With Typhoon Chan-hom, the 15th of the season, moving unusually from east to west, there is a possibility the heat wave that has scorched the Korean Peninsula will temporarily ease. That is because Chan-hom could induce northerly or northeasterly winds over the peninsula, drawing in relatively cool, dry air. Still, experts said the heat is likely to persist even if it lets up a bit.
According to the Korea Meteorological Administration on the 10th, Chan-hom is expected to pass near Japan, move west, and then weaken into a tropical depression over the East Sea. Unlike typical typhoons that reach the vicinity of the Korean Peninsula and then ride the westerlies to the northeast, this Chan-hom is taking an unusual track from east to west.
In the Northern Hemisphere, winds around a typhoon blow counterclockwise from the center. When a system like Chan-hom approaches from the east of the Korean Peninsula toward the west, winds around the typhoon can produce a northerly or northeasterly flow over the peninsula.
However, how much temperatures drop will likely vary by region. Along the East Coast, winds that have crossed the East Sea can hit the Taebaek Mountains, producing clouds and rain. If clouds and precipitation block sunlight and northeasterly winds are added, temperatures could fall relatively sharply. West of the Taebaek range, the situation is a bit different. As air descends the mountains, it can compress and warm, producing the foehn effect. That is why, even under the same easterly influence, areas west of the East Coast can be warmer.
Cha Dong-hyun, a professor in the Department of Urban and Environmental Engineering at Ulsan National Institute of Science and Technology, said, "If Chan-hom moves toward the Korean Peninsula, winds of a northeasterly type are induced," and added, "As cool air flows in, there is a possibility the heat wave will temporarily subside." He continued, "On the west side of the mountains, including Yeongseo, temperatures may be higher than on the East Coast because of the foehn effect," but said, "Still, I think the heat wave of 35 degrees Celsius or higher will ease somewhat compared with now."
Yoon Jin-ho, a professor in the Department of Environmental and Energy Engineering at Gwangju Institute of Science and Technology, also said Chan-hom could temporarily ease the heat wave. Yoon said, "If the typhoon reaches the East Sea as predicted, counterclockwise airflow could bring northerly winds to Korea," adding, "Northerly winds are basically relatively cool and dry, so it could feel quite refreshing."
However, both professors said Chan-hom's approach does not mean this heat wave is over. That is because, after the typhoon passes, larger-scale pressure patterns, including the North Pacific High, will again control temperatures over the Korean Peninsula. Yoon said, "It may not be as intense a heat wave as last week, but climatologically, Korea remains in a hot period through mid- to late August, so it is hard to say the heat wave will completely disappear."
In the Korea Meteorological Administration's midrange forecast, even from the 14th to the 20th after Chan-hom weakens, nationwide daytime highs are expected to be 28 to 35 C. In most regions, the maximum heat index will rise to 33 C or higher, and in some inland areas to 35 C or higher, with the heat wave and tropical nights forecast to continue.
Changes in the pressure pattern after Chan-hom are key. Cha Dong-hyun, a professor in the Department of Urban and Environmental Engineering at Ulsan National Institute of Science and Technology, said, "Chan-hom does not directly push out the high pressure, but as the overall pressure pattern changes, there is a possibility the currently expanded high pressure will contract somewhat," while adding, "Since this is a midrange outlook, we need to keep watching what follows."
Other tropical cyclones around the Korean Peninsula are also variables. Typhoon Dolphin, which moved into China, may lose typhoon strength but still carry substantial moisture, which can feed into a trough passing north of China.
Cha said, "As northeasterly winds blow with Chan-hom, temperatures could temporarily drop, and if a trough strengthened by moisture supplied by Dolphin passes over the Korean Peninsula and brings rain, temperatures could fall again," adding, "However, when multiple typhoons and tropical cyclones exist, their respective tracks and surrounding pressure fields can affect each other, increasing forecast uncertainty."