Planning for the weather is a good way to make your trip to Atiu relaxing and enjoyable, especially when you're splurging. The hottest months are usually March and February with an average temp of 80°F, while the coldest months are August and September with an average of 75°F. The rainiest months in Atiu are January, March, December, and February, with each month seeing an average of 10 inches of rainfall.