If you’re hoping to get lost in the rain on your romantic getaway, check out these details about year-round temperatures in Koh Lan: The hottest months are usually April and May with an average temp of 85°F, while the coldest months are December and January with an average of 81°F. The rainiest months in Koh Lan are October, September, July, and June, with each month seeing an average of 8 inches of rainfall.