Boats for Typhoon Omais are moored in Seogwipo, Jeju, on Sunday. (Yonhap)
The typhoon was located about 320 kilometers northwest of Okinawa, Japan at 4 a.m. and was slowly moving at 26 km / h towards the Korean peninsula, the Korea Meteorological Administration (KMA) said.
It is forecast that it will pass the southern holiday island of Jeju at night and hit land around midnight.
The typhoon is forecast to bring torrential rainfall of more than 70 millimeters per hour and violent winds to Jeju during the day, with a cumulative rainfall of 100-300 mm by Tuesday.
A low pressure system, which is also approaching the island, is said to bring additional precipitation with lightning and thunder.
The southern port city of Busan is expected to be hit with heavy rainfall of 70mm per hour and gusts of 30 meters per second, with up to 400mm of rain in some areas by Tuesday.
The weather service warned of high winds and a storm surge that could disrupt public traffic to the island until Tuesday, and advised local governments, and residents in low-lying areas in particular, to prepare thoroughly for the storm. (Yonhap)