The later, the better, based on average rainfall patterns.
http://countrystudies.us/united-states/weather/California/half-moon-bay.htm
http://countrystudies.us/united-states/weather/California/pacifica.htm
To really get a handle on what’s happening -this- year though, you’d probably need to start keeping track of ENSO and MJO updates, which tend to be a bit thick and technical, but if you’re so inclined… http://www.cpc.noaa.gov/products/precip/CWlink/MJO/enso.shtml is one starting point, and google will turn up many more.
Also, if you’re planning for the beach, keep the winds in mind, they tend to be anywhere from brisk to downright unpleasantly strong during the spring, and are predominantly northwest (e.g. in your face at many local beaches).
