South Korea is suffering under a relentless heat wave, with Seoul, Busan, and other regions breaking records for consecutive tropical nights, data by the country's weather agency showed Friday.

As of Friday, Seoul and Jeju have each experienced 33 and 39 straight nights of sweltering temperatures, respectively, according to the Korea Meteorological Administration.

A tropical night refers to overnight temperatures remaining at or above 25 degrees from 6:01 p.m. to 9 a.m. the following day.

Seoul had experienced three tropical nights before the current streak began on July 21, bringing the total number of tropical nights this year to 36. This is the longest period of tropical nights since modern weather observation began in Seoul in 1907. In 1994, a total of 36 days of tropical nights occurred, making this the year with the most tropical nights on record.

Jeju came in second with 39 consecutive tropical nights, equaling the record set in 2016. Jeju's longest streak of tropical nights was 44 days in 2013.

The hot and humid southwesterly winds have kept temperatures from dropping at night, resulting in tropical nights across much of the country.

Tropical nights are forecast to continue, with sleepless nights expected nationwide Friday and throughout the weekend, especially in urban centers and coastal areas.

The heat will continue during the day. Daytime highs on Friday will be between 31 and 36 degrees Celsius, with wind chills reaching up to 33 C and 35 C.

After the pressure ridge that scattered rain mainly in the central region passes, the western Tibetan high-pressure system will expand its power and settle the hot and dry air on the Korean side, resulting in continuous heat due to the development of high pressure and hot westerly winds.

Showers of 5 to 20 millimeters may fall by evening Friday in the Seoul metropolitan area, inland and the mountainous areas of Gangwon Province, Chungcheong Province, Jeolla Province, and Jeju Island, but the amounts will be small, which observers say is not enough to relieve the heat.