Children cool off by playing in a fountain at Gwanghwamun Square, Seoul, Sept. 17, during the Chuseok holiday, as if it were mid-summer. A thermometer placed in the square displays an unusually high temperature of 36 degrees Celsius, an exceptional figure for mid-September. Yonhap

Korea experienced its hottest September on record, with unprecedented heatwaves and tropical nights persisting throughout the Chuseok holiday, marking the highest temperatures recorded in 52 years of weather observations.

According to the Korea Meteorological Administration's "Climate Analysis for September 2024," released on Tuesday, the average nationwide temperature last month was 24.7 degrees Celsius, which is 4.2 degrees higher than the usual average.

The extreme conditions were attributed to a combination of a double high-pressure system and continuous inflows of hot, humid air. This made it the hottest September since national weather monitoring began in 1973, surpassing the previous record of 22.6 degrees set last year.

Notably, new daily temperature highs for September were recorded at 46 out of 66 key weather stations, including 37.4 degrees Celsius on Sept. 19 in Miryang, South Gyeongsang Province.

Heatwaves and tropical nights also reached record highs, with the country averaging six days of extreme heat in Septembe r— far exceeding the usual 0.2 day. This surpassed the former second-highest September heatwave count of 1.3 days recorded in 2010.

Overall, 2023 marked the second-highest annual total of heatwave days at 30.1, just behind 31 days set in 2018. Seven regions, including Seoul and Icheon, experienced September heatwaves for the first time.

A temperature of 31 degrees Celsius is displayed on a dust alert board in a Seoul apartment complex, even as dusk settles in on Sept. 10 when a "September heatwave warning" was issued in Seoul for the first time ever. Yonhap

Tropical nights, defined as nights when temperatures remain above 25 degrees Celsius, also reached an all-time high. The nation averaged 4.3 tropical nights last month, surpassing the previous record of 0.9 day set in 1992.

This year, up until September, the nation experienced an average of 24.5 tropical nights, nearly triple the usual average of 6.6 days.

Some regions, such as Jeju (19 nights), Busan (15 nights), Incheon (10 nights), and Seoul (9 nights), saw tropical nights persist for extended periods. Four regions, including Chuncheon, experienced tropical nights in September for the first time.

Even the surrounding seas were warmer than usual. The average sea surface temperature around South Korea last month was 27.4 degrees, 3.2 degrees higher than the 10-year average of 24.2 degrees, making it the hottest sea temperature over the past decade.

Precipitation was also 54.6 percent higher than usual, with the national average rainfall reaching 241 millimeters — 85.9 millimeters more than the average.

The prolonged heat, including temperatures surpassing 35 degrees and heatwave warnings well into September, was attributed to the double high-pressure system.

The Tibetan high-pressure system in the upper atmosphere intensified sunlight, while the North Pacific high-pressure system at lower levels facilitated continuous inflows of hot, humid air from the south.

The heat only began to subside after heavy rainfall on Sept. 20-21, as the high-pressure systems receded.

People shield themselves from the sun with umbrellas, hats, and coverings as they walk barefoot along the shore at Gwangalli Beach in Busan, amid ongoing tropical nights and extreme heat, Sept. 19. Yonhap

This article from the Hankook Ilbo, a sister publication of The Korea Times, is translated by a generative AI and edited by The Korea Times.