Updated

Hundreds of people living below fire-stripped mountains were under orders to leave their homes Wednesday as another Pacific storm churned toward Southern California on the heels of powerful systems that have flooded coastal communities, spawned a tornado and killed one person.

Los Angeles County and city authorities issued mandatory evacuation orders in advance, saying residents of more than 600 homes would have to be out by 9 a.m., just ahead of the storm's expected midday arrival.

The homes are in communities in the foothills and canyons below the rugged San Gabriel Mountains, where more than 250 square miles of forest burned away last summer, and public safety officials warned that basins designed to capture debris-laden runoff were full after two days of storms.

The National Weather Service said the new storm would pack 60 mph gusts along the Southern California coast and valleys and up to 80 mph at higher elevations, while dropping rain at up to 1 1/2 inches per hour.

Up to 5 inches of rain was forecast through the day for some mountain areas, forecasters said.

Warnings for coastal flooding, gales, snow and high surf were posted up and down the state, but the concern was extreme in Southern California, where vast areas scorched by wildfires in the past two years have left landscapes denuded of vegetation that would normally capture or slow runoff.

The foothills northeast of Los Angeles already have received almost 5 inches of rain since Sunday, Department of Public Works Director Gail Farber said.

County Fire Chief P. Michael Freeman begged residents to heed their evacuation orders. He said public safety officials are racing against Mother Nature.

"And if she wins the race there's no way we can assure that firefighters, as well-equipped and as trained as they are, will be able to get into your neighborhood and make rescues," Freeman said.

Residents were told to be prepared to be away from their homes for as many as five days.

In the foothills of La Canada Flintridge, just northeast of Los Angeles, County Public Works crews used bulldozers and shovels to move mud out of cul-de-sacs. The storm left fist-sized rocks strewn across a winding, canyon road.

One resident, Gary Stibal, had lined his backyard with sandbags a couple of feet high to divert the floodwater. His hard work kept out the rocks and debris on Tuesday, but Stibal, whose home was threatened by one of last year's wildfires, said he was worried that water from the third storm would reach his home.

"The ground is really saturated right now from the two storms we had come through yesterday and today, so I'm really concerned," he said as he surveyed his work.

The storm did serious damage Tuesday, crushing a woman to death with a fallen tree, flooding coastal neighborhoods and leaving thousands without power as lightning and tornados surged ashore with fierce winds in Santa Barbara, Los Angeles County beach towns and areas of Orange and San Diego counties.

San Diego sheriff's Lt. Mike Munsey said a woman was killed when a eucalyptus tree with a 10-foot diameter trunk crushed her trailer and a neighbor's in a mobile home park near El Cajon. On Monday, a man was killed near Bakersfield when a tree fell on his home.

In San Pedro, a working class neighborhood near the Port of Los Angeles, several blocks were flooded with about six feet of water when storm drains clogged with debris. Police said 16 people were displaced from flooded homes.

Jerry Bazan spent the afternoon sweeping several inches of water out of his living room, where toys, sodden clothing and furniture were strewn about and a thick layer of mud coated the floor. The water rose quickly in his apartment and some of it was contaminated with sewage.

"It was a heavy downpour, and the drainage system was clogged," he said. "There was nowhere for the water to go, and it just rose up."