After mild June, South Korea braces for heat dome

South Korea’s summer has felt less oppressive than usual so far, thanks to a delayed monsoon and lower humidity. But that brief relief may not last.

Weather experts say the country could face stronger heat after the rainy season ends, as two high-pressure systems may expand over the Korean Peninsula and trap hot air near the ground.

According to the Korea Meteorological Administration, Seoul’s average humidity in June was 61 percent, lower than last year’s 70 percent and the long-term average of 66 percent.

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READ: Heat wave alert issued for entire Seoul

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Seoul’s average temperature for the month was still high at 24 degrees Celsius, the same as last year and 1.3 degrees Celsius above the long-term average, but the drier air made the heat feel less muggy.

The unusual start to summer was largely linked to the late arrival of the monsoon. Cooler and drier air stayed over the peninsula longer than usual, while the North Pacific high-pressure system, which brings hot and humid air from the south, was slower to move north.

Now the concern is what comes after the rain.

Central regions, including Seoul and Gangwon Province, entered the monsoon season about six days later than usual.

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The rainy season in central Korea typically ends around July 26, though the exact timing depends on how the seasonal rain front moves and how far the North Pacific high-pressure system expands.

READ: Is Seoul getting hotter?

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Once the rain front moves away, Korea could see a heat dome-like pattern, experts say.

A heat dome forms when strong high pressure covers a wide area like a lid, trapping hot air close to the surface. The pattern can push up daytime temperatures and keep nights hot, increasing the risk of prolonged heat waves and tropical nights.

In Korea, the effect could be stronger if the North Pacific high-pressure system from the south and the Tibetan high-pressure system from the north expand at the same time.

Weather experts often describe the pattern as a “double heat dome,” with the two systems covering the peninsula like layers of blankets.

A similar pattern last summer helped push daytime temperatures toward 40 degrees Celsius in some areas. Western parts of the country, including Seoul, were hit especially hard as winds from the southeast became hotter and drier after crossing the Sobaek Mountains.

Shrinking Arctic sea ice and high sea surface temperatures in the North Indian Ocean and North Pacific this year also add to concerns that Korea could see stronger summer heat.

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Seoul’s average high temperature in July is around 29 degrees Celsius, but recent forecasts show some days could rise above 33 degrees Celsius. With high humidity, the temperature felt by the body could be much higher than the actual reading. /dl