U.S. Drought: Weekly Report for August 15, 2023

According to the August 15, 2023 U.S. Drought Monitor, moderate to exceptional drought covers 25.9% of the United States including Puerto Rico, an increase from last week’s 25.5%. The worst drought categories (extreme to exceptional drought) increased from 2.3% last week to 2.6%.

A strong ridge of high pressure continued to dominate the upper-level circulation across the contiguous U.S. during this U.S. Drought Monitor (USDM) week. The ridge was anchored over the southern Plains to the Gulf of Mexico but extended across the western U.S. then northward across western Canada. It was part of a subtropical ridge system that extended eastward across the Caribbean and North Atlantic, and westward into the North Pacific. 

An upper-level trough was over eastern Canada and extended into the northeastern U.S., with another trough poking into Alaska. Pacific weather systems weakened as they penetrated the western ridge, then strengthened as they moved into the eastern trough and directed cold fronts across the eastern half of the contiguous United States. The ridge inhibited precipitation, so the western and southern tier states were mostly dry this week, as were Hawaii, Puerto Rico, and the U.S. Virgin Islands. But the fronts and their surface low-pressure systems tapped Gulf of Mexico moisture to spread above-normal precipitation across parts of the Plains and much of the Midwest and Northeast to Tennessee Valley. 

Weekly temperatures averaged warmer than normal across the southern Plains, Puerto Rico, and the U.S. Virgin Islands, where a relentless heat wave continued, and across the coastal Southeast and the West Coast. It was near to cooler than normal from the Southwest to the central and northern Plains, and across the Great Lakes to the Tennessee Valley. Alaska had a mixed pattern of temperature and precipitation anomalies. 

Drought or abnormal dryness contracted or was reduced in intensity in areas that were wetter than normal, especially in the central Plains to Mid- and Upper-Mississippi Valley. But drought or abnormal dryness expanded or intensified where it continued dry, especially from the Southwest to the Lower Mississippi Valley, across the Gulf of Mexico Coast, in the Mid-Atlantic, and in Hawaii and parts of Alaska. 

Nationally, expansion exceeded contraction, so the nationwide moderate to exceptional drought area increased this week. Abnormal dryness and drought are currently affecting over 120 million people across the United States including Puerto Rico—about 38.7% of the population