If you’re looking forward to lots of outings with your partner, check out these details about year-round temperatures in Rach Gia: The hottest months are usually March and April with an average temp of 83°F, while the coldest months are January and December with an average of 80°F. The rainiest months in Rach Gia are September, October, July, and May, with each month seeing an average of 14 inches of rainfall.