National Climatic Data Center
16 October 2007
September 2007 is Eighth Warmest on Record for Contiguous United States
Drought Worsens Across Southeast and Tennessee Valley
Temperatures in September 2007 were the eighth warmest on record, hot enough to break 1,000 daily high records across the United States, according to scientists at NOAA's National Climatic Data Center in Asheville, N.C.
The heat also helped spread the worsening drought to almost half of the contiguous U.S., with conditions across the Southeast, Mid-Atlantic and Tennessee Valley hardest hit. The global surface temperature was the fifth warmest on record for September, and the extent of Arctic Sea ice reached its lowest amount in September since satellite measurements began in 1979, shattering the previous record low set in 2005.U.S. Temperature Highlights
The average temperature for September in the contiguous U.S. was 67.5 degrees F (19.7 degrees C), which was 2.1 degrees F (1.2 degrees C) above the 20th century mean, and made the month the eighth-warmest September since records began to be kept in 1895, based on preliminary data.
38 of the 48 contiguous states were warmer than average, and no state was cooler than average for the month. The remaining 10 states were near average.
Raleigh-Durham International Airport reached a high of 101 degrees F (38 degrees C) on September 10, the latest date in any calendar year with a maximum daily temperature greater than 100 degrees since records began in 1944.
It was the 12th warmest September in Alaska, 2.6 degrees F (1.4 degrees C) above the 1971-2000 mean for the state. Nome was completely frost free for the months of June, July, August and September.U.S. Precipitation Highlights
In September, the drought expanded in the Southeast and parts of the mid-Atlantic and Ohio Valley. Drought affected 78 percent of the Southeast, with almost one-quarter of the region affected by exceptional drought conditions, the highest stage of drought, according to the federal U.S. Drought Monitor.
Overall, drought affected 46 percent of the nation, including the Upper Midwest, where persistently dry and warmer than average conditions have helped bring Lake Superior's water level to its lowest point on record for this time of year, according to NOAA's Great Lakes Environmental Research Laboratory.
Levels of all the Great Lakes, which together make up about 20 percent of the world's fresh surface water, have been in decline since the late 1990s. Lakes Huron and Michigan were about two feet below their long-term average levels, while Lake Superior was about 20 inches off, Lake Ontario seven inches below, and Lake Erie three inches below normal in September.
In large parts of the Southwest, the most recent water year (October 2006 - September 2007) was especially dry. Pasadena, Calif., experienced its driest water year since records began in 1878.
September began with numerous large fires burning across the northern Rockies, but fire activity dissipated by the end of the month, as rain and high elevation snow dampened the region. By the end of September, more than eight million acres had burned across the nation, most of it in the West.
September 2007 was the twelfth wettest on record in Anchorage, Alaska, with 4.30 inches of precipitation, 1.43 inches above normal. However, dry conditions in northern Alaska contributed to a very large, late-season wildfire. The Anaktuvuk River wildfire, caused by lightning, burned over 250,000 acres, setting a record for the largest fire on the North Slope.
Tornadoes were reported in conjunction with each of three storms that affected the southeastern U.S. (Tropical Storms Gabrielle and Humberto, and Tropical Depression 10). Between September 10 and 22, each of the states in the Southeast region reported tornadic activity.Global Highlights
The combined global land and ocean surface temperature for September was the fifth warmest on record, 0.92 degrees F (0. 51 degrees C) above the 20th century mean. The global land surface temperature for September was the second warmest since records began in 1880.
The average Arctic sea ice extent for the month of September was 4.28 million square kilometers (1.65 million square miles), the lowest September extent since records began in 1979, according to the National Snow and Ice Data Center, shattering the previous record for the month, set in 2005, by 23 percent.
Heavy monsoon-related rainfall affected parts of South Asia during September. In India, nearly three million people were affected by the worst flooding in years from September 6 through12.