Short answer
The best time to visit Thailand is November to February for Bangkok, Chiang Mai and most of the country, when the 1991 to 2020 normals give only 1 to 4 rainy days a month in Bangkok and 0.7 to 3 in Chiang Mai. The Andaman coast (Phuket, Krabi) is driest from December to March, while the Gulf islands such as Koh Samui are best from February to April and wet from October to December. March to May is hot, and the north has a burning season from February to May.
The short answer: November to February, with two exceptions
For most of Thailand the cool, dry months are November to February. In Bangkok the 1991 to 2020 normals give 1.0 to 3.8 rainy days a month in those four months and daytime highs of 32 to 34 degrees Celsius. In Chiang Mai they give 0.7 to 3.0 rainy days a month. The Thai Meteorological Department (TMD) calls mid-October to mid-February the winter or north-east monsoon season, the mild part of the year, with real cold only in upper Thailand in December and January.
The two exceptions are the sea coasts. The Gulf of Thailand side of the south is wettest in exactly these months, and the Andaman coast only dries out properly from December. TMD's seasonal outlook of 15 October 2026 adds that this year's cool season should be about two degrees warmer than normal because of El Niño, and run to around mid-February 2027. On 28 October TMD said the season could not yet be declared.
Andaman coast: Phuket, Krabi and Phang Nga from December to March
The Andaman side has a long wet season, so the window is shorter. The Phuket Airport normals give 66 mm of rain in January and 32 mm in February, on 5.1 and 3.1 rainy days, against 399 mm on 19 days in September. December (86 mm) and March (117 mm) are good too. April is hotter, with a mean high of 33.5 degrees, and the rains build from May. TMD says the west coast's rain peaks in September.
The marine parks follow the same calendar. Our Similan Islands day runs from 15 October to 14 May, and the Department of National Parks declared the Andaman park season open on 15 October 2026. Maya Bay is closed every year from 1 August to 30 September, so a Phi Phi day in those months sees it from the boat only. November is a transition month at Phuket Airport, with 219 mm on 14 days, still far below the September and October figures.
Gulf islands: Koh Samui, Koh Phangan and Koh Tao from February to April
The Gulf calendar runs the other way. Koh Samui has its fewest rainy days in February (4.3), March (4.7) and April (6.1), with 64 mm in February and 83 mm in April. From May to September the island sees 10 to 11 rainy days a month and 102 to 134 mm. Then comes the wet season: 295 mm in October, 445 mm in November and 263 mm in December. TMD's older averages show the south-east coast gets more rain in winter than in the rainy season.
That matters for a Christmas trip. TMD's outlook of 15 October 2026 warned of heavy rain along the Gulf coast from Chumphon southwards in November and December, with waves of two to four metres possible, The Thaiger reported. Ang Thong National Marine Park is closed to visitors from 1 November to 15 December 2026. If your dates are December and you want the sea, the Andaman coast is the safer choice that month.
Bangkok, Ayutthaya and Pattaya: November to February
Bangkok's driest months are December (12 mm on 1 day) and January (24 mm), and November has 45 mm. The wet peak is September, with 336 mm on 18 days, and October brings 289 mm. March to May is hot: the normals give a mean high of 34.7 degrees in March, 35.7 in April and 35.1 in May. Pattaya, on the east side of the Gulf, follows the same pattern, with 12 mm in December and 214 and 225 mm in September and October.
Heat shapes sightseeing more than rain does. TMD calls April the hottest month, and says maximum temperatures in upper Thailand usually reach near 40 degrees from March to May. Our Grand Palace, Wat Pho and Wat Arun tour starts at about 8:30 am, and most of the visit is outdoors, so bring water, a hat and sunscreen in any month. The palace can also close for royal ceremonies, so check its official calendar.
Chiang Mai and the north: November to January, and watch the smoke
Chiang Mai is at its best from November to January: 3.0, 1.2 and 1.0 rainy days, with highs of 30.8, 29.2 and 30.0 degrees and January nights of 15.7. The hot season follows, with a mean April high of 36.7 degrees. The rains arrive in May and peak in August at 223 mm on 17 days. If you want mountain cool, TMD's outlook puts the coldest period from late December to early February, with 10 to 12 degrees possible in the upper North.
The northern burning season runs from February to May. The National Environment Board has declared Chiang Mai, Chiang Rai, Lamphun and Mae Hong Son pollution control zones for those months, according to Thairath, and Chiang Mai banned open burning from 1 January to 31 May 2026. On 4 March 2026 the Pollution Control Department reported that PM2.5 exceeded the standard in 16 northern provinces. For a trip in February or March, check the daily air reading before you plan outdoor days.
March to May, and the rainy months: when to go anyway
Off-peak months can work if you plan for them. March to May suits the Gulf islands, where Samui has 83 to 132 mm a month, and it suits travellers who accept 35-degree afternoons. The rainy months, May to October on the Andaman side, give showers rather than washed-out days: a rainy day in the statistics means at least 1 millimetre. TMD notes a dry spell of one to two weeks in upper Thailand in June and early July. Our rainy-season guide explains it coast by coast.
What changes in the wet months is the sea. The UK Foreign Office warns of strong riptides during the monsoon and says jellyfish can reach the shore from May to October. If your trip is built around the Similan Islands, Maya Bay or the Ang Thong viewpoint, match the dates to the park calendar first, then to the weather. Our guides to the Similan season and Maya Bay list the dates.
Where a Phi Phi day fits in the calendar
Our Phi Phi and Maya Bay speedboat tour is from $75 per person and runs about 8.5 hours, with hotel pickup between about 7:00 and 8:30 am. It runs through the year, but the best fit is the dry window of December to March, when rain is lowest and Maya Bay is open for the boardwalk walk. In August and September Maya Bay is closed and the day keeps Pileh Lagoon and Bamboo Island.
The operator warns that the speedboat can be bumpy in the open sea, and if the sea is unsafe the trip is moved to another date or refunded. The national park fee, 400 baht per adult and 200 per child, is collected in cash on the tour; that is what the operator collects, not an official rate. For the route, read our Phi Phi travel guide, and for times and packing, the tour schedule.
Practical checklist
- Choose the coast first: Andaman from December to March, Gulf islands from February to April, Bangkok and the north from November to February.
- For Chiang Mai in February or March, check the daily air reading before you book outdoor days.
- For a Similan day, travel between 15 October and 14 May; for Maya Bay, avoid 1 August to 30 September.
- Add a spare day on any sea itinerary in the wetter months, and book boat days a few days ahead.
- Pack a hat, water and sunscreen for March to May, and a light layer for January mornings in the north.
Questions and answers
What is the best month to visit Thailand?
There is no single month. February is dry on the Andaman coast (32 mm at Phuket Airport), in Bangkok and Chiang Mai, and it is Koh Samui's driest month (64 mm). For a first trip, December to February works for most regions.
What is the hottest month in Thailand?
April. TMD calls it the hottest month, and the 1991 to 2020 normals give a mean high of 36.7 degrees in Chiang Mai and 35.7 in Bangkok, against 33.5 at Phuket Airport.
When is the best time to visit Phuket?
December to March, when Phuket Airport records 32 to 117 mm of rain a month. The Similan Islands are open from 15 October to 14 May, and Maya Bay is closed in August and September.
When is the best time to visit Koh Samui?
February to April, with 4.3 to 6.1 rainy days a month. November is the wettest month at about 445 mm, and Ang Thong is closed from 1 November to 15 December 2026.
Is it worth going to Thailand in the rainy season?
Yes, with flexibility. Rain comes mostly as showers, temples and inland sights work in it, and boat days run when the sea allows. Allow a spare day for the sea, and avoid the Gulf in November.
When is the burning season in Chiang Mai?
February to May, according to Thairath, which says the National Environment Board declared the northern provinces pollution control zones for those months. Check the daily PM2.5 reading before you plan outdoor days.