Thailand Weather by Month and Region: Rain, Heat, Haze

Pick your coast before your month, because Phuket and Koh Samui are wet at opposite ends of the year. Phuket is driest in February and wettest in September, while Koh Samui is wettest in November. Bangkok peaks in September and Chiang Mai in August.

Pick your coast before you pick your month, because Phuket and Koh Samui are wet at opposite ends of the year.

Which season are you in?

Thailand’s year runs hot from mid-February to mid-May, rainy from mid-May to mid-October and cool from mid-October to mid-February. The southwest monsoon brings the rain from mid-May, and the northeast monsoon then takes over from about mid-October. That second one turns the south rainy, especially on its east side.

This is why the Andaman coast and the Gulf peak at different times. Phuket and Krabi sit on the west coast, while Surat Thani, home of Koh Samui, is on the east. Treat the dates as a guide, because the rainy season can start 1 to 2 weeks early or late.

Rain, month by month

On the Andaman side, Phuket is driest in February and wettest in September, with October close behind. Koh Samui runs the other way round: November is its wettest month and February its driest. From late October to December, the Gulf is the wetter coast.

On the mainland the picture is simpler. Bangkok peaks in September, stays wet through October and is driest in December. Chiang Mai peaks in August and is driest in February. Pattaya peaks in October, and Khon Kaen in September.

How hot does it get?

April is the hottest month on the mainland, with Bangkok reaching 35.7 °C and Chiang Mai 36.7 °C. If you would rather avoid that, December is the coolest month in both. Phuket is steadier, with the hottest month in March.

Northern haze and the burn ban

If you are heading to Chiang Mai, know that January to April is the hazy stretch, and March is the worst month, with haze on 26.8 days. That is a count of hazy days, not an air-quality reading, so check live air quality on Air4Thai (air4thai.pcd.go.th or the Air4thai app) before you book.

Open burning in Chiang Mai province was banned in all areas until 31 May 2026. Burning rubbish or other things in the open that causes a nuisance carries up to 3 months in jail, a fine of up to THB 25,000, or both.

When the island parks close

Check closure dates before you book a boat, because the island parks shut on set dates each year. These are the 2026 dates for the parks most visitors ask about.

The Similan Islands park opened for the season on 15 October 2026, and the other Andaman marine parks have opened too. Some sites can still change their opening with the weather.

Where to go next

For island advice month by month, read Best Thai Islands by Month, and see jellyfish and rip currents for the wet months. Park entry rates are in national park fees. For a base, start with Phuket, Koh Samui or Chiang Mai. To see the whole country at once, read the best time to visit Thailand, and when you are ready for a route, try the 2-week Thailand itinerary.

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Not confirmed: Each region is one weather station, so a resort away from that station gets different rain. The closure table lists the island parks covered here, not the full annex.

Prices, timetables and opening hours change; check with the operator before you travel. See how guides are checked.

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