Korea's latest-ever monsoon season to begin in Jeju on Tuesday night as heat wave grips central regions

This year's monsoon season is expected to begin in earnest in Jeju on Tuesday night.

The Korea Meteorological Administration said the North Pacific high-pressure system is expanding and pushing the stationary front northward. It forecast that Jeju will enter the monsoon season on Tuesday, with southern regions following on Wednesday.

The stationary front is currently positioned from Shanghai, China, to the southern coast of Japan's Kyushu. As the North Pacific high continues to strengthen, the front is gradually moving north. A pressure trough descending from the northwest is expected to bring rain centered on Jeju and the southern coast.

Rain in Jeju is forecast to begin Tuesday and continue through early Thursday morning, while the southern coast can expect rain from early Wednesday through the evening. Projected rainfall totals are 30 to 100 millimeters for Jeju and up to 180 millimeters or more in mountainous areas, with 5 to 30 millimeters along the southern coast. The weather agency warned that heavy-rain advisories may be issued in parts of Jeju, where rainfall could reach around 30 millimeters per hour.

The monsoon rains are expected to ease temporarily. Dry air moving south from the north is forecast to push the stationary front back toward the south on Thursday. The front is then expected to reactivate when the North Pacific high expands again around July 3 to July 4, bringing renewed rain centered on Jeju, South Jeolla Province and areas south of the Chungcheong region.

The start of the monsoon season is significantly later than usual. The average onset dates are June 19 for Jeju, June 23 for the southern regions and June 25 for the central regions. With Jeju's monsoon now forecast to begin Tuesday night, this year's rainy season is on track to be one of the latest on record.

According to the weather agency, a July monsoon onset in Jeju has occurred only twice in 53 years of meteorological observation — in 1982 (July 5) and 2021 (July 3). Under the current forecast, rain beginning Tuesday night would technically fall short of a "July monsoon," but the season would still likely rank among the latest monsoon starts ever recorded.

The timing of the monsoon's arrival in the central regions remains highly uncertain. The weather agency said the rainfall zone could shift considerably depending on the intensity and track of the pressure trough from the northwest and the position of the stationary front, making it difficult to predict when the monsoon will reach central Korea for the time being.

Heat wave advisories in effect for the Greater Seoul area and central inland regions are expected to continue for now. The weather agency urged residents to prepare for potential flooding in low-lying areas and landslides, particularly in Jeju where heavy rain is anticipated, while also taking extra precautions against heat-related illness.