Thailand weather by month: compare regions.
Choose your month and the places you will actually visit. Compare Bangkok, the north, the Andaman coast and the lower Gulf separately; a national average is not a forecast for every stop.
Seasons and conditions
A useful month-by-month weather guide should explain Thailand's seasonal progression without pretending that each month has one national forecast. The structure should begin with TMD's monsoon framework and then show how the north, central plain, Andaman coast, and Gulf side diverge.
January sits in the cooler, drier part of the year for much of upper Thailand. February is a transition month: still relatively cool early in the month but moving toward hotter conditions, with northern haze risk beginning to matter in some years. March is distinctly hot and increasingly dry in upper Thailand, while smoke can become severe in the north. April is normally the hottest core of the year and includes Songkran.
Around mid-May, the southwest monsoon usually establishes the rainy season over much of the country. June and July are green-season months with recurring showers and thunderstorms. August and September are often wet across upper Thailand. September is especially important for sustained rainfall in many areas. October is a transition month as the main upper-country rainy season recedes, but southern patterns begin to separate more sharply.
Regional differences
November and December bring cooler conditions to much of northern and central Thailand and generally improve the Andaman coast. The lower Gulf can still receive major northeast-monsoon rain later in the year, which is why “December is beach season everywhere” is not reliable.
The year moves from cooler/drier upper-country conditions into hot season, then the southwest-monsoon rainy season, then back toward cooler conditions. Southern coasts diverge. The north has an more late-dry-season PM2. 5 problem that a pure rain-and-temperature calendar misses.