Ask when to visit Thailand and you will get a confident answer that is right for one third of the country. Thailand has three climates running on different schedules: the Andaman coast, the Gulf coast, and everything inland. November is glorious in Phuket and the wettest month of the year on Koh Samui. The trick is not finding the best month. It is matching the month you have to the right region.
How the seasons work
The Thai Meteorological Department counts three seasons. A hot season from mid-February to mid-May, with April as the furnace. A southwest monsoon from mid-May to mid-October, wettest in August and September for most of the country. And a “winter” from mid-October to mid-February, which means pleasant twenty-something evenings, not coats.
The complication is the south. The two coasts face different seas, and the northeast monsoon that ends the rain everywhere else pushes it onto the Gulf coast instead. That is why the islands never agree with the mainland about anything.
The Andaman coast: Phuket, Krabi, Koh Lanta
Dry season runs roughly mid-November to April: 26 to 32 C, calm seas, long boat trips that leave on schedule. This is high season and priced like it.
May to October is the wet side of the year, with June to September the heart of it. It rains in bursts rather than all day, but the sea is the real cost: swells close swimming beaches, dive trips get cancelled, and the smaller islands feel cut off. If you get a cheap Phuket deal for July, that is what you are being paid to accept.
The Gulf islands: Samui, Phangan, Tao
Flip the calendar. The Gulf side stays relatively dry from January to August, with February to April the calmest stretch. June to August, when the Andaman is at its roughest, is the Gulf’s quiet second season and the best reason to know this split exists: mid-year beach weather does exist in Thailand, just not on the coast most people fly to.
The bill comes in autumn. October brings around 295 mm of rain to Samui and November roughly 445 mm, the wettest month of its year. Ferries get bumpy, dive visibility drops, and beach days become reading days. December is still showery but settling. Samui and Phangan share this cycle exactly, so the choice between them is never about weather.
Bangkok and the central plains
Bangkok is hot all year; the question is which kind of hot. November to February is the dry, bearable version, with December nights around 22 C. March to May is brutal, 35 C and up with the humidity of a rice cooker. June to October is the rainy season, which in Bangkok means a hard afternoon downpour and flooded sois, not a ruined trip. Mornings usually behave.
If Bangkok is a two-day stop on the way somewhere else, the season barely matters. If you plan to walk the old city between temples, it does.
Chiang Mai and the north, including the part nobody advertises
November to February is the north at its best: days of 28 to 30 C, nights down to 13 to 16 C, clear mountains, low humidity. It is the best winter weather in the country.
Then comes the smoke. From late February into April, rice-stubble and forest burning fills the mountain basins, and Chiang Mai regularly posts some of the worst air-quality numbers in the world. This is not a vague haze warning: on 29 March 2026 the city topped the global pollution ranking with an air quality index of 263, and late-March daily readings ran between 150 and 220, levels where healthy adults are advised to limit time outdoors. March is the peak. Trekking, viewpoints and doorless cafes all lose their point.
If the north is the heart of your trip, go November to early February. The Chiang Mai guide assumes you did.
Month by month
| Month | Andaman coast | Gulf islands | Bangkok | The north |
|---|---|---|---|---|
| Jan | Excellent | Good | Excellent | Excellent |
| Feb | Excellent | Excellent | Very good | Good, smoke starting |
| Mar | Very good | Excellent | Hot | Smoke, avoid |
| Apr | Good, hot | Excellent | Hottest | Smoke, avoid |
| May | Rain starting | Very good | Rainy | Rain clears the air |
| Jun | Wet, rough seas | Good | Rainy | Green, wet |
| Jul | Wet | Good | Rainy | Wet |
| Aug | Wettest | Good | Rainy | Wet |
| Sep | Wet | Mixed | Wettest | Wet |
| Oct | Improving | Rain arriving | Wet, improving | Improving |
| Nov | Excellent | Wettest | Very good | Excellent |
| Dec | Excellent | Showery | Excellent | Excellent |
Two dates to plan around
Songkran, the Thai new year, runs 13 to 15 April every year, and in 2027 that again means three days of nationwide water fighting, closed offices, and booked-out transport. It is either the best reason to be in Thailand or a reason to leave, and nothing in between.
Loy Krathong follows the twelfth full moon: 24 November in 2026, with Chiang Mai’s lantern festival, Yi Peng, held on the same nights. The dates shift each year with the lunar calendar, so check them for your year before locking flights.
What low season pays you
Rainy-season room rates drop by roughly a third to a half against high season, and beach hotels swing hardest; a mid-range Phuket resort that asks around 4,500 baht a night in January can sit near 2,200 in May. Peak weeks around Christmas and New Year go the other way, with island prices up as much as three quarters. The same room varies enough by month that it pays to compare your dates directly on Booking.com before assuming high season is the only version of the trip you can afford.
Low season, summed up: Bangkok and the north are fine, the Andaman is a gamble, and the Gulf holds out until October. Cheap has a reason, but the reason is not always yours.
FAQ
What is the worst month to visit Thailand?
Is rainy season a dealbreaker?
When is the sea calmest for island hopping?
How do I keep up with ferry and flight changes?
Seasons follow Thai Meteorological Department definitions; 2026 Chiang Mai air readings are IQAir’s. Checked September 2026.
The Booking.com link above is an affiliate link. Booking through it costs you nothing extra and helps keep Atli running.
