Seasons in Thailand
Thailand's weather service divides the year into three seasons. The southwest monsoon brings the rainy season from mid-May to mid-October, the northeast monsoon brings the dry and cool season from mid-October to mid-February, and the hot summer season runs from mid-February to mid-May.[2] April is the hottest month of the year, especially in upper Thailand, the area north of the Gulf of Thailand, and rain increases in every part of the country as summer thunderstorms begin.[3] In our data the average April high is 37.6 °C in Sukhothai and about 36 °C in Chiang Mai and Chiang Rai, against 35 °C in Bangkok.
The south does not follow this calendar. The northeast monsoon brings abundant rain to the east coast of the south in November and in the first half of December, while cold air from China keeps upper Thailand dry.[1] The Andaman side gets its heaviest rain during the southwest monsoon: in our data Phuket and Krabi are wettest from August to October.
The dry season is also the smoky season in the north. From January to April farmers in the northern provinces burn crop residues to prepare their fields, and the dry, still air and the basin-shaped terrain in places keep the smoke hanging close to the ground.[4] In late winter, when cold air from China weakens for a spell, calm winds and a temperature inversion near the ground add to this, so fine particles build up across upper Thailand.[4] Smoke from neighbouring countries drifts in as well: ASEAN's weather centre has activated its highest haze alert for the Mekong sub-region in March in several recent years, with moderate to dense smoke haze observed over northern Thailand.[5] In our data fine particles (PM2.5) peak in March, with a monthly mean of 66 µg/m³ in Chiang Mai and 85 µg/m³ in Chiang Rai, against 14 to 19 µg/m³ from June to September.
Region by region
North (Chiang Mai, Chiang Rai)
The north has the clearest cool season in the country. In December and January cold air from China brings chilly weather to the northern provinces, with morning fog and very cold nights on the mountain tops.[2] Chiang Mai and Chiang Rai average lows of 14 to 16 °C in December and January and get under 20 mm of rain a month from December to February. October is also rated best in both places, at about 100 to 110 mm of rain. TMD says cool weather starts in upper Thailand from the middle of October.[6]
From March the north gets hot, with average highs of 35 °C in March and 36 °C in April. This is also the smoke haze season. Between February and April air pollution from the burning of farmland and forest in northern Thailand and neighbouring countries blankets the north.[7] In March fine particles (PM2.5) typically reach a monthly mean of 66 µg/m³ in Chiang Mai and 85 µg/m³ in Chiang Rai, and in April 60 and 69 µg/m³, which is why both places are rated mixed in those two months. The March mean reached 55 µg/m³ or more in 9 of the last 10 years in Chiang Rai and in 8 in Chiang Mai. If you want clear air, choose November to January, when the monthly means stay between 20 and 32 µg/m³.
Bangkok and the central plains
Bangkok is hot all year, with average highs of 32 to 35 °C in every month. From November to February it is also dry (7 to 37 mm a month), with highs of 32 to 33 °C and lows of 22 to 24 °C. Air pollution is the catch of the cool months: fine particles (PM2.5) typically average 43 µg/m³ in January and 37 µg/m³ in December and February, against 13 to 16 µg/m³ from June to September. Diesel vehicles, open burning and factories are among the main sources of fine particles in Thailand.[4] The wettest months are September and October, at 289 and 220 mm. TMD describes September as the month with the heaviest rain of the year for most areas.[6]
Sukhothai, in the northern plains, is hotter than Bangkok in the hot season (37.6 °C average high in April) and cooler at night in winter (18 °C average low in January). It is rated best from November to February and in June and July. It shares the northern smoke season: fine particles (PM2.5) typically average 44 µg/m³ in February and 56 µg/m³ in March, and March is rated mixed. Its Loy Krathong and Candle Festival at Sukhothai Historical Park ran from 8 to 17 November in 2024.[8]
East coast (Pattaya, Ko Chang)
Pattaya and Ko Chang are on the same coast but behave very differently. Pattaya is rated best or good in ten months of the year, and only September and October are mixed (241 and 258 mm). Ko Chang is far wetter: 512 to 598 mm a month from June to September, which our table rates as poor, against 14 mm in December.
Ko Chang is rated best from November to April. TMD notes that tropical cyclones approaching Thailand in September and October may come near the eastern part of the country.[6]
Gulf of Thailand (Hua Hin, Chumphon, Ko Samui)
The Gulf coast has the opposite pattern to the Andaman coast. Ko Samui is rated best from January to September, with 52 to 128 mm of rain a month, then turns wet: 265 mm in October, 363 mm in November and 228 mm in December. The cause is the northeast monsoon, which TMD says brings abundant rain to the east coast of the south in November and the first half of December.[1] Ko Phangan and Ko Tao lie off the same coast, so the same northeast monsoon reaches them.
Hua Hin is the driest of the beach places on our map from June to August, with 46 to 93 mm a month, and it is rated best in every month except September (good) and October (mixed). Chumphon, the mainland port for Ko Tao, is wetter: October and November are mixed (282 and 247 mm), and December to April is rated best. Tropical storms are rare: our 1995 to 2024 record has one storm within 200 km of Ko Samui in each of January, November and December. TMD adds that in October tropical cyclones may move toward the upper Gulf of Thailand and the south.[6]
Andaman coast (Phuket, Krabi)
Phuket and Krabi are rated best from December to March, with February the driest month (47 mm in Phuket, 39 mm in Krabi). In November the Andaman side already gets far less rain than the Gulf: 195 mm in Phuket and 209 mm in Krabi, against 363 mm on Ko Samui. From May to October the southwest monsoon takes over, and every month is rated mixed or good, with Phuket at 311 to 350 mm from August to October.
The marine parks follow the monsoon. The Similan Islands close for about five months every year, and in 2026 the closure ran from 16 May to 14 October.[9][10] Dive and snorkel trips to the Similan and Surin Islands therefore only run in the open season. The Department of National Parks says the opening of some attractions and overnight areas can change with the weather, so check before you book boat trips.[11] Maya Bay on Ko Phi Phi has its own annual closure from 1 August to 30 September.[12]
Deep south (Hat Yai)
Hat Yai follows the Gulf side of the south rather than the Andaman side. It is rated best or good from January to September, with 27 to 141 mm of rain a month, then turns wet: 242 mm in October, 370 mm in November and 387 mm in December, its wettest month. TMD says rain on the east coast of the south is abundant mostly in the first half of December, and that tropical cyclones may move near the lower part of the south in that month.[1]
Our 1995 to 2024 record has one storm within 200 km of Hat Yai in each of January and December.
Thailand month by month
Thailand in January
Chiang MaiChiang RaiBangkokSukhothaiPattayaKo ChangHua HinChumphonKoh SamuiPhuketKrabiHat Yai
Great or good weather: Bangkok, Chiang Mai, Chiang Rai, Sukhothai, Pattaya, Ko Chang, Hua Hin, Chumphon, Koh Samui, Phuket, Krabi, and Hat Yai.
Most rain: Koh Samui, 120 mm.
Hottest days: Krabi, 33 °C on average.
January and February are the two months when every one of the 12 places is rated best. The north is coldest now, with Chiang Mai and Chiang Rai averaging lows of about 14 °C and almost no rain. TMD names January as the coolest month for most of Thailand, with morning fog.[2] The Gulf coast is still catching the end of its wet season, with 120 mm on Ko Samui and 98 mm in Chumphon. In Bangkok fine particles (PM2.5) typically average 43 µg/m³ as a monthly mean, the highest of the year.
Thailand in February
Chiang MaiChiang RaiBangkokSukhothaiPattayaKo ChangHua HinChumphonKoh SamuiPhuketKrabiHat Yai
Great or good weather: Bangkok, Chiang Mai, Chiang Rai, Sukhothai, Pattaya, Ko Chang, Hua Hin, Chumphon, Koh Samui, Phuket, Krabi, and Hat Yai.
Most rain: Koh Samui, 52 mm.
Hottest days: Krabi, 34 °C on average.
February is the driest month in Phuket (47 mm), Krabi (39 mm), Hat Yai (27 mm), Ko Samui (52 mm) and Chumphon (50 mm). From the middle of the month hot southerly winds replace the northeast monsoon and temperatures rise, which marks the start of the summer season.[2] Chiang Mai's average high climbs from 30 °C in January to 33 °C in February. The smoky season in the north is under way: fine particles (PM2.5) typically average 44 µg/m³ in Chiang Mai, 46 µg/m³ in Chiang Rai and 44 µg/m³ in Sukhothai.
Thailand in March
Chiang MaiChiang RaiBangkokSukhothaiPattayaKo ChangHua HinChumphonKoh SamuiPhuketKrabiHat Yai
Great or good weather: Bangkok, Pattaya, Ko Chang, Hua Hin, Chumphon, Koh Samui, Phuket, Krabi, and Hat Yai.
Most rain: Ko Chang, 126 mm.
Hottest days: Sukhothai, 36 °C on average.
March is rated best in Bangkok, Pattaya, Ko Chang, Hua Hin, Chumphon, Ko Samui, Phuket, Krabi and Hat Yai, and mixed in Chiang Mai, Chiang Rai and Sukhothai. Highs reach 35 °C in Chiang Mai and 36 °C in Sukhothai. Smoke is what pulls the northern ratings down: fine particles (PM2.5) typically reach a monthly mean of 66 µg/m³ in Chiang Mai, 85 µg/m³ in Chiang Rai and 56 µg/m³ in Sukhothai. Between February and April air pollution from burning blankets the north.[7]
Thailand in April
Chiang MaiChiang RaiBangkokSukhothaiPattayaKo ChangHua HinChumphonKoh SamuiPhuketKrabiHat Yai
Great or good weather: Pattaya, Ko Chang, Hua Hin, Chumphon, Koh Samui, Bangkok, Phuket, and Hat Yai.
Most rain: Phuket, 149 mm.
Hottest days: Sukhothai, 38 °C on average.
April is the hottest month of the year, especially in upper Thailand.[3] Sukhothai averages a high of 37.6 °C, and Chiang Mai and Chiang Rai about 36 °C. Smoke haze lingers in the north: fine particles (PM2.5) typically average 60 µg/m³ in Chiang Mai and 69 µg/m³ in Chiang Rai, and both are rated mixed. In recent years ASEAN's weather centre has lowered its haze alert level for the Mekong sub-region between mid-April and early May as showers increase.[5] Songkran, the Thai New Year, is celebrated on 13 to 15 April and is recognised by UNESCO as intangible cultural heritage, with events across the country.[13] The Gulf side is rated best now: Pattaya, Ko Chang, Hua Hin, Chumphon and Ko Samui.
Thailand in May
Chiang MaiChiang RaiBangkokSukhothaiPattayaKo ChangHua HinChumphonKoh SamuiPhuketKrabiHat Yai
Great or good weather: Hua Hin, Koh Samui, Hat Yai, Pattaya, Chumphon, and Krabi.
Most rain: Ko Chang, 336 mm.
Hottest days: Sukhothai, 35 °C on average.
May is the month the seasons change: TMD describes the first half as sweltering with thunderstorms, sometimes with hail, and the rainy season starting in the second half.[3] Hua Hin, Ko Samui and Hat Yai are still rated best, while Ko Chang (336 mm), Phuket (237 mm), Bangkok and the north are mixed. The Similan and Surin Islands close in mid-May for about five months.[9][10]
Thailand in June
Chiang MaiChiang RaiBangkokSukhothaiPattayaKo ChangHua HinChumphonKoh SamuiPhuketKrabiHat Yai
Great or good weather: Bangkok, Chiang Mai, Sukhothai, Pattaya, Hua Hin, Koh Samui, Hat Yai, Chiang Rai, Chumphon, and Krabi.
Most rain: Ko Chang, 512 mm.
Hottest days: Bangkok, 34 °C on average.
In June Bangkok, Chiang Mai, Sukhothai, Pattaya, Hua Hin, Ko Samui and Hat Yai are all rated best. TMD says rain is abundant in the first half of June and then often eases, with a dry spell of one to two weeks possible, especially in upper Thailand.[14] The exceptions are Ko Chang, rated poor with 512 mm, and Phuket, rated mixed with 242 mm.
Thailand in July
Chiang MaiChiang RaiBangkokSukhothaiPattayaKo ChangHua HinChumphonKoh SamuiPhuketKrabiHat Yai
Great or good weather: Sukhothai, Pattaya, Hua Hin, Koh Samui, Hat Yai, Bangkok, Chiang Mai, Chumphon, and Krabi.
Most rain: Ko Chang, 537 mm.
Hottest days: Bangkok, 33 °C on average.
July is quiet on the Gulf side: Pattaya, Hua Hin, Ko Samui and Hat Yai are rated best, and so is Sukhothai. TMD says the dry spell from late June often continues through the first half of July, before abundant rain returns in the second half.[14] Ko Chang gets 537 mm and is rated poor, while Chiang Rai (246 mm) and Phuket (234 mm) are mixed.
Thailand in August
Chiang MaiChiang RaiBangkokSukhothaiPattayaKo ChangHua HinChumphonKoh SamuiPhuketKrabiHat Yai
Great or good weather: Pattaya, Hua Hin, Koh Samui, Hat Yai, Bangkok, Chiang Mai, Sukhothai, and Chumphon.
Most rain: Ko Chang, 598 mm.
Hottest days: Bangkok, 33 °C on average.
August typically brings more rain than the months before it, according to TMD.[14] Pattaya, Hua Hin, Ko Samui and Hat Yai are still rated best, while Phuket (311 mm), Krabi (283 mm) and Chiang Rai (280 mm) are mixed and Ko Chang is poor with 598 mm. Maya Bay on Ko Phi Phi closes to visitors from 1 August to 30 September.[12]
Thailand in September
Chiang MaiChiang RaiBangkokSukhothaiPattayaKo ChangHua HinChumphonKoh SamuiPhuketKrabiHat Yai
Great or good weather: Koh Samui, Chiang Mai, Chiang Rai, Sukhothai, Hua Hin, Chumphon, and Hat Yai.
Most rain: Ko Chang, 564 mm.
Hottest days: Bangkok, 33 °C on average.
September is the wettest month of the year for most areas, TMD says.[6] Only Ko Samui is rated best, with 121 mm; Bangkok (289 mm), Pattaya (241 mm), Phuket (325 mm) and Krabi (294 mm) are mixed, and Ko Chang is poor with 564 mm. TMD adds that tropical cyclones approaching Thailand in September may come near the eastern part of the country.[6]
Thailand in October
Chiang MaiChiang RaiBangkokSukhothaiPattayaKo ChangHua HinChumphonKoh SamuiPhuketKrabiHat Yai
Great or good weather: Chiang Mai, Chiang Rai, Bangkok, and Sukhothai.
Most rain: Phuket, 350 mm.
Hottest days: Bangkok, 33 °C on average.
October is a transition month. TMD says rain eases and temperatures drop in upper Thailand, with cool weather starting from mid-month, while the rain belt moves to the south and the Gulf in the second half.[6] Chiang Mai and Chiang Rai are rated best (109 and 102 mm) and Bangkok and Sukhothai good, but every place from Pattaya southward is mixed, from 222 mm in Hua Hin to 350 mm in Phuket. The Similan Islands reopen on 15 October after the five-month closure.[15][11]
Thailand in November
Chiang MaiChiang RaiBangkokSukhothaiPattayaKo ChangHua HinChumphonKoh SamuiPhuketKrabiHat Yai
Great or good weather: Bangkok, Chiang Mai, Chiang Rai, Sukhothai, Pattaya, Ko Chang, Hua Hin, Phuket, and Krabi.
Most rain: Hat Yai, 370 mm.
Hottest days: Bangkok, 33 °C on average.
November is the start of the cool dry season in upper Thailand, with much less rain and cool weather all month, TMD says.[1] Bangkok, Chiang Mai, Chiang Rai, Sukhothai, Pattaya, Ko Chang and Hua Hin are all rated best, while Ko Samui (363 mm) and Hat Yai (370 mm) are rated poor. Loy Krathong is held on the full moon of the 12th month of the Thai lunar calendar, so the date changes every year: it fell on 15 November in 2024, when Chiang Mai's Yi Peng festival ran from 14 to 17 November.[8]
Thailand in December
Chiang MaiChiang RaiBangkokSukhothaiPattayaKo ChangHua HinChumphonKoh SamuiPhuketKrabiHat Yai
Great or good weather: Bangkok, Chiang Mai, Chiang Rai, Sukhothai, Pattaya, Ko Chang, Hua Hin, Chumphon, Phuket, and Krabi.
Most rain: Hat Yai, 387 mm.
Hottest days: Bangkok, 32 °C on average.
December is the driest month in Bangkok and Hua Hin (7 mm each), and it is rated best everywhere except Ko Samui (mixed, 228 mm) and Hat Yai (poor, 387 mm). Chiang Mai and Chiang Rai have cool nights, with lows around 15 °C. TMD says rain on the east coast of the south falls mostly in the first half of the month and that tropical cyclones may approach the lower south.[1]
Frequently asked questions
What is the rainy season in Thailand?
Thailand's official rainy season runs from mid-May to mid-October, under the southwest monsoon.[2] It differs by coast: the Andaman coast (Phuket, Krabi) is wettest from May to October, while Ko Samui and the Gulf islands get their heaviest rain from October to December.
Is October a good time to visit Thailand?
October is a transition month and depends on where you go. Chiang Mai and Chiang Rai are rated best and Bangkok good, but every place from Pattaya southward is rated mixed, with 222 to 350 mm of rain. Rain eases in upper Thailand and cool weather starts from mid-October.[6]
When is the best time to visit Phuket?
December to March, when Phuket is rated best, with February the driest month at 47 mm. From May to October Phuket is rated mixed. The Similan Islands, a popular day trip, close from 16 May to 14 October.[9]
When is the best time to visit Ko Samui?
Ko Samui is rated best from January to September and is wettest from October to December, with 363 mm in November. The wet season comes from the northeast monsoon, which brings abundant rain to the east coast of the south in November and early December.[1]
When is the burning season in Chiang Mai and northern Thailand?
Air pollution from burning blankets the north between February and April.[7] In March fine particles (PM2.5) typically average 66 µg/m³ in Chiang Mai and 85 µg/m³ in Chiang Rai, against 14 to 19 µg/m³ from June to September. For clearer air, plan your visit between November and January, when Chiang Mai is rated best and nights are cool.
When is Songkran in Thailand?
Songkran, the Thai New Year, is celebrated on 13 to 15 April.[13] It falls in the hottest month: Chiang Mai and Chiang Rai average about 36 °C, while the Gulf beaches average 32 to 34 °C.
About the data
Temperatures and rain are long-term averages for 1991 to 2020 from TerraClimate, the typhoon risk counts tropical storms from NOAA IBTrACS and fine particles (PM2.5) come from SatPM2.5 satellite estimates for 2015 to 2024. The ratings use the same rules for every country. How the rating works.
Long-term averages, not a forecast. The weather in a given year can be quite different.
Travel guide: Thailand
Sources and background
Numbers in the text such as [1] refer to these sources.
- [1] Thai Meteorological Department: 3-month Climate Prediction of Thailand, November 2024 to January 2025 (30-year normal 1991 to 2020). Retrieved October 15, 2026.
- [2] Thai Meteorological Department: 3-month Climate Prediction of Thailand, December 2022 to February 2023 (30-year normal 1991 to 2020). Retrieved October 15, 2026.
- [3] Thai Meteorological Department: 3-month Climate Prediction of Thailand, March to May (30-year normal 1991 to 2020). Retrieved October 15, 2026.
- [4] Pollution Control Department, Regional Environment Office 2 (Lampang), Ministry of Natural Resources and Environment: Knowledge on fine particulate matter (PM2.5): sources, seasonal pattern and monitoring in northern Thailand (in Thai). Retrieved October 22, 2026.
- [5] ASEAN Specialised Meteorological Centre (ASMC): ASMC Alerts. Retrieved October 22, 2026.
- [6] Thai Meteorological Department: 3-month Climate Prediction of Thailand, August to October 2026 (30-year normal 1991 to 2020). Retrieved October 15, 2026.
- [7] National Assembly Library of Thailand (Secretariat of the House of Representatives): The toxic dust problem in northern Thailand (radio script, April 2023, in Thai). Retrieved October 15, 2026.
- [8] Tourism Authority of Thailand (TAT Newsroom): Loi Krathong Festival 2024: Experience Thailand's Enchanting Festival of Lights. Retrieved October 15, 2026.
- [9] Office of Natural Resources and Environmental Policy and Planning (ONEP), quoting the head of Mu Ko Similan National Park: 22 May 2026: Similan Islands close for 5 months to recover (in Thai). Retrieved October 15, 2026.
- [10] Government Public Relations Department (Region 1): Surin and Similan Islands National Parks announce closure to tourism and overnight stays for five months from 15 May 2026 (in Thai). Retrieved October 15, 2026.
- [11] Department of National Parks, Wildlife and Plant Conservation (DNP): Minister opens the Andaman Sea tourism season, orders DNP to tighten safety (in Thai). Retrieved October 15, 2026.
- [12] Government Public Relations Department (Thailand): Maya Bay and nearby areas closed to visitors until 30 September 2024. Retrieved October 15, 2026.
- [13] Tourism Authority of Thailand (TAT Newsroom): Songkran festival 2026 to proceed nationwide, welcoming global visitors to Thailand's UNESCO-recognised New Year celebration. Retrieved October 15, 2026.
- [14] Thai Meteorological Department: 3-month Climate Prediction of Thailand, June to August 2026 (30-year normal 1991 to 2020). Retrieved October 15, 2026.
- [15] Department of National Parks, Wildlife and Plant Conservation (DNP): Similan Islands park joins Phang-nga partners for "Collect and SAVE Similan" activity, ready to open on 15 October (in Thai). Retrieved October 15, 2026.
