Weather can make or break a roadtrip, so here's some data about year-round temperatures in Fanning Island to help you plan yours: The hottest months are usually June and July with an average temp of 82°F, while the coldest months are January and February with an average of 80°F. The rainiest months in Fanning Island are May, April, March, and June, with each month seeing an average of 12 inches of rainfall.