South Korea expects nationwide heavy rain and strong winds starting Tuesday, May 26, with some areas seeing intense hourly precipitation [1].
These weather conditions pose a significant risk of flooding and wind damage, particularly in the mountainous regions of Jeju Island and along the southern coast where the most extreme rainfall is concentrated.
Forecasters expect rainfall to reach 50mm per hour in Jeju and the southern coast [1]. Total accumulation for Jeju's mountainous areas is projected to be between 250mm [1] and 300mm [2], while the southern coast may see between 150mm [1] and 200mm [3]. While the primary impact begins Tuesday, some reports indicate the weather system will persist through Wednesday, May 27 [4].
The severe weather is driven by a low-pressure system approaching from the southwest. This system is pulling large amounts of hot, humid air into the peninsula. The resulting pressure difference between the southwestern low and a southeastern high-pressure system, combined with strong lower-level jet streams, is triggering the heavy rain and wind.
"Due to the pressure gradient force between the low pressure in the southwest and the high pressure in the southeast, Jeju Island and the southern coast will be affected by the lower-level jet," said Lee Kwang-yeon, a forecast analyst at the Korea Meteorological Administration. Lee said the region should expect very strong and heavy rain at the level of a heavy rain advisory.
Reporter Kim Min-kyung said the intensity is due to the low-pressure system from the southwest pulling hot and humid air into the country in large quantities.
Local authorities are monitoring the situation as the system moves across the region. The combination of high humidity and atmospheric pressure differences creates an environment prone to sudden, intense bursts of precipitation that can overwhelm drainage systems, and trigger landslides in mountainous terrain.
“Jeju Island and the southern coast will be affected by the lower-level jet.”
The convergence of a lower-level jet and a significant pressure gradient indicates a highly unstable atmosphere. When hot, humid air is rapidly displaced by a low-pressure system, it often results in concentrated 'water bombs' or extreme hourly rainfall. For South Korea, this increases the immediate risk of flash floods in urban areas and debris flows in the mountainous terrain of Jeju, necessitating high-alert emergency management through May 27.
