Seoul and Incheon were hit by an unusual "September tropical night" from late Monday to early Tuesday. It was the first such tropical night in September in 88 years, according to the weather agency, citing data.

Tropical nights refer to hot evenings with the lowest temperature at over 25 degrees Celsius from 6 p.m. to 9 a.m. the following day, according to the Korea Meteorological Administration. As of 8 a.m. Tuesday, temperatures remained above 25 degrees not only in Seoul and Incheon, but other cities including Cheongju in North Chungcheong Province, Gunsan in North Jeolla Province, Jeju City and Seogwipo on Jeju Island and Yeosu, South Jeolla Province.

In the case of Seoul, the lowest nighttime temperature between Monday night and Tuesday morning was 25 C, exceeding the previous record of 24.9 C on Sept. 8, 1935. Tropical nights in September had only appeared in Seoul four times since 1904, when the country started to keep official climate records. The nation's capital had three tropical nights in September before Monday this week, on Sept. 2 in 1914 and Sept. 7 and 8 in 1935.

Incheon, Cheongju and Gunsan recorded their hottest September nights since observation, with lows of 25.6 C, 25.6 C and 25 C, respectively, between Monday night and Tuesday morning.

Also, according to KMA records, Incheon and Seoul saw their second and third latest tropical nights ever recorded.

The unusual tropical night in September is due to east winds blowing along the high-pressure edge of northeastern China, which have heated as they crossed Taebaeksan, warming up the western part of the mountainous area.

The KMA explained it will remain hot for the time being, as the east winds flow in, with daytime temperatures rising above 30 C in the Seoul metropolitan area, North and South Chungcheong provinces, western North and South Gyeongsang provinces and the North and South Jeolla provinces.

From Tuesday to Wednesday, many areas are expected to see midday temperatures rise above 30 C, and showers are also expected in areas where daytime temperatures rise steeply due to temperature differences between the upper and lower atmospheres.