During the past 30 days, subnormal rainfall and above normal temperatures led to drought intensification and expansion from the lower Mississippi Valley northeastward into northern New England. Meanwhile, moisture from tropical systems - Hermine in the eastern Gulf and southern Atlantic Coasts, Julia in the southeastern Virginia and eastern North Carolina, and Newton in the Southwest - plus a strong trough of low pressure in the northern Rockies and Plains, brought surplus 30-day precipitation to much of the eastern Great Basin, northern Rockies and Plains, parts of the Four-Corners region, most of the Plains and Midwest, and the eastern Gulf and southern Atlantic States. The Far West remained unchanged as September is normally dry. Not surprisingly, 4-week drought changes included degradation in much of New England, mid-Atlantic, and interior Southeast while improvement was noted in the Four Corners Region, northern Rockies, most of the Plains with the exception of deterioration in eastern Oklahoma, and the lower Great Lakes region. Excess rains in the small drought areas of Hawaii and Puerto Rico also brought improvements.

The drought outlook valid for October 2016 is based on the updated CPC October precipitation and temperature outlooks, WPC QPF 7-day totals, Extended Range Forecasts (Days 6-10 and 8-14), Weeks 3-4 precipitation forecast, recent precipitation anomalies starting at the 12Z Sep. 27 cutoff date of the latest US Drought Monitor, and climatology. In addition, the potential influence of tropical storms is weighed.  

Hurricane Hermine and Tropical Storm Julia brought ample rains to the eastern Gulf, southern and mid-Atlantic Coasts, but missed the interior Southeast, mid-Atlantic, and New England as temperatures averaged above normal. Currently, a stalled upper-air low over the Ohio Valley has brought late September heavy rains to parts of the mid-Atlantic, and is expected to produce more heavy rains northward into parts of the Northeast, including the lower Great Lakes region and coastal New England, hence improvement is depicted. In western New York and northern New England, however, the heavy rains are not expected to extend that far north, hence persistence was maintained. In addition, Hurricane Matthew (currently located in the south-central Caribbean) may also affect the Atlantic Coast States in early October (current consensus track is northward just off the East Coast to Hatteras, then northeastward), injecting a dose of uncertainty to the MDO in the Northeast.  However, persistence and some development is expected across the interior Southeast and into the lower Mississippi Valley as all time-scale forecasts (QPF, ERFs, Week 3-4, updated 1-month LLF) point toward sub-median precipitation. The one fly in the ointment is Matthew, especially if it tracks farther west and makes landfall in the central Gulf, although not many model ensembles have this scenario. 

Drought improvement and removal is generally expected for the central Plains and north-central Rockies. With a relatively wet pattern forecast for the next 2 weeks plus recent surplus rains in these regions, Montana, Wyoming, and South Dakota should see continued improvements, although some areas with longer-term drought may persist. In the Southwest, Great Basin, and California, a dry October climatology favors persistence of drought. Relatively dry outlooks for the southern Plains should maintain small areas of drought after recent wetness brought improvement here. Drought persistence is expected across the Intermountain West (eastern Oregon), but improvement is forecast for coastal Oregon and Washington as the QPF predicts decent rains, the extended range and weeks 3-4 outlooks favor above-median precipitation, and late October normally marks the start of the Pacific Northwest rainy season (wet climatology).

The small remaining drought area across Puerto Rico is expected to be removed by the end of October as the climatology is favorable. Recent rains, some from tropical moisture, have chipped away at the drought in Hawaii, leaving only small areas on leeward sides of Kauai and Maui. Favorable odds of above-median October rains should provide continuing improvement.

Forecaster: David Miskus

Next Monthly Drought Outlook issued: October 31, 2016 at 3pm EDT