The best time to visit Thailand, by region and month

Thailand has three seasons rather than four. The Tourism Authority of Thailand, TAT, describes a cool season from November to February, a hot summer from March to May, and a rainy season from May to October. Those dates hold for Bangkok, the central plains and the north, which is where most trips start.

The south is where it gets complicated. The peninsula has two coasts that face different monsoons, so Phuket and Koh Samui peak at different times of year, and even the official sources give different windows for the Gulf side.

TAT's newsroom puts the cool season at November to February, with temperatures of 18°C to 28°C, the summer at March to May with averages of 28°C to 38°C, and the rainy season from May to October. Its Bangkok note for the cool season is 18°C to 32°C, and says the North and Northeast can fall to around 10°C in the morning and at night. For most visitors the cool season is the easy choice: lower humidity, clearer days, and the best conditions for walking Bangkok or exploring Chiang Mai.

The hot season is not a hardship everywhere. TAT's March page calls March "a complete hot season of around 30-40°C throughout every region" and points visitors to beaches and rivers, and its April page says April holds the highest temperatures, with up to 42°C in the North and Northeast. The rainy season follows from mid-May. TAT says the South has the highest rainfall of the six regions in May. The Thai Meteorological Department adds that August brings "densely abundant" rainfall, and that for most areas September has the most abundant monthly rainfall of the whole year.

January is the coldest month, especially in the mountains of the North and Northeast. TAT calls it "an ideal time to go to the beach at both the Gulf of Thailand and the Andaman Sea," with clear water and blue skies, and points to Thai Sakura blossom at Doi Ang Khang and Doi Inthanon in Chiang Mai province. February is the changeover: the start of the month is still cool, and from the middle of the month the hot season begins, though not as hot as March and April. TAT lists February to April as the driest months for Ko Phi Phi.

March is fully hot. April is the hottest month and holds the Songkran holiday, when TAT says most people head to the beach or to big provinces. It also notes that Ko Tachai, in Phang Nga, is open from February to April and then closes for six months because of the monsoon, a sign of how the Andaman season shuts down. May is the last month of summer and the start of the rainy season, which TAT dates from mid-May.

June and July are the green months. TAT's June page says "the competitive rates offered by hotels" and the green waterfalls, mountains and fields reward flexible travelers, and its July page adds the rafting season and the Candle Festival on Buddhist Lent Day. August is the middle of the rainy season, and TAT recommends the North for morning mist and cultural events such as the Akha Swing Festival in Chiang Rai at the end of the month. September is what TAT calls the end of the rainy season and the revival of tourism; it recommends the Gulf of Thailand "because the monsoon season still lingers in Andaman Sea."

October is described by TAT as the bridge between the rainy season and winter, with temperatures starting to drop in almost every region. The Thai Meteorological Department says cool weather begins in the middle of the month in the upper country, while the south and the Gulf still get "densely abundant rainfall" in the second half of the month. November is the exact cool season, and TAT says the Andaman monsoon is gone, with Krabi, Ko Phi Phi and the Satun islands lively again. December has the lowest average temperature of the year and is, in TAT's words, Chiang Mai's high season month, with the monsoon gone from the south on both coasts.

The Andaman coast on the west, with Phuket, Krabi, Koh Lanta and the Phi Phi islands, faces the southwest monsoon. TAT's guidance is that Phuket, Krabi and the Phi Phi Islands are best visited from November through April. The UK government's travel advice describes the rainy season as generally May to October and warns about strong riptides and rough seas during the monsoon, and about jellyfish that can swim close to shore from May to October. Thailand uses a flag system at lifeguarded beaches, and the advice is to follow warning signs, especially red flags. If you want island-hopping by small boat, the sensible months are the dry ones.

The Gulf coast on the east, with Koh Samui, Ko Pha-ngan and Ko Tao, is where the sources disagree, so read this carefully. TAT's newsroom says Samui and Phangan are best visited from December through June. TAT's own monthly pages also recommend the Gulf in September and October because the Andaman monsoon lingers. The UK government's advice says the rainy season in Koh Samui and south-east Thailand is usually from November to March. And the Thai Meteorological Department's notes for October describe continued heavy rain in the south and the Gulf in the second half of the month.

What to do with that? Treat the Gulf as the flexible coast. The windows that overlap across sources are April, May and June, when it is not described as wet by the UK page and falls inside TAT's best window. January to March is where the sources conflict, so book islands with free cancellation and check the Thai Meteorological Department forecast a few days ahead. Do not plan a Gulf island trip for November on the assumption that it will be dry. The Ko Pha-ngan, Ko Tao and Koh Samui comparison helps you choose between the three once you have your dates, and the Phi Phi, Ko Lanta and Railay comparison does the same for the Andaman side.

A rule for choosing your coast

If your dates fall between November and April, choose the Andaman side first. If they fall between May and October, look at the Gulf, but expect rain anywhere in the south and keep the first and last days of the trip loose. If you have one fixed week in November, December or January and want a beach, the Andaman coast has the stronger official support, and Krabi or Ao Nang are the practical bases.

Bangkok is hot in all seasons, so the cool season is the easy time to walk the old city. In the rainy season, plan temples and markets for the morning and keep afternoons for museums, malls or river boats. The UK government's safety and security page notes that heavy rain can bring flash flooding and transport disruption, especially in northern, north-eastern and mountainous areas, and says lakes, caves and waterfalls are particularly at risk.

The north is where the cool season is most noticeable. TAT's January page calls January the coldest month, with mountain activities such as hiking and camping around Chiang Mai, Chiang Rai and Mae Hong Son, and its December page notes frost at Doi Ang Khang. The rainy season turns the landscape green; TAT's June and September pages point to the Pa Bong Piang rice terraces near Chiang Mai, and to waterfalls and rafting. For a base with more of a backpacker rhythm, the Chiang Mai to Pai and Pai in 3 days guides are the next step.

Air quality

The UK government's health advice says Bangkok and Chiang Mai are affected by seasonal regional smoke haze caused by farmers burning trees and crops, with particle counts that "sometimes reach dangerous levels." It recommends checking air quality on the World Air Quality Index website. It does not give dates, so treat the hot, dry end of the dry season as the time to check before you book the north, especially if you have asthma or sinus conditions.

Songkran, the Thai New Year, is celebrated around 13 to 15 April, and TAT's April page lists Bangkok's Siam Square, Khao San Road and Silom Road and Chiang Mai's city moat among the main water-splashing places. An official 2026 holiday list published by Thailand's mission to ASEAN shows Songkran holiday days on 13 and 14 April, so check the official calendar for your year. Book buses, trains and domestic flights early, keep your phone in a waterproof pouch, and avoid the week entirely if you want a quiet temple morning.

Loy Krathong falls on the full moon of the twelfth lunar month, and TAT places it in November every year. People float small offerings on rivers, and in Chiang Mai the Yi Peng lantern festival runs alongside it. TAT also names Sukhothai's Loi Krathong and Candle Festival and Tak's festival as other places to see it. The date moves each year, so check TAT's calendar before you fix flights. Other dated events that shape a trip include the Candle Festival in July, the Vegetarian Festival in October, when TAT notes Phuket among the most famous places to see parades and restaurants serving meatless menus, and the International Balloon Festival at Singha Park in Chiang Rai, which TAT says is held in February.

The entry rules changed this autumn, and they affect how long a winter trip can be.

The same page says you may be asked to show enough money for your stay (at least 10,000 Thai baht per person or 20,000 Thai baht per family) and evidence of onward or return travel, that people who entered before 15 September 2026 will usually be allowed to stay for the period granted, and that an overstay carries a fine of 500 baht a day up to 20,000 baht. It also notes health screening for travelers arriving from regions affected by Ebola, with a quarantine or self-isolation period of at least 21 days, so check your own government's advice before a trip that includes a stopover in an affected region. The Thailand entry rules guide covers who is exempt and how to extend a stay. If you want more than 30 days across the cool season, sort out a visa before you fly rather than planning on an extension.

For a two-week trip in the cool season, book the islands first, because that is where rooms run out. Then fit Bangkok and the north around them: both work through the dry season, and the transport planning page covers trains, buses and flights between them. Add travel insurance with weather and trip delay cover if you travel in the wet months, and set up data with the connectivity guide.

In the cool season, light clothes are enough for Bangkok and the beaches, but bring a fleece or light jacket for the north, where TAT reports mornings around 10°C and, on mountain tops in December, temperatures at or below freezing. Check the dress rules for any temple you plan to visit before you pack.

In the hot and rainy seasons, pack for heat and water: breathable clothes that dry fast, sandals you can wade in, a compact umbrella and a dry bag for boat trips. Sun protection matters all year. If you plan to snorkel or swim off exposed beaches in the wet months, read the UK government's warnings on riptides and jellyfish and follow the flag system at lifeguarded beaches.