October - December 2008

Latest Seasonal Assessment - The tropical weather systems that effected the CONUS have chipped away at the edges of the drought areas over Texas and the southeast. Unfortunately the heaviest precipitation from the tropical systems missed the core drought areas for both of these regions. At the moment the tropics are relatively quiet but the forecast models are suggesting a more active pattern over the Atlantic, Caribbean and Gulf of Mexico in about 10 days to two weeks. For the shorter ranges the models have now backed off on the idea of a tropical system developing in the western Gulf Of Mexico. Even in the absence of an organized tropical system anomalous easterly flow suggests that coastal sections of southeast Texas would receive beneficial rainfall to alleviate drought conditions for this region. Strong high pressure over the northwest Atlantic in combination with weak disturbances forming on a frontal system off the southeast coast will produce anomalous easterly flow along the coast of the Carolinas which is likely to produce precipitation along the North Carolina coast. In general the new drought outlook is more pesimistic with regard to the probabilitiy of improvement over the southeast mainly due to the recent reduction in Atlantic tropical system activity. This may have to be reevaluated in subsequent outlooks if the upturn in tropical activity predicted by the models in about 10 days occurs. The decrease in tropical activity also leads to a more pessimistic forecast of improvement for interior Texas. The drought area over the northern Plains should see some improvement as medium range forecasts valid for late September indicate above normal precipitation for this region. Climatological considerations suggest improvement for the drought area over northern California, especially along the coast. The area of drought over southern California is expected to persist.

Tools used in the Drought Outlook included the official precipitation outlook for October 2008, the long lead forecast for October-December 2008, various medium- and short-range forecasts and models such as the 6-10 day and 8-14 day forecasts, the soil moisture tools based on the GFS model, evaluation of expected tropical system activity, the CFS seasonal forecast of precipitation anomalies over the U.S. for Oct-Nov-Dec, and climatology.

The tropical weather systems that effected the CONUS have chipped away at the edges of the drought areas over Texas and the southeast. Unfortunately the heaviest precipitation from the tropical systems missed the core drought areas for both of these regions. Currently the tropics have become much quieter and this is the main reason the new drought outlook is much more pessimistic for improvement over the southeast. Global models and MJO considerations suggest that the tropics will again become active in about a week to ten days so this will have to be closely monitored. In the short range, strong high pressure over the northwest Atlantic in combination with disturbances forming on a frontal system off the southeast coast will cause anomalous easterly flow and precipitation along coastal North Carolina. This is the main reason improvement is shown over a small area of coastal North Carolina. The idea that tropical activity may once again increase in the Atlantic over the next two weeks is a primary reason why areas of South Carolina, Gerogia and Alabama are depicted as showing some improvement. The drought areas of eastern Tennessee, southwest North Carolina, southeast Kentucky, and Southwest Virginia are less likley to be impacted by tropical systems and are forecast to have drought persist.
Confidence for the Southeast and mid-Atlantic: Moderate

Rainfall associated with a frontal system and the remnants of Pacific Tropical Storm Lowell brought some relief to western Texas while rainfall associated with Hurricane Ike did the same for eastern Texas. Recently global models have suggested tropical system development in the western Gulf of Mexico, although the very latest runs have backed off of this idea. Even in the absence of an organized tropical system anomalous easterly flow suggests that coastal sections of southeast Texas would receive beneficial rainfall to alleviate drought. For this reason an area of improvement is indicated over southeast coastal Texas. Further inland, HPC forecasts no rain over the area in the 1-5 day period. Medium and longer range forecasts have near normal or equal chances over interior Texas, and soil moisture anomaly change tools show worsening conditions. For these reasons the drought area over interior Texas is forecast to persist.
Confidence for Texas: Moderate

Over the mid-West, the patchy areas of drought saw some relief from precipitation associated with the remnants of hurricane Ike. Light precipitation is expected over these areas in the 1-5 day period. Medium range forecasts indicate near to above normal precipitation for the region while longer range forecasts have equal chances for this region. Soil moisture anomaly changes show worsening conditions while the seasonal CFS precipitation forecast for Oct-Nov-Dec indicates wet as the most likely category for the region. For these reasons areas of some improvement are indicated over the mid-West.
Confidence for the mid-West: Moderate

In Colorado recent rains have eliminated the drought area near Denver. Drought is ongoing over eastern Colorado/southwestern Kansas. Little rain is expected for days 1-5 while medium and longer range forecasts show near normal precipitation or equal chances for above/below. Soil moisture anomaly change indicators are mixed and weak. The seasonal CFS precipitation forecast for Oct-Nov-Dec shows a slight tilt of the odds towards drier than normal. For these reasons an area of some improvement is indicated.
Confidence for eastern Colorado/southwest Kansas: Moderate

The Northern Plains has received some beneficial rains over the last 30 days. Light precipitation is forecast over the area in the 1-5 day period. Above median precipitation is forecast over the area for the 6-10 day and 8-14 day periods. Current 30 day and 90 day forecast have equal chances for above or below normal precipitation. Soil moisture change charts show a mixed signal with some suggestion of worsening conditions. The seasonal CFS precipitation forecast for Oct-Nov-Dec shows near to above normal as the most likely categories for precipitation for the region. For these reasons the current drought area indicates some improvement over the area.
Confidence for the Northern Plains: High

Over the west little precipitation has fallen recently as this is climatologically a dry time of year. Some precipitation is forecast over Northern California during the 1-5 day period. The 6-10 day forecast indicates near normal precipitation over Northern California while the 8-14 day forecast shows above normal precipitation. Medium and longer range forecasts generally show warmer and drier than normal conditions for Southern California. Palmer drought indicator probability forecasts show a high probability of improvement for Northern California. For these reasons an area of improvement is indicated over Northern California, an area of some improvment is shown for central California and an area of persist is progged for Southern California and Southern Nevada.
Confidence for the west: Moderate

In Hawaii, the eastern section of the Big Island and all of Lanai are now in D1 drought. The current forecast indicates that these areas will persist.
Confidence: Moderate

In Puerto Rico, recent rains associated with tropical systems have eliminated the drought region for the island.