NOAA Monthly Drought Outlook – August

Drought (D1 or drier) continued to remain at historically low levels (3.04%) across the lower 48 States as of July 23, slightly less than a month ago (3.30% on June 25). For August 2019, however, persistence and some short-term drought expansion should be more common than improvement since there was very little drought in the contiguous U.S. at the end of July.

In the Northwest, good odds for above normal temperatures and minimal rainfall (their dry season) is expected as drought should persist and slightly expand eastward.

August normally brings monsoonal moisture from Mexico northward into the Southwest, and with favorable chances for above-normal rainfall, this should finally eliminate the small D1 area in New Mexico from what was still left from a protracted and intense drought in the Four Corners Region during 2018 and into early 2019.

In the Plains and Midwest, a wet Spring and early Summer discouraged deep (subsoil) root penetration for most plants, and with recent dryness and heat, the topsoil moisture has rapidly declined, leading to adverse crop impacts. With most forecasts favoring subnormal August rainfall, short-term (topsoil) drought development was anticipated in the eastern Corn Belt, upper Great Lakes region, and southern Plains, with expected above-normal monthly temperatures exacerbating the dryness in the latter area.

In the Southeast, the lack of consistent forecasts, along with an unexpected wild card tropical system or two, left the small areas of D1 and D2 to persist.

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

Click Image to Enlarge

Outside the contiguous U.S., the swath of drought across central Puerto Rico should improve in August as a recent increase in tropical waves has brought welcome rains to the island.

With subnormal precipitation and above normal temperatures favored across the southern Alaskan coast during the month, drought should continue in the Kenai Peninsula and across the southeastern Alaskan Panhandle, along with possible development in-between these two areas of persistence. Farther north in the interior, August is typically one of the wettest months of the year, and with rainfall recently increasing, temperatures moderating, and forecasts favoring above-normal precipitation odds, drought should improve there.

In Hawaii, August is a relatively dry time of year in the leeward areas, and they should remain in drought. With the El Niño fading, the normal trade winds are expected to return and bring the windward sides increased rainfall, hence the improvement on the northeast coast of the Big Island.

Forecast confidence is low to moderate in the Southeast.

  • In the Southeast region, most D0-D2 areas along the coast saw some improvement during the past 30 days, although some slight deterioration also occurred in interior sections of Alabama, Georgia, and the Carolinas.
  • Climatologically, August is somewhat wet along coastal areas (especially in Florida) due to the Gulf and Atlantic tropical season ramping up. However, with the precipitation forecasts conflicting (near normal to wet early, subnormal mid-month, and EC for the month overall) and temperatures near to above normal, there was no strong signal for either improvement or development.
  • Additionally, potential tropical systems during August are a wild card, adding more uncertainty to the forecasts.
  • The most-likely scenario would be some improvement and development, but the exact locations of these occurrences are not known. Therefore, persistence of the existing drought areas was the default forecast.

Forecast confidence is moderate for the South.

  • The Spring and early Summer surplus rains have become a fading memory for the southern Plains during July as minimal rainfall with occasional heat, low humidity, and strong winds have taken a toll on the topsoil moisture and the shallow-rooted plants (the latter due to the wet April-June period).
  • With some small D1-D2 areas in southern Texas, scattered small areas of D0 in central Texas and southern Oklahoma, and an overall forecast of subnormal precipitation and above normal temperatures, a large swath of development was added to the southern Plains. Although this does not imply that the entire development area is expected to be in drought by 8/31 but rather most of this area, any drought would be short-term and mainly confined to the topsoil layer.
  • In contrast, states to the east (AR, LA, MS, TN) have been wet during July, and the forecasts are more favorable for them to remain drought-free.

Forecast confidence is moderate for the Midwest.

  • No drought (D1 or drier) existed in the Midwest near the end of July, but several small D0 areas were found in Iowa, Illinois, Indiana, Michigan, and Minnesota.
  • Similar to the High Plains, the wet season is on the decline here during August, though the month still typically brings 10-14% of the annual precipitation, especially to western and northern states, and a bit less (6-10%) to southern and eastern areas.
  • There are conflicting signals as to what precipitation patterns will evolve this month: mostly dry weather in Days 1-5 QPF (except for heavy rains in western Iowa and Missouri); near to above normal odds in 6-10 day ERF; near to above normal chances in 8-14 day ERF except below normal in the upper Midwest; EC for Weeks3-4; and below normal in the Ohio Valley and Great Lakes region but above normal in western Iowa and Missouri (EC elsewhere) in the updated August outlook.
  • Temperatures are expected to be below normal throughout much of August, which may slow the spread and intensity of any short-term drought.
  • Similar to the South and High Plains regions, the very wet spring and early summer has led to shallow-rooted crops, leaving the plants vulnerable to short-term dryness and heat that would deplete the topsoil moisture and adversely impact the crops.
  • Based upon current conditions (where 30-day dryness and temperatures averaging 2-4 degF above normal occurred) and where the precipitation forecasts were not favorable, short-term (topsoil) drought development was added to the east-central Corn Belt and upper Midwest.

Forecast confidence is low for the High Plains.

  • Drought in the High Plains region is currently limited to northern North Dakota. Although the wet season is on the decline, August still typically brings the state 10 to 14% of the annual precipitation.
  • There are only weak signals as to what precipitation patterns will occur this month (slightly above to near normal/EC), but the odds favor subnormal temperatures throughout much of the month.
  • The lower temperatures should help keep the extant drought from greatly expanding, but the D1 area approximation to the subnormal August precipitation chances over the Great Lakes region and Ohio Valley adds a degree of uncertainty to the precipitation confidence. Therefore, persistence is forecast.

Forecast confidence is high in the Northwest, and moderate to high in the Southwest.

  • There are two separate areas of drought in the West Region that have trended in opposite directions.
  • Drought has been worsening and slowly expanding in the Pacific Northwest. With August a normally dry time of the year and precipitation forecasts at EC or below normal, the chances for notable improvement are slim at best. In addition, temperatures are forecast to be above normal which should exacerbate the dryness; therefore, drought is expected to persist and slightly expand in this area.
  • In contrast, long-term moderate drought in western New Mexico was all that was left from the expansive and extreme drought of 2018 and early 2019 in the Four Corners Region. With August rainfall climatologically reaching 15-25% of the normal annual total in most of Arizona and New Mexico, and above-normal rainfall forecast throughout much of the month, this should provide enough moisture to erase the drought.

Forecast confidence is moderate to high in the Northeast.

  • The Northeast region has remained drought-free since early November 2018, and no drought is expected to develop, though some short-term minor rainfall deficits have accumulated in a few areas of western New England and New York.

Forecast confidence is moderate for interior Alaska and moderate (development) to high (persistence) for the southeastern Alaskan Panhandle.

  • Moderate to extreme drought (D1 to D3) coverage remained nearly steady along the southern Alaska Panhandle during July, but with the explosion of wild fires in the interior due to subnormal rainfall and near-record warmth, D1 and D2 was added in east-central Alaska (Yukon Flats) while D0 covered the remainder of the state except for the extreme western and northern sections.
  • Fortunately, August is one of the wetter months of the year in the interior (receives 15-20% of its annual precipitation). With recent rainfall, moderating temperatures, and near to above normal odds for precipitation in the interior, improvement was depicted for east-central portions.
  • However, with subnormal precipitation and above normal temperatures predicted along southern sections, persistence and some expansion of drought is favored here.

Forecast confidence is moderate for Hawaii.

  • With the anticipated demise of the weak El Niño and ENSO-neutral conditions expected soon, the normal trade winds should return to the windward sides of Hawaii, with showers becoming more frequent and heavier.
  • With this in mind, improvement was made for the northeast coast of the Big Island. In contrast, August is typically dry in the leewards, and with no tilt toward wetness here, persistence of existing drought was forecast for the western sides of the islands.

Forecast confidence is low to moderate for Puerto Rico.

  • In Puerto Rico, a relatively dry start to the Atlantic hurricane season (June-Oct) led to an slight increase in abnormal dryness and drought during July in southern and eastern sections. By late July, however, a more active Atlantic tropical wave pattern brought welcome rains to much of the island, most likely providing some improvement.
  • Although indicators are limited, the anticipated demise of the weak El Niño may allow temperature and precipitation patterns to return to more normal conditions during August, thus allowing for increased and widespread shower activity, and possible tropical storm development (a wild card) which lowers forecast confidence.

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