It does rain in Southern California! It may not happen as often as we like, but when we get a good rain it's best to stay out of the water. Don't risk getting sick or a serious infection (see The Inertia article link below).
It's not worth it!
Health officials advise against ocean water contact for 72hrs following a significant rain event due to elevated bacteria levels, especially nears harbors, drain pipes, and rivermouths.
The Inertia: https://www.theinertia.com/surf/surfing-in-dirty-water-what-you-need-to-know-this-winter/
Check the water quality in San Diego: http://www.sdbeachinfo.com/
Check the water quality in Orange County: https://ocbeachinfo.com/