Up to 37 million people were at risk of possibly life-threatening flooding in California overnight and into Sunday, forecasters warned, as an “atmospheric river” brought heavy rain, snow and strong winds with the potential to down trees and power lines across the state. 

The National Weather Service Bay Area warned of “widespread” tree and power line damage across Monterey County and impassable roads and power outages, with gusts of wind expected to top 75 miles per hour. 

In San Jose, a community of “unhoused” people living along the Guadalupe River was ordered to evacuate to local community centers as the river was expected to swell due to the heavy rains in the Santa Cruz mountains, causing risks to life and property, the city of San Jose said in public emergency updates.

The storm marks the second time this week the state will come under pressure from an “atmospheric river” — plumes of moisture that travel hundreds of miles across the Pacific Ocean. Atmospheric rivers caused downpours in the Bay Area on Wednesday, bringing cable car services to a halt, before moving on to Los Angeles and San Diego by Thursday. 

Officials in Santa Barbara County raised evacuation advisories to orders on Saturday, calling on residents to be at a “very high state of readiness.” 

Sheriff’s deputies and search and rescue teams conducted door-to-door evacuation notifications getting residents out, as beaches across the county closed indefinitely. 

California State Parks spokesperson Gloria Sandoval warned the public to “stay out of the ocean during the storms and to respect the temporary closures” as surf spots such as the iconic Old Man’s at San Onofre Surf Beach remained closed for access following January’s storms. Heavy rain and extreme weather caused roadway erosion at San Onofre’s lower parking lot, with images on social media showing sections of the lot collapsing onto the beach below. 

Dangerous flooding across the state is possible through Tuesday, forecasters said, with 6 inches likely and 12 inches of rain or more possible from the lower reaches of the Central Coast to the Los Angeles County coast.

If the upper ends of those estimates are reached, they could break rainfall records for the date and even monthly precipitation records, according to NBC News forecasters.

Flood watches, issued when conditions are favorable for flooding, will cover the coast in Sonoma, Marin, San Francisco, Monterey and San Luis Obispo counties, and all of Southern California’s coast. Some of the watches start late Saturday afternoon and last at least through the end of the weekend.

A Sunday update from the National Weather Service Weather Prediction Center predicted risks of rainfall exceeding flash flood guidance across swathes of the state with “high risk” — estimated at 70% probability — for San Diego and Orange Counties.

8,300 state workers are prepared to respond to storm-related emergencies and damage, according to Governor Gavin Newsom’s office on Saturday. Over twenty teams of swift-water and urban search-and-rescue personnel were staged up and down the state.

The storm comes as the San Diego County Medical Examiner’s Office announced it was investigating three deaths in late January as related to California’s last encounter with heavy storms. 

January 22 was the wettest January day on record in San Diego, which experienced rare and damaging flooding in urban neighborhoods far from the coastline, unusual for the dry southwestern corner of the state. 

Atmospheric rivers cause more than $1.1 billion in yearly flood damage on average, according to a 2022 study in the journal Scientific Reports. 

Climate change increases the potency of storms, as a warmer atmosphere can absorb more water vapor, giving storms capacity to deliver more extreme precipitation. Off the coasts, rising sea levels due to global warming cause waves to be bigger, quickening rates of erosion and contributing to California’s rising tides.