Month by month
| Month | Afternoon | Sea | Rain | Verdict |
|---|---|---|---|---|
| January | 24.9 °C | 28.1 °C | 17 days | Possible, with trade-offs |
| February | 25.5 °C | 28.3 °C | 12 days | Ideal — one of the best times of year |
| March | 26.9 °C | 29 °C | 10 days | Ideal — one of the best times of year |
| April | 27.9 °C | 30.3 °C | 14 days | Possible, with trade-offs |
| May | 28 °C | 30.7 °C | 19 days | Unfavourable season |
| June | 28 °C | 30.4 °C | 16 days | Possible, with trade-offs |
| July | 27.5 °C | 29.9 °C | 18 days | Possible, with trade-offs |
| August | 27.6 °C | 29.8 °C | 18 days | Possible, with trade-offs |
| September | 26.6 °C | 29.5 °C | 20 days | Unfavourable season |
| October | 25.7 °C | 29.3 °C | 27 days | Unfavourable season |
| November | 25.2 °C | 29 °C | 26 days | Unfavourable season |
| December | 24.7 °C | 28.2 °C | 20 days | Unfavourable season |
Before you go
Three things to check once you have picked your dates.
Entry
Entry rules depend on your nationality and change often. Check them before booking.
Safety
Some areas advised against
The country is open, but parts should be avoided.
Official advice updated 30 June 2026
Health
Recommended vaccinations, water quality, mosquitoes: advice depends on the country and the season. Some vaccines need time before departure.
Beau Fixe is not a safety or health authority. These notes summarise public advisories and link to their source; only the competent authorities are authoritative. Alert levels: Foreign, Commonwealth & Development Office (gov.uk), Open Government Licence v3.0.
FAQ
Can you swim in Koh Samui in December?
The sea averages 28.2°C in December — yes, pleasant swimming.
How hot is Koh Samui in December?
Expect 24.7°C in the afternoon and 21.8°C at night, averaged over the last 10 years.
Does it rain a lot in Koh Samui in December?
Around 20 days with rain (≥ 1 mm) in the month — 64% of days.