U.S. Drought: Weekly Report for August 29, 2023

According to the August 29, 2023 U.S. Drought Monitor, moderate to exceptional drought covers 28.8% of the United States including Puerto Rico, an increase from last week’s 27.5%. The worst drought categories (extreme to exceptional drought) increased from 4.8% last week to 6.2%.

The upper-level circulation over the contiguous U.S. (CONUS) during this U.S. Drought Monitor (USDM) week (August 23–29) continued to be dominated by a strong ridge of high pressure, with an upper-level trough of low pressure just off the West Coast. 

Weather systems moved along the periphery of the ridge—Pacific weather systems moved along the U.S.-Canadian border, Tropical Storm Harold and its remnants dropped rain along the Rio Grande Valley at the beginning of the week before dissipating over the Southwest, and Hurricane Idalia took aim at the Florida Gulf Coast as the week ended. The ridge was centered squarely over the Mid-Mississippi Valley as the week began, then shifted to the west as an upper-level trough developed over the Great Lakes and extended southward. The eastern trough eventually helped steer Hurricane Idalia into Florida in the days following. The week was wetter than normal along the Rio Grande and into parts of the Southwest due to moisture from Harold, over the northern Rockies from leftover moisture as the remnants of last week’s Hurricane Hilary were pulled northward earlier this week, and over parts of the Midwest, Mid-Atlantic, and Northeast from cold fronts associated with the eastern trough. However, these weather systems were fighting against the dominant upper-level ridge. 

The ridge inhibited precipitation, resulting in a drier-than-normal week across the Southeast and Gulf Coast and much of the Plains, Midwest, and West. It also brought warmer-than-normal temperatures to most of the CONUS, with the relentless heat continuing in the South and Plains and extending eastward into the Midwest and Southeast. Much of Puerto Rico, the U.S. Virgin Islands, and the southern Hawaiian Islands were drier than normal with above-normal temperatures persisting in the Caribbean, while Alaska had a mixed temperature and precipitation anomaly pattern. 

Above-normal rain contracted abnormal dryness and drought or reduced its intensity in southern Texas, along the Rio Grande Valley, and in parts of the Midwest and eastern Great Lakes. But continued hotter- and drier-than-normal weather expanded abnormal dryness and drought or increased its intensity in the Pacific Northwest, Upper Midwest, Southwest to Lower Mississippi Valley, and parts of the Mid-Atlantic, with drought expanding on Hawaii’s Big Island. 

Nationally, expansion exceeded contraction, so the nationwide moderate to exceptional drought area increased this week. Abnormal dryness and drought are currently affecting over 111 million people across the United States including Puerto Rico—about 35.9% of the population.