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Over 12-day streak of tropical nights leaves Korea sleepless
People cool off at Cheonggye Stream in central Seoul, Tuesday. Yonhap
By Park Ung
Korea's average number of "tropical nights" nationwide hit a record high of 12.1 days since June through Tuesday, the highest average since the country expanded its weather observation network in 1973.
For Seoul, its overnight low temperature recorded 29.1 degrees Celsius Tuesday night, extending its tropical night streak to 14 straight days, according to the Korea Meteorological Administration (KMA).
A tropical night is defined as a night when the temperature does not drop below 25 degrees. Seoul nearly reached the threshold for a “super tropical night,” a term the KMA does not officially use but refers to a night when the overnight low is 30 degrees or higher. Gangneung in Gangwon Province experienced a super tropical night on July 31 night, reporting 30.2 degrees as its overnight low.
Tuesday's overnight lows also approached 30 degrees in other parts of the country, including 29 degrees in Seogwipo, Jeju Island, 28.8 degrees in Cheongju, North Chungcheong Province, and 27.8 degrees in Jeonju, North Jeolla Province.
“I'm dying from these tropical nights. Korea was never like this before. What's going on here?” Kim Hye-joon, 30, said. “I don't even think about going anywhere now unless it has air conditioning.”
Graphic by Bae So-young
The national average number of tropical nights, which factors in readings from 62 weather observation stations, is calculated by adding up the number of stations recording a tropical night. For example, a tropical night at every station counts as one day, and at 31 stations as half a day.
Behind the high temperature is a recent shift in atmospheric pressure that has kept the heat from escaping overnight. That has raised each day's starting temperature, making daytime highs climb more easily and fueling a cycle between heat waves and tropical nights.
A warmer ocean and atmosphere, driven by climate change, are also pushing summer temperatures higher across the board.
Ocean winds that once cooled the air overnight no longer do so as effectively, as rising sea temperatures have weakened that effect. Moist air moving in instead traps heat near the ground like a blanket, especially along the coast.
The same warming is also helping the North Pacific high-pressure system develop earlier and more strongly. As a result, it now expands toward Korea sooner and holds its strength longer, extending the season for tropical nights.
The data clearly reflects that shift. According to KMA, tropical nights nationwide averaged 12.2 days a year from 2016 to 2025, nearly three times the 4.1-day average from 1973 to 1982.
The tropical night season has grown longer as well. Tropical nights used to begin in late July but now start in early or mid-July. They used to end in early or late August, but in some years, they now stretch into early September, particularly along the south coast and Jeju Island.
This year's first tropical night was recorded May 30, 19 days earlier than last year's June 18.
The heat wave and tropical nights are expected to persist. A high-pressure system of hot, dry air from the Tibetan Plateau sits over the peninsula with a hot, humid North Pacific high below it, trapping heat like a lid that is expected to hold for now.