Tens of millions of people are under tropical storm warnings as Tropical Storm Hilary brings “life threatening to locally catastrophic” flooding to southern California and beyond, the National Weather Service said during a Sunday advisory.

The storm has already impacted parts of Mexico, and is also expected to impact Arizona and Nevada.

Although the storm weakened from a Category 4 hurricane to a tropical storm over the weekend, it is still expected to bring moderate to high flash flooding to communities to the north and northeast of Los Angeles, California. That level of flooding is strong enough to endanger lives and property.

So far, one person has drowned and another four people were rescued on Saturday in the town of Santa Rosalia, Mexico. Videos of water flooding the streets posted by local authorities as the storm travels along Mexico’s Baja California coast.

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California Gov. Gavin Newsom ordered a state of emergency for the state on Saturday, deploying more than 7,500 personnel and opening the state’s emergency services office to monitor Hilary’s impact. “We’re mobilizing all of government as we prepare and respond to this unprecedented storm,” Newsom said.

Tropical Storm Hilary will be the first to impact Southern California in more than 80 years. Here’s what to know.

Who will be affected

Dozens of people have already sought refuge at shelters in resorts in Los Cabos, Mexico, and some 850 people were evacuated from islands off the Baja coast.

The storm is expected to reach California on Sunday, bringing heavy rainfall through Monday morning. Swells generated by Tropical Storm Hilary will cause “life-threatening surf and rip current conditions” across the Baja California peninsula and southern California, the National Weather Service San Diego tweeted.

In preparation, officials closed California state parks and beaches in the affected regions until Monday. Camping reservations have been canceled through Tuesday, according to the California Department of Parks and Recreation.

Evacuation orders are currently in place for communities of Oak Glen, Forest Falls, Mountain Home Village, Angelus Oaks, and Northeast Yucaipa in San Bernardino County.

The storm is expected to significantly impact the Antelope Valley and San Gabriel Mountains areas, which will likely see between three to seven inches of rain and winds as fast as 70 miles per hour, Fire Chief Kristin Crowley said during a Sunday press conference. Los Angeles, she added, is expected to experience less rain and winds, although Mayor Karen Bass still signed a declaration of local emergency on Saturday.

“As we head into this weekend, I urge Angelenos to continue monitoring the hurricane and be mindful of extreme weather warnings,” said Mayor Karen Bass. “We know the severe impact that weather can have on our communities. I am making sure Los Angeles is prepared on behalf of our residents.”

Southern California Edison utility workers are also tracking the storm to better predict damages to power lines and are currently consulting with emergency management teams to learn how to best respond to residents’ needs.

“We are watching the progression of this storm very carefully,” said Thomas Jacobus, SCE principal manager of Business Resiliency, in a press release on Thursday. “We are collaborating with departments across the company to coordinate efforts in preparation for any storm-related risks.”

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