Osan Weather in September
What's the weather like in Osan (Gyeonggi Province) in September 2025?
The climate in Osan during September can be summarized as warm, humid and wet.
September is in the fall / autumn in Osan and is typically the 4th warmest month of the year. Daytime maximum temperatures average around a muggy 26°C (78°F), whilst at night 15°C (59°F) is normal.
| Daytime temperature | 25.5°C 77.8°F |
|---|---|
| Nightly temperature | 14.8°C 58.6°F |
| Average temperature | 20.1°C 68.2°F |
| Daily sunshine | 7.5 hrs |
| Avg rainfall | 143 mm 5.6 ins |
| Rainy days | 8 days |
| Sea temperature | 22.9°C 73.3°F |
| Humidity | 79% |
| Windspeed | 4.7kph 3 mph |
On average September is the 3rd wettest month of the year in Osan with around 143mm 5.6 inches of rain making it a wet time to visit. This rainfall is typically spread over 8 days, although this may vary considerably.
On the flip side this corresponds to an average of 7.5 hours of sunshine per day.
September temperatures in Osan
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 Osan in September 2025.
Other monthly averages
Best places to visit in September
Osan weather stats
| Hottest month: | August | 29.6°C 85.3°F |
|---|---|---|
| Driest month: | December | 25mm 1ins |
| Sunniest month: | October | 7.5hrs |
| Coldest month: | January | 1.2°C 34.2°F |
| Wettest month: | July | 309mm 12.2ins |
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