Weather will likely play an important role when you plan your trip to Ko Yai, but bear in mind that cheaper options are usually available when the weather isn't as good. The hottest months are usually June and May, with an average temperature of 28°C, while the coldest months are January and February, with an average of 26°C. The rainiest months in Ko Yai are November, December, October and January, with each month seeing an average of 333 mm of rainfall.