Sejong weather in September

In September, Sejong sees average daytime highs of 26°C and overnight lows near 17°C, with 143 mm of rain across 8.5 wet days and about 12.2 hours of daylight. It is the 4th-warmest and 3rd-wettest month of the year here.

Highs ease over the month, from about 28°C in the first days to 24°C by the end. The sky is clear or mostly clear about 33% of the time in September, and the air most often feels humid.

Daylight stretches from about 12 h 48 min at the start of September to 11 h 42 min by month's end. Set against the rest of the year, September is Sejong's 9th-clearest and 11th-windiest month. For the whole year in context, see Sejong's year-round climate.

Daytime high
26°
4th warmest
Overnight low
17°
9th coldest
Rainfall
143 mm
8.5 wet days
Daylight
12 h 12 min
6:18 AM – 6:32 PM
Cloud cover
58%
9th clearest
Wind
8 km/h
11th windiest
Solar energy
4.22 kWh/m²
Travel score
6.8
out of 10

Temperature in September

Average highAverage lowShaded bands: 10–90% of days

Highs ease over the month, from about 28°C in the first days to 24°C by the end.

A typical September day in Sejong reaches about 26°C in the afternoon and slips back to 17°C overnight — a 9°C spread between the day's warmth and the night's chill. On most days the high lands between 22°C and 29°C. Set against its neighbours, September runs about 4°C cooler than August and about 6°C warmer than October.

10°20°30°151015202530
Avg high (°C)Avg low (°C)
12820
22820
32820
42819
52819
62719
72719
82719
92718
102718
112718
122718
132618
142617
152617
162617
172617
182616
192616
202516
212516
222515
232515
242515
252515
262414
272414
282414
292414
302414

How September really feels in Sejong

Once humidity and wind are folded in, September averages 0 days that feel above 32°C and 0 that feel at or below 0°C — the comfort signal a plain temperature reading hides.

Days feeling ≥ 32°C
0
heat index over the day's high
Days feeling ≤ C
0
wind chill below the day's low

September sits comfortably in between — no days that feel dangerously hot or drop to a hard freeze once humidity and wind are folded in.

Sejong weather by month

How September compares with the rest of the year at a glance. September is the 4th-warmest and 3rd-wettest month here — the current month is highlighted below.

MonthHigh / Low (°C)Rainfall (mm)Wet daysSnow daysDaylight (hours)Travel score
Jan / -5°224.32.29.80.0
Feb / -3°304.31.510.60.7
Mar12° / 496.71.111.73.6
Apr19° / 797.4012.96.5
May24° / 13°867.5013.97.2
Jun28° / 18°1228.5014.56.1
Jul29° / 22°25616.1014.24.5
Aug30° / 22°22615013.44.4
Sep26° / 17°1438.5012.26.8
Oct20° / 10°584.8011.17.4
Nov13° / 435.90.2104.0
Dec / -3°234.51.49.50.5

Cloud cover in September

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 33% of the time in September.

Beyond those clear spells, partly cloudy skies cover about 15% of September, with mostly cloudy or overcast conditions the remaining 52%. Skies tend to open up as the month goes on.

0%25%50%75%100%151015202530
Clearer (%)Cloudier (%)
14258
24258
34258
44357
54357
64357
74456
84456
94456
104555
114555
124555
134654
144654
154753
164753
174852
184951
195050
205050
215149
225248
235248
245248
255248
265347
275347
285446
295446
305545

Chance of precipitation in September

Any precipitation

Sejong gets around 143 mm of rain over 8.5 wet days in September. The line is the day-by-day chance of measurable precipitation.

Day to day, the chance of measurable rain averages around 29% and peaks near 42% on the wettest days. The odds ease toward the end of the month.

0%10%20%30%40%50%151015202530
Rain chance (%)
142
241
340
439
538
637
736
835
934
1033
1132
1232
1331
1430
1529
1628
1727
1826
1925
2024
2124
2223
2323
2422
2522
2621
2721
2820
2920
3019

Humidity in September

DryComfortableHumidMuggyOppressiveMiserable

Most of September feels humid — the stacked bands show each day's mix of comfort levels, read off the dew point.

By dew point, September lands in the humid band about 29% of days. Sticky, muggy-or-worse air turns up on roughly 26% of them.

0%25%50%75%100%151015202530
Dry (%)Comfortable (%)Humid (%)Muggy (%)Oppressive (%)Miserable (%)
11112932252
22123131232
32123330221
43133429201
53143628181
64153727171
75163726151
86173826130
97183825120
108193824110
111020382390
121221372280
131422362170
141623342060
151825331960
162026311850
172227301640
182428291540
192630271430
202931261220
213131251120
223332231020
23353322910
24373321810
25393320710
26423319610
27443218510
28463217500
29493116400
30513015400

Wind in September

Winds average 8 km/h in September.

Across September, daily wind ranges from about 8 km/h on the calmest days to 8 km/h at its breeziest. It stays fairly steady from day to day.

051015151015202530
Wind speed (km/h)Feels
18calm
28calm
38calm
48calm
58calm
68calm
78calm
88calm
98calm
108calm
118calm
128calm
138calm
148calm
158calm
168calm
178calm
188calm
198calm
208calm
218calm
228calm
238calm
248calm
258calm
268calm
278calm
288calm
298calm
308calm

Sunrise & sunset in September

DaylightNight

Daylight runs from about 12 h 48 min at the start of September to 11 h 42 min by month's end. The lit band spans sunrise to sunset each day.

Days shrink by about 66 minutes over September. Sunrise moves from 6:06 AM to 6:30 AM, and sunset from 6:55 PM to 6:10 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202530
Daylight (h)Sunrise (AM)Sunset (PM)
112.86:066:55
212.86:076:54
312.76:086:52
412.76:086:51
512.76:096:49
612.66:106:48
712.66:116:46
812.56:126:44
912.56:136:43
1012.56:136:41
1112.46:146:40
1212.46:156:38
1312.36:166:37
1412.36:176:35
1512.36:176:34
1612.26:186:32
1712.26:196:30
1812.16:206:29
1912.16:216:27
2012.16:226:26
2112.06:226:24
2212.06:236:23
2312.06:246:21
2411.96:256:20
2511.96:266:18
2611.86:276:16
2711.86:276:15
2811.86:286:13
2911.76:296:12
3011.76:306:10

Solar energy in September

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in September, about 4.22 kWh/m².

For context, solar energy here swings from a low near 2.3 kWh/m² to a high of 5.89 kWh/m² in May across the year — September's 4.22 kWh/m² falls in the middle.

012345151015202530
Solar energy (kWh/m²)Level
14.3Bright
24.3Bright
34.3Bright
44.3Bright
54.3Bright
64.3Bright
74.2Bright
84.2Bright
94.2Bright
104.2Bright
114.2Bright
124.2Bright
134.2Bright
144.2Bright
154.2Bright
164.2Bright
174.2Bright
184.2Bright
194.2Bright
204.2Bright
214.2Bright
224.2Bright
234.2Bright
244.1Bright
254.1Bright
264.1Bright
274.1Bright
284.1Bright
294.1Bright
304.1Bright
Planning a trip in September

Hazard calendar for Sejong

In seasonPeak

In September, Sejong sits inside its rainy season season. The full year is below, with each hazard's peak months called out.

Sejong's rainy season runs June–September, when most of the year's rain falls.

Rainy season
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec

Is September a good time to visit Sejong?

Our two travel scores rate September for general sightseeing and for beach or pool weather — 0 (poor) to 10 (ideal).

6.8
Sightseeing
3rd-best month of the year
6.5
Beach & pool
2nd-best month of the year

September is a reasonable time to visit Sejong for sightseeing. The water and warmth also suit a beach or pool day.

What to pack for Sejong in September

From September's temperature range, rain chance, sun and wind — what's worth putting in the bag.

In September, Sejong sees daytime highs around 26°C and nights near 17°C. Worth packing: light clothes and rain gear. About 9 days see rain.

light clothesrain gear

UV index in Sejong in September

LowModerateHighVery highExtreme

Clear-sky midday UV in September peaks around 8 — enough to warrant sun protection. The full-year curve, shaded by WHO exposure level, is below.

Under clear skies, the midday UV index in Sejong peaks around August 14 at about 8 (very high) — sunscreen, a hat and midday shade are essential. It bottoms out near December 23 at about 2 (moderate).

The index reaches 3 or more — the level where the WHO recommends sun protection — in 10 months of the year.

025710JanFebMarAprMayJunJulAugSepOctNovDecModerateHighVery highHighModerateAug 14UV 8Dec 23UV 2
UV index (midday)Level
Jan2Moderate
Feb3Moderate
Mar5Moderate
Apr6High
May7High
Jun7Very high
Jul8Very high
Aug8Very high
Sep8Very high
Oct5High
Nov3Moderate
Dec2Low

Air quality in Sejong in September

GoodModeratePoorUnhealthyVery unhealthy

Average fine-particle pollution (PM2.5) through the year — so you can see where September falls, not just the annual average.

Air quality in Sejong is worst in March — around 80 µg/m³ PM2.5 (unhealthy), about 1.8× the cleanest month (July, 45 µg/m³).

Modeled monthly averages (CAMS reanalysis, 2015–2024).

0306090JanFebMarAprMayJunJulAugSepOctNovDecUnhealthyPoorUnhealthyMar 1479 µg/m³Jul 2345 µg/m³
PM2.5 (µg/m³)Level
Jan69Unhealthy
Feb72Unhealthy
Mar80Unhealthy
Apr65Unhealthy
May58Unhealthy
Jun54Poor
Jul45Poor
Aug45Poor
Sep56Unhealthy
Oct67Unhealthy
Nov72Unhealthy
Dec65Unhealthy
Location & terrain

Where is Sejong?

Sejong sits at 36.6°N, 127.3°E, 49 m above sea level, in South Korea. The nearest listed city is Cheongju-si, 18 km away.

Seonghwan

Topography around Sejong

How much the land rises and falls, and what covers it, within 3, 16 and 80 km of Sejong.

Within 3 km, the terrain around Sejong has only modest variations in elevation — a maximum elevation change of 148 m around an average of 39 m above sea level; within 16 km, significant variations in elevation — a maximum elevation change of 445 m; within 80 km, very significant variations in elevation — a maximum elevation change of 1,213 m.

The land around Sejong is covered by cropland (43%), artificial surfaces (28%) and trees (21%) within 3 km, trees (54%) and cropland (22%) within 16 km, and trees (62%) and cropland (23%) within 80 km.

3 km
148 m
16 km
445 m
80 km
1,213 m
treesgrasslandcroplandartificial surfacesbare terrainwater
September weather nearby: Cheongju-si 18 km · Gongju 21 km · Cheonan 27 km · Daejeon 28 km · Chinch'ŏn 32 km · Asan 33 km · Jungpyong 34 km · Seonghwan 39 km

South Korea travel facts

Travel advisory
Level 1
Exercise Normal Precautions
Power plugs
Type C / F
220 V · 60 Hz
Prices
≈ 57% of US
price level, 2025
GDP per capita
$36,227
2025
Happiness
6.0 / 10
World Happiness, 2025
Safe drinking water
99%
of population, 2024
Homicide rate
0.5
per 100k, 2023
Road deaths
8.6
per 100k/yr, 2019
Income group
High
World Bank
English
Moderate
EF EPI 522
Religion
none 60%Protestant 17%Buddhist 16%Catholic 6%

Sources: World Bank, US State Department, World Happiness Report, WHO/UNICEF, EF EPI, CIA World Factbook.

Data sources

Temperature, precipitation, cloud, humidity, wind and solar figures are a 1991–2020 climatology for Sejong (36.5924°, 127.2922°, elevation 49 m), computed from hourly ERA5 reanalysis — contains modified Copernicus Climate Change Service information. Sun figures are astronomical calculations, not observations. City data © GeoNames, CC BY 4.0. Map outlines from Natural Earth (public domain); interactive map © Google. UV index is derived from CAMS (Copernicus Atmosphere Monitoring Service) clear-sky UV data — contains modified Copernicus Atmosphere Monitoring Service information. Monthly air-quality (PM2.5) seasonality is from the CAMS EAC4 reanalysis (Copernicus Atmosphere Monitoring Service), scaled to the WHO annual mean where available. Topography is sampled from the Copernicus DEM GLO-90 elevation model (© ESA/Airbus) and ESA WorldCover 2021 land cover (CC BY 4.0).