If you’re hoping to get lost in the rain on your romantic getaway, take a look at these details about year-round temperatures in Chiang Saen: The hottest months are usually April and March, with an average temperature of 27°C, while the coldest months are January and December, with an average of 20°C. The rainiest months in Chiang Saen are August, July, September and June, with each month seeing an average of 318 mm of rainfall.