 12 months) (low elevation station precipitation maps for the last 1, 2, 3, 4, 6, 9, 12, 24, 36, 48, 60 months). (climate engine model percent of normal precipitation map for September).
Temperatures across Puerto Rico and the USVI have been warmer than normal for the last 1 to 12 months (low elevation station temperature anomaly maps for the last 1, 2, 3, 4, 9, 12 months). Root zone analyses indicated that soil conditions continued dry along the immediate southern coast of Puerto Rico and in the eastern interior. There were some low streams in eastern and southwestern Puerto Rico. A small patch of abnormal dryness remained on the south central coast of Puerto Rico on the September 29th USDM map, while abnormal dryness continued on St. Thomas, St. John, and St. Croix.
CONUS State Precipitation Ranks
September 2020 was drier than normal across most of the West, central to northern Great Plains, and Northeast, and parts of the Ohio Valley, Great Lakes, and central Gulf of Mexico coast. Record dryness occurred in parts of the Southwest, Northeast, and Midwest. Twenty-three states in these regions had a precipitation rank in the driest third of the 126-year historical record for September, including Maine with the driest September on record. Six other states ranked in the top ten driest category, including Arizona (fifth driest), California (sixth driest), New Hampshire (seventh driest), Utah (eighth driest), and Nevada and North Dakota (each ninth driest).
July-September was drier than normal across the West and New England, and parts of the Plains and Midwest. Record dryness occurred in parts of the West and Northeast. Twenty states in these regions had a precipitation rank in the driest third of the historical record for July-September, including Arizona, Utah, and Rhode Island with the driest July-September on record. Eleven other states ranked in the top ten driest category, including Nevada and Wyoming (each second driest), California (third driest), New Mexico and Montana (each fifth driest), Maine (sixth driest), Colorado (seventh driest), Massachusetts (eighth driest), and Idaho, Connecticut, and New Hampshire (each ninth driest).
April-September was drier than normal across most of the West, Plains, and Northeast, and parts of the Midwest. Record dryness occurred, again, in much of the Southwest. Twenty-one states in these regions had a precipitation rank in the driest third of the historical record, including Arizona and Utah with the driest April-September on record. Seven other states ranked in the top ten driest category, including New Mexico (second driest), Colorado (third driest), Nevada (fifth driest), Rhode Island (sixth driest), Maine and Wyoming (each seventh driest), and Connecticut (tenth driest).
January-September had a similar precipitation anomaly pattern to the above seasons — drier than normal across much of the West, Plains, and Northeast, and parts of the Midwest. Record dryness occurred, again, in parts of the West. Twenty states in these regions had a precipitation rank in the driest third of the historical record, including Utah with the driest year to date on record. Nine other states ranked in the top ten driest category, including Colorado (second driest), New Mexico (fourth driest), Nevada and Rhode Island (each sixth driest), Arizona (eighth driest), Connecticut and Massachusetts (each ninth driest), and Maine and Wyoming (each tenth driest).
October 2019-September 2020 had the same story — drier than normal across much of the West and Plains, and parts of the Northeast and Midwest. Fourteen states in these regions had a precipitation rank in the driest third of the historical record, including three that ranked in the top ten driest category — Colorado (third driest), Utah (sixth driest), and Nevada (eighth driest).
During September 2020, the Primary Corn and Soybean agricultural belt was generally near to cooler than normal and had a mixed precipitation anomaly pattern with very dry areas and very wet areas. The month ranked as the 48th driest and 45th coolest September, regionwide, in the 1895-2020 record.
March marks the beginning of the growing season for the Primary Corn and Soybean agricultural belt. March-September 2020 had a mixed anomaly pattern for temperature and precipitation. The period ranked as the 49th wettest and 36th warmest March-September, regionwide.
As of September 29, drought affected approximately 35 percent of cattle inventory, 29 percent of corn production, 22 percent of soybean production, 28 percent of hay acreage, 32 percent of winter wheat production, and 35 percent of spring wheat production. Except for corn and soybean production, these were all increases compared to the end of August.
As of September 30, the Secretary of the U.S. Department of Agriculture (USDA) had designated 523 counties as experiencing primary drought disaster incidents in 2020, based on USDM criteria, with 273 additional contiguous counties designated as experiencing drought. Just under 29 million dollars (US) has been paid out to recipients under the USDA Livestock Forage Disaster Program, based on the USDM, through 2020 to date.
As reported by the USDA, at the end of September (September 27), topsoil moisture was short or very short (dry or very dry) across 50 percent or more of all of the states in the West and Great Plains except Arizona, Kansas, Oklahoma, and Texas, and ranged from 55 percent in North Dakota to 86 percent in New Mexico. Topsoil moisture was short or very short in the states from Indiana to New York and three in New England, and ranged from 57 percent in Ohio and New York to 100 percent in Maine and New Hampshire. Subsoil moisture was short or very short across 80 percent of California, 79 percent of Colorado, 53 percent of Delaware, 65 percent of Idaho, 72 percent of Indiana, 55 percent of Iowa, 98 percent of Maine, 66 percent of Montana, 58 percent of Nebraska, 60 percent of Nevada, 83 percent of New Hampshire, 86 percent of New Mexico, 54 percent of Ohio, 85 percent of Oregon, 64 percent of Pennsylvania, 91 percent of Rhode Island, 52 percent of South Dakota, 50 percent of Texas, 60 percent of Utah, 58 percent of Washington, 52 percent of West Virginia, and 81 percent of Wyoming. Pasture and rangeland were in poor to very poor condition in Arizona (53 percent), California (55 percent), Colorado (47 percent), Connecticut (92 percent), Iowa (42 percent), Maine (88 percent), Massachusetts (92 percent), Montana (52 percent), Nevada (40 percent), New Hampshire (80 percent), New Mexico (51 percent), Oregon (82 percent), Pennsylvania (56 percent), Rhode Island (100 percent), Washington (53 percent), and Wyoming (64 percent). Nationwide, 45 percent of the topsoil and 44 percent of the subsoil was short or very short of moisture, 40 percent of the pasture and rangeland was in poor to very poor condition, and 24 percent of the cotton crop, 14 percent of the corn crop, and 10 percent of the soybean crop were in poor to very poor condition. These national figures were all the same or slightly less than a month ago.
U.S.-Affiliated Pacific Islands
The NOAA National Weather Service (NWS) offices, the Pacific ENSO Applications Climate Center (PEAC), and partners provided reports on conditions across the Pacific Islands.
In the U.S. Affiliated Pacific Islands (USAPI) (maps — Federated States of Micronesia [FSM], Northern Mariana Islands, Marshall Islands [RMI], Republic of Palau, American Samoa, basinwide), September 2020 was drier-than-normal in the Marianas, Palau, and western and southern FSM. It was wetter than normal at Pago Pago (American Samoa), in the eastern FSM, and in the RMI.
Monthly precipitation amounts were below the monthly minimum needed to meet most water needs (4 inches in the Marianas and Pago Pago, and 8 inches elsewhere) at Koror (Palau); Nukuoro, Pingelap, and Kapingamarangi (FSM); and Jaluit and Wotje (RMI). September precipitation was above the monthly minimums at the rest of the USAPI stations in Micronesia and American Samoa. The 4- and 8-inch thresholds are important because, if monthly precipitation falls below the threshold, then water shortages or drought become a concern.
The tropical Pacific climatology can experience extremes in precipitation, from very low precipitation during the dry season to very high precipitation during the wet season. This can result in monthly normal precipitation values that are well above the monthly minimum needed to meet most water needs. This was the case during September 2020. The monthly precipitation was enough to end or stay out of drought, but still was below normal because the normals were so high. Examples include Guam (September 2020 precipitation 10.96 inches, September monthly normal mean 14.17 inches), Saipan (September 2020 precipitation 7.46 inches, September monthly normal mean 10.21 inches), and Yap (September 2020 precipitation 10.98 inches, September monthly normal mean 13.76 inches).
As measured by percent of normal precipitation, Guam, Kapingamarangi, Koror, Saipan, and Yap were drier than normal in the short term (September and the last 3 months [July-September 2020]) and long term (year to date [January-September] and last 12 months [ October 2019-September 2020]). Chuuk was drier than normal in the long term but wetter than normal in the short term. Kwajalein and Lukonor were wetter than normal for September but near to drier than normal for the other three time periods. Kosrae and Pohnpei were wetter than normal for September and one of the long-term time periods, but drier than normal for the last 3 months and the other long-term time period. Majuro was drier than normal for the last 3 months but near or wetter than normal for the other three time periods. Pago Pago was wetter than normal for all four time periods. As noted earlier, the monthly normal precipitation amount can vary significantly from month to month due to the strong seasonality of equatorial Pacific precipitation resulting from the seasonal migration of the Inter-Tropical Convergence Zone (ITCZ) and occurrence of tropical cyclones. Most of the stations in Micronesia have September monthly normal precipitation amounts that are above (and in some cases well above) the monthly minimum threshold for drought. As a result, it is possible for a station to have below-normal precipitation this time of year and still be above the monthly minimum for drought.
Based on percent of normal average (instead of normal median values), in the Marianas Islands, precipitation during September and August-September was wetter than normal at some stations and drier than normal at other stations. But precipitation was drier than normal at all of the primary stations at all time scales from the last 3 to 9 months. At longer time scales, it was wetter than normal at some southern stations (on the island of Guam) but continued drier than normal at the stations to the north (percent of normal precipitation maps for the last 1, 2, 3, 4, 6, 9, 12, 24, 36, 48, 60 months). In the Marshall Islands, the precipitation anomaly pattern was mixed for September but mostly drier than normal for the last 2 to 3 months, mostly wetter than normal for the last 4 to 12 months. The western islands were generally drier than normal and eastern islands wetter than normal at 24 months, with a mixed anomaly pattern at longer time scales (percent of normal precipitation maps for the last 1, 2, 3, 4, 6, 9, 12, 24, 36, 48, 60 months).
According to the September 30th USDM produced for the USAPI, drought improved in the Marianas but worsened in the southern FSM. Abnormally dry (D0) conditions ended at Rota and Saipan (in the Marianas) and Ailinglaplap and Kwajalein (RMI). Kapingamarangi (southern FSM) worsened from severe drought (D2) to extreme drought (D3) and abnormal dryness developed at Jaluit (RMI). Severe drought continued at Wotje (RMI). The rest of the stations in Micronesia, and Tutuila in American Samoa, were free of drought and abnormal dryness. Storage in the Majuro reservoir briefly dipped below the 80 percent of maximum threshold for concern on the 20th to 25th, but was above that threshold for the rest of the month, ending September at about 30.4 million gallons, which is 84 percent of maximum and above the 80 percent threshold for concern. The National Weather Service office in Guam issued three Drought Information Statements for the drought in September and early October (on September 5, September 18, and October 2) discussing the conditions in the USAPI. Drought impacts during September progressively worsened in the southern FSM. Observers in Kapingamarangi reported that household water tanks were around 10 percent of capacity and some were empty, and community water tanks were being tapped. As of September 30, only three of the six community water tanks were full (two tanks were empty and one tank was one-fourth full). Observers estimated that the remaining community water supply would last them about 1.5 months with no additional rainfall. Vegetation was mostly brown with no banana or breadfruit left. Taro crops were still producing as of the September 30 report. Wotje and Utirik had reverse osmosis units on site to help mitigate the effects of the drought.
The last one to 12 months have been especially dry at some of the islands in Micronesia (based on monthly and seasonal precipitation ranks) and the last 4 to 12 months have been dry at others. September 2020 was the fourth driest September in a 40-year record at Saipan, in a 29-year record at Kapingamarangi, and in 38 years at Nukuoro. It was fifth driest at Pingelap (37 years) and Jaluit (37 years), eighth driest at Ulithi (37 years), and ninth driest at Koror (70 years) and Wotje (37 years). Going back farther, Kapingamarangi had the driest August-September (26 years) and May-September (21 years) through December-September (20 years), second driest July-September (24 years), June-September (22 years), and November-September (20 years), and third driest October-September (19 years). Nukuoro had the driest July-September (37 years). Pingelap ranked third driest for August-September (36 years). Yap had the second driest July-September (70 years). Ulithi had the third driest June-September (36 years) and fourth driest March-September (35 years). Saipan ranked second driest for June-September (40 years) through November-September (31 years) and had the fourth driest 12-month period (October-September) in 31 years of data. Lukonor had the sixth driest January-September and December-September in 24 years, and fifth driest November-September and October-September (23 years). Jaluit ranked third driest for August-September (37 years) and fourth driest for July-September and June-September (36 years).
The following analysis of historical data for the USAPI stations in the Global Historical Climatology Network-Daily (GHCN-D) dataset, augmented with fill-in data from the 1981-2010 Normals, helps put the current data into historical perspective by computing ranks based on the period of record. The table below lists the precipitation ranks for September 2020, April-September 2020 (last 6 months), and October 2019-September 2020 (the last 12 months). Some stations have a long period of record and their dataset is fairly complete, while other stations have a shorter period of record and the dataset has some missing data.
|Station||September 2020||Apr-Sep 2020||Oct 2019-Sep 2020||Period of Record|
NOAA Regional Climate Centers
More information, provided by the NOAA Regional Climate Centers and others, can be found below.
As noted by the Southeast Regional Climate Center, temperatures were near average across much of the Southeast region and Puerto Rico for the month of September, and precipitation was variable with a few wet and dry extremes recorded. The driest locations were found across central Alabama, southern Georgia, and eastern Florida. Monthly precipitation totals ranged from 70 to less than 25 percent of normal across these locations. Tuscaloosa, AL (1948-2020; 9th driest) received only 0.85 inch (22 mm) of precipitation, over 2 inches (51 mm) below normal for the month. Most of Puerto Rico and the US Virgin Islands received normal amounts of precipitation for the month.
The entire Southeast region and Puerto Rico remained drought-free for the month of September. At the beginning of the month, small pockets of abnormally dry conditions (D0) were found in Georgia, Alabama, western Florida, and southern Puerto Rico. By the end of the month, however, only small pockets of abnormally dry conditions (D0) in Georgia, Alabama, and southern Puerto Rico remained. Some crops were damaged due to heavy rains and wind from Hurricane Sally. Livestock and pastures, on the other hand, were in mostly good condition.
As explained by the Southern Regional Climate Center, temperatures for the month of September ranged from slightly above normal to below normal across the Southern region, with the region as a whole experiencing its forty-ninth coldest September on record. Precipitation values for the month varied spatially across the region. Parts of northwestern Arkansas, southeastern Louisiana, southern Mississippi, northern Oklahoma, and northern and western Texas received 50 percent or less of normal precipitation. Parts of northern and western Texas received 25 percent or less of normal precipitation, while parts of western Texas received 2 percent or less of normal precipitation. In contrast, parts of central and southern Arkansas, northern Louisiana, eastern Mississippi, southern Oklahoma, eastern Tennessee, and central, eastern, and southern Texas received 150 percent or more of normal precipitation, while parts of central and southern Arkansas, northwestern Louisiana, southern Oklahoma, and central and eastern Texas received precipitation 200 percent or more of normal. The region as a whole experienced its thirty-first wettest September on record.
At the end of September, drought conditions both improved and deteriorated across the Southern region. Exceptional drought conditions developed and persisted across western and northwestern Texas. Extreme drought conditions persisted across southwestern Oklahoma and northern Texas, with new areas developing or expanding across western Oklahoma and western Texas; however, areas in northern and western Texas saw improvement or removal. Severe drought classifications were removed or diminished across parts of central and northern Texas as well as southwestern Oklahoma, but areas expanded across western Texas. Moderate drought classifications were removed or diminished across parts of northeastern Arkansas, western Oklahoma, and central, western, northern, and eastern Texas; however, moderate drought conditions expanded or developed across western Oklahoma, northwestern Arkansas, and western Texas. There was a decrease in the overall area experiencing abnormally dry conditions, with conditions eliminated across western Tennessee, northeastern Arkansas, southwestern and northeastern Louisiana, western Mississippi, southeastern Oklahoma, and eastern and central Texas. However, abnormally dry conditions persisted or expanded across parts of northern and eastern Mississippi, northwestern Arkansas, southeastern Louisiana, northern Oklahoma, and northern Texas.
As described by the Midwest Regional Climate Center, September precipitation in the Midwest ranged from less than 0.50 inch (13 mm) in southern Indiana to more than 6.00 inches (152 mm) in eastern Iowa, northern Illinois, and extreme southwestern Wisconsin. Much of the region had precipitation totals that fell below normal. Total precipitation for the region was 2.86 inches (73 mm) which was 0.58 inch (15 mm) below normal. Significantly dry areas were observed across Minnesota, southern Illinois, and southern Indiana. The totals in southern Indiana were less than 25 percent of normal with a few areas below 10 percent of normal. September temperatures ranged from near normal to below normal. The average temperature for the region was 62.2 degrees F (16.8 C) which was 0.7 degrees F (0.4 C) below normal.
Drought significantly improved in Iowa and northern Illinois during September. Soaking rainfall from September 8th to 14th aided in eliminating extreme drought from Iowa and led to a 35 percent decrease in Iowa drought coverage as of the September 29th USDM. However, drier weather across southern Missouri, southern Illinois and Indiana led to an expansion of drought and abnormally dry conditions in these areas. Overall, drought coverage dropped by five percent in September, while abnormally dry conditions increased by five percent.
As explained by the Northeast Regional Climate Center, the Northeast had its 18th driest September on record with 2.32 inches (58.93 mm) of precipitation, 59 percent of normal, and the month averaged out to be 61.2 degrees F (16.2 degrees C), 0.5 degrees F (0.3 degrees C) warmer than normal. Maine had its driest September on record, while New Hampshire had its seventh driest and Rhode Island had its 11th driest. Ten of the 12 Northeast states were drier than normal, with precipitation ranging from 23 percent of normal in Maine to 103 percent of normal in New Jersey.
The USDM released on September 3 showed 28 percent of the Northeast in a severe or moderate drought and 26 percent as abnormally dry. These areas included much of New England and parts of New York and Pennsylvania. Conditions worsened during September, with moderate and severe drought expanding in the region and the introduction of extreme drought in New England for the first time since February 2017. In fact, at month's end, all of Rhode Island was in an extreme drought for the first time in the USDM's history (since 2000). The USDM for September 29 released on October 1 showed 45 percent of the Northeast in an extreme, severe, or moderate drought and 25 percent as abnormally dry.
There were numerous impacts from the drought and abnormally dry conditions. During September, streamflow and groundwater levels were much below normal in many of the drought areas, with some sites setting daily record low streamflows. In fact, the Aroostook River at Masardis and Washburn, Maine, dropped to an all-time record-low flow. In New Hampshire, officials were performing dam releases in the Lamprey River watershed to help stressed aquatic species. To protect fish populations in the Salmon River and its tributaries, which were experiencing low water levels due to drought conditions, New York State officials closed a section of the river to fishing and delayed a scheduled baseflow increase. Low streamflow and warm temperatures in the Farmington River in Connecticut caused officials to delay restocking trout and salmon. Water restrictions were enacted or remained in place for numerous locations in Massachusetts and several locations in Connecticut, Maine, New York, and Pennsylvania. As of September 30, 165 community water systems, seven municipalities, and some private well users in New Hampshire had restrictions in place. In addition, dry wells were reported across New England and in New York. Some well drilling contractors in New Hampshire and Rhode Island had a 6 to 12 week wait.
Agriculture continued to suffer across the region. A press release from the Maine Drought Task Force noted crops across the state continued to experience drought stress and there were irrigation issues, particularly in Aroostook County, leading the Maine Department of Environmental Protection to issue an irrigation warning. Aroostook County was declared a primary natural disaster area by the U.S. Department of Agriculture due to drought, which reduced some crop yields by 50 percent. Portions of southern Maine saw forage crop yields reduced by up to 60 percent, with similar conditions in parts of New Hampshire. Farmers in both states, as well as in other states affected by drought, were buying hay to feed livestock this winter. Purchasing hay and irrigating crops increased expenses for farmers. For instance, in New Hampshire, one farmer spent around $14,000 on feed for livestock, while another farmer had $30,000 in irrigation-related costs including equipment and additional workers to perform the tasks. For the week ending September 27, topsoil moisture was rated short or very short for all of Maine and New Hampshire and over 90 percent of Rhode Island. Subsoil moisture was rated short or very short for more than 90 percent of Maine and Rhode Island and more than 80 percent of New Hampshire. For the same period, pasture and rangeland conditions were rated very poor (the lowest level) for 90 percent of Rhode Island and 73 percent of Massachusetts and Connecticut, while 10 percent of Pennsylvania's corn crop was rated very poor, making it some of the worst corn condition ratings in the country.
There have been fewer ticks and mosquitoes, and in turn, fewer insect-related illnesses, this year in New England due to a lack of moisture. Fire risk remained elevated in areas of New England, New York, and Pennsylvania that were experiencing drought and abnormal dryness. Much of New England was seeing an unusually high number of fires or atypical fire behavior. Massachusetts has seen more than 1,000 wildfires this year, with 41 of those occurring during the week ending September 22, which is unusual for September. With 1000 wildfires as of September 24, Maine had its worst year for fires in 20 years. There were at least four ground fires in Vermont this year, which is atypical. Rhode Island officials were seeing unusual fire behavior such as fires climbing trees and were concerned that items like lawn mowers and chains could spark wildfires, which is a typical wildfire behavior in the western U.S. and unusual for the Northeast. The governor of New Hampshire enacted an emergency drought law banning outdoor fires and smoking near public woods. In addition, several New Hampshire communities as well as the White Mountains National Forest enacted burn bans. Across New England, fires have burned deeper and taken longer to extinguish. In addition, drought conditions have dried up or reduced water supplies that some firefighters rely on to fight fires.
As summarized by the High Plains Regional Climate Center, the month of September brought a variety of extreme weather to the High Plains region. Temperatures varied across the region during the month and the month as a whole was dry. The majority of the region had below-normal precipitation, with only a few isolated areas observing above-normal precipitation. The driest areas of the region, which primarily included portions of the Dakotas and Nebraska, had less than 25 percent of normal precipitation. The persistent dryness, combined with above-normal temperatures, led to increasing and worsening drought conditions for portions of the High Plains. By the end of September, over 60 percent of the High Plains region was experiencing drought. Some locations ranked in the top 10 driest Septembers on record, including Sioux Falls, SD (4th driest); Laramie, WY (6th driest); and Grand Forks, ND (7th driest). Precipitation deficits had also become quite impressive in some locations. For instance, by the end of September, Omaha, Nebraska had a year-to-date precipitation deficit of 12.19 inches (310 mm).
Pasture conditions continued to worsen across areas of Colorado, Wyoming, Kansas, and Nebraska, which has had a significant impact to livestock. According to the Drought Condition Monitoring Observer Reports, many pastures in these states had little to no green grass, which has left livestock with little to eat and is forcing ranchers to use supplemental feed. In western Nebraska, "catastrophic" crop losses were reported, with one agricultural producer reporting that crop production in 2020 was less than 10 percent of what it was in 2019. The continuation of dry conditions also exacerbated wildfires in Colorado and Wyoming. The Cameron Peak Fire, which became Colorado's third largest wildfire in recorded history, continued to burn across the northern part of the state and was only 42 percent contained by October 1st. In Wyoming, the Mullen Fire quickly grew in size at the end of the month, with more than 151,000 acres burned as of October 5th. The smoke from these fires, combined with smoke from the wildfires along the West Coast, plagued the region with hazy skies and poor air quality throughout the month. According to USGS WaterWatch, both above-normal and below-normal streamflows were present across the High Plains in September. Streamflows remained below normal at many locations across Colorado, Wyoming, northern North Dakota, and southwestern Nebraska as persistent dryness continued in these areas. Lake and reservoir levels were also quite low in some areas due to worsening drought conditions, which was impacting agricultural and recreational activities. For instance, some irrigation districts in northeastern Colorado and western Nebraska have begun to run out of water. Recent dryness in eastern South Dakota provided some benefit, however. On September 30, the James River near Stratford finally fell below flood stage. The river had been above flood stage for 546 consecutive days at this location. This was an unprecedented event for a river in the Lower 48 in modern times of flood control.
Drought conditions expanded and intensified in portions of the High Plains through September. According to the USDM, the area experiencing drought (D1-D4) in the region increased by approximately 12.5 percent between August 25th and September 29th. A continuation of below-normal precipitation led to worsening conditions throughout much of the High Plains. While precipitation that fell early in the month looked promising, it did little to improve drought conditions across the region. Exceptional drought conditions (D4) developed in a small area of western Colorado, and remained in place over a pocket of eastern Colorado. Extreme drought conditions (D3) expanded over parts of Colorado and Wyoming, with D3 conditions being introduced in portions of Nebraska and western Kansas as well. Severe drought (D2) persisted over parts of all High Plains states, and new areas of D2 developed in northern North Dakota and southeastern South Dakota. Areas of moderate drought (D1) conditions expanded significantly across Nebraska and North Dakota, with some expansion across northwestern Kansas. Abnormally dry conditions (D0) increased in coverage across large swaths of the High Plains region, filling in areas of South Dakota, Nebraska, and Kansas. Meanwhile, conditions improved in southeastern Kansas in September, as heavy rains led to the removal of D1.
As described by the Western Regional Climate Center, September marked yet another month of anomalously warm temperatures and unseasonably dry conditions across parts of the West — including Arizona, California, Nevada, and Oregon where average temperatures fell into the top 10th percentile or record warmest. In California and Oregon, numerous large wildfires — exacerbated by the extreme hot and dry conditions — burned hundreds of thousands of acres, produced dense smoke, and degraded air quality conditions into the unhealthy-to-hazardous range across the West Coast states affecting metropolitan areas including San Francisco, Portland, and Seattle. With the Southwest monsoon season ending, numerous records were broken across the region for the driest monsoon on record including Las Vegas (tied for driest) and numerous localities across the Four Corners states — record or near-record dryness occurred across much of Arizona including Flagstaff, Page, Prescott, Tucson, Williams, and Window Rock. Elsewhere in the West, precipitation for September was above normal (about 110-250% of normal) across western portions of Oregon and Washington as well as in isolated areas of southern Colorado, central Idaho and Wyoming, and north-central Montana while the remainder of the region was dry. By the end of August, 76% of the West was experiencing drought according to the USDM — with areas of Extreme (D3) and Exceptional (D4) drought in the Four Corners states and Nevada. In terms of statewide reservoir conditions, below-average storage levels were observed (Sept. 1) in Arizona, California, Colorado, Nevada, New Mexico, and Oregon.
In Alaska, slightly above-normal temperatures prevailed across much of the state with the greatest departures along the North Slope, central Interior, and in areas of the Panhandle. For the month, precipitation was below normal in the Panhandle (less than 85% of normal) after a wet summer season while further to the north above-normal precipitation was observed across the central and northeast Interior, North Slope, and in the Northwest Gulf climate divisions. For the summer, the South Panhandle climate division recorded its wettest June-August period on record. In the Hawaiian Islands, drought conditions intensified leading to implementation of water restrictions in areas of Maui County (Upcountry and West Maui). For September, select rainfall totals were as follows: Hilo Intl AP 8.79 in (223 mm; 88% of normal), Honolulu Intl AP 0.07 in (1.8 mm; 10% of normal), and Lihue AP 1.26 in (32 mm; 59% of normal).