Korea braces for another scorching week under 'double heat dome'

South Korea is forecast to swelter under temperatures reaching up to 37 degrees Celsius this week. With heat wave advisories in effect across most of the country, the Korea Meteorological Administration has raised its heat response to the highest level, issuing a "major heat wave alert" — a designation used for the first time — for parts of North Gyeongsang Province.

Apparent temperatures — the "feels-like" reading — are expected to climb to around 33 C across most of the country Monday, the KMA said. In the central regions, North Jeolla Province and North Gyeongsang Province, the apparent temperature could surge to around 35 C. Morning lows are forecast at 23 to 27 C, with afternoon highs ranging from 30 to 37 C.

Showers of 5 to 40 millimeters are expected in the Greater Seoul area, the Chungcheong provinces and North Jeolla Province from the afternoon into the evening, but the rain is unlikely to provide meaningful relief from the heat. Once the showers pass, temperatures are expected to climb again amid high humidity, leaving conditions muggy and oppressive.

The KMA issued the major heat wave alert for Gyeongsan and Pohang in North Gyeongsang Province at 10 a.m. Sunday. The designation is the highest-level heat warning, newly created 18 years after the heat wave advisory system was introduced in 2008 — and Sunday marked the first time it has ever been issued. The top-level alert is triggered when an area that has recorded a daily maximum apparent temperature of 35 C or above for two consecutive days is forecast to see a daily maximum apparent temperature of 38 C or above, or a daily high of 39 C or above.

A tropical night advisory — another measure the KMA introduced this year and has been operating since last month — was also issued for most of the country, including all of Seoul, from 5 p.m. Sunday. The advisory is issued when the maximum apparent temperature remains at or above 33 C for two or more consecutive days, or when the overnight low meets or exceeds the region-specific threshold set by the KMA commissioner.

Meteorologists attribute the current heat wave to a "double heat dome" effect, in which the upper-level Tibetan high and the mid-to-lower-level North Pacific high are simultaneously blanketing the Korean Peninsula. The overlapping high-pressure systems trap hot air and drive a descending airflow that compresses and heats the atmosphere further.

The suppression of cloud formation has allowed intense sunlight to persist, while an influx of hot, humid air from the south has pushed apparent temperatures even higher, the KMA said. Southern North Gyeongsang Province has been hit hardest, where a foehn effect — hot southerly winds growing even warmer as they cross mountain ridges — has combined with the region's topography to produce the most extreme heat in the country.

The heat will continue Tuesday, with morning lows forecast at 23 to 27 C and afternoon highs at 28 to 36 C. Apparent temperatures are expected to reach around 33 C across most of the country, and tropical nights are likely in many areas.

However, rain beginning in Jeju Island in the early hours of Tuesday will spread to the Greater Seoul area and South Chungcheong Province in the morning, extend to the rest of the central regions and the Jeolla provinces in the afternoon, and reach the entire country by night. Forecast rainfall for Tuesday through Wednesday totals 30 to 80 millimeters for the Greater Seoul area, Gangwon Province's inland and mountain areas, and the Chungcheong provinces; 20 to 60 millimeters for North Jeolla Province; 5 to 40 millimeters for Gwangju, South Jeolla Province and the Yeongnam region; and 20 to 60 millimeters for Jeju Island. Northern Gyeonggi Province and the northern inland and mountain areas of Gangwon Province could receive more than 100 millimeters.

The KMA said heat waves and tropical nights are expected to persist across most of the country for now, and urged the public to avoid outdoor activities and stay hydrated in accordance with heat safety guidelines.