My understanding is that California has dry summers because (very
roughly) the pacific ocean is cold at our latitude, which in turn
cools the air above the ocean and makes it more dense, thus inhibing
convection, and more generally fostering high pressure. In winter, it
rains because the air above the ocean is generally cooler than the
ocean, and thus tends to be warmed by the ocean.

My question is, is the temperature of the pacific the main factor in
California's seasons? Or to put it another way, let's say the surface
temperature of the Pacific off the California coast were raised to,
say, 90 degrees farenheit (I'm not proposing we try this...) -- would
that lead to a rainy-summer-type climate?