Tools used in the U.S. Monthly Drought Outlook (MDO) include the Climate Prediction Center (CPC) temperature and precipitation outlooks for September, various short- and medium-range forecasts and models such as the 7-day quantitative precipitation forecast (QPF) totals from the Weather Prediction Center (WPC), the 6-10 day and 8-14 day CPC extended-range forecasts (ERFs), dynamical models at the monthly time scale, climatology for September, and initial conditions such as soil moisture. Given the ongoing ENSO episode and the expectation for it to continue into 2024, correlations with ENSO conditions were considered. The U.S. Drought Monitor valid on August 29, 2023 was used for initial drought conditions.

The monthly Drought Outlook is a tricky one in the Western Region. Two factors could potentially bring improvement to part of the region. First, an early-month plume of tropical moisture is expected to bring moderate to heavy precipitation to an area extending from Desert Southwest northward across Utah and into the Intermountain West. After the first few days of the month, however, drier conditions should prevail, and there are currently no strong indicators of substantial precipitation at any time during the rest of the month. The forecast calls for improving conditions in the drought areas that are expecting heavy early-month rains, but little or no precipitation over the ensuing weeks may undo any improvement made if the tropical plume of moisture is not as robust as forecast. Farther north, odds favor above-normal precipitation in the Pacific Northwest, but climatology makes this a difficult forecast. September is one of the drier months of the year there, usually bringing only 2 percent to 5 percent of the annual precipitation total. Given the meager climatology and the relatively long-term nature of the drought, even this above-normal precipitation is not expected to be sufficient for notable relief, although the contradictory indicators make this a low-confidence forecast. In other parts of the West Region, precipitation may be slightly above-normal around mid-month across the northern Rockies, but forecast indicators are weak, and the odds for persistence outweigh the chances for improvement. Finally, in the southern Rockies, most of the month is expected to be unusually warm and dry, either keeping drought intact as is or prompting some deterioration east of the tropical plume of moisture.

Confidence in the West Region is generally low, but moderate across New Mexico and adjacent areas.

The September monthly outlook favors drier than normal weather in roughly the southeastern half of High Plains Region, with no discernible tilt of the odds toward unusually dry or wet weather from the Nebraska Panhandle northward and westward across the west half of Colorado, most of Wyoming and North Dakota, and the northwest half of South Dakota. Meanwhile, there are robust indicators pointing toward a considerably warmer than normal month throughout this region, especially the eastern and southern sections. During the first week of September, daily high temperatures are expected to average 10 to 15 degrees F above normal from central South Dakota and eastern Wyoming southward through most of eastern Colorado and Kansas. Given the expected heat, drought persistence or intensification is the only reasonable forecast in the southeast half of the Region, with drought forecast to expand broadly to cover the entire Region to the south and east of central South Dakota by the end of the month. Farther north and west, temperatures are expected to average closer to normal, and light to moderate precipitation is possible around mid-month. The only current area of drought falling into this area is across northern North Dakota. Drought is not expected to improve, but the less extreme weather anticipated should squelch any rapid deterioration or expansion.

Forecast confidence in the High Plains is high in most of the southern and eastern parts of the region, and moderate farther north.

Conditions vary significantly by location across the South Region. Central Oklahoma, most of Arkansas and Kentucky, and much of Mississippi and Alabama are currently free of drought. In contrast, drought generally covers a portion of northern Oklahoma and large parts of Texas, Louisiana, and southern sections of the central Gulf Coast. The worst conditions extend from eastern Texas eastward across the Lower Mississippi Valley into southern Mississippi. At least extreme drought (D3) currently covers this area, with patches of exceptional drought (D4) reported in central Texas, southeastern Texas, and southwestern Louisiana. Long periods of exceptional heat have affected these areas in addition to subnormal precipitation, and there is no relief in sight through the first week of daily high temperatures, with daily highs expected to average 8 to 14 degrees F above normal. There are enhanced chances for a drier than normal September over central and eastern sections of the South Region while tools point toward slightly wetter weather farther east, especially early in the month. The entire region has significantly increased odds of above-normal temperatures in the 6- to 10-day, the 8- to 14-day, and week 3-4 outlooks, in addition to the month as a whole. From the Louisiana Bayou eastward across southern Mississippi, some tropical moisture is expected to trigger areas of heavy rain early in the month, partially fueled by Hurricane Idalia as it passes east of the South Region. In these areas, some degree of improvement is expected, although drought removal is only expected in a small area on the fringes of the region. In other areas where only light rainfall is expected, drought will likely persist or intensify, expanding to cover the remainder of northwestern Texas, Oklahoma, and western Arkansas where the strongest signals for warmer and drier than normal September conditions are found. Recent tropical rainfall farther south in Texas is expected to preclude any expansion there.

Forecast confidence in the South Region is high in the western half and moderate in the eastern half.

The Midwest Region is a mixed bag, with areas of severe to extreme drought common across the Upper Midwest and the west side of the Middle Mississippi Valley while only a few isolated areas of drought can be found on the east side of the Middle Mississippi Valley, Indiana, Ohio, and most of Michigan. This dichotomy may not be the case by the end of the month. Surface moisture shortages have begun to intensify during the past few weeks in most areas not currently experiencing drought over the eastern Great Plains, Illinois, and Indiana. The monthly long-lead forecast favors subnormal September precipitation regionwide, with the best chances for significantly lower than normal precipitation covering the Middle Mississippi Valley. At the same time, temperatures are expected to average higher than normal for September, with the best odds in western parts of the region. Given increased short-term dryness and with most tools pointing towards an unusually warm and dry September. Areas of existing drought are expected to persist, and drought is anticipated to broadly expand by the end of the month, leaving only easternmost Indiana, most of Michigan, and Ohio out of drought at September’s end. The drought development area has been limited to locales with an elevated chance for a drier than normal September in the Long-Lead Outlook, but expansion farther to the south and east would not be too surprising.

Forecast confidence in the Midwest Region is high in the western half and moderate in the eastern half.

In the Southeast Region, only a few patches of drought are identified along the central Gulf Coast, in the western Florida Peninsula, the central and eastern Carolinas, and northwesternmost Virginia. Most areas north of Florida and south of Virginia are being inundated by rainfall from Hurricane Idalia as it pushes across the region, squelching most areas of existing drought before mid-month. Additional tropical moisture could bring rains to southern Alabama and western Florida as well early in the month before drier weather prevails. Drought removal or improvement is the only reasonable forecast regionwide with the exception of northern Virginia, which is expected to miss the early-month precipitation. Persistence with slight expansion into current areas of surface moisture shortages is expected there.

Forecast confidence for the Southeast Region is high, except moderate in northern Virginia.

Only two small areas of drought exist in the Northast Region: One across central Maryland and adjacent Pennsylvania, and another in upstate New York. Along with the rest of the Lower 48, a warmer-than-normal temperature is forecast regionwide, and there is a slight tilt of the odds toward unusually dry weather in upstate New York. Some tools highlight the chance for increased rainfall in southern parts of the East Region later in the month, but with low confidence. Both areas of drought are expected to persist through September, with a little expansion into southwestern parts of the East Region where surface moisture stress is already observed. But given weak signals, these forecasts aren’t of great condfidence.

Forecast confidence in the Northeast Region is moderate in upstate New York, and low farther south.

No drought exists in Alaska and none is expected to develop.

Forecast confidence in Alaska is high.

Drought expanded to cover a large part of Hawaii in August, and at least some degree of dryness (D0 or worse) exists throughout the state. The ongoing ENSO which should persist into 2024 favors continued drier than normal weather, so existing areas of drought should persist or perhaps intensify in spots by the end of September. Some expansion of drought into other areas is probable, but there is not enough confidence to identify any specific area as being at greatest risk for drought development.

Forecast confidence in Hawaii is moderate.

Moderate drought continues to affect part of northwestern Puerto Rico, as has been the case for several months. Conditions have marginally improved recently, but complete removal of drought is not strongly indicated. Limited improvement is anticipated, which should be enough to remove current areas of nominal drought. This is only based on increased rainfall climatology heading into later summer and autumn, and recent trends, and is thus a low-confidence forecast.

Forecast confidence in Puerto Rico is low.

Extreme drought (D3) is assessed in the western Virgin Islands at St. Croix and St. Thomas while moderate drought (D1) exists farther east in St. John. With weak forecast indicators, the outlook is based on the climatological increase in rainfall observed during September. This should be enough to provide a little relief in the most severely affected areas of St. Croix and St. Thomas, but will likely be insufficient to remove drought completely from St. John.

Forecast confidence in the Virgin Islands is low.

Forecaster: Rich Tinker

Next Monthly Drought Outlook issued: September 30, 2023 at 8:30 AM EDT