Children play in a fountain on Jeju Island amid ongoing tropical nights, Saturday. Yonhap

Seoul, Busan and many other parts of the country have been breaking records for the longest streak of consecutive tropical nights, with Seoul having 28 such nights as of Sunday, according to the Korea Meteorological Administration (KMA).

As the intense heat is forecast to persist for the time being despite forecasts of heavy rain across the country early this week, the regions are expected to continue setting new records every day.

The KMA said Seoul's lowest temperature from Saturday night to Sunday morning was 27 degrees Celsius, marking the 28th consecutive tropical night since July 21.

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's 28 nights were the longest stretch of tropical nights since modern meteorological observations began in Seoul in 1907. The previous record was 26 nights set in 2018.

Busan has experienced 24th tropical nights in a row since July 25, the most for the region, with its previous record of 21 consecutive days set in 1994 and matched again in 2018.

On Jeju Island, tropical nights have persisted for the 34th consecutive day since July 15, surpassing a month of unrelenting heat. This marks the third-longest stretch in the province since observations began there in 1923, behind the 44-day record set in 2013 and a 39-day streak in 2016.

Incheon had its 26th consecutive tropical night since July 23, matching the current record of 26 days established in 2018.

The KMA expects the number of tropical nights to increase as the heat wave shows no signs of abating.

The weather agency attributes this unprecedented stretch of tropical nights to warm winds sweeping over the Korean Peninsula each evening.

Traditionally, tropical nights occur when the radiant heat from daytime temperatures doesn't cool down after sunset. This year, however, a consistent warm southerly wind has compounded the effect, keeping nighttime temperatures elevated since last month.

Even though heavy rain is forecast across the country on Monday, temperatures are expected to rise again quickly once the rain subsides, leaving tropical nights largely unaffected.

Starting in the morning, the rain is forecast to reach Jeju Island, and move into the southern coastal areas of South Jeolla Province and South Gyeongsang Province by evening. On Tuesday, the rain is expected to spread to most regions nationwide.

The KMA announced it would publish its first-ever white paper on heat waves by the end of the year.

The KMA has previously issued white papers on monsoon seasons, typhoons and El Nino — a phenomenon where sea surface temperatures in the tropical eastern Pacific rise above average. However, this marks the first time the agency has dedicated a white paper to heat waves.

The decision to compile it stems from the increasing severity of heat waves in recent years, including this year's, which the agency sees as having reached a disaster level.

Heat wave was included as a natural disaster under the law on disaster safety in 2019, a year after the country suffered its then-worst heat wave.

The white paper will document Korea's heat wave records, analyze the causes and mechanisms behind heat waves, provide a medium- to long-term heat wave outlook and examine the social impacts of these extreme weather events.