Foreign tourists shade themselves with parasols as they wait for a bus near N Seoul Tower on Sunday, when heat advisories blanketed the capital despite the arrival of Cheosu — the solar term traditionally marking the end of summer heat. [Yonhap]
Foreign tourists shade themselves with parasols as they wait for a bus near N Seoul Tower on Sunday, when heat advisories blanketed the capital despite the arrival of Cheosu — the solar term traditionally marking the end of summer heat. [Yonhap]

Heat advisories and tropical night warnings blanketed the country Sunday, even as the day marked Cheosu — the traditional solar term said to signal a break in the summer heat. The North Pacific high pressure system, which drives hot weather onto the Korean Peninsula, is staying longer than it used to, causing the ancient seasonal calendar to diverge from actual conditions.

The Korea Meteorological Administration issued a heat advisory for all of Seoul at 11 a.m. Sunday. Such advisories are issued when the maximum perceived temperature exceeds 33 degrees Celsius for two or more consecutive days, or when severe heat damage is anticipated. It came just four days after the city's heat alerts were lifted at 6 p.m. Thursday.

A heat warning — a step above an advisory — took effect in the Daegu and North Gyeongsang Province area, while the cumulative number of heat-related patients in South Gyeongsang Province climbed to 304. North Jeolla Province also saw daytime highs reach 35 degrees, prompting both heat warnings and advisories there.

Starting at 6 p.m. Sunday, a tropical night advisory took effect for southwestern Seoul. Such advisories are issued when the maximum perceived temperature stays at or above 33 degrees for two or more consecutive days and the overnight low is expected to meet or exceed the threshold set by the KMA chief for each region — 26 degrees in Seoul's case. The seven districts covered are Gangseo, Gwanak, Yangcheon, Guro, Dongjak, Yeongdeungpo and Geumcheon-gu.

The reason heat persists even through Cheosu is that the behavior of the North Pacific high pressure system — the engine behind the Peninsula's summer heat — has changed from the past. The system is a massive air mass centered over the Pacific Ocean near Hawaii.

As the North Pacific high expands toward the Korean Peninsula each summer, hot and humid air from the seas to the south flows inland, producing sweltering conditions. The high pressure also generates a descending air current — air sinking from above — that suppresses cloud formation, bakes the surface and drives temperatures higher.

In an analysis of changes in heat wave and tropical night patterns published last July, the KMA found that the North Pacific high has continued to sit south of the Peninsula even in late August over the past decade. As a result, tropical nights are ending roughly 10 to 20 days later than before — somewhere between mid-August and early September — and along the southern coast and in Jeju, tropical nights persist into early September even after heat waves officially end. Last year, heat waves continued after Cheosu, pushing the late-August national average temperature to 27.8 degrees — 3.9 degrees above the historical norm.


park.jiyeong@heraldcorp.com