The Kei Islands have a tropical monsoon climate. The dry season runs from approximately October to March, with calm seas, good visibility for diving, and reliable weather for boat trips. This is the best time to visit.
The wet season (April to September) brings rougher seas and can make boat travel to Kei Besar and the outer beaches difficult or impossible. Rain doesn't fall all day every day, but the swells make open-water crossings uncomfortable and sometimes dangerous for small boats. Some guesthouses reduce their services or close entirely in the wettest months.
October and November are generally the best months: the dry season has re-established itself, seas are calm, and the islands are relatively uncrowded before the Indonesian school holiday period. Indonesian public holidays (particularly Lebaran and the August independence day period) bring a surge of domestic visitors to Pasir Panjang; avoid these periods for a quieter experience.