Overnight from Friday into Saturday, Seoul marked its 27th consecutive tropical night, the longest since modern weather records began in 1907, the Korea Meteorological Administration said.
A tropical night is defined as one where temperatures do not fall below 25 degrees Celsius between 6:01 p.m. and 9:00 a.m. the following day.
Busan, the country's second-largest city, has experienced the phenomenon for 23 successive days, shattering previous records since observations began in 1904. The southern port city may see some relief starting Monday when rain is forecast, the KMA said.
Incheon, west of Seoul, has endured 25 straight tropical nights, just one day short of its 2018 record. The southern island of Jeju has faced 33 consecutive nights of stifling heat, tying for the third-longest streak.
The meteorological agency forecast oppressive nighttime heat will persist for some time, especially in western regions and southeastern coastal areas. It urged people to take necessary precautions for their health.