Best time to visit Thailand: choose your coast by the month

Thailand has three climates running on different schedules: the Andaman coast, the Gulf coast, and everything inland. November is usually dry in Phuket and the wettest month of the year on Koh Samui, so the best month depends on which region you are visiting.

How the seasons work

The Thai Meteorological Department counts three seasons. The hot season runs from mid-February to mid-May, and April is the hottest month. The southwest monsoon runs from mid-May to mid-October and is wettest in August and September for most of the country. The cool season runs from mid-October to mid-February, when Bangkok evenings drop into the low twenties.

The south works differently. The two coasts face different seas, and the northeast monsoon that ends the rain everywhere else brings it to the Gulf coast instead, so the Gulf islands get their heaviest rain in October and November.

Illustration of one beach split in two: sunbathers and swimmers on the left, umbrellas under a rainstorm on the right — The Gulf coast gets its wettest months while the rest of the country dries out.

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 half of the year, and June to September is the wettest part. It rains in bursts rather than all day. The bigger problem is the sea: swells close swimming beaches, dive trips get cancelled, and the smaller islands are harder to reach. Low-season prices in Phuket reflect this.

Illustration of a monsoon beach with heavy surf, longtail boats tied up on the sand and empty deck chairs — Swells close swimming beaches from May to October, and dive trips get cancelled.

The Gulf islands: Samui, Phangan, Tao

The Gulf side stays relatively dry from January to August, and February to April is the calmest stretch. June to August, when the Andaman is at its roughest, is the Gulf’s quieter second season, so a mid-year beach trip works better on this side.

October brings around 295 mm of rain to Samui and November roughly 445 mm, the wettest month of its year. Ferries get rough and dive visibility drops. December is still showery but improving. Samui and Phangan share the same cycle, so weather does not decide between them.

Bangkok and the central plains

Bangkok is hot all year. November to February is the dry, more comfortable stretch, and December nights are around 22 C. March to May is the hottest, 35 C and up with high humidity. June to October is the rainy season, which in Bangkok usually means a hard afternoon downpour and flooded sois rather than whole days of rain. Mornings are usually dry.

For a two-day stop on the way somewhere else, the season barely matters. For days of walking between temples in the old city, November to February is much easier.

Chiang Mai and the north

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.

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. 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 and mountain views suffer most.

If the north is the heart of your trip, go November to early February. The Chiang Mai guide covers the city itself.

Illustration of temple roofs before a city and mountains lost in brown smoke haze, the sun a pale disc — On 29 March 2026 Chiang Mai topped the global pollution ranking with an air quality index of 263.

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.

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.

Illustration of a Songkran street party, water guns and hoses arcing water around a pickup loaded with barrels — Offices close and transport books out during Songkran, 13 to 15 April.

Low-season prices

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 to compare your dates directly on Booking.com.

In low season, Bangkok and the north are fine, the Andaman coast depends on the sea, and the Gulf islands stay mostly dry until October.

FAQ

What is the worst month to visit Thailand?

No single month is bad everywhere. September is the wettest for Bangkok and the Andaman coast, November for the Gulf islands, and March for northern air quality. If you must pick a single all-round month, choose January or February.

Is rainy season a dealbreaker?

Inland, no. Bangkok and Chiang Mai rain tends to fall in hard afternoon bursts with dry mornings, and everything is cheaper and greener. On the coasts it matters more, because rough seas cancel boats and close beaches.

When is the sea calmest for island hopping?

On the Andaman side, December to March. On the Gulf side, February to April. Ferries run year round on both coasts, but in the wrong months they run late, rough, or not at all on the smaller routes.

How do I keep up with ferry and flight changes?

Check them from the pier on the day rather than from last night’s screenshot; schedules move with the season. The Thailand eSIM guide covers the networks and what a fortnight uses.

Seasons follow Thai Meteorological Department definitions; 2026 Chiang Mai air readings are IQAir’s. Checked September 2026.

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