Why is the Pacific ocean typically cold off of the West Coast of the United States?
The primary ocean current along the West Coast of the United States is often referred to as the "California Current" and follows a clockwise pattern, bringing cold water from the Gulf of Alaska southeasterly, where it eventually meets the beaches of Washington, Oregon and California.
The further south you go typically the warmer it gets so while surfers may be out in a thick wetsuit in June in San Francisco you may well see surfers and swimmers from Santa Barbara southward in shorts or a spring suit.