Climate averages 1991–2020
Seosan weather
in September.
A warm, wet month: the 4th warmest and the 10th driest of the year. Meets the pleasant-weather rule
Long-term climate patterns, not a forecast for a particular trip.
September is a warm month in Seosan: daytime highs average 24.2°C and nights cool to about 18.4°C. By daytime temperature it is the 4th warmest of the 12 months.
Expect about 133 mm of rain on roughly 8 days, which makes September a wet month (the 10th driest of the 12 months). Daylight, from sunrise to sunset, lasts about 12 h 27 min on an average September day.
The nearest other city in this atlas is Hongseong (28 km away). In September its highs average 25.1°C, 0.9°C warmer than Seosan, with 145 mm of rain.
Among the 79 cities listed in South Korea, Seosan ranks joint 69th of 79 for the warmest September highs and joint 23rd of 79 for the driest September (rainfall, lowest first). The mean September high of those 79 cities is 24.8°C; Seosan is 0.5°C cooler than that mean.
From September to October, average highs fall by 5.6°C to 18.6°C, and monthly rainfall falls from 133 mm to 55 mm.
The annual picture
September in context
Monthly rainfall
Average total · mmAverages from hourly ERA5 reanalysis data. Actual weather varies from year to year. How these numbers are calculated
Every month, side by side
Seosan climate table
| Month | Average highHigh / low | Average low | Rainfall mm/month | Rain days ≥1 mm/day | Daylight hours/dayDaylight h/day |
|---|---|---|---|---|---|
| January | 2.5°C-2.8°C | -2.8°C | 22 | 4.8 | 9.910 h |
| February | 4.4°C-1.9°C | -1.9°C | 28 | 4.3 | 10.811 h |
| March | 9.0°C1.7°C | 1.7°C | 41 | 5.6 | 11.912 h |
| April | 15.1°C6.8°C | 6.8°C | 69 | 6.8 | 13.113 h |
| May | 20.3°C12.2°C | 12.2°C | 79 | 7.0 | 14.114 h |
| June | 24.6°C17.3°C | 17.3°C | 116 | 7.7 | 14.615 h |
| July | 27.0°C21.9°C | 21.9°C | 245 | 14.8 | 14.414 h |
| August | 27.9°C22.9°C | 22.9°C | 225 | 13.7 | 13.614 h |
| September, selected | 24.2°C18.4°C | 18.4°C | 133 | 7.5 | 12.512 h |
| October | 18.6°C12.3°C | 12.3°C | 55 | 5.3 | 11.311 h |
| November | 11.7°C5.7°C | 5.7°C | 49 | 7.2 | 10.210 h |
| December | 5.0°C-0.5°C | -0.5°C | 26 | 6.1 | 9.710 h |
Rainfall is the average of the 30 separate monthly totals. A rain day is a local calendar day with at least 1 mm of precipitation. Daylight is the calculated sunrise-to-sunset length, not measured sunshine.
Compare places
September in nearby cities
- Hongseong in SeptemberSouth Korea · 28 kmHigh 25.1°C · Low 17.4°C · 145 mm rain
- Asan in SeptemberSouth Korea · 49 kmHigh 25.0°C · Low 17.1°C · 137 mm rain
- Boryeong in SeptemberSouth Korea · 50 kmHigh 24.8°C · Low 18.7°C · 143 mm rain
- Hwaseong-si in SeptemberSouth Korea · 57 kmHigh 23.9°C · Low 18.4°C · 127 mm rain
- Pyeongtaek in SeptemberSouth Korea · 61 kmHigh 24.9°C · Low 17.1°C · 127 mm rain
- Cheonan in SeptemberSouth Korea · 62 kmHigh 25.2°C · Low 17.1°C · 139 mm rain
- Ansan-si in SeptemberSouth Korea · 69 kmHigh 24.3°C · Low 17.8°C · 127 mm rain
- Osan in SeptemberSouth Korea · 69 kmHigh 24.8°C · Low 16.9°C · 124 mm rain
Read the numbers correctly
Climate, not a promise.
These patterns help compare months. They cannot tell you the weather on a specific day of your trip.
Sources, method and limitsHow these numbers are made (what the highs, lows and rain days mean, the sources and the model cell used for Seosan) is explained once on the Seosan year overview and on the Sources, method and limits page.