Heat waves and tropical nights to be observed throughout the week
Record-breaking downpours have now subsided, but Korea is expecting a new round of weather extremes: sweltering heat.
According to the Korea Meteorological Administration, this summer is expected to be longer and hotter than average, with extreme shifts between heat waves and localized rain showers continuing throughout the season.
As of Monday, heat wave advisories and warnings were reissued across the nation, as apparent temperatures were expected to exceed 33 degrees Celsius and 35 degrees Celsius for two or more consecutive days. Such heat waves, accompanied by tropical nights, are expected to last for most of the summer season, the KMA said.
From July 24 to 29, daily lows nationwide are forecast to hover between 23 C and 26 C, with high temperatures reaching 30 C to 35 C. High humidity built up by last week's prolonged rainfall is expected to make it feel even hotter, with some parts of Korea expected to see apparent temperatures reaching 38 C.
Sweltering heat has taken hold after last week's record-breaking torrential rainfall, which caused floods and landslides in some regions.
According to the Central Disaster and Safety Countermeasures Headquarters, from July 16 to Sunday, Sancheong-gun in South Gyeongsang Province saw the highest amount of accumulated rainfall over the five days at 793.5 millimeters.
Hapcheon-gun and Hadong-gun in South Gyeongsang Province followed with 699 mm and 621.5 mm of rain, respectively, while Gwangyang in South Jeolla Province and Seosan in South Chungcheong Province saw 617.5 mm and 578.3 mm of rain, respectively.
The ministry added that over the five days, Seosan as well as Pocheon in Gyeonggi Province recorded the highest amounts of hourly rainfall, with Seosan seeing 114.9 mm of rain per hour on July 17 and Pocheon seeing 104 mm on Sunday.
The southern region received more rain last week than it did during the monsoon season, which started on June 19 and ended on July 3.
Gwangju, which last week was one of the worst-hit cities in the southern parts of Korea, saw only five days of rain during the monsoon, marking the second shortest monsoon season in history. Cumulative rainfall during the monsoon season in Gwangju was 147.2 mm. However, as of 10 p.m. on Saturday, when the city’s heavy rain warning was lifted, Gwangju was reported to have seen cumulative rainfall of up to 527.2 mm.
According to the KMA, the dry monsoon season and the extreme downpours that followed can be explained by an intense and persistent expansion of the North Pacific high-pressure system.
Traditionally, Korea’s summer monsoon rains occur when the cool, dry air mass from the north collides with warm, moist air pushed up by the North Pacific high-pressure system from the south. A stationary front forms between the two, shifting up and down the Korean Peninsula for an average of 31 days during a typical monsoon season, based on average weather records recorded between 1991 and 2020.
This year, however, the KMA said the North Pacific high-pressure system expanded rapidly, causing the monsoon to start five to seven days earlier than usual and end earlier than usual.
The record-breaking downpours that followed were also linked to the high-pressure system's significant influence over the Korean Peninsula. Cold air from the north clashing with this dominant high-pressure system and strong winds along the edge of the system drew in tropical moisture and built up the “fuel” needed for torrential rain, according to the state weather agency.
The strengthening of the North Pacific high-pressure system can also be attributed to rising sea level temperatures caused by global warming.
“As waters located to the south of the Korean Peninsula — especially the Philippine Sea — continue to heat up due to global warming, the North Pacific high-pressure system continues to grow stronger,” professor Kim Baek-min of Pukyong National University’s Division of Earth and Environmental System Sciences told The Korea Herald.
“The monsoon season used to resemble a tug-of-war between the high-pressure system and cold air from the north. But now, that balance has tilted, making the monsoon season more volatile and harder to predict.”
Professor Kim added that the recent intense rainfalls can be defined as “the new normal.”
“Compared to average weather records from the last 30 years, this level of rainfall is highly unusual. But we’re seeing similar extreme downpours almost every year now, including the intense rainfall that flooded Seoul three years ago,” Kim added. “With the seas surrounding Korea heating up, the atmosphere is increasingly saturated with moisture. The necessary conditions for intense weather events like this are being met every year.”
