Pohnpei is one of the wettest places on earth, recording up to 7,500 mm of rain a year in the interior — more rain than almost anywhere outside the Amazon and Congo basins. There is no real dry season. Rain can fall on any day of the year, and the island is often partially clouded even in the nominally drier months between January and March.
The best conditions for diving and boat trips are roughly December to April, when the wind tends to be more consistent and seas slightly calmer. Water temperatures stay around 28–29°C year-round. Typhoons occasionally affect the region, primarily between July and November, though direct hits are rare. Don't let the weather statistics put you off — tropical downpours tend to be brief and fierce, and Nan Madol visited in mist and drizzle has its own atmosphere.