Tropical Storm Hilary floods U.S. Southwest

Aug. 22, 2023
The weather pattern broke several rainfall daily records in Southern California as it continues to bring flash flooding and damage to communities.

Communities across the southwestern United States are reckoning with flood and mudslides as Post-Tropical Cyclone Hilary continues to bring dangerous weather conditions.

Many communities in southwestern states have shut down parks and businesses in anticipation for the extreme weather event. Some emergency personnel have mobilized in response to flash flooding, and many residents have suffered basement flooding.

The storm prompted formal flood watches across several states, including Southern California, northwest Arizona, Nevada, Utah, Oregon, Idaho, and Washington, according to CBS News.

Some residents in areas particularly at risk to the storm have been warned not to drive, as road conditions can be dangerous and many major roadways have experienced flash flooding.

On Monday, Aug. 21, Hilary flooded streets across Southern California. It dumped 4-5 inches of rain on coastal areas and 10 inches or more in the mountains. The storm also caused mudslides and rock slides in multiple areas.

The weather pattern was previously classified as Hurricane Hilary while it was off the coast of Mexico’s Baja California peninsula. When it hit the Mexican peninsula, it caused widespread flooding and one confirmed death.

Before making landfall in Mexico, it was downgraded to a tropical storm. Early in the morning of Monday, Aug. 21, it downgraded again to a post-tropical cyclone.

The National Weather Service of Los Angeles reported that, “as of 3AM, virtually all rainfall daily records have been broken thus far.”

Many residents of arid regions, such as Southern California, were unprepared for the heavy rainfall not only in runoff management but also in financial risk management: many victims of flood damage do not have flood insurance.

Rainfall is already a rare occurrence for Southern California. The last time a tropical storm had reached the region was 1939, bringing flooding to Los Angeles and killing roughly 100 people, according to the New York Times.

About the Author

Jeremy Wolfe | Editor, Stormwater Solutions

Jeremy Wolfe is a former Editor for Stormwater Solutions.