Tropical Storm Hilary unleashes heavy rains and flooding on Southern California

Updated August 20, 2023 at 9:29 PM ET

The center of Tropical Storm Hilary reached Southern California on Sunday afternoon, bringing fierce winds and the potential for historic rainfall to areas that have not seen tropical storm conditions in more than 80 years.

As of 5 p.m. local time on Sunday, the storm was 25 miles south-southwest of Palm Springs and traveling at 23 miles per hour with maximum sustained winds of 50 mph. It is expected to sweep across Southern California and move north through Nevada on Monday morning, according to the National Weather Service.

Some roadways in Southern California have flooded and water rescues have been performed, LAist reported. Parts of Los Angeles County have seen rainfall totals of more than 4 inches over two days as of Sunday afternoon.

In anticipation of the rare tropical storm, Nevada's Clark County, where Las Vegas is located, issued an emergency declaration on Sunday. Meanwhile, parts of Southern California have been under a state of emergency since Saturday evening.

Portions of Southern California and southern Nevada are expected to average between 3 to 6 inches of rainfall — but could receive up to 10 inches. Some parts will likely accumulate more rain in just a matter of hours than they typically do in an entire year, forecasters said. Winds will also be particularly strong and gusty on elevated terrain.

Hilary, which was downgraded from a hurricane on Sunday, made landfall over the northern Baja California peninsula in Mexico earlier on Sunday. At least one person died of drowning in the Mexican town of Santa Rosalia amid the storm. Mexico's hurricane watch has ended, but the Baja California coast is still under threat of flash floods.

The heaviest rainfall is expected to pour overnight

The downpour is expected to last in Southern California until early Monday morning.

Areas in eastern San Diego, northern Los Angeles, San Bernardino, Riverside and Death Valley have the greatest risk for flash flooding, according to Michael Brennan, the director of the National Hurricane Center.

"To make it even more dangerous is, the heaviest rainfall and flooding potential is going to largely occur overnight. So you want to be in your safe place certainly no later than this afternoon," he said during the center's livestream on Sunday morning.

Brennan warned that flooding conditions like washed out roads are more difficult to see at night. That will be especially dangerous on major highways like I-10, I-8 and I-40, which are expected to be impacted by the intense downpour.

A majority of Nevada and parts of southwestern Utah and western Arizona will also be at risk of flooding, Brennan said. There is also a risk of tornadoes in parts of the Mojave Desert, Lower Colorado River Valley and southeastern California.

The last time Southern California was hit by a storm this strong was 1939

Much of Southern California is under its first-ever tropical storm warning, given that the region is most frequented by disasters like wildfires and earthquakes. Meteorologists say the last time a storm of this strength hit Southern California was back in 1939.

On Saturday night, California Gov. Gavin Newsom issued a state of emergency for several counties, including Fresno, Imperial, Inyo, Kern, Los Angeles, Riverside, San Diego, San Bernardino, Tulare, Orange and Ventura. Some of those communities, like parts of San Bernardino County, have already received evacuation orders.

The Flood Operations Center, Cal Fire and the California National Guard are on standby with water vehicles and water rescue teams amid flood threats. State officials also urged residents to sign up for flood and evacuation alerts from their counties, as well as prepare their pets and family in case they need to evacuate.

NPR's Julia Simon and James Doubek contributed reporting.

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