Drought Summary September 2021

During September, drought conditions largely remained the same or improved in the northern Great Plains and in New England. Meanwhile, flash drought developed in the southern Great Plains, particularly across Oklahoma, where widespread 2- to 4-category degradations occurred over the course of the month. By the end of September, moderate drought covered large sections of Oklahoma, with pockets of severe and extreme drought developing as well. Drought degradation also occurred in parts of eastern Colorado, while some improvement occurred in Arizona. At the end of the month, moderate drought coverage had increased slightly from 39.03 to 40.05%. Severe drought coverage dipped slightly during the middle of September, but ended the month at 30.61%, unchanged from the beginning of the month. Extreme drought coverage decreased from 20.47 to 19.32% during September, and exceptional drought coverage dropped slightly from 6.62 to 6.07%. 

During October, the National Weather Service Climate Prediction Center is forecasting removal of or improvement in drought conditions in the central United States and in portions of the Pacific Northwest. Meanwhile, across much of the western United States and the northern Great Plains, drought is forecast to persist. Drought is forecast to persist in Hawaii, and to develop in southern and eastern Puerto Rico.

September temperatures were generally within 3 degrees of normal in the eastern and southeastern United States and in the Pacific coast states. In the Great Plains and western portions of the Midwest, temperatures from 6 to 9 degrees above normal were quite common.

During September, there were a few very dry areas in the continental United States. Most of central and eastern Montana received less than half of their normal precipitation for September. Most of the southern Great Plains was dry; in particular, central Oklahoma and northeast Texas were very dry. Large parts of the two states received less than half of their normal September rainfall, with some areas receiving less than a quarter of normal September rains. Some above-normal precipitation occurred in the Pacific Northwest, Pennsylvania and southern New York, and southern Louisiana and southern Mississippi, the latter two areas having received copious rainfall from Hurricane Ida and its remnants at the beginning of the month.

September began in the Northeast with a small area of moderate drought in West Virginia, and moderate and severe drought in northern reaches of Maine, New Hampshire, and Vermont. The coverage of the moderate and severe drought in New England was reduced over the course of September. During the first week of the month, the moderate drought in West Virginia and adjacent Virginia ceased, after widespread heavy rainfall struck with the remnants of Hurricane Ida. Parts of Pennsylvania, southern New York, and southern New England ended September with well above normal rainfall, following severe flash flooding in some locations brought on by Ida’s remnants. Temperatures in the Northeast were generally a bit above normal, though over the course of the month, most areas did not exceed 3 degrees warmer than normal. Severe drought coverage across the Northeast dropped from 1.54 to 0.8%, and moderate drought coverage dropped from 12.13 to 3.14%.

Moderate drought was removed from Virginia after heavy rain associated with Ida at the beginning of September. At the beginning of September, this moderate drought area had covered 0.64% of the region. Otherwise, the Southeast remained free of drought, though some abnormal dryness developed in the middle of the month in Georgia, South Carolina, and North Carolina. Aside from northern Virginia, September temperatures in Virginia were generally near or a couple degrees below normal. Eastern North Carolina and northern South Carolina had below-normal rainfall, while northern Virginia received above-normal rainfall. Otherwise, drier and wetter weather was scattered about the remainder of the region.

During September, flash drought developed across parts of the South region, particularly in Oklahoma, Texas, and Arkansas. Widespread moderate drought, with pockets of severe and extreme drought, covered much of Oklahoma by the end of the month. In much of Oklahoma and the Texas Panhandle, temperatures from 4 to 6 degrees above normal and well below normal rainfall contributed to the rapid onset of abnormal dryness and drought. In contrast, near to slightly below normal temperatures combined with well above normal rainfall in Louisiana, and drought and abnormal dryness avoided the state. At the end of September, moderate drought coverage across the region had ballooned from 1.27 to 13.94%. Severe drought coverage increased from 0.10 to 3.29%, and extreme drought was introduced, covering 0.35% of the region by the end of the month.

Aside from Kentucky, which saw slightly below normal temperatures, September was a warmer than normal month across the Midwest. Temperatures from 3 to 4 degrees above normal were common in Missouri, northern Illinois, southern Iowa, southwest Lower Michigan, and northwest Indiana. Dry weather recurred across much of Wisconsin, northern Illinois, Iowa, and northern Missouri. Above-normal rainfall fell from central Kentucky to southeast Lower Michigan, and in parts of Minnesota, leading to some improvement in drought conditions. Drought re-intensified from northern Illinois to central Iowa. Moderate drought coverage decreased slightly from 24.54 to 23.36%, severe drought coverage decreased from 12.68 to 12.29%, extreme drought coverage dropped from 6.38 to 4.16%, and exceptional drought coverage of 1.15% at the beginning of the month was eliminated.

Precipitation anomalies varied widely across the High Plains region in September. Very dry conditions occurred in southeast Nebraska, northern North Dakota, southwest Nebraska, southeast Wyoming, and northeast Colorado. Above-normal rainfall fell in parts of central Nebraska, central and western Kansas, and south-central South Dakota. The entire region was warmer than normal during September, and temperatures from 3 to 5 degrees above normal were widespread. A mix of degradation and improvement occurred in Kansas, Nebraska, and North Dakota, while eastern Colorado mostly saw degrading conditions. South Dakota had primarily improving conditions, with the exception of the southwest corner of the state. Across the region, moderate drought expanded its footprint from 61.28 to 63.58% of the region. Severe drought coverage increased from 42.33 to 43.69%, extreme drought coverage decreased from 21.41 to 18.57%, and exceptional drought coverage decreased from 1.58 to 0.86%.

Drought continued to be widespread in the West region in September. Some cooler than normal temperatures were found in parts of Oregon. Otherwise, generally speaking, temperatures were near or warmer than normal across the region, particularly in Montana and New Mexico. Below-normal precipitation occurred from Nevada to central and eastern Montana, while above-normal precipitation fell in northern California, Oregon, and Washington. Some above-normal precipitation also occurred in southeast Arizona during September. Overall, drought coverages decreased slightly during September across the west. Moderate drought coverage fell from 94.97 to 93.35%, severe drought coverage decreased from 83.13 to 81.07%, extreme drought coverage dropped from 60.51 to 58.72%, and exceptional drought coverage decreased from 22.81 to 21.77%.

In southeast Alaska and in the Aleutian Islands, temperatures across September were generally within a couple degrees of normal. In other parts of the state, temperatures from 2 to 5 degrees colder than normal were common. Near- or above-normal precipitation was common in northern and southeast Alaska, while some parts of central and southern Alaska received below-normal precipitation. The state was free of drought or abnormal dryness throughout September.

September temperatures in Hawaii were mostly within a couple degrees of normal, but tended toward the cool side in most locations. Above- and below-normal rainfall was scattered across the state, though Molokai and southern Oahu stood out as much drier than normal for the month. Extreme drought developed on Molokai, while Oahu saw conditions improve in some areas. Moderate drought coverage dropped from 40.06 to 38.48%, severe drought coverage increased from 19.58 to 20.50%, and extreme drought coverage increased from 4.60 to 6.39%.

Drought conditions in Puerto Rico mostly degraded in September. Southern and eastern Puerto Rico received below-normal rainfall during the month, while above-normal precipitation was common in the north-central and west-central parts of the island. Moderate drought coverage in Puerto Rico started at 4.09%, peaked at 16.45% during the middle of the month, and settled at 11.84% at the end of September.