The last and strongest of three storms to hit Southern California this week slid into the region today, generating periods of heavy rain, which could trigger street flooding, National Weather Service forecasters said.

The weather service at 5:40 a.m issued a flood advisory for most of L.A County and eastern Ventura County and said it would expire at 8:30 a.m. A flash flood watch will be in force until 1 p.m. along the coast.

Rainfall rates were highly variable but generally averaged .15 to .30 inches per hour, with up to .50 inch per hour in some areas.

Long Beach has so far received about .32 inches of rain on Thursday. The city received roughly an inch of rain Wednesday.

“We are on full alert,” Long Beach Mayor Robert Garcia tweeted about the storms.

Along the coast, an extended period of high surf is expected through Friday, the NWS said. A high surf advisory will be in effect in L.A. County until 2 p.m. today, followed by a less serious high surf warning from 2 p.m. today until 9 p.m. Friday.

Breaking waves of 5-8 feet will pound the shore through this morning, then increase to 6-10 feet, then 10-15 feet Friday morning, according to an NWS statement.

“Minor coastal flooding is possible Thursday, with moderate coastal flooding and significant beach erosion likely on Friday, it said.

Amid the high surf, “there is an increased risk for ocean drowning. Rip currents can pull swimmers and surfers out to sea. Large breaking waves can cause injury, wash people off beaches and rocks and capsize small boats near shore,” warned an NWS statement. “Moderate coastal flooding is possible over low-lying coastal areas including beaches, beach parking lots and harbor walkways, and with vulnerable coastal roadways during the highest surf and tides.”

Off the coast, a gale warning expired at 3 a.m. today, and a small craft advisory will follow suit at 9 a.m.

A mix of partly cloudy and sunny days are forecast over the next six days.