Avg High
Seoul in September
Avg Low
Rain
Daylight
12h
What to expect
September in Seoul is early autumn, a shoulder-season window, so you can get a bit of variety across the month. The month is warm and inviting for long walks, with a noticeable cool-down after sunset. The daylight window is balanced for full days without endless late evenings. Most days feel close to what the averages suggest, with straightforward pacing.
September in context
How it compares to the rest of the year in Seoul.
Hottest (avg)
#4 / 12
Wettest (avg)
#4 / 12
Daylight Hours
#6 / 12
Windiest (avg)
#12 / 12
Highest UV
#6 / 12
Most Humid
#3 / 12
Monthly climate breakdown
Temperature
- Daytime high
-
- Nighttime low
-
- Feels like (avg)
-
Sunshine
- Daylight hours
- 12.4 h
- UV index (max)
- 7
- Typical sun hours
- 06:13 - 18:39
Rain & Snow
- Total rain
-
- Rainy days
- 10 days
- Cloud cover (avg)
- 58%
Humidity & Wind
- Humidity (avg)
- 77%
- Wind (avg)
-
- Wind (max gusts)
-
Daily climate explorer
Day 15 selected for September. Typical high 25.9°C and low 17.6°C.
Typical disruptions in September
Based on 30 years of historical data, these are the disruption patterns most likely to affect plans in September.
Rain High impact
Rain disruption Measures: Likely rain disruption days. Observed about 16% of days (4.8 days/month) in September. Historical risk signal only, not a day-by-day forecast.
4.8 days / month
~16% of days
Why this matters
- Expected days 4.8 days / month
- Probability ~16% of days
- Intensity Up to ~68mm (P95)
Rain disruption risk appears on ~5 days. Outdoor plans can become unreliable, so keep an indoor backup and flexibility around start times.
Rain High impact
Washout risk Measures: Washout day risk. Observed about 15% of days (4.6 days/month) in September. Historical risk signal only, not a day-by-day forecast.
4.6 days / month
~15% of days
Why this matters
- Expected days 4.6 days / month
- Probability ~15% of days
- Intensity Up to ~69mm (P95)
Washout conditions are possible on ~5 days. Outdoor plans can become unreliable, so keep an indoor backup and flexibility around start times.
Wind High impact
Stormy conditions Measures: Storm-impact proxy days. Observed about 3% of days (0.8 days/month) in September. Historical risk signal only, not a day-by-day forecast.
0.8 days / month
~3% of days
Why this matters
- Expected days 0.8 days / month
- Probability ~3% of days
- Intensity Up to ~95km/h (P95)
Stormy conditions are possible on ~1 days. Exposed activities and transport links are more likely to be disrupted, so keep sheltered alternatives ready.
Wind High impact
Strong gusts Measures: Strong gust days (>=60 km/h). Observed about 2% of days (0.5 days/month) in September. Historical risk signal only, not a day-by-day forecast.
0.5 days / month
~2% of days
Why this matters
- Expected days 0.5 days / month
- Probability ~2% of days
- Intensity Up to ~96km/h (P95)
Strong gusts are possible on ~1 days. Exposed activities and transport links are more likely to be disrupted, so keep sheltered alternatives ready.
Humidity Moderate
Muggy days Measures: Muggy days (dew point >=20C). Observed about 13% of days (3.9 days/month) in September. Historical risk signal only, not a day-by-day forecast.
3.9 days / month
~13% of days
Why this matters
- Expected days 3.9 days / month
- Probability ~13% of days
- Intensity Up to ~24°C (P95)
Muggy conditions are possible on ~4 days. Fixed-time outdoor plans are safer with a backup option and flexible timing.
Heat Moderate
Hot feels-like days Measures: Hot feels-like days (>=32C). Observed about 8% of days (2.5 days/month) in September. Historical risk signal only, not a day-by-day forecast.
2.5 days / month
~8% of days
Why this matters
- Expected days 2.5 days / month
- Probability ~8% of days
- Intensity Up to ~37°C (P95)
Feels-like heat >=32C is possible on ~3 days. Midday activity often needs adjustment around shade, hydration, and indoor fallback options.
Show all disruptions (21 more)
Rain High impact
Heavy rain days Measures: Heavy rain days (>=10mm). Observed about 12% of days (3.6 days/month) in September. Historical risk signal only, not a day-by-day forecast.
3.6 days / month
~12% of days
Why this matters
- Expected days 3.6 days / month
- Probability ~12% of days
- Intensity Up to ~73mm (P95)
Heavy rain is possible on ~4 days. Outdoor plans can become unreliable, so keep an indoor backup and flexibility around start times.
Rain High impact
Very heavy rain Measures: Very heavy rain days (>=25mm). Observed about 5% of days (1.5 days/month) in September. Historical risk signal only, not a day-by-day forecast.
1.5 days / month
~5% of days
Why this matters
- Expected days 1.5 days / month
- Probability ~5% of days
- Intensity Up to ~95mm (P95)
Very heavy rain is possible on ~2 days. Outdoor plans can become unreliable, so keep an indoor backup and flexibility around start times.
Rain High impact
Washout run Measures: Multi-day washout runs. Observed about 1.1 days/month in September. Historical risk signal only, not a day-by-day forecast.
1.1 days / month
Probability unavailable
Why this matters
- Expected days 1.1 days / month
- Probability —
- Intensity Up to ~80mm (P95)
Multi-day washout runs are possible on ~1 days. Outdoor plans can become unreliable, so keep an indoor backup and flexibility around start times.
Rain High impact
Extreme rain Measures: Extreme rain days (>=50mm). Observed about 2% of days (0.5 days/month) in September. Historical risk signal only, not a day-by-day forecast.
0.5 days / month
~2% of days
Why this matters
- Expected days 0.5 days / month
- Probability ~2% of days
- Intensity Up to ~115mm (P95)
Extreme rain is possible on ~0 days. Outdoor plans can become unreliable, so keep an indoor backup and flexibility around start times.
Visibility Moderate
Fog-likely signal Measures: Fog-likely visibility proxy. Observed about 4% of days (1.2 days/month) in September. Historical risk signal only, not a day-by-day forecast.
1.2 days / month
~4% of days
Why this matters
- Expected days 1.2 days / month
- Probability ~4% of days
- Intensity Up to ~96% (P95)
Fog-likely conditions are possible on ~1 days. Fixed-time outdoor plans are safer with a backup option and flexible timing.
Cloud Minor
Cloudy days Measures: Cloudy days (cloud cover >=60%). Observed about 50% of days (15.0 days/month) in September. Historical risk signal only, not a day-by-day forecast.
15.0 days / month
~50% of days
Why this matters
- Expected days 15.0 days / month
- Probability ~50% of days
- Intensity Up to ~100% (P95)
Cloudy skies are possible on ~15 days. Fixed-time outdoor plans are safer with a backup option and flexible timing.
Rain Minor
Wet days Measures: Wet days (>=0.1mm). Observed about 44% of days (13.1 days/month) in September. Historical risk signal only, not a day-by-day forecast.
13.1 days / month
~44% of days
Why this matters
- Expected days 13.1 days / month
- Probability ~44% of days
- Intensity Up to ~41mm (P95)
Measurable rain is possible on ~13 days. Fixed-time outdoor plans are safer with a backup option and flexible timing.
Humidity Minor
High humidity Measures: High humidity days (RH >=80%). Observed about 43% of days (13.0 days/month) in September. Historical risk signal only, not a day-by-day forecast.
13.0 days / month
~43% of days
Why this matters
- Expected days 13.0 days / month
- Probability ~43% of days
- Intensity Up to ~93% (P95)
High humidity is possible on ~13 days. Comfort and pace can drop quickly, so plan shorter outdoor blocks with air-conditioned backup stops.
Rain Minor
Rainy hours Measures: Rain-hours signal (>=3h rain). Observed about 33% of days (9.8 days/month) in September. Historical risk signal only, not a day-by-day forecast.
9.8 days / month
~33% of days
Why this matters
- Expected days 9.8 days / month
- Probability ~33% of days
- Intensity Up to ~22h (P95)
Several rainy hours are possible on ~10 days. Outdoor plans can become unreliable, so keep an indoor backup and flexibility around start times.
Humidity Minor
Humid days Measures: Humid days (dew point >=18C). Observed about 32% of days (9.7 days/month) in September. Historical risk signal only, not a day-by-day forecast.
9.7 days / month
~32% of days
Why this matters
- Expected days 9.7 days / month
- Probability ~32% of days
- Intensity Up to ~23°C (P95)
Humid conditions are possible on ~10 days. Comfort and pace can drop quickly, so plan shorter outdoor blocks with air-conditioned backup stops.
Cloud Minor
Mostly cloudy days Measures: Mostly cloudy days (cloud cover >=80%). Observed about 31% of days (9.4 days/month) in September. Historical risk signal only, not a day-by-day forecast.
9.4 days / month
~31% of days
Why this matters
- Expected days 9.4 days / month
- Probability ~31% of days
- Intensity Up to ~100% (P95)
Mostly cloudy skies are possible on ~9 days. Fixed-time outdoor plans are safer with a backup option and flexible timing.
Rain Minor
Wet most of day Measures: Wet-most-of-day signal (>=6h rain). Observed about 22% of days (6.5 days/month) in September. Historical risk signal only, not a day-by-day forecast.
6.5 days / month
~22% of days
Why this matters
- Expected days 6.5 days / month
- Probability ~22% of days
- Intensity Up to ~24h (P95)
Wet-most-of-day conditions are possible on ~7 days. Outdoor plans can become unreliable, so keep an indoor backup and flexibility around start times.
Cloud Minor
Overcast days Measures: Overcast days (cloud cover >=95%). Observed about 15% of days (4.5 days/month) in September. Historical risk signal only, not a day-by-day forecast.
4.5 days / month
~15% of days
Why this matters
- Expected days 4.5 days / month
- Probability ~15% of days
- Intensity Up to ~100% (P95)
Overcast skies are possible on ~5 days. Fixed-time outdoor plans are safer with a backup option and flexible timing.
Wind Minor
Gusty days Measures: Gusty days (>=40 km/h). Observed about 12% of days (3.5 days/month) in September. Historical risk signal only, not a day-by-day forecast.
3.5 days / month
~12% of days
Why this matters
- Expected days 3.5 days / month
- Probability ~12% of days
- Intensity Up to ~74km/h (P95)
Gusty conditions are possible on ~4 days. Exposed activities and transport links are more likely to be disrupted, so keep sheltered alternatives ready.
Humidity Minor
Convective risk Measures: Convective storm risk proxy. Observed about 10% of days (3.0 days/month) in September. Historical risk signal only, not a day-by-day forecast.
3.0 days / month
~10% of days
Why this matters
- Expected days 3.0 days / month
- Probability ~10% of days
- Intensity Up to ~24°C (P95)
Convective risk signal appears on ~3 days. Fixed-time outdoor plans are safer with a backup option and flexible timing.
Heat Minor
Warm nights Measures: Warm nights (min >=22C). Observed about 4% of days (1.3 days/month) in September. Historical risk signal only, not a day-by-day forecast.
1.3 days / month
~4% of days
Why this matters
- Expected days 1.3 days / month
- Probability ~4% of days
- Intensity Up to ~24°C (P95)
Warm nights are possible on ~1 days. Fixed-time outdoor plans are safer with a backup option and flexible timing.
Other Minor
Low visibility proxy: same as fog-likely (RH ≥90% AND cloud ≥95%) — true visibility requires hourly visibility data Measures: Low visibility proxy: same as fog-likely (RH ≥90% AND cloud ≥95%) — true visibility requires hourly visibility data. Observed about 4% of days (1.2 days/month) in September. Historical risk signal only, not a day-by-day forecast.
1.2 days / month
~4% of days
Why this matters
- Expected days 1.2 days / month
- Probability ~4% of days
- Intensity Up to ~96 (P95)
Low visibility proxy: same as fog-likely (RH ≥90% AND cloud ≥95%) — true visibility requires hourly visibility data is possible on ~1 days. Fixed-time outdoor plans are safer with a backup option and flexible timing.
Heat Minor
Hot days Measures: Hot days (>=30C). Observed about 2% of days (0.7 days/month) in September. Historical risk signal only, not a day-by-day forecast.
0.7 days / month
~2% of days
Why this matters
- Expected days 0.7 days / month
- Probability ~2% of days
- Intensity Up to ~32°C (P95)
Hot days are possible on ~1 days. Midday activity often needs adjustment around shade, hydration, and indoor fallback options.
Heat Minor
Very hot feels-like Measures: Very hot feels-like days (>=35C). Observed about 2% of days (0.5 days/month) in September. Historical risk signal only, not a day-by-day forecast.
0.5 days / month
~2% of days
Why this matters
- Expected days 0.5 days / month
- Probability ~2% of days
- Intensity Up to ~38°C (P95)
Very hot feels-like conditions are possible on ~0 days. Midday activity often needs adjustment around shade, hydration, and indoor fallback options.
Heat Minor
Heat stress risk Measures: High heat stress days. Observed about 2% of days (0.5 days/month) in September. Historical risk signal only, not a day-by-day forecast.
0.5 days / month
~2% of days
Why this matters
- Expected days 0.5 days / month
- Probability ~2% of days
- Intensity Up to ~38°C (P95)
Heat stress is possible on ~0 days. Midday activity often needs adjustment around shade, hydration, and indoor fallback options.
Heat Minor
Feels-like heatwave Measures: Feels-like heatwave runs (>=3 days). Observed about 0.4 days/month in September. Historical risk signal only, not a day-by-day forecast.
0.4 days / month
Probability unavailable
Why this matters
- Expected days 0.4 days / month
- Probability —
- Intensity Up to ~36°C (P95)
Feels-like heatwave runs are possible on ~0 days. Midday activity often needs adjustment around shade, hydration, and indoor fallback options.
Frequently asked questions
Is September a good time to visit Seoul?
Typical September days in Seoul reach highs of 25°C (77°F) with nights around 17°C (63°F). It usually feels warm by day and mild after dark. Overall, September sits in the middle of the Seoul climate range.
What are temperatures like in September?
Daytime temperatures in September typically peak near 25°C (77°F), while nights drop to around 17°C (63°F). Expect warm afternoons and mild evenings.
How much does it rain in September?
Rainfall in September averages 128 mm (5.0 in) across roughly 10 days. Overall it is a quite rainy time of year, so a light rain jacket and waterproof shoes are very handy.
How many hours of daylight are there in September?
You can expect about 12 hours of daylight in September. Sunrise is typically around 06:13 and sunset near 18:39. Daylight is fairly typical, with enough time for sightseeing.
How strong is the sun in September?
UV levels are often high (around 7). Regular sunscreen and a hat are recommended.
Is it windy in September?
In September, average wind speeds are around 8 km/h (5 mph), with gusts on the windiest days reaching about 41 km/h (25 mph). On the ground, it is it often feels breezy, especially in more exposed spots or along the coast.