LOS ANGELES (CNS ) - A low-pressure system out of the Gulf of Alaska will slide into the Southland on Wednesday night, raising fears of mudslides, minor debris flows and flooding over areas of L.A., Orange, Ventura and Riverside counties that wildfires have recently stripped of vegetation.

The storm began moving across California's Central Coast Wednesday afternoon and into Ventura County. The system will reach Los Angeles County by tonight and linger into Thursday, according to the National Weather Service. Cool temperatures will prevail through the weekend.

Ahead of the storm, residents were making preparations in Malibu, much of which was devastated by the Woolsey Fire this month. In Orange and Riverside counties, residents near the Holy Fire burn area were being urged to evacuate before the rain began falling. Mandatory evacuation orders were issued late Wednesday afternoon for some areas of Lake Elsinore in Riverside County.

"All Malibu residents are urged to prepare for potential flooding, mudslides, power outages and evacuations," the city said in a statement Tuesday. But those preparations must not involve removing debris, which contains hazardous materials. No debris removal from burned properties is allowed until inspections by state and county health officials have been completed.

The Los Angeles County fire and sheriff's departments both deployed additional staffing into the burn area in light of the threat of potentially damaging flooding. Officials with both agencies stressed the need for residents to adhere to evacuation orders, if they are implemented.

"Evacuation orders should not be taken lightly and are ordered because there is a threat to life and property," according to a joint statement from the agencies.

In Orange County, the sheriff's department issued a voluntary evacuation order for homes within Trabuco Canyon, Rose Canyon and the Mystic Oaks and El Cariso areas. Those orders could be upgraded to mandatory if debris flows are spotted, or if bridges or roads become impassible due to flooding, said Carrie Braun, a spokeswoman for the Orange County Sheriff's Department.

Orange County officials plan to set up an incident command post near City Hall in Rancho Santa Margarita Thursday morning, Braun said.

Most areas should see between a half-inch and two inches of rain, although three inches could fall at higher elevations and foothills.

A flash flood watch will be in effect for the Santa Ana mountains and foothills and inland Orange County throughout the day Thursday and into early Friday morning.

The rain is expected to start falling in Los Angeles County Wednesday evening, then increase overnight, strengthened by moisture from the Eastern Pacific, making the Thursday morning commute challenging, said NWS meteorologist Curt Kaplan. By Thursday afternoon, showers are expected.

Forecasters say the rain will fall on the sites of the Woolsey Fire in L.A. and Ventura County, the Hill Fire in Ventura County and the Thomas Fire in Ventura and Santa Barbara counties in December 2017.

According to an NWS statement Wednesday afternoon, the heaviest rain is expected in Orange County and inland areas late Thursday morning.

"Hourly rainfall rates in stronger showers and isolated thunderstorms could approach one-half to one inch in an hour," according to the NWS. "This could lead to mudslides and debris flows at recent burn scars. The time window of greatest concern is from late Thursday morning through early Thursday evening."