Last updated: October 30, 2025
Seoul, South Korea, experiences a dynamic September characterized by warm temperatures and significant humidity. With a maximum of 31°C (88°F) and an average temperature of 21°C (70°F), the month offers a pleasant blend of warmth and cool evenings, dipping to a minimum of 10°C (50°F). However, expect 133 mm (5.2 in) of rainfall over 9 days, contributing to a humidity level of 77% that may enhance the feel of warmth. This mix of conditions sets the stage for a vibrant autumn transition, making September an intriguing month in Seoul’s climate calendar.
As September arrives in Seoul, South Korea, the city begins its transition from the sweltering summer heat to a more moderate fall climate. With minimum temperatures hovering around 10°C (50°F) and averaging 21°C (70°F), the month offers a pleasant retreat from the scorching August, which often sees highs reaching 38°C (101°F). This shift is accentuated by the maximum temperatures falling to a comfortable 31°C (88°F), creating a perfect environment for outdoor activities and sightseeing. September’s weather presents a gentle balance, inviting residents and visitors alike to enjoy the stunning autumn foliage while basking in the warmth of the sun during the day and cool breezes at night.
September in Seoul witnesses a significant drop in rainfall compared to the heavy downpours of the preceding months. With 133 mm (5.2 in) of precipitation spread across 9 days, it marks a shift from the height of summer rains in July and August, which boast over 250 mm. This reduction in precipitation heralds the transition into autumn, characterized by cooler temperatures and clearer skies. The shifting patterns not only ease the humidity but also offer a refreshing respite, paving the way for the colorful foliage that Seoul is famous for in the months ahead. Despite the decrease, September still holds its own in rainfall, suggesting that monsoon influences linger, balancing beautifully with the onset of the fall season.
As summer fades and September arrives in Seoul, South Korea, the city's humidity takes a noticeable dip to 77%, marking a refreshing change from the sweltering, muggy days of July and August, which both soar to a staggering 91%. This decrease signifies the transition into autumn, as the humidity levels ease, reminiscent of the slightly drier conditions seen in early spring. The trend throughout the year reveals that while humidity peaks in the summer months, it maintains a relatively high average, reminding residents of Seoul's subtropical climate. With October following closely at 79%, the air remains pleasantly crisp, setting the stage for the vibrant fall foliage that captivates the city.
As September unfolds in Seoul, South Korea, the UV Index reflects a significant transition toward the end of summer. With a UV Index of 9, categorized as very high, this month necessitates caution as the burn time decreases to just 15 minutes. This marks a slight drop from the extreme levels seen in July and August, where an index of 11 demanded even more vigilance. Although the UV levels in September are still perilously high, it signals a gradual return to moderate exposure levels that will come with the cooler months ahead. For those venturing outdoors, it's essential to stay informed and protect your skin adequately during this time. For more details, check the Seoul UV Index.
UV Risk Categories
As summer fades, September in Seoul welcomes a gentle shift in daylight, with an average of 262 hours of sunshine lighting up the city. This month continues the trend of abundant sunlight established in the preceding summer months, although it does see a slight dip from the peak hours recorded in June. The gradual decrease from the vibrant summer reflects the transition into autumn, yet September still boasts more sunshine than several spring and late autumn months like November. Notably, May and June, with their 311 and 317 hours respectively, set the stage for the sunny days enjoyed throughout the summer, while September gracefully ushers in a beautiful, softer light that prepares the city for the colorful foliage of autumn.
September in Seoul, South Korea, offers a refreshing shift in weather patterns, with a 41% chance of sunny days. This marks a slight increase from the peak summer months of July and August, both sitting at only 30%. As the city transitions from the sweltering heat to the more temperate days of autumn, September often sees more favorable weather for outdoor activities. Although the likelihood of sunshine is lower than in the early months of the year, such as November and December, which boast chances of 58% and 64% respectively, September serves as a pleasant bridge toward the clearer skies of fall. With the days gradually becoming brighter and milder, it’s an opportune time to enjoy the city's stunning landscapes as they begin to change colors.
In September, Seoul begins to transition from the vibrant summer days into the crispness of autumn, with daylight lasting approximately 12 hours. This marks a slight reduction from the 13 hours of sunlight experienced in August, indicating the gradual shortening of days as the season changes. Following a steady climb from the 9 hours in January to a peak of 14 hours in June and July, this subtle dip in September hints at the impending arrival of fall. As the month progresses, residents can expect a rich tapestry of colors in the foliage, illuminated by the softer and gradually waning daylight, heralding the beauty and change that autumn brings.
As September unfolds in Seoul, the winds become a gentle whisper of change, with an average speed of 2.4 m/s (5 mph). This slight increase from the summer months—where July and August flaunted the calmest breezes at 1.8 m/s (4 mph) and 2.2 m/s (5 mph)—suggests a transition towards the more invigorating breezes of autumn. While the winds are still relatively mild compared to the brisk gusts of winter, September's winds carry a refreshing chill, hinting at the vibrant colors soon to grace the city's landscapes. This month serves as a delightful bridge between the languid summer heat and the invigorating cool of fall, making it a perfect time to enjoy the outdoors as the breeze begins to stir.
Weather in Seoul varies notably across the year, with each month offering distinct climate conditions. This page compares September’s weather to other months in Seoul, focusing on differences in temperature, rainfall, humidity, and UV levels.
September and January present strikingly different weather profiles. In September, temperatures range from a mild 10°C (50°F) at night to a warm 31°C (88°F) during the day, with an average of 21°C (70°F). The month sees considerable rainfall, totaling 133 mm (5.2 in) over about 9 days, and humidity levels are relatively high at 77%. In contrast, January experiences frigid conditions, with temperatures dropping as low as -18°C (1°F) and peaking at only 13°C (55°F), averaging -2°C (28°F). Precipitation is minimal, at just 19 mm (0.8 in) over 2 days, and the humidity is lower, at 71%. For more details, check out Seoul weather in January.
September and February present contrasting weather conditions. In September, temperatures range from a mild 10°C (50°F) at night to a warm 31°C (88°F) during the day, with an average of around 21°C (70°F). This month also experiences a significant amount of rainfall, totaling 133 mm (5.2 in) over about 9 days, accompanied by a high humidity level of 77%. In contrast, February is much colder, with temperatures dipping as low as -14°C (7°F) and averaging around 0°C (32°F), peaking at 18°C (65°F). Precipitation is minimal in February, with only 22 mm (0.8 in) falling over just 4 days, and humidity is notably lower at 65%. For more detailed information on February weather, check out Seoul weather in February.
September and March present contrasting weather patterns, reflecting the transition from summer to autumn and winter to spring, respectively. In September, temperatures range from a comfortable 10°C (50°F) to a warm 31°C (88°F), with an average of 21°C (70°F). The month sees significant rainfall, totaling 133 mm (5.2 in) over 9 days, accompanied by a high humidity level of 77%. In contrast, March experiences much cooler temperatures, with a minimum of -7°C (20°F) and a maximum of 21°C (70°F), resulting in an average temperature of only 7°C (44°F). Precipitation is lighter, totaling 46 mm (1.8 in) over just 5 days, and humidity is lower at 65%. For further details on March weather, visit Seoul weather in March.
The weather in September is generally warmer than in April, with September's temperatures ranging from a chilly 10°C (50°F) to a hot 31°C (88°F), whereas April experiences a minimum of 0°C (32°F) and a maximum of 28°C (82°F). Additionally, September tends to be wetter, receiving 133 mm (5.2 in) of precipitation over approximately 9 days, compared to April's lighter showers totaling 55 mm (2.2 in) across 6 days. Humidity levels are relatively similar, being slightly higher in September at 77% compared to 75% in April. For more details, you can check Seoul weather in April.
In comparing the weather of September and May, we see some notable differences and similarities. September experiences a wider temperature range, with minimums around 10°C (50°F) and maximums reaching up to 31°C (88°F), while May has slightly cooler temperatures, ranging from a minimum of 6°C (43°F) to a maximum of 32°C (89°F). Both months have similar average temperatures, with September at 21°C (70°F) and May at 18°C (64°F). Despite having similar precipitation days—nine in each month—September receives slightly more rain, totaling 133 mm (5.2 in) compared to May's 111 mm (4.4 in). Additionally, humidity levels are quite close, with September at 77% and May at 81%. For more detailed insights, you can check Seoul weather in May.
September and June exhibit notable differences in weather patterns. In September, temperatures range from a minimum of 10°C (50°F) to a maximum of 31°C (88°F), with an average of 21°C (70°F). The month is characterized by higher precipitation, totaling 133 mm (5.2 in) over 9 days, and a humidity level of 77%. In contrast, June tends to be warmer, with a minimum temperature of 12°C (54°F), an average of 22°C (72°F), and a maximum reaching 35°C (94°F). Precipitation in June is lower at 86 mm (3.4 in), occurring over 8 days, and humidity is slightly higher at 85%. For more detailed insights, check out Seoul weather in June.
When comparing the weather in September to that of July, there are notable differences in temperature, precipitation, and humidity. September experiences milder temperatures, with a minimum of 10°C (50°F) and an average of 21°C (70°F), in stark contrast to July's warmer range of 18°C (64°F) to a maximum of 36°C (97°F). Additionally, September sees less overall precipitation, totaling 133 mm (5.2 in) over 9 days, compared to July's 252 mm (9.9 in) across 15 days. Humidity levels are also higher in July at 91%, compared to 77% in September. For more detailed information, you can refer to Seoul weather in July.
In comparing the weather between August and September, we see a noticeable shift in both temperature and precipitation. August tends to be warmer, with average temperatures reaching about 26°C (80°F) and maximums peaking at 38°C (101°F). This month also experiences higher humidity at 91% and significant rainfall, totaling 269 mm (10.6 in) over 16 days. In contrast, September cools down considerably, with average temperatures dropping to 21°C (70°F), and maximums reaching 31°C (88°F). The month sees a decrease in both precipitation and humidity, with 133 mm (5.2 in) of rain over just 9 days. For more detailed information, you can check Seoul weather in August.
September and October present a notable shift in weather. September boasts warmer temperatures, with minimums around 10°C (50°F) and maximums reaching 31°C (88°F), maintaining an average of 21°C (70°F). Precipitation is relatively high, with 133 mm (5.2 in) falling across 9 days, and humidity levels at 77%. In contrast, October cools down significantly, featuring a minimum temperature of 0°C (32°F) and a more moderate maximum of 28°C (83°F), resulting in an average of 14°C (58°F). Although the month experiences less rainfall—63 mm (2.5 in) over 6 days—humidity slightly increases to 79%. For more details, you can check out the Seoul weather in October.
September and November showcase a stark contrast in weather patterns. September enjoys warmer temperatures, with minimums around 10°C (50°F) and maximums peaking at 31°C (88°F), while averaging a comfortable 21°C (70°F). The month also experiences higher rainfall, totaling 133 mm (5.2 in) over about 9 days, coupled with a humidity level of 77%. In contrast, November ushers in a chill, with temperatures dropping significantly, featuring minimums of -7°C (21°F) and an average temperature of just 7°C (45°F). Though the maximum reaches a mild 21°C (70°F), November sees much less precipitation, with only 54 mm (2.1 in) falling over 5 days and humidity slightly rising to 80%. For more details, visit Seoul weather in November.
September and December present strikingly different weather conditions in Seoul. In September, temperatures range from a pleasant minimum of 10°C (50°F) to a warm maximum of 31°C (88°F), with an average of 21°C (70°F). Humidity is relatively high at 77%, and the month receives considerable rainfall, totaling 133 mm (5.2 in) over about 9 days. In contrast, December brings much colder weather, with temperatures dropping to a minimum of -15°C (5°F) and only reaching an average of -1°C (31°F), peaking at 12°C (54°F). This winter month sees a significant decrease in precipitation, recording just 22 mm (0.9 in) across 4 days, and humidity remains slightly lower at 74%. For more detailed insights, you can explore Seoul weather in December.
As September unfolds in Seoul, the weather transitions from the sweltering summer heat to the refreshing embrace of autumn. With an average temperature of around 21°C (70°F), the month is marked by a notable drop in humidity compared to the peak summer months, making the atmosphere feel more comfortable. However, occasional rain showers, totaling about 133 mm, bring much-needed moisture and a vibrant backdrop to the changing leaves. This unique blend of warmth and coolness, coupled with the onset of a more temperate climate, sets September apart as a delightful prelude to the crispness of fall. For a detailed look at the city's climate, visit Seoul Climate.