Ko Samui weather in September
September in Ko Samui: sweltering, soaked, with clean air — a great time to visit.
#10 of 12 months in Ko Samui · #395 of 604 destinations to visit in September · comfort 73/100 (tier B)
Updated June 2026 · climate normals from ERA5 reanalysis
Ko Samui climate normals — September
| Daytime high | 29°C / 84°F | 🔥 sweltering |
|---|---|---|
| Nighttime low | 27°C / 80°F | |
| Feels like (high) | 34°C / 93°F | |
| Rainfall | 158 mm / 6.2 in | ⛈ soaked |
| Rainy days | 22 days | |
| Humidity | 79% | 💦 very humid |
| Dew point | 24°C / 75°F | |
| Sunshine | 8.4 h/day | |
| Daylight | 12.2 h | |
| Wind | 22 km/h / 14 mph | |
| Air quality (US AQI) | 27 | 🍃 good |
Monthly averages from ERA5 reanalysis. AQI is the mean US Air Quality Index for the month.
Where is Ko Samui?
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Ko Samui in September — FAQ
- Is September a good time to visit Ko Samui?
- September in Ko Samui: sweltering, soaked, with clean air — a great time to visit. It ranks #10 of 12 months for Ko Samui on SeasonMap's comfort score (73/100).
- What is the weather like in Ko Samui in September?
- In September, Ko Samui averages a daily high of 29°C and a low of 26.6°C, with about 158 mm of rain over roughly 22 rainy days.
- What is the air quality in Ko Samui in September?
- Ko Samui has a mean US Air Quality Index of about 27 in September.