At least seven people were injured by lightning strikes, including a 57-year-old man playing golf on Catalina Island, about 20 miles offshore. The lightning also started two brush fires.
Ninety minutes later, lightning hit packed beaches in Los Angeles. Witnesses described at least four lightning strikes in the Venice Beach area.
A man who gave his name only as Paul told the Los Angeles Times he was briefly unconscious.
"I was in the water, I was boogie-boarding, and then next thing I know, I was trying to get my head above the water for air," he said. "It was a very bizarre incident. I mean, I wouldn't have been in the water if I thought lightning was going to strike, so yeah, it was pretty scary."
A 20-year-old man who was in the water when he was hit died.
Bill Patzert, a climatologist with the National Aeronautics and Space Administration, said the storm, unusual for the area, was caused by a high-pressure system that pulled in moisture-laden air from the Gulf of Mexico.