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Heat shimmer rises from a road in Nam District, Ulsan, on July 23, as a heat wave warning remains in effect for a second consecutive day in the city. / Photo courtesy of Yonhap News Agency

This year's monsoon season is set to end early next week, giving way to full-blown heat waves and tropical nights across the Korean Peninsula. As both the North Pacific High and the Tibetan High expand over the region, an "overlapping heat dome" phenomenon—akin to covering the peninsula with a double-layered blanket—may materialize.

The Korea Meteorological Administration (KMA) announced during a regular briefing on July 23 that Jeju Island concluded its monsoon season on July 19 as it came under the influence of the North Pacific High. As the North Pacific High continues to expand toward the Korean Peninsula, the monsoon season in the central and southern regions is projected to end around July 27.

Monsoon rains, however, will persist primarily across the central region through this weekend. Rains driven by a stationary front are forecast for the Seoul metropolitan area and Gangwon Province from July 24 to 25, while shower activity is expected in regions south of Chungcheong Province. The rain is forecast to expand to North Jeolla and North Gyeongsang Provinces on July 26 before the monsoon season terminates around July 27 as the stationary front weakens and dissipates.

If current forecasts hold, the conclusion of this year's monsoon season will align closely with historical averages. On average, the monsoon season ends on July 20 in Jeju, July 24 in the southern region, and July 26 in the central region.

Intense heat waves are expected to take hold once the monsoon retreats. Starting late next week, the North Pacific High occupying the lower and middle atmosphere and the Tibetan High occupying the upper atmosphere will simultaneously envelope the Korean Peninsula, driving daytime high temperatures up to around 37 degrees Celsius through August 2. If an "overlapping heat dome" forms—trapping hot air from above and below—heat accumulated during the day will be unable to dissipate at night, raising the potential for a prolonged stretch of tropical nights.

Despite the intense heat, localized torrential downpours remain a possibility. "Because the North Pacific High carries high temperatures and moisture, localized, intense rain clouds can still develop," a KMA official explained. "Even after the monsoon season concludes, sudden heavy rainstorms could occur at any time."

                                                                                                           Kim Hong-chan