Planning for the weather is a good way to make your trip to Koh Rong relaxing and enjoyable, especially when you’re splurging. The hottest months are usually May and April, with an average temperature of 29°C, while the coldest months are January and December, with an average of 27°C. The rainiest months in Koh Rong are September, July, August and June, with each month seeing an average of 631 mm of rainfall.