Swathes of the US state of California were flooded and hundreds of thousands of people were without power after a dangerous storm brought heavy rains and prompted a state of emergency.
"This is a serious storm with dangerous and potentially life-threatening impacts," said Governor Gavin Newsom as he declared the state of emergency for eight counties in Southern California.
Affected areas include Los Angeles, Orange, Riverside, San Bernardino, San Diego and Santa Barbara.
Nearly 700,000 customers were without power early this morning local time, according to the electricity supply tracker PowerOutage.us.
Dozens of flights in and out of Los Angeles airport were delayed or cancelled, according to flightaware.com.
The National Weather Service had earlier issued a warning that a "strong Pacific storm system would bring impactful and dangerous flooding rains, heavy snow, strong winds, coastal flooding, and high surf to California".
"Heavy rainfall will bring the threat for life-threatening flash, urban, and river flooding as well as debris flows and mudslides," said NWS.
Explained: 'Pineapple Express' storms hitting California
The storm, packing gusts of 96km/h or greater, is part of a "Pineapple Express", a weather phenomenon that grows in Hawaii from near where the tropical moisture is coming.
The NWS described it as "the largest storm of the season".
The severe conditions prompted the NWS Bay Area office to issue a rare hurricane-force wind warning for Big Sur and nearby areas.
"This has the potential to be a historic storm, severe winds, thunderstorms, and even brief tornadoes," Los Angeles Mayor Karen Bass told a news conference.
The San Francisco Bay Area and Los Angeles county were not only getting drenched but the storm was expected to stall over some areas into tomorrow, creating severe risk of flooding mudslides.
"This is a DANGEROUS SYSTEM with major risks to life and property. Substantial flooding. Residents should heed any evacuation orders," the Los Angeles office of the NWS said on social media.
"Stay off the roads, especially the freeways...through at least Monday morning."
Near Los Angeles, the port city of Long Beach could get more rain this week than it does during an entire year, said Mayor Rex Richardson, who is expecting 13-18cm of rainfall by tomorrow.
California's southern and central coasts are bracing for 25mm of rain an hour and totals 7-15cm, the US National Weather Service said. As much as 15-30cm are expected in the foothills and lower-elevation mountains.
The Los Angeles and Santa Barbara areas were both at high risk for excessive rainfall, with forecasters anticipating "near continuous rainfall" for the next 24 hours.
Evacuation orders were issued for some of those counties' residents, as well as residents of the San Jose region and Ventura County.
The US West Coast endured a difficult winter last year when a series of atmospheric rivers dumped billions of gallons of rain and snow.
That brought widespread flooding and travel disruption, as well as problems with the power grid.
But it also replenished severely depleted reservoirs, which had sunk to record lows after years of intense drought.
While wet weather is not unusual during California's winters, scientists say human-caused climate change is altering the planet's weather patterns.
This makes storms wetter, more violent and more unpredictable, while causing dry periods to be hotter and longer.
