January — rain fades out
Rain tails off after the monsoon (about 127 mm, 8–9 rain days) and it is the coolest month (average high around 29 °C).
Seasonal guide
Koh Samui weather by month
Koh Samui is on the Gulf of Thailand side, so its rainy season is different from Phuket's: the wettest months are October to December, while February to April are the driest. Long-term averages below — real weather varies from year to year.
Advisory: Rough sea forecast for the lower Gulf, 15 Nov: waves 2 m (TMD)
Rough sea forecast (TMD): speedboats, snorkel and island trips may be cancelled; car ferries usually run but can be delayed. This is not an operator cancellation.
Source: Thai Meteorological Department (TMD)Checked 14 Nov 2026, 21:07 ICTValid until 16 Nov 2026, 00:00
Now and next 3 days
Live forecast coming soon
For official warnings and forecasts, use the Thai Meteorological Department.
Sea today
Lower Gulf sea forecast
Rough sea forecast
Speedboats, snorkel and island trips may be cancelled; car ferries usually run but can be delayed. This is not an operator cancellation: confirm with your operator.
- wind
- Wind Easterly 11–18 kt
- waves
- Waves 2–2 m (higher in thundershowers)
Official TMD shipping forecast, original text in English.
Lower: Easterly winds 11-18 knots or 20-35 km./hr. Wave height about 2 meters and above 2 meters in thundershowers.
Issued 15 Nov 2026, 00:00 · fetched 00:07 · TMD shipping forecast
Today, tonight and tomorrow on Samui →
Pick a month
Each month has its own page with rain, sea conditions, what's open and events.
Climate averages
| Month | Max °C | Min °C | Rain (mm) | Rain days |
|---|---|---|---|---|
| January | 29.0 | 24.2 | 127 | 8.5 |
| February | 29.4 | 24.9 | 64 | 4.3 |
| March | 30.4 | 25.4 | 116 | 4.7 |
| April | 31.8 | 26.0 | 83 | 6.1 |
| May | 32.9 | 25.7 | 132 | 11.0 |
| June | 32.7 | 25.3 | 134 | 10.3 |
| July | 32.3 | 25.1 | 117 | 10.7 |
| August | 32.4 | 25.1 | 102 | 10.5 |
| September | 31.9 | 24.8 | 118 | 10.6 |
| October | 30.6 | 24.3 | 295 | 15.8 |
| November | 29.7 | 24.1 | 445 | 16.5 |
| December | 29.3 | 24.0 | 263 | 11.6 |
| Year | 31.0 | 24.9 | 1994 | 120.6 |
The seasons in short
February to April — driest time
The fewest rain days of the year (about 4–6 a month); February is the driest month. It gets hotter through April.
May to September — hot, moderate showers
The hottest daytime highs (around 32–33 °C) with moderate rain: roughly 100–135 mm and 10–11 rain days a month, much drier than October to December. Showers are often short.
October to December — northeast monsoon
The main rainy season on the Gulf side. November is the wettest month (about 445 mm, 16–17 rain days). The Thai Meteorological Department issues heavy-rain and strong-wave warnings in this season — ferries and boat trips can be cancelled.
What it means for your plans
- Beach and snorkel days: calmer and clearer seas are most likely from February to September.
- October to December: keep flexible days for boat trips and check the operator on the day. Ang Thong Marine National Park is often closed for part of this period — check the park's announcement.
- Rainy day? See our guides for indoor ideas, or ask the AI planner for a rainy-day plan. →
Live forecast & warnings: For the actual forecast and storm or wave warnings use the Thai Meteorological Department (TMD). TMD weather warnings
Holidays & festival dates
Thai holidays follow the lunar calendar, so dates change every year. On some Buddhist holidays the sale of alcohol is banned (licensed hotels, entertainment venues and airports may be exempt).
| Holiday | 2026 | 2027 | Alcohol sale ban |
|---|---|---|---|
| Chinese New Year (not a national holiday) | 17 Feb 2026 | 6 Feb 2027 | No |
| Makha Bucha | 3 Mar 2026 | 21 Feb 2027 | Yes |
| Songkran (Thai New Year) | 13 Apr 2026 – 15 Apr 2026 | 13 Apr 2027 – 15 Apr 2027 | No |
| Visakha Bucha | 31 May 2026 | 20 May 2027 | Yes |
| Asahna Bucha | 29 Jul 2026 | 18 Jul 2027 | Yes |
| Khao Phansa (start of Buddhist Lent) | 30 Jul 2026 | not yet announced | Yes |
| Ok Phansa (end of Buddhist Lent) | 26 Oct 2026 | not yet announced | Yes |
| Loy Krathong (festival, not a public holiday) | 24 Nov 2026 | not yet announced | No |
Dates: Bank of Thailand holiday notifications and Thai press; check before you travel.