With hundreds of homes in the San Gabriel foothills under threat of mudslides and debris flows Friday, coastal communities are also facing their own series of threats from the storm: Rock slides, high surf and potential flooding.
As a second, more powerful storm sweeps across the region, the National Weather Service has issued a flood advisory for much of the coast from Long Beach north to Santa Barbara. A flash flood watch was also issued for nearly the entire Orange County coast all the way down to the U.S.-Mexico border.
High wind and surf advisories are also in effect for several areas along the Los Angeles County coastline.
Law enforcement agencies in those coastal communities have been working to spread the word about potential dangers and are closing some roads near potential problem spots.
An alert issued by the Malibu emergency services office early Friday said authorities anticipate the full closure of Pacific Coast Highway between Yerba Buena and Decker Canyon Road all day "for fear of rock slides."
In Long Beach, police said significant rainfall was forecast to coincide with high tides, bringing with it potential flooding. City officials planned to monitor water levels in Naples and other areas throughout the city "to mitigate any flooding if possible," according to a citywide alert.
Newport Beach was also prepared for the high tide flooding, positioning portable water pumps at low-lying areas if needed.
In Orange County, the Seal Beach Police Department said weather officials had declared a coastal flooding warning and offered sandbags for pickup.
On Saturday, surf in the area is expected to build to 12 to 16 feet with a 6.1-foot high tide at 8:52 a.m.
And in El Segundo, officials are letting the rain do the street cleaning for them, keeping employees off the road.
Officials with the National Weather Service expect about two to four inches of rain Friday through Saturday night in the coasts and valleys, with four to eight inches expected in the foothills and mountains.
The strongest rain is expected Friday morning through the afternoon.
"We're starting to get some really strong amounts here and the winds are starting to kick up," meteorologist Kathy Hoxsie said early Friday.