South Korea is experiencing an increase in extreme hourly rainfall events exceeding 100mm during August and September [1].
These weather patterns signal a shift in seasonal precipitation that threatens infrastructure and public safety as the region moves into autumn.
Recent data shows a trend of high-intensity rain moving later into the year. On Aug. 17, 2026, the city of Geoje experienced record-breaking rainfall [1]. In the southern coastal region of Gyeongsangnam-do, three separate occurrences of rainfall exceeding 100mm per hour were observed [1].
This volatility is not isolated to a single year. In 2023, the country recorded 15 total extreme rain events, with 11 of those occurring specifically between August and September [1]. For the same period in 2026, seven extreme rain events have already been recorded [1].
Atmospheric conditions have further intensified these events. On Sept. 21, 2026, Typhoon Pulasan triggered extreme rain across five southern locations, with each receiving more than 100mm per hour [1].
Weather analysts said the increase is driven by a combination of high sea-surface temperatures and abundant atmospheric moisture. A seasonal shift in atmospheric pressure patterns, compounded by broader climate-change trends, is creating the necessary conditions for these bursts of precipitation [1].
"Extreme heavy rain of more than 100mm per hour has recently become more frequent through August and September," an anchor for YTN said [1].
Experts said the risk of these events will not subside immediately. The combination of high temperatures and atmospheric instability suggests that the danger of extreme rainfall will persist into the autumn months [1].
“Extreme heavy rain of more than 100mm per hour has recently become more frequent through August and September”
The shift of extreme precipitation into late summer and autumn suggests that South Korea's traditional monsoon patterns are evolving. When hourly rainfall exceeds 100mm, urban drainage systems often reach capacity, increasing the risk of flash flooding in densely populated areas like Seoul and coastal hubs like Geoje. This trend indicates that climate-driven sea-surface warming is fueling more intense, localized storms that defy historical seasonal expectations.
