When to go where: Thailand's weather, month by month.
The system, in one minute
Thailand's weather runs on two monsoons. The southwest monsoon (roughly May–October) blows rain onto the Andaman coast — Phuket, Krabi, Khao Lak, Koh Lanta, Koh Lipe — and waters the North and the central plains. The northeast monsoon (roughly October–December) wraps around and dumps its rain on the Gulf coast — Koh Samui, Koh Phangan, Koh Tao — which sat protected all summer.
The result is a see-saw: the two island coasts are rarely wet at the same time. Add the North's own rhythm (gloriously cool November–February, smoky in the late spring burning season, lush and green in the summer rains) and you can build a great trip in any month — if you point it at the right regions.
Month by month: where's dry?
| Month | Andaman coast (Phuket · Krabi · Lanta · Lipe) | Gulf islands (Samui · Phangan · Tao) | North (Chiang Mai · Pai · Chiang Rai) |
|---|---|---|---|
| January | Prime — dry, calm, peak season | Dry and lovely | Cool & clear — best of the year |
| February | Prime | Dry, seas calm | Great weather; smoke season begins late month |
| March | Hot & dry | Hot & dry | Burning season — air quality can be poor |
| April | Very hot; Songkran mid-month | Hot & dry | Peak heat + smoke until rains arrive |
| May | First storms; big discounts | Still largely dry | First rains clear the air — green returns |
| June | Monsoon builds; rough seas | One of Samui's driest stretches | Green season — showers, lush, quiet |
| July | Wet; some boats curtailed | Reliably good — the smart pick | Green season |
| August | Wet, humid, big waves | Mostly dry, brief showers | Green season |
| September | Wettest month on this coast | Showers increase late month | Rainiest month up North — still workable |
| October | Tapering; shoulder deals | Gulf monsoon arrives | Rains end — everything is emerald |
| November | Dry season returns; Lipe boats resume | Wettest month on the Gulf | Superb — cool, clear, Loy Krathong lanterns |
| December | Prime — book beds early | Drying out; festive crowds | Peak season perfection |
The three seasonal wrinkles worth planning around
Burning season in the North (roughly late February–April)
Agricultural burning across the region fills the northern valleys with smoke haze. Some years are mild, some are genuinely unhealthy — Chiang Mai has topped global air-pollution rankings on bad days. If your trip falls in this window and mountains were the draw, consider swapping north time for islands, or at minimum check live AQI before committing. This is the single most common seasonal mistake we see in Thailand itineraries, and almost no generic planner flags it.
Songkran (April 13–15)
Thai New Year is a nationwide water fight — three days of joyous, soaking chaos. It's either the best possible time to be in Chiang Mai or Bangkok, or your travel nightmare, depending entirely on your temperament. Either way: waterproof phone pouch, book rooms well ahead, and don't plan intercity travel on the 13th.
Full Moon and festival surges
Koh Phangan's Full Moon Party inflates ferry loads and room rates island-wide for several days each lunar cycle — check the date against your island-hopping window even if you're not going. Loy Krathong / Yi Peng (the November full moon) does the same to Chiang Mai, and it's worth it: the lantern release is one of the great sights in Asia.
Stop cross-referencing weather tables
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