On the morning of Aug. 25, the temperature in Seoul dropped to 24.9 degrees Celsius, marking the first time in 35 days that the city’s temperature fell below 25 degrees. This break ended Seoul’s longest-ever streak of tropical nights, defined as nights when the temperature doesn’t drop below 25 degrees, at 34 days—just 0.1 degrees shy of continuing the record. The previous longest stretch was 26 days in 2018.
Although the streak has ended, experts predict that tropical nights could continue into early September, potentially setting a new record for the total number of tropical nights in a year. Seoul has already experienced 37 tropical nights this year, surpassing the previous record of 36 days set in 1994.
While there was a brief reprieve from the tropical nights between the night of Aug. 24 and the morning of Aug. 25, the Korea Meteorological Administration (KMA) forecasts that the minimum temperature in Seoul will hover between 24 and 26 degrees Celsius from Aug. 26 to Sept. 4. Even if temperatures dip slightly below 25 degrees at night, the small drop may not provide much relief, and it is likely to still feel hot.
The KMA predicts that the heat will persist through early September, with daytime highs reaching between 30 and 34 degrees on Aug. 26 and between 28 and 33 degrees on Aug. 27. However, the heat may temporarily ease in the middle of the week as cold, dry air from the north influenced by Typhoon Shanshan moves over the Korean Peninsula. This could lead to cooler mornings, with temperatures dropping to the point where some areas, particularly inland, may feel “refreshing.” On Aug. 28-29, minimum temperatures are expected to fall to between 22 and 24 degrees across most of the country, excluding Jeju, effectively ending tropical nights for the first time in a month.
“While the heat index will still exceed 30 degrees during the day, leading to persistent daytime heat, humidity levels that have remained in the 70-80% range may temporarily drop to around 50% in some areas, reducing the sensation of stickiness,” said a Korea Meteorological Administration official.
However, as early September approaches, the Tibetan High Pressure system is expected to expand over the upper atmosphere in South Korea, bringing warm and dry westerly winds. This, combined with warm and humid southerly winds, is likely to result in another round of sweltering heat and tropical nights. Such conditions are uncommon in September; the average number of heatwave days in September is only 0.2, and while tropical nights have sometimes continued into September, they have mostly been confined to the southern regions and were rare in central areas like Seoul.
This August has already surpassed the heatwave records set during the notorious summers of 2018 and 1994. Between Aug. 1 and 24, South Korea experienced 14.8 days of heatwaves, defined as days with temperatures exceeding 33 degrees Celsius, meaning more than half of the month saw extreme heat. This figure surpasses the 14.1 days recorded in August 2018 and the 9.8 days recorded in August 1994.
In those years, the total number of annual heatwave days reached 31 and 29.6 days, respectively, making them the top two hottest years on record. The fact that this August has been hotter than those years indicates that 2023 is on track to break more records. The average temperature from Aug. 1 to 24 this year was 28.3 degrees Celsius, 0.4 degrees higher than the 27.9-degree average in 2018 and 2.7 degrees above the long-term average of 25.6 degrees.
The year with the most heatwave days in August since related statistics began being recorded in 1973 was 2016, with 16.6 days. Given that August still has about a week remaining, there is a high likelihood that this record will also be surpassed.
