The first of two severe storms drenched California on Thursday, bringing intense downpours that flooded roads and toppled trees. But the worst is far from over – officials warned residents to prepare for a “significant threat” as largerstorm is expected to douse the state over the weekend.

“Confidence is increasing for another impactful storm system to move through Sunday into Monday,” the National Weather Service’s Bay Area division wrote on Twitter/X Thursday afternoon.

The back-to-back storms, caused by strong atmospheric river systems, will pack more of a punch because of their close timing. Areas across the state were soaked by Thursday morning, adding to the potential dangers posed by the incoming storm.

The firstfast-moving storm kicked off with heavy rain and gusty winds that hit the San Francisco Bay Area and then moved south, arriving in Los Angeles in time to snarl the Thursday morning commute and cause flooding.

The Marin Headlands and coastal mounts north of the Bay Area were hit the hardest, with many areas getting more than 4in of rain. The 2.35in of rain that fell in San Francisco was enough to push the city’s seasonal totals past the average even after a somewhat slow start.

Along with wet weather that submerged streets and caused traffic hazards, the storm came with a rare flash of lightning spotted over San Francisco Bay, high surf that thrashed against the shore, and gusty winds that pulled tall trees across roads.

Service on San Francisco’s cable cars was halted as a safety precaution, and Pacifica, a coastal city in San Mateo county, saw more than an inch (2.5cm) of rain in a single hour.

Widespread coastal flooding was reported on Wednesday in Humboldt county, said the weather service office in the northern California city of Eureka, which recorded a daily record with more than 2in of rainfall. Scattered power outages were reported.

But as the storm moved south,the Los Angeles and San Diego areas were in the bull’s-eye for heavy precipitation.

As sheets of rain fell in San Diego, Ruben Gomez cleaned debris from storm drains in his parents’ neighborhood, which was hit hard by flooding from a storm in January.

He piled sandbags around what was left of their home after the previous deluge. Firefighters had had to rescue his parents, both 82, after the home filled with water reaching 6ft (2 metres). His father spent two days in the hospital with hypothermia, and his mother spent a week there, after water entered one of her lungs.

“Every hole in the house, I’ve got plugged with plastic and paper to make sure water doesn’t go up so high again,” Gomez said.

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On Thursday, southern Los Angeles county was hit hard by flash flooding. Vehicles plowed through water on low-lying sections of freeways and at least one underpass beneath a rail crossing in Long Beach was inundated, submerging a car.

Seal Beach, south of Los Angeles, saw flooding along the Pacific Coast highway, which temporarily closed parts of the freeway. An employee swept water out of a storefront in the city’s downtown as onlookers dodged puddles after the rain slowed around noon.

In nearby Costa Mesa, a rescue team pulled someone from a flowing storm channel. The person was taken to a hospital in stable condition, the Orange county fire authority said in a social media post. The fire authority also rescued a man who had been trapped on a small island in the Santa Ana riverbed, surrounded by rushing water. A paramedic had to be lowered by a helicopter to grab the man and whisk him to safety.

The storms also brought heavy snowfall to areas of higher elevation, a promising sign for the state’s meager snowpack, which currently stands at just 52% of the annual average. The Mammoth Mountain ski resort in the Sierra Nevada reported 12-14ins (30-36cm) of snow overnight. Heavy snowfall was also reported in mountains east of Los Angeles.

The storm came a week after heavy rain caused flash flooding that inundated homes, caused the river to surge and overturned cars in the county. Hundreds of people had to be rescued as the waters rose.

The “Pineapple Express” – a long plume of moisture pulled from thePacific to near Hawaii – will be followed by an even more powerful storm on Sunday, forecasters said.

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Last winter, California was battered by numerous drought-busting atmospheric rivers that unleashed extensive flooding, big waves that hammered shoreline communities and extraordinary snowfall that crushed buildings. More than 20 people died in storms described as one of “the most deadly natural disasters in the modern history” of California.

The second storm headed to the state this week is already predicted to be “the largest storm of the season”, according to the National Weather Service. The worst part of the storm will hit late Sunday into Monday as it stalls over Point Conception in Santa Barbara county.

“This system will likely produce 24 to 36 hours (or more) of continuous rain,” the weather service wrote Thursday.

Models suggest it could intensify as it approaches the coast of California, a process called “bombogenesis” in which a spinning low-pressure system rapidly deepens, Swain said in an online briefing on Tuesday. The process is popularly called a bomb cyclone.

That scenario would create the potential for a major windstorm for the San Francisco Bay Area and other parts of northern California as well as heavy rain, said Daniel Swain, a climate scientist at the University of California, Los Angeles.

Gabrielle Canon contributed reporting

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