Afetna, Northern Mariana Islands offers 4 beaches perfect for sunbathing, surfing, swimming, and more. Afetna, Saipan, Northern Mariana Islands, is known for the historic World War II site, the Grotto, a popular diving spot. The best time to travel to Afetna, Northern Mariana Islands, is from December to June, with average air temperatures around 80°F (27°C) and water temperatures near 82°F (28°C). Sandee provides detailed maps, photos, and reviews from fellow beachgoers to help you Choose Your Beach™ and plan your perfect beach vacation!