The best time to visit Andaman is from the end of November to the end of April. December and January is the busiest season. If you don’t like crowded beaches, then visit in the month of March, before spring break when all the crowds come back.
There are two rainy seasons, one from June to mid-September and the other from November to mid-December. The rainy season, June to mid-September, can be hot & humid.
