Courtesy of OnScene.TV
Courtesy of OnScene.TV

A thunderstorm generating lightning strikes developed near Santa Monica Thursday morning without producing immediate signs of damage, but forecasters warned of high surf, some coastal flooding and the possibility of mud flows over fire-denuded slopes as the Southland’s latest Pacific storm continued to drench the region.

The National Weather Service office in Oxnard said Doppler radar was tracking the thunderstorm, which was moving east at around 30 miles per hour. Such thunderstorms can produce dime-size hail, winds exceeding 40 mph, and roadway flooding. Its impact on the Southland this morning was being tallied.

“Scattered showers and isolated thunderstorms will persist across the burn areas of Ventura and Los Angeles counties through today,” an NWS statement said, warning of a possibility of a half-inch to three quarters of an inch per hour near the sites of thunderstorms — rainfall rates able to cause flash flooding and debris flows, especially over slopes previously stripped bare by wildfires.

A flash flood watch was in effect until noon today for the burn areas in the San Gabriel and Santa Clarita valleys, the San Gabriel Mountains and several areas of Ventura County.

The coastline, meanwhile, was being battered by what an NWS statement called “very large damaging surf.”

A high surf warning will be in force in Los Angeles County until 4 a.m. Friday, and a coastal flood advisory is due to expire at noon Thursday. NWS forecasters warned that the surf will build to between 10 and 14 feet, with sets of 16 feet expected this morning.

In Orange County, a high surf warning was in effect until 10 p.m. Friday, and a flash flood watch will be in effect until noon today.

The combination of high astronomical tides, onshore winds and very large surf will cause minor overflow of sea water into low-lying areas today, especially during the times of highest today,” an NWS statement said.

The NWS blamed the high surf on a series of long-period westerly swells.

“A high surf warning means that large and battering surf could damage coastal structures and will make swimming and rock jetties very dangerous,” a statement said. It added that swimmers who become trapped in rip currents should swim parallel to shore until able to free themselves.

Three El Nino-caused weather systems hit Southern California this week, including one that slammed into the region late Wednesday morning. Thursday’s temperatures were expected to be like Wednesday’s — in the 50s and low 60s.

—City News Service

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