Last summer was tallied as the hottest on record in Korea. From mid-June, heat waves and tropical nights occurred, starting an early heat, and warm, humid air flowed in through Oct., keeping temperatures high. This summer also has a high chance of being hotter than average.

As daytime temperatures in Seoul rise above 30 degrees Celsius, citizens take shelter under shade canopies on Sejong-daero in Jongno-gu, Seoul, on the afternoon of the 5th of September last year. /Courtesy of News1

According to the "2025 annual climate characteristics" that the Korea Meteorological Administration released on the 6th, last summer's national average temperature was 25.7 degrees, the highest on record. Last autumn's national average temperature was also 16.1 degrees, the second highest on record. These rankings cover the 53 years since 1973, when the meteorological observation network was greatly expanded nationwide.

Last year, June and Oct. were particularly hot. The monthly average temperature was 22.9 degrees in June and 16.6 degrees in Oct., both the highest on record. These were 1.5 degrees and 2.3 degrees higher than the average, respectively. The average temperatures for July, Aug., and Sept. were the second highest on record.

Time series of nationwide daily average temperatures for the summer and autumn of 2025. /Courtesy of Korea Meteorological Administration

The annual nationwide number of heat wave days was 29.7, and the number of tropical night days was 16.4, ranking third and fourth on record, respectively. They were 2.7 times and 2.5 times more than average. Last year, even Daegwallyeong, known as a "place without heat waves," saw its first heat wave since observations began in 1971, and the number of tropical nights in Seoul during summer reached 46 days, the highest on record.

This summer also has a high likelihood of higher-than-average temperatures. According to the recent "six-month outlook" predicted by the Korea Meteorological Administration, the average temperature in June, the beginning of summer, was forecast to have a 60.8% probability of being above average. The probability of being similar to average was 26.2%, and of being below average was 13%. A detailed summer climate outlook will be released on the 23rd of next month.

June climate outlook from the Korea Meteorological Administration's six-month outlook. /Courtesy of Korea Meteorological Administration

Meanwhile, last year's rain tended to pour down large amounts at once in the summer. Although the monsoon period was short and nationwide monsoon rainfall and the number of rainy days were lower than average, extreme downpours were concentrated in certain regions over short periods. From July to Sept. last year, at 15 sites including Seosan, Gapyeong in Gyeonggi, Hampyeong in South Jeolla, Ongjin in Incheon, and Gunsan in North Jeolla, the maximum one-hour rainfall exceeded 100 mm.

There was frequent rain in last autumn. Oct. rainfall reached 173.3 mm, the highest on record. Also, the number of rainy days in autumn was 34.3, which was 11.7 days more than the average (22.6 days), the second most on record. The Korea Meteorological Administration said, "It rained once every two days in Sept.–Oct."

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