Spring: air 14°C, water 12°C. Summer: air 20°C, water 16°C. Fall: air 12°C, water 12°C. Winter: air 4°C, water 8°C. Season is year round in principal, but May to October is the best. Wetsuit is necessary, especially in spring and autumn. Winter can be really cold. In summer a shorty is sufficient.
Due to environmental regulation it is illegal to kite here from September the 1st until June 1st. No kiting with offshore winds (North/Northeast). Don't cross the channel. Don't launch your kite on the grass in front off the beach club, but walk a bit further on the beach and choose the sandy part of the beach.