If you’re hoping to get lost in the rain on your romantic getaway, check out these details about year-round temperatures in Chiang Saen: The hottest months are usually April and March with an average temp of 80°F, while the coldest months are January and December with an average of 68°F. The rainiest months in Chiang Saen are August, July, September, and June, with each month seeing an average of 13 inches of rainfall.