Monsoon and burn season
Thailand is a two-calendar country plus a smoky north, not one winter. Phuket and Krabi are easier November to April. Samui and Phangan are easier January to September. Check Chiang Mai air before you book March.
The southwest monsoon hits the Andaman first. Phuket, Krabi, Lanta, Lipe, and Khao Lak are the November to April trip. The Lower Gulf (Samui, Phangan, Tao) is the January to September trip. October is the messy overlap. Do not stack both seas on a first week. Bangkok to either coast is about 70 to 85 minutes by air.
The north has a different problem. Crop and forest smoke sits in the Chiang Mai and Chiang Rai valleys at the end of the dry season. Station averages for 2023 to 2026 put Chiang Mai's nastiest month in April. May rain usually clears it. Bangkok heat is year-round and is not this page.
Coast calendar
| Place | Go | Think twice | Why |
|---|---|---|---|
| Phuket, Krabi, Lanta, Lipe, Khao Lak | November to April | May to October | Andaman swell. Passenger boats fail. Similan National Park is shut 16 May to 14 October. |
| Samui, Phangan, Tao | January to September | October to December | Lower Gulf wind. Tao cancels first. Full Moon still runs in the wet; the boat may not. |
| Koh Chang and Koh Kood | November to February | May to October | Eastern Gulf. Not the Samui calendar. Do not copy a Lower Gulf blog onto Trat. |
| Hua Hin | Most months; best November to April | September and October | Upper Gulf mainland. Usable in July when Phuket is a coin toss. |
| Khao Sok / Cheow Lan | After rain for a full lake, November to April for easier roads | A same-day Phuket dash in a downpour | Inland Andaman side. Trails slick. Lake tickets still cash. |
Burn season in the north
Chiang Mai's 2026 open-burning ban ran 1 January to 31 May. That is a provincial order, not a promise of clean air. The months that photograph grey are March and April. Mae Hong Son and Chiang Rai can read worse than the city. 2025 was a mild haze year. 2026 was not as kind. Do not plan a viewpoint week on a 2025 memory.
Check the Pollution Control Department live map at air4thai.pcd.go.th the week you fly, not a Facebook group. An FFP2 or N95 filters PM2.5. A cloth mask does not. If anyone in the group has asthma, pick the south in March or wait for May.
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Common questions
- Is there one best month?
- December to February if you want Bangkok plus the Andaman. July if you want Samui and can take Bangkok heat. March is a north gamble.
- Can you visit Phuket in August?
- Yes. Some days are beautiful. Boat days cancel. Prefer Samui that month unless a resort is the whole point.
- Where do you check the air?
- air4thai.pcd.go.th, station by station. IQAir is a mirror, not the official desk.