Weather can make or break a road trip, so here's some data about year-round temperatures in Fomboni to help you plan yours: The hottest months are usually March and December, with an average temperature of 28°C, while the coldest months are August and September, with an average of 25°C. The rainiest months in Fomboni are January, February, March and December, with each month seeing an average of 228 mm of rainfall.