Winter (November to April) is the dangerous season here. Hawaii Ocean Safety describes north shores in winter as having consistent, huge and dangerous swells, and says novice surfers and swimmers of any skill level should stay out of the water there during high surf. Summer (May to October) is typically flat to small, though spots exposed to the trade winds can see larger swells. Conditions still change day to day. Check the National Weather Service Honolulu surf forecast (weather.gov/hfo), and ask the lifeguard on duty or your school before going in.