Rain And Chilly Temperatures Sweep South Korea Monday

As South Korea approaches the end of September, residents are bracing for a distinct shift in weather, with a cool snap and bouts of rain forecasted for Monday, September 29, 2025. According to the Korea Meteorological Administration (KMA), a combination of lingering precipitation and falling temperatures will define the start of the week for much of the country, especially in the southern coastal regions and Jeju-do.

For those waking up in Seoul and its surrounding areas, the morning will greet them with a brisk chill. The KMA predicts that the morning low in Seoul will dip to 17 degrees Celsius—a temperature that, while not quite wintery, marks a notable change from the milder nights of recent weeks. This coolness will be echoed across other major cities: Incheon is set for a low of 18°C, Busan 20°C, and Jeju 22°C. Most regions will see morning lows range between 15 and 20 degrees Celsius, a range that’s fairly typical for late September but still a reminder that autumn is firmly settling in. By afternoon, temperatures are expected to climb, with highs between 23 and 27 degrees Celsius. Seoul should top out at 25°C, while Busan could reach as high as 27°C, and Jeju will hover around 26°C.

But it’s not just the temperature that will have South Koreans reaching for an extra layer or two. Rainfall is also in the cards, especially for the southern coastal areas and Jeju-do. According to Yonhap News, “the southern coastal areas and Jeju-do are expected to have rain until the morning of September 29.” The forecast calls for intermittent showers and drizzle through the early hours, so those in these regions would be wise to keep an umbrella handy for their morning commute or school run. The KMA has also warned that in Jeju-do, rain and drizzle may be mixed, making conditions particularly slippery and visibility potentially reduced—caution is advised, especially for those involved in marine and fishing activities.

Precipitation amounts are expected to vary by region. The Jeollanam-do area is forecast to receive between 10 and 40 mm of rain, while Jeju-do could see anywhere from 10 to 60 mm by the end of the day. Chungcheong and Gyeongsang regions, meanwhile, are likely to experience lighter drizzle, with about 5 mm expected. These figures were echoed by both MoneyS and Edaily, which noted that “regional precipitation is forecasted to be 10 to 40 mm in Gyeonggi and Chungcheong areas, and 10 to 60 mm in Jeju-do.”

As the day progresses, the skies will remain mostly cloudy over the central region, while the southern and coastal areas will see a mix of clouds and occasional clear patches. The KMA expects “the central region will have many clouds and the southern coastal areas and Jeju-do will have many clouds as well,” according to Yonhap News. For those in the central-western and northern Gyeonggi areas, a brief spell of drizzle—about 5 mm—is likely between 3 PM and 6 PM. Similarly, the northern and central-northern mountainous areas of Gyeonggi and Chungcheong could see light showers late in the afternoon.

While the rain is expected to taper off by midday in Jeju-do and the southern coastal areas, the aftermath will leave the air feeling noticeably cooler. Edaily highlights that “after the rain, the temperature will drop significantly, and Monday morning will be chilly, especially in the Seoul metropolitan area, where the lowest temperature will fall to 17 degrees.” For many, this will be the first real taste of autumn’s crispness, signaling a transition away from the lingering warmth of early fall.

Amid these shifting weather patterns, the KMA has issued several cautions. In Jeju-do, there’s a risk of thunderstorms and gusty winds, particularly over the sea. Mariners and those involved in fishing are advised to monitor conditions closely. The agency notes, “there are areas where rain and drizzle are mixed, so caution is required in marine and fishing activities.” The southern sea and southern coastal areas may also experience waves driven by swells, with the possibility of high surf reaching beaches or even washing over coastal rocks. For those venturing out to sea or working along the coast, vigilance is key.

Despite the unsettled weather, there’s some good news for those concerned about air quality. The KMA forecasts that “fine dust levels across all regions are expected to be 'good to normal',” thanks to strong atmospheric dispersion. This should provide a welcome respite for sensitive groups and outdoor enthusiasts alike, who can enjoy the crisp autumn air without worrying about pollution.

Looking at the broader meteorological setup, South Korea finds itself on the edge of a high-pressure system moving eastward from central China. This system is responsible for the generally cloudy conditions in the north and the scattered showers further south. As the day unfolds, a trough will influence the central and northern regions, bringing the possibility of brief, localized showers.

The sea conditions are also worth noting. According to Yonhap News, “the waves in the East Sea will range from 0.5 to 1.5 meters, while the West Sea and South Sea will see waves of 0.5 to 1.0 meters.” In offshore areas up to 200 kilometers from the coastline, wave heights could reach up to 2.0 meters in the East Sea and 1.5 meters in the West and South Seas. While not extreme, these conditions could pose challenges for smaller vessels or those unaccustomed to choppier waters.

For those planning their day by region, the morning and afternoon weather outlooks are as follows: Seoul is expected to start clear, becoming cloudier by afternoon, with temperatures ranging from 17 to 25°C. Incheon will remain mostly clear, also with a mild temperature swing. Cities like Gwangju and Jeonju will see more cloud cover, and Jeju will start the day with scattered rain before transitioning to cloudy skies, with highs up to 26°C. Busan, meanwhile, is set for a cloudy day, with temperatures peaking at 27°C.

In summary, Monday, September 29, will bring a blend of rain, clouds, and a noticeable drop in temperatures across South Korea. While conditions will vary from region to region, the overall theme is one of transition—from the last echoes of summer to the unmistakable onset of autumn. For most, it means dressing a bit warmer, keeping an umbrella at the ready, and perhaps savoring the fresh, clean air that often follows a good rain. The KMA’s detailed forecasts and timely warnings ensure that, come rain or shine, South Koreans can step into the new week prepared for whatever the weather has in store.