Los Angeles Mayor Antonio Villaraigosa addressed hundreds of Californians to obey evacuation orders and flee their homes before a dangerous storm hits their area Wednesday morning.
Forecasters expect even stronger storms Wednesday and Thursday, following torrential rainfall Tuesday that unleashed flooding and spawned a rare tornado warning in southern California.
Officials said they had issued evacuation orders for more than 480 homes in areas prone to mudslides.
Forecasters also warned of damaging winds.
"A powerful Pacific storm, likely the strongest of the week, will bring strong and damaging winds to much of southwestern California on Wednesday," the National Weather Service said.
The storm could bring winds of about 80 mph in mountain areas, as well as a downpour of more than 1 inch an hour in parts of Los Angeles County, the weather service said.
Storms Monday and Tuesday already caused floods and left thousands of households without electricity.
Monday's storm was blamed for at least one death, that of a 21-year-old man from Kern County, who died after a 100-foot tree crashed into his home.
Weather-related problems also affected central California, where Fresno's Yosemite International Airport lost the ability to send passengers through security because of a power outage.
Landings and takeoffs were not affected, because a backup system kicked in for some areas, said airport spokeswoman Vikkie Calderon.
CNN International has contributed to the report.