Ko Samui Weather in September
What's the weather like in Ko Samui (Surat Thani) in September 2025?
The climate in Ko Samui during September can be summarized as hot, humid and wet.
September is in the fall / autumn in Ko Samui and is typically the 6th warmest month of the year. Daytime maximum temperatures average around a steamy 31°C (87°F), whilst at night 24°C (75°F) is normal.
| Daytime temperature | 30.8°C 87.4°F |
|---|---|
| Nightly temperature | 23.6°C 74.5°F |
| Average temperature | 27.2°C 81°F |
| Daily sunshine | 5.9 hrs |
| Avg rainfall | 141 mm 5.5 ins |
| Rainy days | 17 days |
| Sea temperature | 29.1°C 84.4°F |
| Humidity | 78% |
| Windspeed | 7.2kph 5 mph |
On average September is the 6th wettest month of the year in Ko Samui with around 141mm 5.5 inches of rain making it a wet time to visit. This rainfall is typically spread over 17 days, although this may vary considerably.
On the flip side this corresponds to an average of 5.9 hours of sunshine per day.
September temperatures in Ko Samui
September rainfall
September hourly sunshine
The data used in these monthly averages covers a period of over 100 years right up until last year. As such they are a valid prediction of what to expect for the weather in Ko Samui in September 2025.
Other monthly averages
Best places to visit in September
Ko Samui weather stats
| Hottest month: | April | 31.6°C 88.9°F |
|---|---|---|
| Driest month: | February | 39mm 1.5ins |
| Sunniest month: | February | 8.7hrs |
| Coldest month: | January | 28.4°C 83.1°F |
| Wettest month: | November | 463mm 18.2ins |
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