If you’re looking forward to lots of outings with your partner, take a look at these details about year-round temperatures in Ko Lanta: The hottest months are usually March and February, with an average temperature of 29°C, while the coldest months are January and February, with an average of 28°C. The rainiest months in Ko Lanta are September, October, August and July, with each month seeing an average of 367 mm of rainfall.