- The short answer
- Three seasons, region by region
- Month by month
- Best time for each activity
- Festivals worth planning around
- Crowds and prices
The short answer
November to February is the best time for most of the country: dry and relatively cool in Bangkok and the north, calm and clear on the Andaman coast. It is also peak season, with the highest prices from mid-December to early February.
But the two sides of the southern peninsula have different rainy seasons. The Andaman coast — Phuket, Krabi, Phi Phi, Lanta, Khao Sok — is wet from about May to October. The Gulf islands — Samui, Phangan, Tao — stay mostly dry until September and take their heavy rain from October to December. So in July and August, head for the Gulf; from December to April, either works, and the Andaman is at its best.
Three seasons, region by region
Cool and dry (November–February)
Clear skies, lower humidity and cold nights in the northern mountains. Ideal for trekking, cycling, climbing and wildlife. Seas are calm in the Andaman; the Gulf islands are still drying out in early December and breezy in January.
Hot (March–May)
Inland temperatures reach 35–40°C. In the north, smoke from agricultural burning usually spoils the air and the views from late February to mid-April — the one time we suggest avoiding Chiang Mai, Chiang Rai and Pai. On both coasts, however, the sea is flat and clear: this is prime time for diving, snorkelling and island-hopping. Songkran, the water festival, falls in mid-April.
Rainy or “green” (June–October)
The south-west monsoon brings rain to most of the country, typically in heavy bursts with dry spells between, building to a peak in September and October. Forests are lush, waterfalls and rivers are at full strength and prices drop. The Andaman Sea is rough, and the Similan and Surin islands are closed from mid-May to mid-October. The Gulf islands enjoy their second high season.
Month by month
A simplified guide. “Best” means reliably good conditions; “mixed” means workable with flexibility.
| Month | North | Bangkok & centre | Andaman coast | Gulf islands |
|---|---|---|---|---|
| January | Best: cool, clear | Best | Best | Mixed: improving |
| February | Good; haze begins late | Best | Best | Best |
| March | Hot, smoky | Hot | Best: calm seas | Best |
| April | Hot, smoky until mid-month | Very hot; Songkran | Good: hot, calm | Best |
| May | First rains clear the air | Hot, showers | Mixed: monsoon begins | Good |
| June | Green, showers | Showers | Wet; surf season | Good |
| July | Green; rivers high | Showers | Wet | Good: high season |
| August | Wet; lush | Wet | Wet | Good: high season |
| September | Wettest | Wettest | Wettest | Good to mixed |
| October | Rains ease | Wet, easing | Wet, easing late | Wet |
| November | Best: festivals | Best | Good: season opens | Wettest |
| December | Best: cold nights | Best | Best | Wet early, improving |
Best time for each activity
- Trekking in the north: November to February; June to October for green landscapes if you accept mud and leeches.
- White-water rafting: June to October, when rivers are high.
- Rock climbing at Railay: November to April; shaded and overhanging walls stay dry enough all year.
- Diving the Andaman (Similans, Phi Phi, Koh Haa): November to April, with February to April the clearest.
- Diving and courses on Koh Tao: February to September; avoid November.
- Sea kayaking: all year in Phang Nga Bay and the mangroves; Ang Thong from February to September.
- Surfing in Phuket: May to October.
- Wildlife in Khao Yai: November to February; waterfalls from June to October.
- Waterfalls (Erawan, Doi Inthanon, Khao Sok): July to November.
The adventures by activity page links each of these to the right destinations.
Festivals worth planning around
- Chinese New Year (January or February): lion dances and crowds, especially in Bangkok’s Chinatown and Phuket.
- Songkran (13–15 April): Thai New Year and a nationwide water fight, most intense in Chiang Mai and Bangkok.
- Vegetarian Festival (September or October): nine days of processions and meat-free food, most dramatic in Phuket.
- Loy Krathong and Yi Peng (full moon, usually November): candle-lit floats on water everywhere, and sky lanterns in Chiang Mai.
- Full Moon Party (monthly): Haad Rin, Koh Phangan — worth knowing about even if only to avoid the ferries.
Accommodation prices rise and transport sells out around all of these, and over Christmas and New Year.
Crowds and prices
Peak: mid-December to February everywhere; July and August on the Gulf islands. Shoulder: November, March and April. Low: May to October on the Andaman coast and in the north, when hotel rates can halve and popular trails and beaches are quiet. Travelling in the green season is a reasonable trade if your plans are flexible and your activities do not depend on the open sea.
