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2 rain fronts to bring flash-flood threats, high surf to Southern California

by in News

Leftovers from tropical cyclone Rosa and a separate Pacific storm will both arrive over parched Southern California over the next few days, bringing flash flood watches for Inland deserts, debris flow concerns for burn areas, and high surf warnings for the coast.

Rosa, heading from northern Baja toward southwest Arizona, will bring the first moisture of the two systems, with rainfall possible Sunday night into Monday for some areas. The Pacific system, a cold front riding an atmospheric river off the California coast, is expected around Wednesday and will be the first winter storm of the season, the National Weather Service said.

The NWS said the Rosa rain could bring debris flow threats for the area of the Cranston fire near Idyllwild in the San Jacinto Mountains, while the Pacific storm could bring the same worries for Holy fire and Valley fire burn areas. The rain from Rosa is expected chiefly in mainly for the mountains and deserts, with less chance to reach the west, while the Pacific storm will bring rain mostly along the mountains and west of them. Both systems have a slight chance of thunderstorms.

In August, Caltrans worked on a guardrail damaged from the Cranston fire. The agency also prepared for possible floods from late-summer thunderstorms in the San Jacinto Mountains, Calif. (Photo by Cindy Yamanaka, The Press-Enterprise/SCNG)

Flash flood watches were issued for Monday morning through late Tuesday for Riverside County desert areas, and Monday afternoon through late Tuesday night for counterpart areas in San Bernardino County. The NWS said periods of local heavy rain are possible, which could lead to the flash floods.

The flash flood watches will officially end early Wednesday.

Affected areas for the two counties include the Chiriaco Summit, Chuckwalla Mountains, Chuckwalla Valley, Palo Verde Valley, Salton Sea, Joshua Tree National Park, Cadiz Basin, Death Valley National Park, the eastern Mojave Desert, including the Mojave National Preserve, the Morongo Basin,  and the San Bernardino County-Upper Colorado River Valley.

People in those areas should monitor weather forecasts and be ready to act immediately if there is heavy rain and flooding, or if a flash flood warning is issued, the NWS said.

The high surf warnings started Saturday night and will last through Tuesday morning for Orange County; for Los Angeles County beaches the warning starts Sunday night and also lasts into Tuesday morning

For Orange County beaches, waves of 5 to 8 feet are forecast with occasional sets of 9 to 10 feet, along with strong rip currents. Los Angeles County beaches will see surf from 6 to 10 feet with local sets to 12 feet, and strong rip currents.

The surf will be highest at south-facing beaches, the NWS said. The surf conditions are dangerous for inexperienced swimmers, and rip currents can pull swimmers and surfers away from the shore. People on shoreline rocks and jetties are in danger of being swept away.