A supermoon, an exceptionally bright full moon at its closest distance to Earth, is to rise Friday, a state-run maritime research agency forecast Thursday.
It will be the third of the four supermoon phenomena expected this year.
Two occurred in April and May.
The last supermoon is expected on Dec. 4.
The Korea Hydrographic and Oceanographic Agency warned of possible flood damage in coastal lowlands, as the sea level, which is influenced by the gravitation of the moon, is expected to rise.
Until next Monday, the maximum sea level may increase by 3 to 10 centimeters than the levels recorded in May, it said.
"During the upcoming supermoon period, the sea level change will also be affected by a seasonal factor -- higher water temperature, so extra care is required," said Lee Dong-jae, the director-general of the KHOA.