Hot weather has continued throughout the country with tropical nights appearing in Seoul and several other regions, but heavy rain is expected to cool the country for a moment, the weather agency said Tuesday.

The heavy rain advisories had been issued in Seoul and surrounding areas, Gyeonggi Province, islands in the West Sea and Chungcheong Province as of 6 p.m.

The Seoul metropolitan area, Gangwon Province, Chungcheong Province, and Jeju Island will receive 50 to 100 mm of rain, while the east coast and southern Gyeongsang Province will receive 20 to 60 mm of rain. The weather agency warned that some regions might be hit by torrential rain in a short time, accompanied by gusts, thunder, and lightning.

The rain is expected to continue until Wednesday morning and will gradually stop in the Seoul metropolitan area in the afternoon. The KMA called for caution, saying that additional downpours could cause facility damages or human casualties as the ground has been already weakened due to heavy rain last week.

After the heavy rainfall, Korea will plunge back into a nationwide heat wave from Wednesday afternoon, with the temperature reaching a high of 33 C in some regions which is likely to be followed by tropical nights.

Tropical nights are ones on which the temperature stays above 25 degrees Celsius from 6 p.m. to 9 a.m. the next day. The areas that showed tropical nights from Monday evening to Tuesday morning were Seoul, Cheongju and Jeonju, with overnight lows of 25.6 C, 25.8 C and 25 C, respectively.

The Korea Meteorological Administration explained that tropical nights have appeared as the heat accumulated during the day could not escape due to clouds, along with a continuous inflow of high-temperature and humid southwest winds.

Seoul and Cheongju saw their second wave of tropical nights this year between Monday and Tuesday. Their first tropical nights were recorded between Wednesday and Thursday. This year marked the second time that Seoul's tropical nights began in June, as Seoul saw its first tropical nights last year on June 26.

The average number of tropical nights in a year was 4.2 days in the 1970s. That increased to 5.8 days in the 1990s and to 9 days in the 2000s. Last year, there were 13 tropical nights, the fourth highest number ever.