U.S. Drought Outlook Monthly – Sept.

The Monthly Drought Outlook for September 2019 is based on official temperature and precipitation outlooks from WPC and CPC (including CPC’s updated temperature and precipitation outlooks for September), current soil moisture information, climatology, recent precipitation deficits and surpluses, and dynamical model guidance.

For the Southeast, the MDO is largely based on the latest National Hurricane Center forecast track of Hurricane Dorian, which, as of 2pm ET today (8/31) still takes Dorian close to the east coast of Florida before recurving it northward. Drought areas near the Southeast coast of the United States are favored to be improved and/or removed, as they are expected to be well within the range of Dorian’s precipitation shield.

However, for northern portions of Georgia and Alabama, which are expected to be far enough removed from Dorian’s predicted track, drought persistence is favored. The Northeast CONUS is expected to be drought-free in September.

Frontal activity and cooler weather are predicted to result in drought improvement/removal across the current drought areas of the Midwest, and also northeastern North Dakota. Given the very wet spring in this region, there were significant delays in crop planting, which now exposes them to early season killing freezes before they have a chance to reach maturity.

In the South, the best chances for drought improvement and/or removal include the Texas Panhandle (and extreme southern Texas), extreme southwestern Oklahoma, and up into southwestern Kansas. Forecast precipitation at nearly all time-scales out to a month in advance favor above normal amounts of precipitation. These locations also have the added advantage of a wet September climatology.

In contrast, central and eastern Texas tend to be drier in September, and most precipitation outlooks out to a month in advance favor drier-than-normal conditions there. An area of drought development has been introduced from central and northeastern Texas into northern Louisiana.

In southern portions of the West, despite CPC’s updated monthly precipitation outlook calling for above normal precipitation in September, it is thought that whatever rain does fall will not be enough to justify a one-category improvement in the drought designation.

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

Click Image to Enlarge

The Southwest Monsoon has not been very favorable for this region either, and monsoon season typically winds down during September. A wildcard to consider is the possibility of a stray eastern Pacific hurricane that recurves into the American Southwest, with an accompanying Gulf moisture surge.

For the northern portions of the West, drought persistence is anticipated from the Pacific Northwest to the far Northern Rockies, with the typical onset of the rainy season being about a month from now.

Outside of the Lower 48 states, September is a climatologically favorable time for the southern Alaska coast, with the seasonal renewal of significant cyclone activity. Therefore, at least a one-category improvement in the Alaska drought depiction is predicted.

In Hawaii, the Big Island is considered to have the best chance for drought mitigation, as model forecasts indicate prolonged periods of high pressure farther north.

Finally, drought persistence is favored across the Commonwealth of Puerto Rico, despite the rainy season typically continuing into November. Despite the close call with Dorian, there are no tropical systems currently predicted to affect Puerto Rico for at least the forseeable future.

Forecast confidence for the Southeast Region is moderate (inland) to high (coast).

  • According to the USDM, there is significant coverage of abnormal dryness (D0), moderate drought (D1), and even a few localized patches of severe drought (D2) over the Southeast Region.
  • The Advanced Hydrologic Prediction Service (AHPS) Departure from Normal Precipitation (DNP) map for the past 30-days shows a rather unorganized and incoherent pattern over the Southeast. The DNP map for the past 7-days depicts a much more coherent pattern, with near to above normal rainfall over most of the Southeast Region, except for below-normal rainfall near the Southeast Coast and much of the Florida Peninsula.
  • The main issue for this region is the predicted impact of major Hurricane Dorian, which is currently (11am EDT 8/31) a high-end category 4 hurricane on the Saffir-Simpson wind scale, with maximum sustained winds of 150 mph. Dorian is also about 415 miles east of West Palm Beach, Florida, and is still predicted by the National Hurricane Center to affect the east coast of Florida; though the very latest prediction indicates Dorian could recurve just off the Florida coast and head towards the Carolinas.
  • Of course, the exact track this hurricane takes will determine which drought areas across the Southeast get removed, or at least improved. The latest track guidance suggests that areas farther inland (northern Georgia and northern Alabama) may be far enough removed from the heavy precipitation shield associated with Hurricane Dorian to warrant a forecast of drought persistence.

Forecast confidence for the South is low to moderate.

  • Abnormal dryness and drought expanded across the South during August. Climatology favors wetness over western and southern portions of Texas in September, with dryness favored over much of the remainder of the region.
  • AHPS 30-day DNPs show how Texas has largely missed out on the axis of heavier precipitation that has dominated the month of August from the Northern and Central Great Plains towards the Lower Mississippi Valley and central Gulf Coast region.
  • One to three inch deficits are widespread across Texas. Although soil moisture is near normal for much of the state, values have trended drier during the past 1-month and 3-month periods.
  • CPC’s official extended-range outlooks (days 6-14) favor warmer-than-normal temperatures for the current drought areas across the South, while its Week-3/4 outlook favors above normal and EC, depending on the exact location in question. For comparison, an equally weighted CFS/ECMWF blended temperature forecast predicts near normal temperatures.
  • For precipitation, forecasts at nearly all time-scales out to a month in advance show the best chance of above normal precipitation and resulting drought improvement/removal is over western Kansas, southwestern Oklahoma, and the Texas Panhandle region. Drought removal is also indicated for a tiny portion of extreme southern Texas, near the mouth of the Rio Grande River, and is based largely on precipitation anticipated during the first week of September.
  • An area of drought development has been introduced from central and northeastern Texas into northern Louisiana. This area has generally received about 10-50 percent of its normal rainfall during the past 30-days, and is predicted to receive little to no rainfall during September.

Forecast confidence for the Midwestern Region is low to moderate.

  • Coverage of abnormal dryness and moderate drought has increased over the Midwest during the past month. Localized patches of moderate drought are depicted on the USDM map where Upper Michigan meets Lower Michigan, and near/over the western and eastern state borders of Illinois.
  • Climatology favors a tilt in the odds toward wetter-than-normal conditions across the Upper Mississippi Valley/Upper Great Lakes region, drier-than-normal conditions over Kentucky, and near-normal conditions elsewhere across the Midwest Region during the month of September.
  • Soil moisture is near normal in the areas noted above as being in moderate drought, with much of the surrounding areas having above normal soil moisture values.
  • Perhaps the greatest concern in the Midwest is related not to precipitation, but to temperature. After a very wet spring, there was a significant delay in the planting of cash crops such as corn and soybeans. A significant fraction of these crops may not reach maturity before the first killing freeze puts an end to the growing season.
  • CPC’s extended-range outlooks, as well as the 30-day updated temperature outlook, favor below normal temperatures, while the Week-3/4 outlook indicates a slight tilt toward anomalous warmth is possible for much of this region.
  • Though the constituent precipitation outlooks that contribute to the monthly outlook as a whole display considerable variability, the updated monthly precipitation outlook tilts the odds towards either above normal or Equal Chances (EC). Therefore, drought improvement/removal is deemed the best bet for September.

Forecast confidence for the High Plains Region is low to moderate.

  • The High Plains Region is largely free of drought; the few exceptions being northeastern North Dakota, extreme southwestern Colorado, and southwestern Kansas. The area in North Dakota is the largest of these fairly small patches of drought, and the longest lived.
  • The shorter-term climatology (past 15 years) depicts a tendency towards wetter-than-normal conditions for most of North Dakota in September.
  • As noted above in the discussion for the South, the 30-day AHPS DNP map shows the axis of heaviest rainfall during the past month extends from the Northern Plains to the Central Gulf Coast region, and just misses the small drought area in northeastern North Dakota. Current soil moisture values are near to below normal in this localized area.
  • Relatively cool, wet conditions are anticipated for this area in the extended-range period and for the month of September as a whole, similar to the Midwestern states. A one-category improvement of drought is indicated for this small patch of moderate to severe drought (D1 to D2) in North Dakota.
  • Though the updated 30-day precipitation outlook also shows elevated odds for above normal precipitation for the drought area in Colorado, it may not be enough to justify a one-category improvement in the drought. As noted earlier in the discussion for the South, drought removal is indicated for southwestern Kansas.

Forecast confidence for the southern portion of the West is low to moderate; for the northern portion of the West, confidence is moderate.

  • The areas of concern across the West include New Mexico, Arizona, and from the Pacific Northwest eastward across far northern Idaho and adjacent parts of northwestern Montana.
  • The southern portion of the West (Arizona and New Mexico) have experienced a sub-par monsoon season thus far, and no major changes are anticipated during its climatological winding down phase in September, though climatology does favor a relatively wet New Mexico.
  • During the extended-range period (days 6-14), and for September as a whole, there are enhanced chances of above normal temperatures across the Southwest, and near to above normal rainfall. At least for the first half of September, this pattern appears to be due more to a deepening mid-tropospheric trough over the western CONUS rather than significant monsoon activity. Whatever rain does fall, however, is not expected to be enough to justify improvement or removal of drought areas in this region.
  • A wildcard in this forecast is the possibility of a Gulf surge associated with a recurving eastern Pacific hurricane, but this scenario is somewhat more likely to occur in October.
  • In California, most of the state continues to be free of drought and dryness, with the climatological commencement of the rainy season now on the proverbial horizon.
  • For the northern portion of the West (Pacific Northwest to Northern Rockies), persistence is considered the best bet at this time. This normally wet region already has plenty of water available, even though strictly by the numbers there is a large precipitation shortfall of 12 to 20 inches since the start of the Water Year (Oct 1, 2018). Once the rainy season gets going, improvements in the USDM depiction are anticipated well before there is a major dent in the long-term deficits.
  • As September is still climatologically a dry time of year, it is thought that October may be a more likely time to experience some drought improvement in this region.

Forecast confidence for the Northeast Region is moderate to high.

  • Climatology for the past 123 years indicates September is neither a particularly wet nor particularly dry month for the Northeast Region, though in the short-term (past 15 years) there has been a tilt toward dryness over much of New England.
  • The U.S. Drought Monitor depicts scattered areas of abnormal dryness (D0) over the Northeast Region. Soil moisture ranges from near to above average.
  • With near to below normal temperatures favored for most of the upcoming month, near to above normal precipitation during the first half of the period, and near to below normal precipitation favored during the second half of September, it is unlikely that drought will have a chance to develop across the Northeast.

Forecast confidence is moderate to high for Alaska, low to moderate for Hawaii, and moderate for Puerto Rico.

  • Climatologically, the stormy season returns to the southern Alaska coast during September, as reinvigorated westerly winds aloft begin to push south with the approach of autumn. Improvement/Removal of drought is therefore indicated for southern Alaska. For the southern Panhandle region, a longer-term hydrologic drought is still expected to continue, even if the area sees some improvement in conditions.
  • In Hawaii, the best chances for drought improvement and/or removal is over the Big Island. The more northern islands will be closer to mid-latitude high pressure areas that pass through the region.
  • In Puerto Rico, drought persistence is thought to be the best bet, despite the fact that the rainy season typically continues for several more months.

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