NOAA Seasonal Drought Outlook – Aug., Sept., Oct.

A transition from El Niño to ENSO-neutral is expected in the next month or two, with ENSO-neutral most likely to continue through Northern Hemisphere fall and winter.

As of July 9, drought coverage in the contiguous U.S. remained extremely low (3.23%), slightly decreasing from last month’s 4.12% on June 11.

During the past 30 days, surplus rains fell on much of the northern and central Plains, the southern Great Plains, the Mississippi and Ohio River Valleys, mid-Atlantic, northern New England, and Florida.

Moisture from the remnants of minimal Hurricane Barry, which made landfall in central Louisiana, dumped locally heavy rains (more than 10 inches) on parts of the lower Mississippi Valley. In contrast, subnormal precipitation was observed in portions of the west-central Corn Belt, southern New England, parts of the Southeast, the southern High Plains, and most areas west of the Rockies (which is typically dry this time of year).

30-day temperatures averaged above normal in the eastern half of the Nation and Alaska, with subnormal readings in the West, Rockies, and High Plains.

Outside the contiguous states, drought (D1-D2) expanded into much of southwestern and northeastern Puerto Rico during the past 30-days, with most locations reporting under half of normal rainfall (except for surplus rains in northwestern). Historically heavy out-of-season rains occurred on parts of the Hawaiian leewards (e.g. 5.52 inches at Honolulu on June 25-26), especially across Niihau, Kauai, Oahu, and Molokai, easing or removing drought there; however, drought remained on southern Maui and parts of the Big Island which missed the late June heavy rains.

United States Seasonal Drought Outlook Graphic - click on image to enlarge

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In Alaska, extreme heat (highs in the 90’s) and subnormal rainfall increased abnormal dryness and drought in the interior and enhanced wild fire conditions as 1.1 million acres have been scorched this year. In the lower 48 States, only moderate to severe drought existed, with severe drought (D2) limited to small areas of the Pacific Northwest, southern Texas, and southeast Alabama.

By the end of October, drought coverage should still be minimal, but some current areas are expected to persist or expand. Drought is expected to develop and persist in the Northwest, southern Texas, and Puerto Rico, and re-develop along the leeward sides of the western Hawaiian Islands (Kauai, Oahu, and Molokai). Conditions should remain unchanged in leeward portions of Maui and the Big Island and along the southeastern Alaska Panhandle.

In contrast, drought should be gone from eastern and south-central Alaska, northern North Dakota, western New Mexico, and the Southeast. In Hawaii, as ENSO-neutral conditions become established and the trade winds return to normal, drought should disappear from the windward side of the Big Island.

Forecast confidence is moderate for the Southeast Region.

  • Scattered showers and thunderstorms fell on portions of the D0-D1 areas in southern Georgia, northern Florida, and southeastern Alabama, providing some relief to the small moderate drought areas in this region.
  • Lower amounts in eastern Alabama, central and northern Georgia, and coastal Carolinas were enough to prevent deterioration, but insufficient to provide any relief.
  • To the west (South region), Hurricane Barry dumped moderate to heavy rains (2-6 inches, locally over 10 inches) on most of Louisiana, Mississippi, extreme western Alabama, eastern Arkansas, western Tennessee, and southeastern Missouri, but most of this rain fell on non-drought areas.
  • In the short-term, the odds for above-normal rainfall are favorable, but the 1- and 3-month precipitation LLFs were EC.
  • With the anticipated demise of El Niño, more favorable conditions for Atlantic and Caribbean tropical development are likely later in the ASO period, thus possibly providing late summer and early fall surplus precipitation. As a result, improvement to the remaining drought areas are expected by Oct. 31.

Forecast confidence is moderate for Texas, moderate to high elsewhere in the South region.

  • Subnormal rainfall fell on western and southern Texas the past 60 days (and even longer in southern Texas), and with recent heat since mid-June, abnormal dryness and drought has developed and expanded in extreme southern Texas.
  • The rest of the South has measured surplus rainfall at 60-days and longer, including torrential rains from Hurricane Barry (see Southeast summary), so there is no concern for development there.
  • With respect to forecasts, the short-term (QPF, 6-10 day ERF, Week 3-4) was unfavorable to southern Texas with subnormal rainfall and above-normal temperatures likely. Above-normal temperatures were also favored in the August and ASO outlooks, thus persistence of existing drought and an expansion of drought were expected in southern Texas. However, some wild cards for south Texas included potential Gulf of Mexico tropical systems and that October is normally one of their wettest months.
  • The remaining areas of the South should stay drought free through the end of October.

Forecast confidence is moderate to high in the Midwest Region.

  • In the Midwest region, abundant rains have kept most locations adequately to overly moist, with a few exceptions. Some dryness (about 75% of normal) at 60-days were found in northeastern Minnesota, the western UP of Michigan, and parts of Iowa, Missouri, and central Indiana.
  • With a recent and ongoing heat wave and the shallow rooting of crops due to a wet and delayed spring planting season, there was concerns for topsoil flash drought.
  • The latest USDM did not depict any drought in the Midwest, and although the short-term forecasts (QPF and ERFs) had a mixed bag with respect to rainfall, temperatures should drop from above-normal levels by late July.
  • With both the August and ASO outlooks predicted EC temperatures and a slight tilt toward above-normal rainfall in western sections of the Midwest, there was no obvious reason to add development.

Forecast confidence is moderate to high in the High Plains region.

  • With surplus and frequent rainfall, the drought in the northern Plains has gradually shrunk (improved) over the past few months, leaving only two small D1 areas in extreme northern ND.
  • With more rain expected in the short-term (QPF) and favored at longer time scales (Week 3-4, 1- and 3-month precipitation outlooks), along with either sub-normal or EC temperatures, the remaining D1 areas are expected to disappear sometime during the ASO period.
  • Elsewhere, normal or wet conditions covered the rest of the High Plains, and with above-normal precipitation likely in the medium and long-terms (and EC temperatures), development of drought is not expected by late October, even though the precipitation climatology of the High Plains becomes much drier later in the ASO period.

In the West region, forecast confidence is moderate to high.

  • In the Far West, the ASO precipitation climatology is rather dry for California, Nevada, Oregon, and Washington, with some climate divisions normally receiving less than 5% of its annual total during this 3-month period.
  • In the Southwest, however, the monsoon season (JAS) provides critical moisture to most of Arizona, New Mexico, and western Texas, with some areas typically measuring 40-45% of its annual total.
  • With this in mind, the ongoing drought in the Pacific Northwest should persist, and possibly expand eastward and southward as 1- and 3-month temperature outlooks favor above-normal odds.
  • In New Mexico, where a small D1 area remained, the southwest monsoon is forecast to be active in the short-term (ERFs and Week3-4), with EC in the 1- and 3-month precipitation outlooks. With the ongoing wet trend in this area and somewhat favorable rainfall expectations, removal of the D1 in NM was expected.

Forecast confidence is moderate to high for the Northeast Region.

  • The Northeast region has remained drought-free since early November.
  • Although there have been small areas of subnormal precipitation the past 30-60 days and above-normal temperatures since mid-June which resulted in the addition of a small D0 in southwestern Massachusetts and northwestern Connecticut on the July 16 USDM, long-term conditions are still normal to wet, there have been no reported drought impacts, and the outlooks do not favor prolonged dryness. Therefore, no development is forecasted.

Forecast confidence is moderate to high for Alaska.

  • Drought has persisted in the southeastern Alaskan Panhandle, and now D0 has spread across much of the interior (and D1 in eastern and south-central sections) due to extreme heat, spotty rainfall, and widespread wild fires (1.1 million acres burned this year).
  • Fortunately, the short and long-term forecasts provide some hope for improvement in interior Alaska with favorable chances of above-normal rainfall, and to a lesser extent, near to below-normal temperatures in the short-term. This time of the year is also climatologically wet in the interior, so with the favorable forecasts, improvement is expected in the interior sections of the state.
  • Unfortunately, the outlooks are less favorable along the southeastern Panhandle (above normal temperatures, EC or below normal precipitation), and since this drought is longer-term, it will take a prolonged period of wetness to reduce the deficits. Therefore, persistence is forecasted for this region.

Forecast confidence is moderate for Hawaii.

  • Unseasonably heavy rains in late June (e.g. 5.52 inches at Honolulu during June 25-26) removed D1 along the leeward sides of Niihau, Kauai, Oahu, and Molokai, but drought remained on leeward Maui and parts of the Big Island which missed the late June rains.
  • But with a dying El Niño, the trade winds are expected to return to normal along the windward sides during August and ASO, increasing rainfall there, hence the removal of D1 in northeastern Big Island.
  • But the leewards generally do not benefit rain-wise from increased trade winds, so persistence in north and south Big Island and the leeward of Maui, and a return (development) to D1 (currently D0) for the leewards of Kauai, Oahu, and Molokai by end of October.

Forecast confidence is low to moderate for Puerto Rico.

  • Drought coverage has gradually increased across Puerto Rico during the past 30-days as subnormal rainfall covered most of the island except in the northwest. Less than 25% of normal rain had fallen across southern sections, and less than 50% in the east, with 30-day deficits of 1-2 inches along the southern coast and 4-5 inches in the normally wetter eastern areas.
  • With the anticipated demise of the El Niño and return to ENSO-Neutral conditions, atmospheric conditions should gradually become more favorable for convective activity in the Caribbean. However, several models forecast near to below-normal ASO rainfall, and with the ongoing dryness, existing drought was forecast to persist, along with an expansion of drought where the current D0 areas were located.
  • As always, a wild card to this forecast would be tropical system(s) that could drop ample rains on the island during their normal June-October hurricane season.

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