As a rule of thumb, November to February tend to be the most temperate months to visit Thailand. In the north and centre of the island there's no rain but the sticky heat hasn't set in yet so trawling Bangkok and hiking into the hill regions is lovely. The west coast (and Koh Kood on the east) is also a good shout at this time of year as the diving is fantastic and the humidity is gentle. The rains arrive between May and June, which makes the more remote areas less accessible and the beaches lose their shine. However, this is the ultimate time to see the wildlife of Khao Sok National Park. The islands and beaches along the Gulf of Thailand operate on their own timeline with sunny skies and dynamic seas from December to February (calling all water sport lovers!) and after a scorching April and May, the monsoon arrives by September so coastal trips are best avoided. If you fancy experiencing the true party scene of Thailand, it's worth planning to go near a full moon.