Practical guide
The wettest month for much of the country, and the cheapest.
September is the month I'd skip if your dates are flexible. It's the wettest month of the year in Bangkok, on the Andaman coast (Phuket, Krabi, Phi Phi) and in the northeast, Maya Bay is still closed until 30 September, and boat trips are often canceled. It's also the cheapest month, and the Gulf islands (Koh Samui, Koh Phangan, Koh Tao) and Hua Hin get far less rain than the rest of the country. If September is your only window, go to the Gulf and enjoy the prices.
Averages for eight weather stations, one for each part of the country. Tap a region in the table to jump to it, or switch to °F and inches.
| Region | High | Low | Rain | Rain days | Sea |
|---|---|---|---|---|---|
| Bangkok | 33°C | 25°C | 336 mm | 18 | – |
| Chiang Mai | 32°C | 24°C | 207 mm | 15 | – |
| Phuket | 32°C | 25°C | 350 mm | 19 | 29°C |
| Koh Samui | 32°C | 25°C | 118 mm | 11 | 29°C |
| Pattaya | 31°C | 25°C | 214 mm | 13 | 29°C |
| Hua Hin | 32°C | 25°C | 130 mm | 11 | – |
| Koh Chang | 31°C | 24°C | 816 mm | 22 | 29°C |
| Isan | 32°C | 24°C | 246 mm | 15 | – |
Central plains and the capital
Highs of 33°C and lows of 25°C, 336 mm of rain on about 18 days, 4.3 hours of sun a day.
The wettest month of the year, with the highest humidity. Storms come most days and streets flood after the heaviest ones, though the trains keep running.
The north: Chiang Mai, Chiang Rai, Pai
Highs of 32°C and lows of 24°C, 207 mm of rain on about 15 days, 5.1 hours of sun a day.
Very wet, though slightly less than August. Green and quiet, with the season's last heavy rains.
Andaman coast: Phuket, Krabi, Koh Lanta, Khao Lak
Highs of 32°C and lows of 25°C, 350 mm of rain on about 19 days, sea at 29°C.
The wettest month on the Andaman coast, with rough seas and red flags on the west-coast beaches. The cheapest hotels of the year.
Gulf islands: Koh Samui, Koh Phangan, Koh Tao
Highs of 32°C and lows of 25°C, 118 mm of rain on about 11 days, sea at 29°C.
Rain starts building on the Gulf islands but stays well below the Andaman side, with many dry days. The better beach choice this month.
Upper Gulf: Pattaya, Koh Samet, Rayong
Highs of 31°C and lows of 25°C, 214 mm of rain on about 13 days, sea at 29°C.
Wetter than the summer months, as Pattaya's own rainy peak approaches in October.
Western Gulf: Hua Hin, Cha-am, Pranburi
Highs of 32°C and lows of 25°C, 130 mm of rain on about 11 days, 4.8 hours of sun a day.
Wetter than July and August, but still one of the drier spots on the coast.
Eastern seaboard: Koh Chang, Koh Kood, Koh Mak
Highs of 31°C and lows of 24°C, 816 mm of rain on about 22 days, sea at 29°C.
Very wet, with rain on most days, and some smaller resorts stay closed until the season returns.
Northeast: Khon Kaen, Udon Thani, Korat, Buriram, Ubon
Highs of 32°C and lows of 24°C, 246 mm of rain on about 15 days, 4.8 hours of sun a day.
The wettest month in the northeast. Rice fields are at their greenest.
Source WMO Climatological Standard Normals 1991–2020 (Thai Meteorological Department stations). Averages for 1991–2020, and rain days count days with at least 1 mm. Sea temperatures: Climates to Travel monthly sea-surface averages. Koh Chang uses the Trat station on the facing mainland and Isan uses Khon Kaen.
Arriving in Koh Samui
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The Gulf is the safest bet for beaches, with Koh Samui, Koh Phangan, Koh Tao and Hua Hin getting the least rain. Bangkok works for a city trip if you plan indoor afternoons.
Even in September, rain usually comes as heavy storms rather than all day, with sunny spells between them. The problems are flooded streets in Bangkok for an hour or two after a storm, rough seas, and canceled ferries and boat trips on the Andaman coast.
September is quiet. The Full Moon Party on Koh Phangan falls on 15 September 2027, and in some years the Phuket Vegetarian Festival starts at the very end of the month, since it follows the Chinese lunar calendar.
A light jacket or a compact umbrella, used most days.
Bangkok streets flood briefly after heavy storms.
Ferries and flights to the islands are delayed or canceled more often in September.
For anything that has to stay dry on a boat or in a downpour.
Common questions about thailand in september.
Other months, and the whole year at a glance
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Written by
Mac Kiley
I lived in Bangkok for four years and traveled the country from there. The guides are my own opinions, written the way I'd explain them to a friend planning a trip.
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