Due to the effects of extratropical cyclones that changed from typhoon No. 4, atmospheric conditions became unstable over a wide area from western Japan to northern Japan.
In Kochi prefecture, rain clouds that developed from late night on the 4th to early dawn on the 5th continued to fall, and a "linear precipitation zone" was confirmed.
In the morning when Typhoon No. 4 landed, "record short-time heavy rain information" was announced one after another in northern Kyushu and in Hokkaido and Aomori prefectures from noon, and sediment disasters and inundation damage were reported.
Why was it a record heavy rain over such a wide area?
Rain clouds that continued to exceed the expectations of the Japan Meteorological Agency Why?
The reasons are
"wet winds from typhoons" and
"warm and moist air around the edge of the Pacific High."
Typhoon No. 4 was located on the sea south of Nagasaki Prefecture, about 400 km away, before dawn on the 5th when the "linear precipitation zone" was confirmed in Kochi Prefecture.
At this time, in western Japan, a counterclockwise southerly wind was blowing due to the influence of typhoon No. 4, and warm and moist air was flowing clockwise around the edge of the Pacific High, which is located far east of Japan. I was there.
In Kochi prefecture, these two air flows gathered, and in Susaki city, the amount of rain that fell in 12 hours until 1:40 am reached 353.5 mm, which was the highest since we started collecting statistics, and Kubokawa, Shimantocho. It is believed that the amount of rain that fell in 48 hours exceeded 560 mm and reached nearly 1.5 times the amount of July 1 month in normal years, and rain clouds continued to exceed the expectations of the Meteorological Agency.
Then, on the morning of the 5th when Typhoon No. 4 landed near Sasebo City, Nagasaki Prefecture, moist air around the typhoon flowed in, and in northern Kyushu (Nagasaki, Fukuoka, Kumamoto), radar observations showed a ferocious amount of over 100 mm per hour. It seems that it rained, and the Japan Meteorological Agency released "record short-time heavy rain information" one after another.
Heavy rain in northern Japan due to the cold air in the sky
Furthermore, cold air below -6 degrees Celsius moved south over northern and eastern Japan, and atmospheric conditions became unstable, especially in northern Japan, and rain clouds developed locally.
After noon, heavy rain of about 100 mm per hour seems to have fallen in the vicinity of Iwamizawa and Mikasa in Iwamizawa City, Hokkaido, and in the vicinity of Hirosaki City and Owani Town in Aomori Prefecture, according to radar analysis. Information on short-term heavy rain "has been announced.
Northern Japan usually has less rain than western and eastern Japan, and even short-term rains tend to increase the risk of disasters, so it is necessary to prepare for sudden changes in the situation.
Do you increase the risk of disaster due to long rain? Be careful on the morning of the 6th
The extratropical cyclone that changed from typhoon No. 4 is expected to travel along the southern coast of Honshu over the 6th.
As warm and moist air continues to flow in, it is necessary to be cautious about sediment-related disasters caused by long-lasting rain, flooding of rivers, and inundation of low land from Kanto to Shikoku.
Evacuation may be difficult if it rains heavily during the night hours.
If you feel uneasy near a river or slope, it is important to move to a safe place as soon as possible.
Especially in the Kanto region, there is a risk of rain clouds developing during the commuting time on the morning of the 6th.
Please be aware of the latest weather information and information from local governments.
"It becomes an extratropical cyclone and there is a risk of rain over a wide area."
Professor Kazuhisa Tsuboki of Nagoya University, who is familiar with the mechanism of meteorology, boarded an aircraft from the morning of the 5th and conducted meteorological observations over western Japan.
In the morning, he confirmed that a large amount of water vapor was flowing into Shikoku and the Kii Peninsula, which are a little far from the extratropical cyclone.
Professor Tsuboki said, "Since a very large amount of water vapor is observed from low to high atmosphere, it cannot be said that it is safe even if the typhoon becomes an extratropical cyclone. Typhoon No. 4 is relatively powerful as a typhoon. However, the extratropical cyclone may cause the wind to strengthen over a wide area, which may widen the range of rain. "
He said, "We need to be vigilant for heavy rains over the 6th, and be careful even in areas away from low pressure systems."