Use the page for the place, not a national slogan
Thailand does not have one season. The Tourism Authority of Thailand attaches different hints to different provinces, and those hints are the only seasonal claims this guide repeats. Anything more precise belongs to a forecast the week you travel.
Phi PhiTAT says the more temperate months, with less frequent rain, run from November to April, and that rooms around Christmas and New Year should be booked ahead. That does not mean a November sea is automatically calm.
Koh Lanta’s small islandsTAT says islands including Koh Rok, Koh Haa, Hin Daeng–Hin Muang, Koh Hai, and Koh Ma are typically closed from May through October. If your dates sit in that window, plan the west-coast beaches and the cape, not those islands.
Koh TaoTAT names February to April as a good time. Diving still depends on the morning’s wind. A good month is not a permit to ignore a cancelled boat.
KrabiTAT tells visitors to reserve rooms early for late December and early January because the coast is full. That is crowding, not a weather guarantee. It also suggests one-way ferry tickets so a return can change when the sea does.
PhuketThe useful weather rule on the TAT page is not a month. It is the red flag. Do not swim against it, in any season.
Samui and the GulfA Surat Thani extract has described April to November as a comfortable window for that province’s islands. Direct checks of some TAT pages were blocked while this edition was built, so treat any Gulf month as something to re-read on the Samui, Phangan, and Tao pages before you pay.
The northChiang Mai’s page talks about cool air and seasonal flowers at Doi Ang Khang, not about a single safe month. Burning-season smoke is a reason to check a current air reading before a summit day. This guide does not invent the months.
What to do with a bad forecast
Coasts: delete the boat, keep the beach you can reach on foot, and use the spare day the southern itinerary already contains. Mountains: delete the summit, keep the town. Parks: assume a closure is possible after heavy rain and have the town or the ruin as the other plan. Do not buy a tighter connection to outrun a storm.
Before you leave
- Re-open the TAT page for your destination. Wording changes.
- Read a marine forecast for any boat, from the operator or a meteorological service, the day before.
- For parks, look at QueQ or the park office for closures. A sunny city forecast is not a trail forecast.
Information Phi Phi, Koh Lanta, and Koh Tao carry the seasonal lines cited above.