What is the "unexpected factor" that typhoon No. 10 "maximum alert" did not develop at 18:39 on September 20?
A surprising factor emerged that Typhoon No. 10, which called for the highest level of caution, did not become as powerful as the forecast in advance.
As a result of detailed analysis of the sea conditions at that time by experts, it was found that it is highly possible that the Kuroshio, which originally delivered warm seawater, played a role in spreading the relatively cold seawater mixed by the preceding typhoon by more than 200 km. I did.
Typhoon No. 10 approached the Daito Islands region of Okinawa, Amami, and Kyushu, and was damaged by storms and heavy rains one after another. Has also weakened.
Professor Naoki Hirose of the Institute of Applied Mechanics, Kyushu University, who specializes in physical oceanography, uses artificial satellite data and meteorological conditions to examine the seawater temperature and current conditions when typhoons 9 and 10 pass in order to explore the background. Based on the above, it was reproduced in detail by computer simulation.
Before Typhoon No. 9 passed, the sea surface temperature in the area was 28 degrees or higher, higher than 27 degrees, which is said to develop, but when Typhoon No. 9 moved northward over the East China Sea on September 3, seawater Due to the agitated effect, it is believed that the temperature dropped below 27 degrees near the course.
Even after that, the area where the water temperature dropped continued to spread to the east, and by noon on the 6th when Typhoon No. 10 approached Kyushu, the area below 27 degrees had expanded to the vicinity of Tanegashima and Yakushima regions in Kagoshima prefecture. It was.
It is more than 200 km away from the course of the typhoon, and according to Professor Hirose, such a phenomenon is rare, but it is relatively cold because the Kuroshio current was flowing so as to connect the course of typhoons 9 and 10. I think the seawater has spread.
Professor Hirose said, "The Kuroshio Current, which is a warm current, is a big change that temporarily becomes a cold current, and I could not imagine it until I saw the result. Generally, the sea surface temperature has a great influence on the intensity of the typhoon, so in the future, It's an element that can't be ignored. "
Expert "Understanding sea surface temperature data closer to reality than the Japan Meteorological Agency"
Although the sea surface temperature data is used in the typhoon forecast of the Japan Meteorological Agency, it is in the form of averaging several weeks' worth of data, so it incorporates extreme fluctuations in sea surface temperature that occur in a short period of time like this time. The reality is that we cannot do it.
Associate Professor Kosuke Ito of the University of the Ryukyus, who is familiar with the mechanism of typhoons, said, "This time, we did not meet the standards for special warnings for typhoons, but due to the progress of global warming, typhoons of similar strength may approach and land. The nature will continue to be sufficient. The Japan Meteorological Agency should work on creating a mechanism to grasp data on sea surface water temperature that is closer to reality by utilizing simulations, etc. By issuing more accurate forecasts, appropriate evacuation of residents will also be possible. I think it will be connected. "