On the 20th, the end of the monsoon was declared in the central region, marking the conclusion of the nationwide monsoon this summer. Immediately after the heavy rain, a heat wave is expected to follow.
According to the Korea Meteorological Administration, the monsoon in the central region, which started on the 19th of last month, is expected to end today. In addition to the earlier declared end in Jeju and the southern regions, the nationwide monsoon has concluded today.
The Korea Meteorological Administration cited the strong collision of a shear low-pressure system from the north and a north Pacific high-pressure system from the south as the cause of the recent unusual heavy rainfall. It is highly unusual for a shear low-pressure system to linger over the north of Korea for an extended period, causing a continuous inflow of cold, dry air. A narrow and elongated "band" of rain clouds formed by colliding different air masses passed over one area, bringing what seemed like "extreme rainfall" targeting only that spot.
As a result, about 800mm of rain fell in Si-cheon-myeon, Sancheong, from the 16th until 11 a.m. today. In particular, there were a total of three instances (in Seosan, Chungcheongnam-do, and Sancheong, Gyeongsangnam-do on the 17th, and Pocheon, Gyeonggi-do, on the 20th) where more than 100mm of rain fell in an hour, and five instances (in Seocheon, Chungcheongnam-do on the 16th, Hongseong, Chungcheongnam-do, and Naju, Jeollanam-do on the 17th, Sancheong, and Incheon Ongjin on the 19th) where approximately 90mm of rain was recorded.
The Korea Meteorological Administration explained, "There is a trend showing an increase in the frequency of extreme rainfall of over 80mm per hour during the months of July to September every year. "
From now on, the time of "heat waves" is coming. The north Pacific high-pressure system, which was in the south, is completely covering Korea. Hot and humid southwesterly or westerly winds will continue, leading to sweltering heat. In Seoul and Chungcheongnam-do's Boryung, as well as in Jeollanam-do's Haenam, Jangheung, Jindo, Mokpo, Wando, and Jeju, a "tropical night" (when the minimum temperature at night exceeds 25 degrees) was already observed last night.
As of 10 a.m. today, a heat wave warning has been issued for Wando, Jeollanam-do, while heat advisories have been activated for Gangneung plain, Donghae plain, Samcheok plain in Gangwon-do, as well as for Jangheung, Gangjin, Haenam, Yeongam, Mu-an in Jeollanam-do, Jeju, and Gwangju Metropolitan City. A heat advisory is issued when temperatures are expected to remain above 33 degrees for two days or longer, while a heat wave warning is issued when temperatures are expected to exceed 35 degrees for the same duration.
Temperatures are expected to rise throughout next week. In particular, many areas will suffer from tropical nights as nighttime heat intensifies. The low temperature on the morning of the 21st is forecasted to be between 21 and 27 degrees, while daytime highs are predicted to be between 30 and 34 degrees.
During the heat wave, occasional showers are also expected. From today until the afternoon of the 22nd, showers reaching 5 to 60mm per hour are anticipated in various inland areas, and such phenomena are likely to be frequent in August as well. The Korea Meteorological Administration stated, "As hot and humid southwesterly and westerly winds continue to flow into Korea, the supply of moisture that becomes the seeds of rain is active, and due to strong solar radiation during the day, the ground heats up, increasing atmospheric instability, which may lead to strong showers," adding, "Preparations for damage from these intense showers are necessary."