A second “atmospheric river” was passing over California on Monday, causing dramatic flooding to roads, knocking out power to hundreds of thousands of people, and prompting the National Weather Service to issue a rare warning about hurricane force winds.

Related: ‘Rivers in the sky’: what are the atmospheric rivers hitting California?

About 550,000 of 15 million electricity customers tracked in the state were without power early Monday, according to poweroutage.us.

And in what was the first “hurricane force wind warning” ever issued by the weather service’s San Francisco Bay Area office, forecasters said winds could gust up to 92 mph (148 kph) from the Monterey Peninsula to the northern section of San Luis Obispo county.

Gavin Newsom, California’s governor, declared a state of emergency for Los Angeles, Orange, Riverside, San Bernardino, San Diego, San Luis Obispo, Santa Barbara and Ventura counties.

Across the San Francisco Bay Area, winds exceeded 60mph (96 kph), with gusts exceeding 80mph (128 kph) in the mountains. In the technology center of San Jose to the south, emergency services pulled stranded motorists out of cars caught in floodwaters and rescued people from a homeless encampment alongside a rising river.

The weather service forecast up to 8in (20cm) of rainfall across southern California’s coastal and valley areas, with 14in (35 cm) possible in the foothills and mountains.

As the storm intensified further south, officials warned of potentially devastating flooding and ordered evacuations for canyons that burned in recent wildfires that are at high risk for mud and debris flows. In Santa Barbara, hit by mudslides in 2018, schools were cancelled Monday.

Evacuation orders and warnings were in effect for mountain and canyon areas of Monterey, Santa Barbara, Ventura and Los Angeles counties.

“If you have not already left, please gather your family, your pets, your medications and leave immediately,” Lindsay Horvath, the Los Angeles county supervisor, told residents of Topanga and Soledad canyons.

“All the freeways are flooded around here,” Ventura county resident Alexis Herrera, who was caught in the deluge, told the Associated Press. “I don’t know how I’m going to move my car.”

Much of California had been drying out from a weather system, known as a “pineapple express”, last week that caused flooding in lower elevations and snowfall in mountains. The expression derives from the signature shape of the plume of moisture across the Pacific to Hawaii.

Ryan Kittell, a meteorologist at the weather service’s Los Angeles-area office, said the slow speed of the storm was exacerbating the rainfall.

“The core of the low pressure system is very deep, and it’s moving very slowly and it’s very close to us,” Kittell said Sunday. “And that’s why we have those very strong winds. And the slow nature of it is really giving us the highest rainfall totals and the flooding risk.”

Nonetheless, precipitation is welcomed by some. Palisades Tahoe, a ski resort about 200 miles (320km) north-east of San Francisco, said Sunday it was anticipating the heaviest snowfall yet this season of up to two feet.