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. The U.S. Drought Monitor valid on August 27, 2024 was used for initial drought conditions.

In the West Region, September starts the climatological transition from the dry summer season to the wet winter in the Intermountain West and the Far West, but precipitation typically does not begin in earnest until later in the year, especially across California. September typically brings less than 1 percent of annual precipitation to a majority of California, with 1 to 5 percent of the annual total typically recorded in Nevada, central and western Idaho, Washington, Oregon, and the remainder of California. In contrast, seasonal monsoon rains are typically winding down during September in the Four Corners Region, but it usually remains wetter than months in New Mexico and parts of adjacent Arizona and Utah (with 10 to 15 percent of annual precipitation typically observed). Elsewhere, September is not particularly anomalous compared to other times of the year along the western edge of the Rockies and across Montana. In most areas, existing drought is expected to persist or possibly worsen by the end of September, given the September outlook favoring drier than normal weather in most of the central and eastern sections of the region. With antecedent dryness and no indications of heavy precipitation in the near future, drought is expected to develop in part of central Idaho, along with southwestern New Mexico and adjacent Arizona. In contrast, the southeastern and northwestern fringes of the West Region are expected to see some relief. The September outlook favors above-normal precipitation in the Northwest, but with normals being low relative to later in autumn and winter, drought improvement or removal is forecast to be limited to areas where normal September precipitation exceeds 3 inches. Meanwhile, heavy rains during the first week of September should bring some drought relief to southeastern New Mexico.

Forecast confidence in the West Region is high.

In the High Plains Region, September is neither a markedly wet nor dry time of year, so the Drought Outlook leans more on the various forecast products and not climatology. The official September Outlook favors subnormal precipitation throughout the region, with odds for notable dryness exceeding 40 percent outside the southern and western tiers. With no significant precipitation forecast in the short-term, drought conditions should persist or intensify where they exist. There is currently no drought along the South Dakota and Nebraska border region, but antecedent precipitation deficits, below-normal soil moisture, and the forecast for a drier than normal September, drought is expected to develop along this corridor.

Forecast confidence for the High Plains Region is high.

Improvement is expected in the areas of drought currently impacting the Southern Region. The September outlook favors above-normal rainfall across most of the region (outside Oklahoma and northwestern Arkansas), with a couple areas of significantly enhanced chances for a wet September. Odds for substantially wetter-than-normal weather exceed 50 percent over interior sections of north-central and west-central Texas, with odds topping 40 percent in surrounding areas, and across southern and eastern sections of Louisiana and easternmost Tennessee. Abundant precipitation is expected to start early in the month across most of this region, with the first week bringing 2 to locally 4 inches of rain to a large part of Texas and the Gulf Coast of Louisiana. Farther north, most other locations are forecast to receive a few tenths of an inch to slightly over an inch during September 1 - 7. Climatologically, September is wetter than most months in central and western Texas, with over 15 percent of the annual precipitation typically falling on the Big Bend. September is unremarkable to slightly dry-leaning relative to other times of the year from extreme eastern Texas eastward, but enough September rains fall to impact existing drought conditions if totals are above-normal. All this considered, drought improvement/removal is the only reasonable forecast to make in most of the region. Most of Oklahoma and portions of Arkansas, however, are notable exceptions, with only light short-term rains expected and no tilt of the odds toward wetness nor dryness for the month as a whole; persistence is forecast there.

Forecast confidence in the South Region is high.

Only small areas of drought exist across the Midwest Region in late August, but one area in southeastern Ohio has experienced significantly worsening drought over the past several weeks. In southeastern Ohio, 30-day rainfall totals are 1.0 to 2.5 inches below normal, and deficits since the end of May range from 4 to 6 inches. Climatologically, September is a little wetter than most months across most of the Great Lakes and upper Mississippi Valley, with generally 10 to 15 percent of the annual precipitation observed. Elsewhere, September is not markedly wetter nor drier than other times of the year. The September outlook favors below-normal precipitation over central and northern sections of the Midwest Region, with no appreciable tilt of the odds noted elsewhere. In the short term, light to locally moderate rainfall is expected during the first week of September, with a few tenths of an inch expected to the west and north of central Illinois, 0.5 to 1.0 inch in eastern parts of the region, and up to 1.5 inches in some spots across Kentucky and southern Missouri. Thereafter, guidance is unremarkable, but there is nothing pointing toward a specific feature that might bring heavy rain to some part of the region. Given these factors, the only reasonable forecast is for drought to persist or intensify where it currently exists. In addition, with conditions notably deteriorating over the past couple of weeks, it seems likely that drought could expand to cover a large part of the central and northern Ohio Valley by the end of the month.

Forecast confidence for the Midwest Region is moderate.

Impactful drought is affecting western parts of the Southeast Region, along with portions of the Appalachians and the northwestern tier of Virginia. The September outlook favors surplus rainfall everywhere outside northern Virginia, with odds of over 40 percent indicated for most areas from Mississippi through the Carolinas. The large area of drought across Mississippi and Alabama is expected to start seeing relief during the first week of September, with 1 to 2 inches forecast by September 7. Farther east and north, scattered areas should see similar amounts, but most locations are expected to record amounts slightly below an inch. With much of the guidance and the official outlook favoring above-normal rainfall, improvement/removal is the only logical forecast in areas of existing drought, with the exception of northernmost Virginia. There, short-term forecast amounts are a little less than normal, and September as a whole is not expected to be significantly drier nor wetter than normal. Therefore, drought persistence or intensification is expected in northern Virginia, similar to the adjacent drought areas in the Northeast Region.

Forecast confidence in the Southeast Region is moderate.

In the Northeast Region, drought is restricted to West Virginia, western Maryland, and adjacent southwestern Pennsylvania. Conditions are worst in central and western West Virginia, where subnormal precipitation dates back several months, with significant impacts noted in streamflows and soil moisture. D4 (exceptional drought, the most severe designation) covers part of west-central West Virginia. The September outlook somewhat favors above-normal rainfall as far north as central West Virginia, with no discernible tilt of the odds across central and northern portions of the drought area. The first two weeks of September may drop 1 to locally 2 inches of rain on the southern half of West Virginia, with amounts dropping off into the tenths of inches farther north and west. Thereafter, the 6- to 10-day outlook favors wetter-than-normal weather throughout the region, but the week-2 forecast leans toward drier than normal weather in the areas experiencing drought. Considering there are no strong indicators pointing to a specific feature that might bring heavy rainfall to the drought area, and given the severity of the drought and how long it’s been in place, drought persistence or deterioration is forecast, though not with great confidence, Some expansion is possible, but surface moisture conditions get wetter fairly quickly as you head into areas from southwestern Pennsylvania and western Maryland to the north and east, there is no specific area at enough risk to put any development on the map.

Forecast confidence for the Northeast Region is low.

Southeasternmost Alaska has been experiencing moderate drought for the past several weeks to months, but the official September forecast along with most of the dynamical model guidance favors a wetter than normal month, so drought removal is anticipated by the end of the month.

Forecast confidence in Alaska is high.

The remnants of Hurricane Hone dumped heavy to excessive rains on the southeastern half of Hawaii, especially the Big Island. Over 2 feet soaked some areas in the northern Big Island. Lingering effects from these heavy rains are expected to bring more drought improvement or removal to Maui and the Big Island. Farther west, August rainfall was not as heavy, and guidance for the month as a whole is unremarkable, so drought persistence is anticipated across central and western Hawaii.

Forecast confidence for Hawaii is moderate.

Abnormally wet weather has prevailed for several months across Puerto Rico. The guidance shows no reason to expect a dramatic decline in rainfall during September, so these areas are expected to remain drought-free until at least October.

Forecast confidence in Puerto Rico is high.

Abnormally wet weather has prevailed for several months across the Virgin Islands. The guidance shows no reason to expect a dramatic decline in rainfall during September, so these areas are expected to remain drought-free until at least October.

Forecast confidence in the Virgin Islands is high.

Forecaster: Rich Tinker

Next Monthly Drought Outlook issued: September 30, 2024 at 3:00 PM EDT