Parts of Jeju will see more than 100 millimeters of rain on Friday the 18th, counting accumulation from the previous day. The rain will begin along the southern coast and spread in the morning to southeastern North Jeolla Province, the Jeolla region, the Gyeongnam region and the southern east coast of North Gyeongsang Province. It will taper off in most areas by the afternoon, though Busan and Ulsan will see rain continue into the evening.
Expected rainfall is 20 to 60 millimeters on Jeju Island excluding its northern and western areas, with more than 100 millimeters in some places, and 5 to 40 millimeters in northern and western Jeju. Busan, Ulsan, the southern coast of Gyeongnam and southern South Jeolla Province are forecast to get 5 to 20 millimeters, while southeastern North Jeolla, Gwangju, northern South Jeolla, inland Gyeongnam and the southern east coast of North Gyeongsang will see about 5 millimeters. Mountainous areas of Gangwon Province are expected to get 5 to 10 millimeters and the province's east coast less than 5 millimeters. Rain will also fall on Gangwon's east coast and parts of Jeju Island through Sunday morning.
In Jeju, where the rain will be heaviest, valley and river levels could rise quickly and low-lying areas and underpasses could flood. Rainfall intensity and volume will vary widely by area.
Morning lows are forecast at 15 to 22 degrees Celsius and daytime highs at 24 to 29 degrees, close to seasonal averages of 13 to 20 degrees in the morning and 24 to 28 degrees during the day.
Winds will also be strong. In parts of Jeju under a strong-wind advisory, gusts will top 70 kilometers per hour through Saturday morning on the 19th, and exceed 90 kilometers per hour in the island's mountainous areas. A strong-wind advisory may also be issued for the southern coast, and gusts of about 55 kilometers per hour are expected in some inland areas through the 18th.
Seas will be rough, mainly in the South Sea, waters off Jeju and the East Sea. Winds will blow at 30 to 55 kilometers per hour with waves of 1.5 to 3.5 meters. Squalls with thunder and lightning are possible in the far reaches of the South Sea and in waters off Jeju.
Strong swells will hit the east coast, the southern coast of Gyeongnam and Jeju's shoreline, with high waves washing over rocky outcrops and breakwaters in some places.
