NOAA Drought Outlook Monthly – Oct.

Rapid drought development and intensification occurred this past month across much of the Southeast, central to southern Appalachians, and the Ohio and Tennessee Valleys. This “flash drought” was a result of sparse rainfall (less than an inch) coupled with abnormal heat (30-day temperatures averaging 3 to 6 degrees F above normal).

According to the U.S. Drought Monitor valid on September 24, moderate drought (D1) coverage increased from 6.97 to 56.2 percent, 0.37 to 60.76 percent, and 0 to 58.67 percent across Georgia, Tennessee, and Kentucky, respectively, during the past four weeks.

The increase in drought coverage throughout the continental United States nearly doubled from 9.07 to 17.37 percent from late August. Parts of the lower Mississippi Valley, Texas, and the Southwest also experienced drought development and intensification.

Conversely, drought recently ended across much of the Pacific Northwest. Although long-term drought persists along the Alaska Panhandle, the seasonal increase in precipitation brought drought relief to southern mainland Alaska.

A dry start to the month along with a continuation of above normal temperatures is likely to result in additional drought expansion across the Southeast, mid-Atlantic, lower Mississippi Valley, and Texas. Prospects for removal increase closer to the Great Lakes, based on the predicted mid-latitude storm track.

Forecast rainfall amounts during the first week of October support removal of short-term drought across parts of southwest Kansas, western Oklahoma, the Texas Panhandle, and southeast New Mexico. Broad scale persistence is forecast across the Southwest where 2019 monsoon rainfall was below normal.

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

Click Image to Enlarge

Drought is forecast to slightly expand across southern Utah and southwest Colorado. Recent drought removal is forecast to continue through October across the Pacific Northwest and the northern Rockies, based on an increasingly wet climatology.

A wet climatology also supports continued short-term drought removal or improvement across southern mainland Alaska during the next month. However, persistence is forecast for the longer term drought in the Alaska Panhandle.

Based on the lack of a strong wet signal, persistence is most likely across southern Puerto Rico. Since early to mid-October is forecast to remain relatively wet, continued improvement or remvoal is forecast for Hawaii.

Forecast confidence is high for the Southeast Region.

  • A persistent and strong subtropical ridge aloft resulted in little rainfall and abnormal heat across the Southeast during September.
  • 30-day precipitation deficits range from 2 to 4 inches throughout the region with the largest deficits (above 4 inches) in the typically wetter areas such as the southern Appalachians and closer to the Gulf Coast.
  • Maximum temperatures averaged as much as 5 degrees F above normal across the interior Southeast during the past 30 days. Montgomery, Alabama recorded 7 days with highs at or above 100 degrees F during September.
  • Soil moisture ranks in the lowest 5th percentile from parts of Alabama and Georgia north to the central Appalachians.
  • 28-day streamflows continue to decrease with parts of Alabama, Georgia, and the Florida Panhandle now in the lowest 10th percentile.
  • Additional drought development is likely across the Southeast during early October with a continued dry pattern and summer-like heat. Persistence is forecast for the ongoing drought areas due to the likelihood for little or no rainfall through early October.
  • Although there is an increasing signal for tropical cyclone development across the western Caribbean Sea by mid-October, the eventual track of this potential tropical cyclone is highly uncertain and was not a factor in this outlook.

Forecast confidence is moderate for the Midwest Region.

  • The rapid onset of drought has also expanded north to affect the Ohio Valley. Lexington, Kentucky has only received a trace of rainfall during September which is the driest month on record. As recently as mid-August, Kentucky was drought-free but moderate to severe drought covers 58.67 and 9.81 percent of the Bluegrass state, respectively.
  • A sharp gradient of precipitation amounts is likely during the first week of October. Heavy rainfall (2 to 5 inches) is likely across the Great Lakes, while little to no rainfall is forecast across the Ohio Valley.
  • Based on this 7-day precipitation forecast, additional drought development is expected across much of Kentucky. Farther to the north, drought removal is more likely across northern parts of Illinois and Indiana along with a small area of drought in lower Michigan.
  • The duration of the short-term drought across Kentucky becomes more uncertain later in October as any southward shift in the mid-latitude storm track could provide much needed relief.

Forecast confidence is high for the Southern Region.

  • The flash drought also has affected parts of the lower Mississippi Valley and Texas during the past month.
  • Excluding the torrential rainfall associated with Tropical Storm Imelda, 30-day precipitation deficits range from 2 to 4 inches from the lower Mississippi Valley west to the Hill Country of Texas. Also, 30-day temperatures have averaged as much as 6 degrees F above normal across these same areas.
  • Only a trace of rainfall was recorded at Dallas-Fort Worth during September and this will be the warmest September on record by close to 2 degrees F.
  • Given the likely the dry and hot start to October, additional development is forecast across the lower Mississippi Valley and parts of Texas.
  • Farther to the west, an axis of heavy rainfall (1 to 3 inches) is forecast across the Texas Panhandle and northwest Oklahoma.
  • Since 30-day precipitation deficits are running at 2 inches or less in the ongoing drought areas, this rainfall in the next week is expected to eliminate drought.
  • Although there is an increasing signal for tropical cyclone development across the western Caribbean Sea by mid-October, the eventual track of this potential tropical cyclone is highly uncertain and was not a factor in this outlook.

Forecast confidence is moderate for the High Plains region.

  • The northern and central Great Plains remain drought-free with parts of North Dakota receiving more than 8 inches of precipitation during the past 30 days. Soil moisture ranks in the 99th percentile from North Dakota south to Nebraska. Therefore, drought development is unlikely for the northern and central Great Plains.
  • Rainfall during the first week of October is expected to nearly eliminate short-term precipitation deficits in southwest Kansas. Therefore, drought removal is forecast for this area.
  • Persistence and development is forecast for southwest Colorado as below normal precipitation is favored at all time scales during the next month.

Forecast confidence is high for the West.

  • During the final week of September, locally heavy rainfall (more than 2 inches) fell across parts of southern and central Arizona. Despite this recent increase in rainfall, 90-day precipitation averages less than 50 percent of normal due to the lack of monsoon rainfall.
  • Although the October precipitation outlook calls for a slight tilt in the odds for above normal precipitation, October is a relatively drier time of year and broad scale persistence is most likely.
  • Tropical Storm Narda is forecast to track northwest along the Mexico coastline to the Gulf of California at the beginning of October. Although enhanced moisture associated with Narda may result in increase rainfall across southeast Arizona, this rainfall is not expected to offest the large 90-day precipitation deficits.
  • Drought is expected to expand across southern Utah due to below normal precipitation favored at all time scales during the next month.
  • Early fall storminess resulted in above average precipitation across the Pacific Northwest during the past 30 days with parts of Oregon and Washington recording more than double their normal September precipitation.
  • Based on this recent wetness and a continued wet pattern at the beginning of October, drought removal is forecast for lingering drought areas in the Pacific Northwest.

Forecast confidence is moderate for the Northeast Region.

  • After the Northeast region remained drought-free dating back to early November 2018, a recent period of below normal precipitation and above normal temperatures resulted in an expansion of moderate drought (D1)north into parts of Delaware, Maryland, and southeast Pennsylvania. As of late September, abnormal dryness (D0) covers half of the Northeast region.
  • 30-day precipitation deficits range from 2 to 4 inches from the mid-Atlantic north to New England.
  • Mostly dry weather along with record heat at the beginning of October is likely to lead to additional drought development across the northern mid-Atlantic.
  • Despite dry intial conditions, forecast confidence is too low to forecast development across a larger spatial area of the Northeast since evapotranspiration rates begin to decrease during October and some precipitation tools indicate near to above normal precipitation across New England.

Forecast confidence is high for Alaska.

  • Drought improved by one to two categories across the southern mainland of Alaska, including the Kenai Peninsula. Since that part of Alaska is experiencing short-term drought and October is a relatively wet time of year, continued improvement or removal is expected.
  • However, persistence is more likely on a monthly time scale for the longer term drought affecting the Alaska Panhandle.

Forecast confidence is low for Hawaii.

  • During September, drought improvement and removal occurred with coverage decreasing from 21.67 to 17.85 percent.
  • Based on the recent wetness and the GFS ensemble mean indicating a continuation of above normal precipitation during the next two weeks, drought removal is favored for exising D1 areas and improvment for D2 to D3 areas across the Hawaiian Islands.

Forecast confidence is low for Puerto Rico.

  • Drought coverage across Puerto Rico decreased slightly from 21.42 to 16.67 percent during September. Although there remains elevated chances for tropical cyclone development in either the main development region of the tropical Atlantic or western Caribbean Sea through early to mid-October, it is not known where a potential tropical cyclone would track at this time lead.
  • Since the most recent CFS forecast for October indicates near average precipitation for Puerto Rico, persistence is most likely for the ongoing drought.



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