Korea experiences hottest May on record as average temperatures reach 18.6 degrees Celsius nationwide

Korea logged its hottest May on record last month, with the nationwide average temperature reaching 18.6 degrees Celsius (65.5 degrees Fahrenheit). 

The heat is set to persist into early summer, with Seoul forecasted to hit 33 degrees Celsius on Tuesday, its highest reading this year.

The May average was the highest since nationwide observations began in 1973, the Korea Meteorological Administration (KMA) said Monday, surpassing the previous record of 18.5 degrees Celsius set in 2017. The monthly average low also reached a record 12.7 degrees Celsius, beating the 12.6 degrees recorded in 2020. That made last month the hottest May on record, both day and night.

Clear skies brought frequent, early bouts of heat above 30 degrees Celsius over the past month. Wando in South Jeolla and Hongseong in South Chungcheong reached 32.6 and 31.6 degrees Celsius, respectively, on Sunday, setting new May high-temperature records.

Gangneung, Gangwon, recorded its first tropical night of the year on Saturday, 19 days earlier than last year. A tropical night occurs when the temperature does not drop below 25 degrees Celsius overnight, from 6 p.m. to 9 a.m. the next day.

"Under the influence of a migratory high-pressure system, clear skies with almost no clouds continued," a forecaster at the KMA said. "Strong sunshine nationwide drove temperatures up sharply."

The scorching weather is expected to continue into early June. Central regions could see heat-wave-level temperatures through Wednesday, driven in part by Typhoon Jangmi, the sixth typhoon of the season, which is moving north. Southeasterly winds driven by the typhoon are expected to warm as they cross mountain ranges, raising temperatures around the greater Seoul area. Seoul's daytime high on Tuesday is forecast at 33 degrees Celsius, the highest so far this year.

In the south and on Jeju, heavy rain of 20 to 30 millimeters (0.8 to 1.2 inches) per hour is expected from Monday night into Tuesday morning as a rain band passes through.

Typhoon Jangmi is expected to pass Okinawa, Japan, on Monday night, then turn northeast and move through the waters south of Japan. As a result, it is unlikely to affect inland Korea. A typhoon advisory could still be issued Tuesday for the far seas off the eastern South Sea, which fall within the storm's strong-wind radius. If that advisory takes effect, Jangmi would be recorded as the first typhoon to affect Korea this year.

Temperatures are expected to ease to around seasonal norms later in the week. Still, the KMA's one-month outlook projects that June will remain mostly under high pressure, keeping temperatures above average.

Some analysts expect humid heat waves to become more frequent as both temperature and humidity climb in early summer. They point to signs of extreme heat ahead, including unusually high sea-surface temperatures in the North Pacific. When North Pacific waters are warm, hot air and water vapor flow toward the Korean Peninsula, raising the chance of muggy, sweltering heat.

"The reason humid heat and tropical nights have been frequent in recent years is that North Pacific sea temperatures are considerably high, and that trend is continuing this year," said Lee Myong-in, a professor at the Ulsan National Institute of Science and Technology and head of its Heatwave Research Center, which is funded by the KMA. 

"If high temperatures persist day and night, they can cause fatal harm to the body."

This article was originally written in Korean and translated by a bilingual reporter with the help of generative AI tools. It was then edited by a native English-speaking editor. All AI-assisted translations are reviewed and refined by our newsroom.

BY CHON KWON-PIL [cho.yongjun1@joongang.co.kr]