Heavy rain pounded the Seoul metropolitan area overnight, prompting heavy rain advisories for the capital region, Gangwon, and South Chungcheong provinces.
As of 6 a.m. on the 18th, very heavy rain of 20 to 40 millimeters per hour was falling across the Seoul metropolitan area, Gangwon, and South Chungcheong.
Rain had been concentrated in North Gyeongsang Province, with the first disaster-level heavy rain emergency text alert sent to the Jisan-dong area of Suseong-gu, Daegu, at around 10:10 p.m. the previous day. The zone of concentrated rainfall has since shifted to the central region. As a mesoscale low-pressure system developed along the stationary front, large amounts of hot, humid air flowed in from the southwest, dumping rain on the metropolitan area overnight, and rain continues to fall. Air with a precipitable water value—the amount of rain if all water vapor in the air were to fall—reaching 70 millimeters continues to flow in.
Heavy rain emergency text alerts were sent at 3:18 a.m. for Bureumdo (Seodo-myeon) in Ganghwa-gun, Incheon; at 4:29 a.m. for the Deungchon-dong area of Gangseo-gu, Seoul; and at 4:47 a.m. for the Gugi-dong area of Jongno-gu. The alerts were issued because rain fell at more than 50 millimeters over one hour and more than 90 millimeters over three hours. In Seoul's Seodaemun-gu and Yangcheon-gu, rain exceeded 60 millimeters per hour.
Rainfall from midnight to 6 a.m. reached 148.5 millimeters in Yangchon-eup, Gimpo, Gyeonggi Province; 138.0 millimeters in Tanhyeon-myeon, Paju; 135.5 millimeters in Seoul's Gangseo-gu and 128.5 millimeters in Eunpyeong-gu; 121.1 millimeters in Dongducheon, Gyeonggi Province; and 120.5 millimeters in Goyang. As much as nearly 150 millimeters of rain fell on the metropolitan area in a short period.
The heavy rain is only beginning. As of 5 a.m., additional rainfall expected through the 19th is forecast at 100 to 150 millimeters for Gangwon (more than 250 millimeters in parts of inland Gangwon and mountainous areas); 80 to 150 millimeters for the metropolitan area (more than 200 millimeters in some areas); 50 to 100 millimeters for Chungcheong, central North Gyeongsang, and northern North Gyeongsang (more than 200 millimeters in parts of Sejong, northern South Chungcheong, central North Chungcheong, and northern North Chungcheong; more than 150 millimeters in parts of Daejeon, southern South Chungcheong, southern North Chungcheong, and northern North Gyeongsang); 30 to 100 millimeters for the five West Sea islands, North Jeolla, Daegu, southern North Gyeongsang, Ulleungdo, and Dokdo (more than 120 millimeters on the North Jeolla west coast); 30 to 80 millimeters for Gwangju and South Jeolla; 20 to 60 millimeters for Busan, Ulsan, and South Gyeongsang; and 5 to 30 millimeters for Jeju.
Flood Alerts for Seoul's Gangseo, Eunpyeong, Mapo Districts; Dongbu Expressway Controlled
With heavy rain falling across all of Seoul overnight, flood alerts were issued for Gangseo-gu, Eunpyeong-gu, and Mapo-gu. Traffic was also controlled along various roads including the Dongbu Expressway. According to the Seoul city government, as of 7:30 a.m. on the 18th, flood alerts had been issued respectively for Gangseo-gu, Eunpyeong-gu, and Mapo-gu due to the concentrated heavy rain. Flood advisories were issued for Mapo-gu and Yangcheon-gu.
A flood alert is issued when rainfall reaches 50 millimeters or more per hour and 90 millimeters or more over three hours, while a flood advisory is issued when rainfall reaches 55 millimeters or more per hour or 20 millimeters within 15 minutes.
As water levels rose from the strong rain overnight, the Han River Flood Control Office issued a flood watch for the Neobudae Bridge point of the Mokgamcheon stream in Seoul at around 4:50 a.m. and advised preparation in areas at risk of flooding.
While the Korea Forest Service issued a landslide crisis alert at the "caution" level across the entire metropolitan area due to the concentrated heavy rain, Eunpyeong-gu and Dobong-gu issued a landslide advisory and a preliminary landslide alert, respectively. Mapo-gu also banned entry into forests and urged preparation for signs of landslides.
At around 5:37 a.m., as the water level of the Jungnangcheon stream rose amid the heavy rain advisory, traffic was fully halted along the entire Dongbu Expressway (Surak Underpass to Seongsu JC). At around 6:53 a.m., a vehicle fire broke out inside the Yongma Tunnel in Jungnang-gu, and traffic inside the tunnel is being fully controlled.
