Southern California storm timeline: When round two of rain and 12-foot surf hits

LOS ANGELES - Southern California’s dry stretch ended early Friday as the first of two Pacific storm systems brought overnight rain, thunder, and power outages to the region. 

Forecasters with the National Weather Service (NWS) expect on-and-off showers to continue through Saturday morning alongside dangerous coastal surf and sharply cooler temperatures.

What we know:

Rain chances

Rain began sweeping across the Southland overnight, ending a period of unseasonably warm weather that had pushed highs into the upper 70s and near 90 degrees. 

As high pressure weakens, daytime highs on Friday and Saturday will settle into the 60s to low 70s with gusty winds, according to the NWS. 

Overall chances for widespread rain sit above 90%, with most areas of Los Angeles and Orange counties expected to receive between a quarter-inch and 1 inch of total rainfall from the two systems combined, though locally higher amounts are possible on mountain slopes and in thunderstorms, officials said. 

As of early Friday morning, rainfall rates generally remained below a quarter-inch per hour, though forecasters observed local rates reaching around 0.5 inches per hour. 

Thunder was reported in several areas, including Santa Monica, where a storm-related outage cut power to residents. For coastal areas of Santa Barbara, Ventura, and Los Angeles counties, the National Weather Service noted a low chance of isolated moderate, flood advisory-level rain impacts, including flooding in low-lying areas and roads, minor mountain mudslides, and increased traffic accidents.

Coastal flooding threat

Along the coast, a Beach Hazards Statement remains in effect for the Malibu coast and Los Angeles County beaches until 2 p.m. Friday, when a High Surf Advisory takes over through 3 p.m. Tuesday. 

A large west-to-northwest swell will generate breaking waves of 4 to 7 feet on Friday before peaking at 7 to 12 feet on Saturday and easing to 6 to 9 feet from Sunday through Tuesday, the NWS said. 

Combined with morning high tides reaching 7.0 to 7.4 feet, these swells will create dangerous rip currents, strong longshore currents, sneaker waves, and heavy shore break capable of causing significant beach erosion and shallow seawater flooding across low-lying walkways, parking lots, and coastal roads, officials warned.

What we don't know:

Officials have not yet determined the exact number of customers affected by the storm-related power outage in Santa Monica, nor have they announced an estimated restoration time. 

While forecasters note there is enough atmospheric instability to maintain a slight chance of thunderstorms through Friday morning—with the highest probability in Orange County and areas to the south—no lightning strikes had been confirmed early Friday, leaving exact localized downpour totals uncertain.

Timeline:

Shower activity from the first system spread across Los Angeles County before dawn on Friday and will continue through the morning before tapering off from northwest to southeast during the afternoon, though isolated showers may linger. 

A second, more widespread round of rain tied to an approaching cold front is scheduled to arrive late Friday afternoon or evening and persist through early Saturday morning before clearing from west to east. 

Dry conditions are expected to return after sunrise on Saturday and last through Sunday, bringing a brief break with daytime highs in the mid-60s to low 70s.

What's next:

After Sunday’s brief dry spell, a broader "storm train" will bring two weaker, colder systems into Southern California next week. 

"Pattern-wise, the 'storm train' is expected to continue with one storm impacting the area Sunday night through Tuesday then another system during the day on Wednesday/Wednesday night," the NWS said.

Forecasters expect these midweek disturbances to deliver additional beneficial rainfall and maintain below-normal temperatures through Wednesday night or Thursday.

What you can do:

Drivers should use caution on wet roads, follow all posted warnings, and never drive around barricades or through standing water on flooded coastal streets. 

Residents are advised to secure outdoor patio furniture or belongings exposed to gusty winds, surf, and rain, and anyone with weekend outdoor plans should adjust them for wet weather. 

Along the coast, beachgoers should stay out of the water or swim only near occupied lifeguard towers, stay completely off rock jetties, and remain alert for sneaker waves and heavy shore breaks.