Look: Rain from Tropical Storm Hilary lashes US and Mexico, swamping roads and trapping cars

Tropical Storm Hilary inundated streets across Mexico’s arid Baja California Peninunsula with deadly floodwaters Sunday before moving over Southern California, where it swamped roads and downed trees, as concerns mounted that flash floods could strike in places as far north as Idaho that rarely get such torrential rain.

Forecasters said Hilary was the first tropical storm to hit Southern California in 84 years, bringing flash floods, mudslides, high winds, power outages and the potential for isolated tornadoes.

Hilary made landfall along the Mexican coast in a sparsely populated area about 150 miles (250 kilometres) south of Ensenada, then moved through mudslide-prone Tijuana, threatening the improvised homes that cling to hillsides just south of the US border.

At least 9 million people were under flash-flood watches and warnings as heavy rain fell across normally sunny Southern California ahead of the brunt of the storm. Desert areas were especially susceptible along with hillsides with wildfire burn scars, forecasters warned.

Mud and boulders spilled onto highways, water overwhelmed drainage systems and tree branches fell in neighbourhoods from San Diego to Los Angeles. Dozens of cars were trapped in floodwaters in Palm Springs and surrounding desert communities across the the Coachella Valley. Crews pumped floodwaters out of the emergency room at Eisenhower Medical Center in Rancho Mirage.

The National Weather Service's Los Angeles office reported in the evening via X, formerly known as Twitter, that “very heavy rain” was continuing in much of Los Angeles and Ventura counties. The highest rainfall totals so far were 6.15 inches (15.62 centimetres) at Leona Valley and 5.94 inches (15.1 centimetres) at Lewis Ranch, the agency added, saying there was significant flooding and urging people to stay off the roads.

The Los Angeles Unified School District, the nation's second largest school system, said all campuses would be closed on Monday.

“There is no way we can compromise the safety of a single child or an employee, and our inability to survey buildings, our inability to determine access to schools makes it nearly impossible for us to open schools," Superintendent Alberto Carvalho said at a media briefing. San Diego schools postponed the first day of classes from Monday to Tuesday.

Southern California got another surprise in the afternoon as an earthquake with a preliminary magnitude of 5.1 hit near Ojai, about 80 miles (130 km) northwest of downtown Los Angeles, according to the U.S. Geological Survey. It was felt widely and was followed by smaller aftershocks. There were no immediate reports of major damage or injury, according to a dispatcher with the Ventura County Sheriff's Office.

Hilary could wallop other Western states with once-in-a-century rains, with a good chance of it becoming the wettest known tropical cyclone to douse Nevada, Oregon and Idaho. Hilary was expected to remain a tropical storm into central Nevada early Monday before dissipating.

By Sunday evening, Hilary had moved over San Diego and was headed north into inland desert areas. Around midday, it had maximum sustained winds of 60 mph (97 kph).

Hurricane Centre Director Michael Brennan said that while Hilary had weakened from a Category 4 hurricane, it’s the water, not the wind, that people should watch out for most — some areas could get as much rain in hours that they typically get in a year.

“You do not want to be out driving around, trying to cross flooded roads on vehicle or on foot," Brennan said during a briefing from Miami. “Rainfall flooding has been the biggest killer in tropical storms and hurricanes in the United States in the past 10 years, and you don’t want to become a statistic.”

Hilary is just the latest major climate disaster to wreak havoc across the US, Canada and Mexico. Hawaii’s island of Maui is still reeling from a blaze that killed over 100 people and ravaged the historic town of Lahaina, making it the deadliest US wildfire in more than a century. Firefighters in Canada are battling that nation’s worst fire season on record.

The Mexican cities of Ensenada and Tijuana closed all beaches and opened a half-dozen shelters at sports complexes and government offices.

One person drowned Saturday in the Mexican town of Santa Rosalia when a vehicle was swept away in an overflowing stream. Rescue workers saved four other people, said Edith Aguilar Villavicencio, the mayor of Mulege township.

Mexican army troops fanned out across Mulege, where some of the worst damage occurred Saturday on the eastern side of the Baja Peninsula. Soldiers used bulldozers and dump trucks to help clear tons of boulders and earth clogging streets and roads that were turned into raging torrents a day earlier.

Power lines were toppled in many places, and emergency personnel were working to restore power and reach those cut off by the storm.

Brennan said rainfall could reach between 3 and 6 inches (7 centimetres and 15 centimetres) in many areas. Forecasters warned it could dump up to 10 inches (25 centimetres) — a year’s worth of rain — in some isolated areas.

• Hurricane Hilary threatens 'catastrophic and life-threatening' flooding in Mexico and California