The hot (or dry) season is from February to May. The season is as it says. Lots of hot sunny days with not much rain. But personally, the highs of 85F during the ‘cold’ season doesn’t feel that much different than the highs of 90F during the hot season. In the north east there will be little rain, and often times serious drought. In the southern provinces it’ll still rain often during this season. If you’re from Bangkok and you’re vacationing on a beach in Koh Samui during the hot season, you might swear it was rainy season.