Tools used in the U.S. Monthly Drought Outlook (MDO) included 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), the Week 3-4 outlooks and tools from CPC, dynamical models at the monthly time scale, the 384-hour total precipitation forecasts from several runs of the GFS, and climatology for September. Initial conditions such as current soil moisture and 30 to 90-day precipitation deficits were also factors. ENSO is currently neutral, but there is a ~60% chance of La Niņa development during Northern Hemisphere Fall 2020 and continuing through Winter 2020-21 (~55% chance).

The Northeast Region has experienced a mixture of drought degradation and imporovement over the past month. New England continued to be the focal point of the degradation, with many areas still experiencing D1-D2 drought. However, above-normal precipitation is favored through the first half of September, with a diminishing signal into the latter half of the month. As such, drought removal (D1) and improvement (D2) are favored throughout the Northeast Region. However, some areas of scattered drought are likely to remain by the end of the month as some locations, particularly in New England, have longer-term rainfall deficits going back 3-6 months, and even a few locations out to 12 months.

Forecast confidence is moderate to high for the Northeast Region.

Currently no drought is present in the Southeast Region. Some short-term dryness in Florida has been mitigated a bit by above-normal precipitation over the past week or two, with D1 removal near Tampa. However, with wet signals in the extended- and long-range forecasts over much of the Southeast, coupled with the potential for tropical activity and the peak of the hurricane season falling within the forecast period, drought development is not favored.

Forecast confidence is high for the Southeast Region.

Eastern portions of the Midwest Region have seen drought conditions improve throughout August, while much of the western Corn Belt and the Upper Midwest have experience drought degradation. With above-normal odds for precipitation and below-normal temperatures favored through the Week-2 period extending from southwestern Missouri to the Ohio Valley, drought removal is forecast, despite below-normal precipitation being favored during the Week 3-4 period. For Iowa, below-normal precipitation is favored, particularly during the Week-2 period and beyond. With the potential in the short-term to see near-to-above normal precipitation and below-normal temperatures, persistence is forecast.

Forecast confidence is moderate for the western Corn Belt, and moderate to high elsewhere for the Midwest Region.

The Southern Plains in the Southern Region saw drought expansion and intensification during August, mainly in Texas. Elsewhere, the region experienced removal and improvement. WPC's 7-day QPF depicts heavy rainfall (in excess of 4 inches) across portions of southern Oklahoma, northern Texas, and northwestern Arkansas, exceeding monthly normals for several locations. Despite drier conditions predicted for much of the region for the latter half of September, drought removal and improvement is favored for western Oklahoma (excluding the Panhandle) and Texas (from the Panhandle, southward to the Big Bend, and eastward), due to the expected heavy rainfall.

Forecast confidence is moderate to high for the Southern Region.

The High Plains Region is favored to experience below-normal precipitation throughout the extended-range and Week 3-4 periods. However, enhanced odds for below-normal temperatures are also depicted, particularly through the extended-range. With the potential for fast-moving systems propagating across the northern tier states early in the period and below-normal temperatures reducing evapotranspiration rates, persistence is favored for much of the Northern Plains. In the Eastern Rockies and along the Front Range, drought persistence is likely, with some development also favored, due to increased probabilities for high pressure to build into the region toward the end of Week-2 and into the latter half of September. Some development is also favored in the Central Plains for areas currently experiencing abnormally dry (D0) conditions. Portions of Nebraska have seen 30-90 day Standardized Precipitation Index (SPI) values in the D1-D3 range, so the dry signal supports development for areas currently experiencing abnormal dryness. In southeastern Kansas, the increased likelihood for heavy rainfall during the first week of September favors drought removal there.

Forecast confidence is moderate for the High Plains Region.

The much below-normal monsoon season continued through August (climatologically their wettest month of the year) and has resulted in drought expansion (particularly Arizona) and degradation across much of the Desert Southwest. There is also an increased likelihood for a below-normal end to the Southwest monsoon as it climatologically dissipates during September. Much above-normal temperatures during August have also been a major factor for drought intensification in the Western Region, associated with high pressure dominating throughout the period. Unfortunately, the precipitation and temperature outlooks at all ranges do not support any relief during September, with above-normal temperatures (all of September) and below-normal precipitation (first half of September), associated with mean ridging that is predicted to dominate the western CONUS through much of the period. As such, drought persistence is favored everywhere in the Western Region. Some development is likely in the remaining abnormally dry (D0) areas in New Mexico due to increased odds for above-normal temperatures and the reduced likelihood for an active end to the summer monsoon season. Some development is also favored for parts of the Pacific Northwest and Northern Rockies with high pressure favored to dominate through much of September, exacerbating the antecedent dryness going back 30-60 days.

Forecast confidence is high for the Western Region.

Some abnormal dryness has been observed over portions of western and southern Mainland Alaska, with D1 drought developing on Kodiak Island during August. With CPC's ERFs depicting odds for above-normal precipitation throughout much of the first half of September, drought removal is favored for Kodiak Island. In addition, no development is favored elsewhere in Alaska, as odds for above-normal precipitation cover most of the state during the first half of September.

Forecast confidence is high for Alaska.

Over the next couple of weeks in Hawaii, odds are increased for above-normal precipitation for western portions of the Hawaiian Islands, with light to moderate trade winds expected to bring scattered show activity into the windward slopes. However, conditions are favored to dry out during the latter half of September, with below-normal precipitation and above-normal temperatures favored. Therefore, drought persistence is likely for Hawaii, with some potential for development on the leeward slopes of the big island and Kauai.

Forecast confidence is moderate to high for Hawaii.

Remnant areas of abnormal dryness in Puerto Rico, left behind after Isaias' passage in late July, were nearly eliminated over the past month. With weak near-normal odds for precipitation favored during September and the increased potential for tropical activity as the peak of the hurricane season nears, no drought development is likely.

Forecast confidence is high for Puerto Rico.

Forecaster: Adam Hartman

Next Monthly Outlook issued: September 30, 2020 at 3 PM EDT