U.S. Drought Monitor Update for September 10, 2019

According to the September 10, 2019, U.S. Drought Monitor, moderate to extreme drought covers 14.3% of the United States including Puerto Rico, an increase from last week’s 11.3%. The worst drought categories (extreme to exceptional drought) increased from 0.4% last week to 0.5% this week. 

There were many atmospheric players at work across the United States during the week. A large upper-level high-pressure ridge dominated the southern contiguous United States, with its epicenter over the southern Plains shifting eastward to the Southeast by the end of the week. It was part of the subtropical high-pressure system that extended into the North Atlantic and North Pacific. Upper-level troughs moving in the mid-latitude jet stream bracketed the ridge along the western and eastern U.S. coasts. Meanwhile, in the tropics to the south of the high pressure, Hurricane Dorian was steered across the Bahamas then northward along the eastern U.S. coast, while Tropical Storm Fernand made landfall on the northeast Mexico coast, bringing rain to southern Texas. Dorian soaked the coastal Carolinas, but the ridge kept most of the southern and central Plains to East Coast dry.  

Canadian fronts moving in the eastern trough brought cooler-than-normal temperatures to the northern Plains to Northeast, while the ridge kept temperatures warmer than normal across the rest of the contiguous United States. Pacific fronts moving in the western trough dropped above-normal rainfall across the Pacific Northwest to northern Plains, while the ridge inhibited the Southwest monsoon, keeping that region drier than normal. 

The end result of this complex scenario was expansion and intensification of drought and abnormal dryness in the Southwest, southern Plains, and parts of the Ohio Valley to mid-Atlantic coast. Drought contraction occurred where heavier rains fell in parts of the Pacific Northwest, Texas, Upper Midwest, and the coastal Carolinas. 

Abnormal dryness and drought are currently affecting over 86 million people across the United States including Puerto Rico—about 27.8% of the population.