Douglas, Isle of Man offers 10 beaches perfect for sunbathing, surfing, swimming, and more. Douglas, Isle Of Man, is known for the annual Isle of Man TT motorcycle races. The best time to travel to Douglas, Isle of Man, is from June to August, when the average air temperature is around 15-18°C (59-64°F) and the average sea temperature is about 13-15°C (55-59°F). Sandee provides detailed maps, photos, and reviews from fellow beachgoers to help you Choose Your Beach™ and plan your perfect beach vacation!