A deluge struck Geoje in South Gyeongsang Province on Monday, dumping more than 570mm of rain in a single day — a record not just for the city but among all weather stations nationwide.
By 1 p.m. Monday, Geoje had recorded 577.4mm of rainfall for the day.
That figure set an all-time single-day record for Geoje since weather observations began there on Jan. 24, 1972. It also ranks as the third-highest single-day rainfall ever recorded among the 97 synoptic weather observation stations tracked by the Korea Meteorological Administration.
Only two readings in recorded history surpassed Monday's Geoje total: Gangneung, which received 870.5mm on Aug. 31, 2002, and Daegwallyeong, which received 712.5mm on the same day — both during Typhoon Rusa, the 15th named storm of that year.
Nearby Tongyeong also broke its own all-time single-day record, logging 409.7mm by 1 p.m. Monday — the highest daily rainfall since observations began there on Jan. 1, 1968.
Geoje was also hit by what the KMA classifies as "extreme rainfall" — 124.5mm in a single hour beginning at 1:32 a.m. Monday. That, too, set a new hourly record for the city since observations began, surpassing the previous mark of 96.5mm set on July 5, 2001.
In the Seoimal area of Geoje's Ilun-myeon, 100.5mm fell in one hour starting at 12:21 a.m., while Gadeokdo island in Gangseo-gu, Busan, received 101.5mm in one hour beginning at 2:59 a.m.
The readings at Geoje and Gadeokdo marked the first time this summer that hourly rainfall exceeded 100mm anywhere in the country.
Tongyeong recorded 97.4mm in one hour starting at 5:11 a.m. — also an all-time hourly record for the city since weather observations began there.
The KMA said the rainfall intensity in Geoje was consistent with a once-in-200-years event, while Tongyeong's was at a once-in-100-years level.
Cumulative rainfall from Saturday — when the rain began on Liberation Day — through 1 p.m. Monday reached 851.1mm in Geoje, 704.8mm in Tongyeong, 441.0mm on Gadeokdo, 380.5mm in Sacheon (Samcheonpo) in South Gyeongsang Province and 377.0mm on Jeju's Hallasan (south wall), confirming that the southern coast and Jeju's mountainous interior bore the brunt of the storm.
Geoje and Tongyeong's average summer rainfall — based on the 1991–2020 climatological normal — stands at 935.1mm and 728.8mm, respectively. That means more than 90 percent of a typical summer's total precipitation fell in less than three full days.
The rain was driven by a low-pressure system that developed from the remnants of Typhoon Dolphin, the 13th named storm of the season, as it approached from the southwest and tracked northeast across the Korean Peninsula over the Liberation Day holiday weekend.
In the Northern Hemisphere, winds circulate counterclockwise around low-pressure systems, so as the system approached, warm and humid air from the south was drawn in. That moist southerly flow collided with terrain along the southern coast and Jeju, triggering the heavy rain.
As the low-pressure system drew closer to the peninsula, it also closed the distance to a high-pressure system to the northeast, narrowing the corridor between them. The resulting intensification of southerly winds drove rainfall to record levels.
Sea surface temperatures in the South Sea, running at 27 to 28 degrees Celsius, were also elevated, loading the southerly winds with abundant moisture — another factor analysts cited for the exceptional rainfall totals.
As of 1:50 p.m. Monday, the rain band responsible for the extreme rainfall had largely moved out of the country.
However, South Gyeongsang Province and Jeju could still see occasional rain through the night, while showers are expected at times across the central regions, Honam and North Gyeongsang Province.
gil@heraldcorp.com
