In California and Mexico, a Rare Hurricane Sends Disaster Prep Into High Gear

As Hurricane Hilary heads north, Southern California and Mexico are bracing for a rare and powerful storm that could produce dangerous flash flooding and sustained winds that have not been seen for decades.

Residents are racing to fill sandbags and fuel up generators before extreme weather arrives, and emergency officials are warning that roads may be inundated and setting up evacuation centers.

The Category 4 hurricane is so unusual that it has prompted the National Hurricane Center to issue a tropical storm watch for California for the first time in its history. Hilary is currently projected to make landfall in Baja California on Sunday and move northward as a tropical storm near San Diego and across the deserts and mountains east of Los Angeles — though its path could still veer elsewhere.

In California, the desert and mountain communities are of particular concern. The National Weather Service warned of five to eight inches of rain for the Coachella Valley, about 120 miles east of Los Angeles. The tropical storm could force numerous evacuations and rescues, as well as deadly runoff that may “rage down valleys while increasing susceptibility to rockslides and mudslides,” the agency said.

“The risk in the southeastern deserts is genuinely alarming,” said Daniel Swain, a climate scientist at the University of California, Los Angeles, referring to areas such as Joshua Tree National Park in the southeast part of the state. “We’re talking, in some cases, it will be multiple years’ worth of rainfall.”

As of Friday, Hilary was about 350 miles south of Cabo San Lucas, Mexico, causing particular worry for the Baja California peninsula. Hilary poses a threat to all of the Mexican state of Baja California, home to 3.8 million residents, local authorities said on Friday during a meeting in Tijuana with reporters and other officials. Catalino Zavala, the state’s secretary general, said that 80 temporary shelters would be available to receive up to 9,000 people.

“It is a little bit more serious than we expected,” said Armando Ayala Robles, mayor of the city of Ensenada.

Of special concern are the rocky island of Cedros, off the west coast of the state and home to about 3,000 people, and San Quintín, an agricultural center for the region that has slowly emerged as a coastal tourist destination.

Hilary will dump up to 10 inches of rain on the state of Baja California from Saturday to Monday — an extremely unusual amount given that the state, known for its dry weather, typically receives around eight inches throughout the year, the authorities said.

Mexico’s national meteorological service predicted that given the rainfall and wind gusts of up to 62 miles per hour, flooding and landslides were expected to occur. Power outages and loss of communications are also likely to happen.

The Mexican Army has deployed nearly 14,000 soldiers to the city of Mexicali, just south of the U.S. border, and the states of Baja California Sur, Jalisco and Colima — which expect up to six inches of rain on Friday even without the hurricane making landfall there. More troops were deployed in other states in western and central Mexico, where intense rains were forecast.

In San Diego County, the southernmost part of California, plans were in place to keep lifeguards on duty throughout the weekend because of dangerous surf conditions, and extra emergency personnel had been tapped to address flooding.

“There are people who live in the canyons and low-lying areas, and we want to be prepared,” said David Gerboth, an assistant fire chief with the San Diego Fire-Rescue Department.

In Orange County to the north, residents were trying to make sense of the fact that a tropical storm was heading their way — a phenomenon that few Californians alive today have ever encountered. The last time one reached landfall in Southern California was in 1939, flooding Los Angeles and killing nearly 100 people.

Under blue skies in downtown Laguna Beach on Friday morning, Suzanne Barber was stacking a dozen sandbags outside her art gallery on the Pacific Coast Highway, across the street from Main Beach. Fresh on her mind was Hurricane Dora, which never made landfall in Hawaii but amplified the winds that contributed to the wildfire disaster on Maui this month.

“I can’t believe it is happening,” she said. “After seeing what happened in Lahaina — that tropical storm — it really frightened me. I just want to be prepared and not take it lightly.”

She added that she received a text from concerned relatives in Tennessee asking if she was going to evacuate. “I said, ‘What?’”

Major League Baseball announced on Friday that it had rescheduled three games that were supposed to be played on Sunday in Los Angeles, San Diego and Anaheim. Those games will be played on Saturday afternoon instead.

Experts say there is almost no risk that the storm will actually touch down in California as a hurricane, because the cool ocean temperatures in this part of the Pacific and the stable atmosphere are not conducive. Hilary is expected to weaken to a tropical storm by the time it reaches Southern California. Still, the effects of such a storm could be devastating.

With potential for significant rainfall, there is heightened concern about the canyons and fire-burn areas where rapid debris and mud flow could occur. Firefighters are also bracing for rain-related rescues and an increase in accidents.

The office of emergency management in Los Angeles County said residents should make a plan for their families, stock up on supplies and stay informed of the news.

“Los Angeles is no stranger to crazy events and phenomena, it’s the nature of where we’re at,” said Emily Montanez, the associate director of the agency.

Ms. Montanez said that over the last two days, her office had been coordinating with county departments as well as leaders in all 88 cities in Los Angeles County. Law enforcement and fire staff have been augmented, and emergency medical workers have been assigned to incident management teams. If needed, beaches, parks and hiking trails and other public spaces may be closed.

“Everybody’s on standby,” she said.

Vik Jolly, Maggie Miles and Candice Reed contributed reporting from Southern California. Elda Cantú contributed reporting from Ensenada, Mexico. Emiliano Rodríguez Mega contributed reporting from Mexico City.