Mild all year, with one thing to know.
Oceanside has the classic coastal Southern California climate: mild winters, warm (not hot) summers, and very little rain outside the winter months. Most homes near the coast get by without air conditioning, though inland neighborhoods run several degrees warmer in late summer.
The one surprise for newcomers is "May Gray" and "June Gloom" — a marine layer that keeps late spring mornings overcast near the water. It usually burns off by afternoon, and September and October are often the best beach months of the year.
Day to day, life here revolves around the water — surfing at the pier, walking the Strand, a sunset at the harbor — with the Sunday farmers market downtown and easy day trips to Carlsbad, Temecula wine country, and San Diego.