Living here I learned that May and June are not good times for out-of-towners to visit coastal California. During most of the months of May and June, the coast is enveloped in a dense marine layer. Unlike the winter marine layers, this one does not burn off by late morning.
My office in Vista, about 6 miles or so inland, is mostly spared of this phenomenon - more often than not it's been sunny and warm out there. Locally the dividing line of good to gloom is about El Camino Real, ~3 miles inland.
Here's a link with more info. on the interesting weather pattern.