September - November 2008

Latest Seasonal Assessment - At the beginning of the period, heavy to excessive rainfall associated with Fay and its remnants will reduce drought across parts of the Southeast. With forecasts of above median rainfall in the short- and medium-range and the monthly outlook along with the increased odds of additional tropical systems, improvement is forecast across the Southeast. Moderate to severe drought has recently spread into Virginia, but forecasts on most time scales favor improvement. Although drought intensified in northern Louisiana during early August, ongoing rainfall should alleviate drought conditions. Since late July, Colorado, Oklahoma, and Texas have experienced drought relief and further improvement is forecast. Drought improvement is also forecast for the small areas of moderate drought in Minnesota. Across the Great Lakes, short-term drought development is possible due to initial conditions, but long-range forecasts are noncommittal. Therefore, no drought development is depicted on the outlook map. A small area of drought development is forecast for northern Montana with improvement forecast for North Dakota. Across the West, the onset of the wet season during the fall should gradually result in improvement across northern California. However, in southern California and the Great Basin, persistence is forecast since potential improvement is not expected until later in the winter. No changes were made to the previous outlook regarding the Hawaiian Islands where expanding drought is forecast in some leeward areas and improvement is expected over windward locations on the Big Island.

Tools used in the Drought Outlook included the official precipitation outlook for September 2008, the long lead forecast for September-November 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 and the Constructed Analogue on Soil (CAS) moisture, the CFS seasonal precipitation forecasts, and climatology.

Drought improvement across the Southeast is weighted heavily towards the effects from Fay, the CPC medium-range forecasts, and the CPC September precipitation outlook. Early in the period, tropical cyclone Fay or its remnant low are currently projected to track slowly west near the Gulf Coast. Heavy to excessive rainfall will alleviate drought, but the exact location remains unclear. The most likely areas for improvement are Alabama and southern Georgia. Additional tropical systems could bring substantial relief, but where exactly that will occur is unknown. It should be noted that hydrological drought indicators such as large reservoirs and groundwater will respond more slowly than small streams, soil moisture, and pasture conditions. As water demands decrease later in the fall, reservoir levels should show gradual improvement. Lake Okeechobee levels in Florida continue to rise. Following Fay’s rainfall across the Florida peninsula, Okeechobee will increase further.
Confidence for the Southeast: High

In Texas, a pair of tropical cyclones, Dolly and Edouard, along with an upper-level low have reduced drought since late July. However, extreme drought continues in south-central Texas. Monsoonal rainfall has eliminated drought in southern New Mexico as forecast in previous outlooks. During the remainder of August, wetter than normal conditions, as depicted in the CPC 6-10 Day outlook, should continue in coastal Texas and Louisiana. The CPC seasonal outlook calls for equal chances of above, below, or near normal precipitation. Improvement is expected across east Texas, coastal Texas, and Louisiana with prospects of improvement decreasing slightly across west Texas.
Confidence for the Texas and Louisiana: Moderate

In Colorado, western Nebraska, and the western Oklahoma panhandle, drought relief and localized flooding has occurred during the past two weeks. Monsoon rains typically continue into September, but precipitation decreases in October and November. With expected convective rainfall during the next five days, some improvement or improvement is forecast.
Confidence for the central and southern high Plains: Moderate

During early August, two small areas of drought have developed in Minnesota. Forecast tools provide a mixed picture for relief prospects. With the Coupled Forecast System leaning wet in this area for the September-November 2008 period, improvement is forecast.
Confidence for Minnesota: Low

There were a few changes to the previous outlook for North Dakota and Montana, with improvement forecast in North Dakota and a small area of development in northern Montana. Climatology and initial conditions favor the development area in northern Montana, while short- and medium-range forecasts favor improvement in North Dakota.
Confidence: Low

Across the West, the beginning of the wet season in the fall should lead towards some improvement across northern California. Although rain and mountain snow increase later in the fall, it will take time to build a snow pack in the Sierras. Early in the period, a series of unseasonably, deep troughs will bring moderate to locally heavy precipitation amounts to the Pacific Northwest. Due to precipitation in the short-term and the onset of the wet season this fall, development previously depicted in the outlook dated August 7 has been removed from the Pacific Northwest. In southern California, persistence is predicted as precipitation typically does not significantly increase until the winter.
Confidence for the West: High

In Hawaii, no changes were made to the previous outlook with development forecast in some leeward areas and improvement forecast in windward sides of the Big Island.
Confidence: Moderate

In Puerto Rico, climatology and prospects for abundant tropical rains in coming weeks continue to suggest drought improvement.
Confidence: High