Pedestrians carrying umbrellas hurry along a street in Seoul as monsoon rain falls on July 21.YONHAP
Why does Korea's weather forecast keep missing the mark? A downpour predicted to drench Seoul on Tuesday instead split the capital in two — parts of the city got 10 times more rain than others, and much of it barely got wet at all.
The Korea Meteorological Administration (KMA) had said Monday afternoon that "very heavy and substantial rain" would fall centered on the central region on Tuesday. It specifically forecast 30 to 50 millimeters (1.2 to 2 inches) of rain per hour in Seoul in the morning, with Incheon and northern Gyeonggi expecting up to 80 millimeters per hour in what it called "extreme downpours."
What actually fell told a different story depending on location. From midnight to noon Tuesday, Eunpyeong District in northern Seoul received 63.5 millimeters of rain, Guro District in southwestern Seoul got 53.5 millimeters and Gangseo District in western Seoul 50.5 millimeters. Gangnam District in southern Seoul saw just 8 millimeters, Gwangjin District in eastern Seoul 6.5 millimeters and Gangdong District, also in eastern Seoul, only 6 millimeters — a roughly tenfold gap within the same city. Incheon and northern Gyeonggi saw meaningful rainfall but not the extreme downpours the agency had warned.
"Trusting the forecast lately makes me feel like a fool," one wrote. "The morning rain they were told to expect simply never came," complained another.
A KMA representative responded that Seoul narrowly missed severe downpours because the storm shifted about 30 kilometers (18.6 miles) to the north. "But when there is a high chance heavy rain will hit some areas, the agency has little choice but to weigh its forecasts toward the more dangerous outcome," the representative explained.
But Tuesday was not an isolated miss. Last Friday, the agency forecast more than 300 millimeters of monsoon rain across the central region over the weekend, but the heaviest rainfall actually fell in Yeongju, North Gyeongsang, at 206.8 millimeters.
A vehicle swept away by the previous day's heavy rain is lodged against Sewol Bridge in Uiseong County, North Gyeongsang, on July 19.YONHAP
The growing gap between forecasts and actual rainfall during monsoon season reflects how much harder these predictions have become, as the causes and shapes of monsoon rain diversify. Narrow, linear rain bands and sudden downpours driven by atmospheric instability have both become more frequent as well.
"Climate change has altered the nature of Korea's monsoon season," said Kim Seung-bae, head of the Korea Natural Disaster Association and former KMA spokesperson. "As the atmosphere has warmed, it has been able to hold more moisture, leading to more frequent and heavier downpours, making rainfall much harder to predict than in the past."
Monsoon rain is expected to continue through the weekend, centered on the central region, but is likely to start and stop unevenly by area. Before heading out, checking real-time radar imagery for rain band movement and using the agency's ultra-short-term precipitation forecasts, updated every 10 minutes, is advised.
"Rainfall associated with the stationary front tends to fluctuate in intensity and shift north and south, so precipitation can vary significantly from one region to another," said KMA forecast analyst Gong Sang-min.
The agency also plans to apply AI to improve prediction accuracy for summer downpours. It will run a pilot of its AI-based ultra-short-term precipitation model, NowAlpha, this summer before putting it into official forecasting use starting in October.
This article was originally written in Korean and translated by a bilingual reporter with the help of generative AI tools. It was then edited by a native English-speaking editor. All AI-assisted translations are reviewed and refined by our newsroom.
