During August, limited drought improvement occurred across the Southwest, with drought intensifying over the Pacific Northwest as numerous large wild fires charred much of the region. Short-term drought continued to affect parts of the Southeast although some relief occurred in portions of Alabama, Georgia, and Florida. Meanwhile, subnormal rainfall and unseasonable warmth persisted across the western Gulf Coast, southern Great Plains, and the lower Mississippi Valley, producing “flash drought” in most of these areas after record wet May and June rains had eliminated long-term drought in the southern Plains. Late in the month, however, heavy rains drenched portions of the western Gulf Coast, providing some drought relief. Increased precipitation stabilized drought conditions in Alaska and Hawaii, but was not great enough to make any improvements. Meanwhile, well below-average rainfall associated with the ongoing El Nino intensified drought across Puerto Rico during the first half of August. After mid-month, however, moisture associated with Tropical Storms Danny and Erika increased rainfall (1 to 5 inches) across most of the island, but storm totals were much less than forecast.

The monthly drought outlook valid for September is based on initial conditions, the updated CPC September precipitation and temperature outlooks, and climatology. The most likely area for drought development across the lower 48 States is the southern Plains and lower Mississippi Valley due to subnormal rainfall and high temperatures during July and August (flash drought), and continued dryness and warmth expected during the first half of September. Similarly, some development is forecast for parts of New England where D0 and D1 currently exist as sub-median rainfall and above-normal temperatures are predicted for early September. Additionally, a dry fall signal is favored in New England during strong El Nino events. In contrast, prospects for some drought improvement or removal increase across Florida and the southern Atlantic Coast as moisture from the remnants of Erika combined with an upper-air low to the west have recently and are expected to drop ample rains on this region during the next few days. Two small D1 areas in the upper Midwest are forecast for removal with recent heavy rains (more than 2 inches) and forecasts of above-median precipitation at all September time periods (short, extended, and monthly).

Since September is climatologically dry and warm, persistence is very likely across the Far West (e.g. California, the Great Basin, and Pacific Northwest). The tail end of the summer monsoon may provide beneficial rainfall to the Southwest, especially in eastern areas where drought has been less in intensity and duration and September is still climatologically wet (e.g. eastern Arizona, New Mexico, and west Texas). Since New Mexico and parts of eastern Arizona have experienced a wet monsoon to date, these factors and expected short-term rains and odds for above-median monthly rainfall increase chances for additional drought improvement/removal (e.g. short-term topsoil moisture) across these two areas. However, opportunities for widespread major improvement to the hydrological drought (e.g. major reservoirs) across the Southwest are not expected until the 2015-16 winter.

With September climatologically wet in Alaska, reduced temperatures, and widespread moderate to heavy August precipitation, removal of drought is expected across interior Alaska and in the southeastern Alaskan Panhandle where even near-median precipitation translates to large totals (10 to 20 inches) in the latter area. With recent and expected active tropical activity in the central Pacific Ocean, widespread rains last week, and increased odds for above-median September rainfall, improvement to the D1 and D2 areas are expected across the Hawaiian Islands. This would be welcome as strong El Nino events typically bring dryness during the winter and spring. Suppressed convection, including a reduction of tropical cyclone activity, is typical during El Nino summers across the Caribbean, and this has occurred in Puerto Rico and the U.S. Virgin Islands. During late August, however, moisture from weak Tropical Storms Danny and Erika finally brought increased but less than forecasted rainfall to parts of the island, limiting relief. With September normally wet and diminished tropical activity expected to continue, persistence was predicted for Puerto Rico.
     
Forecaster: David Miskus

Next Monthly Drought Outlook issued: September 30, 2015 at 3:00 PM EDT