Koh Samui weather by month
Koh Samui runs from about 23°C in December to 27°C in April, with December the wettest month at 304 mm.
warmest month
April
27°C
coolest month
December
23°C
wettest month
December
304 mm
worst air month
January
14 µg/m³
The whole year, month by month.
| Month | Avg temp | Rain | Sun | PM2.5 |
|---|---|---|---|---|
| January | 24°C | 77 mm | 338 h | 14 |
| February | 25°C | 35 mm | 319 h | 12 |
| March | 26°C | 16 mm | 344 h | 12 |
| April | 27°C | 12 mm | 354 h | 12 |
| May | 27°C | 134 mm | 319 h | 6 |
| June | 26°C | 72 mm | 271 h | 5 |
| July | 25°C | 170 mm | 230 h | 7 |
| August | 25°C | 172 mm | 298 h | 6 |
| September | 25°C | 101 mm | 281 h | 5 |
| October | 24°C | 242 mm | 299 h | 5 |
| November | 24°C | 276 mm | 252 h | 9 |
| December | 23°C | 304 mm | 259 h | 11 |
About 3,564 hours of sun a year. Roughly 161 rainy days a year.
These are long-run climate normals, not a forecast. A given year can sit well outside them. PM2.5 is a global model: near the coast it counts sea salt as fine particulate and reads high against ground stations, sometimes by a factor of two. Use the shape of the year, not the absolute number.
where these numbers come from
- · Temperature, rainfall and sunshine: ECMWF ERA5 reanalysis climate normals via Open-Meteo (CC BY 4.0), fetched once and stored.
- · PM2.5: Copernicus CAMS reanalysis, monthly means. Modelled, not station readings; near coasts CAMS counts sea salt as PM2.5 and reads high.
Last reviewed 2026-05-23. Full method, licences and the list of sources we rejected are on the methodology page.