The impact of an active seasonal rain front led to extremely heavy rain, particularly in Northern Kyushu on July 10. Linear precipitation zones in Fukuoka, Saga, and Oita prefectures caused landslides and river flooding. Four people died in Fukuoka and Saga due to landslides and floods as vehicles became submerged in the muddy water. One person suffered cardiac arrest. Search efforts continue for three missing individuals.
The Japan Meteorological Agency initially issued a special heavy rain warning for Fukuoka and Oita prefectures on the morning of July 10. This was later downgraded to a regular warning at 5:30 pm. The agency continues to urge vigilance against landslides and other potential disasters.
While heavy rain in western Japan during the rainy season is not unusual, why is Northern Kyushu seeing so much rainfall?
Kyushu tends to experience heavy rain as the end of the rainy season approaches. In 2017, the Northern Kyushu torrential rains killed 40 people and 2 people went missing in Fukuoka and Oita prefectures. Similarly, the torrential rains in July 2020 resulted in significant damage and a great number of casualties.
Inflow of Warm, Moist Air
According to Dr Tetsuya Takemi, a professor of meteorology at the Kyoto University's Disaster Prevention Research Institute, the increasing strength of the Pacific High causes warm, moist air to flow towards the seasonal rain front. Additionally, Kyushu is located in a position where water vapor flows from the southwest. He explains that this makes Kyushu "more susceptible to heavy rainfall disasters, like those caused by linear precipitation zones, compared to other parts of the country."
Similarly, weather presenter Yasuto Takamori from the Japan Weather Association emphasizes that the prolonged stagnation of the seasonal rain front caused the sudden influx of water vapor, resulting in heavy rainfall. The collision of water vapor flowing from the direction of India and the warm, moist air surrounding the periphery of the Pacific High led to a continuous inflow of water vapor into the Kyushu region.
These weather conditions are conducive to the formation of cumulonimbus clouds. When carried by the wind, these clouds align linearly. This creates a linear precipitation zone that causes heavy rainfall in one area.
Stay Informed and Cautious
Furthermore, the recent rise in sea surface temperatures has also played a role in the increased water vapor. This year in 2023, the sea surface temperatures near Taiwan were said to be approximately 1°C (33.8°F) higher than usual. Additionally, the residual effects of the La Niña phenomenon resulted in elevated sea surface temperatures in the western Pacific near Peru.
Takamori anticipates that the seasonal rain front will continue to stagnate. He also warns of the possibility of further heavy rainfall even after a temporary lull. Given that similar atmospheric patterns can result in heavy rainfall disasters anywhere in the country, he stresses the importance of staying informed and exercising caution.
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(Read the article in Japanese.)
Author: The Sankei Shimbun