My wife and I, and some friends, went to Napa and Carmel in June. Napa will be pretty warm, but Carmel should be perfect. Carmel and the Monterrey peninsula is a beautiful locale, and pretty easy to get to. You can fly into San Jose or San Francisco...less than a 2 hour drive. Rent a car and enjoy the coast. We spent 4 nights in Carmel. I’d go back tomorrow if I could.