Oleai, Northern Mariana Islands offers 2 beaches perfect for sunbathing, surfing, swimming, and more. Oleai, Saipan, Northern Mariana Islands, is known for the American Memorial Park and the Grotto. The best time to travel to Oleai, Northern Mariana Islands, is from December to June, with average air temperatures around 81°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!