Thailand in September: ⚠️ a month best kept for flexible travellers. It is the heart of the monsoon: Bangkok gets 336 mm (13.2 in) (its wettest month) and Phuket 350 mm (13.8 in), with 18 to 19 rain days. The card to play is the Gulf of Thailand: Ko Samui (118 mm (4.6 in), 11 rain days) and Hua Hin stay much drier. Low prices and few people in return.
September is the month when the difference between the two coasts is most useful to know. We compared the official normals of nine weather stations and calculated, for each one, the number of rain days to expect in a week. For the overall picture, see our page on the best time to visit Thailand.
Thailand in September: key facts
- Verdict: ⚠️ monsoon; ✅ Gulf (Ko Samui, Hua Hin), ❌ Andaman and Bangkok
- Bangkok: 33.2 °C (92 °F) in the afternoon, 336 mm (13.2 in), 18 rain days
- Gulf: 118 mm (4.6 in) in Ko Samui, 130 mm (5.1 in) in Hua Hin, about 11 rain days
- Andaman: 350 mm (13.8 in) in Phuket, 319 mm (12.6 in) in Ko Lanta, often rough sea
- Pluses: low prices, few crowds, very green landscapes, end-of-rainy-season festivals
- Entry: visa-exempt tourist stays of up to 30 days per entry for US and UK citizens since 15 September 2026 (Tourism Authority of Thailand); TDAC arrival card mandatory
Thailand weather in September: region by region
| Station | Region | Max °C (°F) | Min °C (°F) | Rain mm (in) | Rain days | Per 7 days | Verdict |
|---|---|---|---|---|---|---|---|
| Ko Samui | Gulf (islands) | 31.9 °C (89 °F) | 24.8 °C (77 °F) | 118 mm (4.6 in) | 10.6 | 2 | ✅ |
| Hua Hin | Gulf (west coast) | 32.3 °C (90 °F) | 25.3 °C (78 °F) | 130 mm (5.1 in) | 10.6 | 2 | ✅ |
| Surat Thani | Gulf (mainland) | 32.9 °C (91 °F) | 23.6 °C (74 °F) | 172 mm (6.8 in) | 14.3 | 3 | ⚠️ |
| Pattaya | Gulf (east coast) | 31.1 °C (88 °F) | 25.4 °C (78 °F) | 214 mm (8.4 in) | 13.2 | 3 | ⚠️ |
| Bangkok | Central | 33.2 °C (92 °F) | 25.4 °C (78 °F) | 336 mm (13.2 in) | 18.0 | 4 | ❌ |
| Chiang Mai | North | 32.0 °C (90 °F) | 23.7 °C (75 °F) | 207 mm (8.1 in) | 14.7 | 3 | ⚠️ |
| Chiang Rai | Far north | 31.4 °C (89 °F) | 23.1 °C (74 °F) | 275 mm (10.8 in) | 14.7 | 3 | ⚠️ |
| Phuket | Andaman | 31.8 °C (89 °F) | 25.1 °C (77 °F) | 350 mm (13.8 in) | 18.9 | 4 | ❌ |
| Ko Lanta | Andaman (Krabi) | 30.9 °C (88 °F) | 24.8 °C (77 °F) | 319 mm (12.6 in) | 17.0 | 4 | ❌ |
Destination de Voyage calculation based on these normals: in September, Phuket gets about 3 times more rain (350 mm (13.8 in)) than Ko Samui (118 mm (4.6 in)), and Bangkok 2.9 times more. In a week, expect on average 4 days with rain in Bangkok and Phuket, 3 in the north, and only 2 in Ko Samui and Hua Hin. Temperatures, by contrast, are uniform: 31–33 °C (88–91 °F) in the afternoon everywhere.
September compared with August and October
| Station | August | September | October |
|---|---|---|---|
| Bangkok | 227 mm (8.9 in) / 15.6 d | 336 mm (13.2 in) / 18.0 d | 289 mm (11.4 in) / 14.4 d |
| Chiang Mai | 223 mm (8.8 in) / 17.1 d | 207 mm (8.1 in) / 14.7 d | 124 mm (4.9 in) / 9.1 d |
| Phuket | 309 mm (12.2 in) / 16.9 d | 350 mm (13.8 in) / 18.9 d | 336 mm (13.2 in) / 19.4 d |
| Ko Samui | 102 mm (4.0 in) / 10.5 d | 118 mm (4.6 in) / 10.6 d | 295 mm (11.6 in) / 15.8 d |
| Hua Hin | 67 mm (2.6 in) / 9.7 d | 130 mm (5.1 in) / 10.6 d | 250 mm (9.8 in) / 12.7 d |
This table shows two opposite calendars. On the mainland and on the Andaman side, September is the peak of the monsoon in Bangkok and one of the wettest months in Phuket; in the north, rain starts to ease compared with August. In the Gulf, on the contrary, September is one of the last calm months: in Ko Samui, rainfall is multiplied by 2.5 between September and October (118 → 295 mm (11.6 in)). If you are aiming for the Gulf, September is therefore better than October; the Tourism Authority of Thailand notes that fine weather is more frequent there in the first half of the month.
Where to go in Thailand in September
The Gulf of Thailand: the best choice for beaches
The Tourism Authority of Thailand recommends the Gulf for the sea in September, as the monsoon persists on the Andaman side. Ko Samui, Ko Phangan and Ko Tao form the easiest archipelago to combine; on the mainland, Hua Hin (130 mm (5.1 in)) and Chumphon are alternatives. See when to go to Ko Samui.
Bangkok and the centre: doable with a plan B
September is the wettest month of the year in Bangkok (336 mm (13.2 in), 18 rain days). Storms are often violent but short; plan temples and markets in the morning and keep museums, cooking classes and malls for the afternoon. See when to go to Bangkok.
The north: green, but still wet
Chiang Mai gets 207 mm (8.1 in) and about 15 rain days: it is still the rainy season, but the landscapes are at their greenest. In September, the Tourism Authority highlights the Pa Bong Piang rice terraces (Chiang Mai province) and the “seas of mist” at Mae Hong Son viewpoints. Trails are muddy: favour short treks. See when to go to Chiang Mai.
The Andaman coast: avoid for a beach stay
Phuket, Krabi and Ko Lanta get 17 to 19 rain days in September and the sea is often rough: respect the red flags. For marine parks such as the Similan Islands, check the opening dates set each year by the Department of National Parks. See when to go to Phuket.
What to do in Thailand in September
- Gulf islands: beaches, snorkelling and diving around Ko Tao, keeping a spare day for crossings.
- Parks and waterfalls: the Tourism Authority cites Sai Yok National Park (Kanchanaburi) and the Rajjaprabha Dam (Surat Thani).
- Temples and food in Bangkok: mornings for sightseeing, afternoons for indoor activities.
- Long-boat races: according to the Tourism Authority, the racing season starts in September and continues into October, notably in Ayutthaya, Chonburi, Phitsanulok and Nan.
- Avoid: caves (at risk of flash flooding in the rainy season, according to the UK FCDO), long night drives, and the provinces and border areas the FCDO advises against (see below).
Festivals and traditions in September
Several Buddhist and Chinese traditions fall during the rainy season and follow the lunar calendar. For September, the Tourism Authority of Thailand cites the Salak Yom festival (Lamphun province), the Por Tor festival of Phuket’s Hokkien community (an ancestors’ festival lasting a month) and the start of the long-boat races. The Phuket Vegetarian Festival falls in September or October depending on the year. Dates change every year: check the Tourism Authority calendar for your year of travel.
Crowds, prices and booking
September is one of the quietest and cheapest months of the year according to our calendar: the end of the summer holidays and the monsoon bring demand down. It is a good month to find upmarket accommodation at reduced prices, particularly on the Andaman coast, provided you accept the weather risk.
What to pack for Thailand in September
- Light, quick-drying clothes
- A poncho or light rain jacket
- Sandals that can get wet and non-slip shoes
- A waterproof pouch for your phone and documents
- Insect repellent
- Clothing that covers shoulders and knees for temples
Entry requirements and safety
US citizens: according to the U.S. Department of State (page last updated August 20, 2026), pre-arrival online registration is required. A passport valid for at least six months beyond arrival is strongly recommended, and you may be asked for an onward or return ticket or proof of funds.
UK citizens: according to the UK FCDO (GOV.UK, updated 12 October 2026), your passport must be valid for at least 6 months after arrival, with 1 blank page. From 15 September 2026, visa-exempt entry is up to 30 days, for tourism only. Visa-exempt entries over land borders are normally limited to 2 per calendar year. You may need proof of funds (10,000 THB per person or 20,000 THB per family) and onward travel. The overstay fine is 500 THB a day, up to 20,000 THB.
The Thailand Digital Arrival Card (TDAC) has been mandatory for all foreign nationals since 1 May 2025 and can be completed within the 3 days before arrival. The U.S. State Department page (last updated August 20, 2026) still mentions 60 days, but it predates the change: under the Thai rules in force since 15 September 2026, US citizens are also limited to 30 days (Tourism Authority of Thailand, 1 September 2026). Check with the Royal Thai Embassy in Washington before you travel.
Safety: the FCDO advises against all but essential travel to Pattani, Yala, Narathiwat and parts of southern Songkhla (Thailand–Malaysia border), and to areas within 20 km (12 mi) of the Cambodian land border; land crossings with Cambodia are suspended. Time difference in September: Thailand (UTC+7, no daylight saving) is 6 hours ahead of London and 11 hours ahead of New York.
Climate note: according to the UK FCDO (GOV.UK, updated 12 October 2026), the rainy season is generally from May to October, and heavy rain can cause flash flooding and road closures.
If September does not suit you
Neighbouring months: Thailand in August is slightly less rainy in Bangkok; Thailand in October marks the end of the monsoon in the north, but the start of the rains in the Gulf. For a full circuit in dry weather, aim for November to February.
Other destinations in September: Bali in September, in the middle of the dry season, or Mauritius in September. All our ideas: where to go in September. For planning your route: our Thailand travel guide.
Frequently asked questions
Is September a good time to visit Thailand?
Yes if you are flexible and favour the Gulf (Ko Samui, Ko Phangan, Ko Tao, Hua Hin). Bangkok and the Andaman coast are then at the heart of the monsoon.
Where is the weather good in Thailand in September?
In the Gulf: 118 mm (4.6 in) of rain and about 11 rain days in Ko Samui, against 336 mm (13.2 in) in Bangkok and 350 mm (13.8 in) in Phuket (1991–2020 normals).
Is September the wettest month in Thailand?
In Bangkok, yes (336 mm (13.2 in)). In Phuket, it is on a par with October; in the north, August is wetter; in the Gulf, the peak comes in November.
Can you visit Phuket in September?
It is possible for sightseeing, but not ideal for the beach: about 19 rain days and an often rough sea. Respect the red flags.
Does it rain all day in September?
Rarely: it is mostly intense, short storms. Occasional flooding is still possible, especially in Bangkok.
How long can you stay without a visa?
No visa is needed for tourism stays of up to 30 days per entry: since 15 September 2026, this exemption applies to both US and UK citizens, according to the Tourism Authority of Thailand (1 September 2026) and the UK FCDO (GOV.UK, updated 12 October 2026). The U.S. State Department page (last updated August 20, 2026) still mentions 60 days, but it predates the change. Check with the Royal Thai Embassy before you travel. The TDAC digital arrival card is mandatory.
Our sources
- Thai Meteorological Department, 1991–2020 climate normals published by the World Meteorological Organization (NOAA NCEI archive): Bangkok Metropolis, Chiang Mai, Chiang Rai, Phuket, Ko Lanta, Ko Samui, Surat Thani, Hua Hin, Pattaya
- Tourism Authority of Thailand (French-language site tourismethai.fr), “September in Thailand”, accessed 23 October 2026
- Verdicts and crowds: calendar from our page on the best time to visit Thailand
- Entry requirements, safety and health checked on 24 October 2026: Tourism Authority of Thailand, TAT Newsroom, 1 September 2026: new 30-day visa exemption rules from 15 September 2026; UK FCDO, GOV.UK foreign travel advice: Thailand (updated 12 October 2026); U.S. Department of State, travel.state.gov: Thailand (last updated August 20, 2026)
- Our methodology
Updated October 2026.