A large southerly swell was expected to produce large waves, rip currents and strong longshore currents in Los Angeles and Ventura counties through Thursday, according to the National Weather Service.
"These areas will potentially see the largest surf seen in recent years, with breakers of 10 to 15 feet possible," said a weather service advisory.
Swimmers and surfers were urged to be aware of dangerous conditions. Forecasters said minor coastal flooding and beach erosion is possible.
The city of Long Beach said it was expecting a storm surge above predicted astronomical tides, and crews were fortifying sand berms.
The city was also making sandbags available to residents of its peninsula area, said Jake Heflin with the Long Beach Fire Department.
"We went door-to-door throughout the community making sure everyone is aware," he said. "We're doing everything we can to make sure people are prepared."
The high surf advisory will be in place for several counties north and south of Los Angeles, including Orange County. But Los Angeles and Ventura counties will likely see the biggest storm surge, according to the NWS advisory.