The Mainichi Shimbun answers some common questions readers may have about typhoons, which can wreak havoc in Japan, especially in autumn.
Question: Why do we often hear news about typhoons in autumn?
Answer: In September, typhoons most often approach the Japanese archipelago, causing significant damage. When a low pressure system develops with a certain sustained wind speed, it is called a typhoon. Because moisture evaporating from warm seawater fuels the storm, typhoons tend to occur from summer through fall when seawater is warm. The higher the seawater temperatures, the more likely typhoons will become stronger.
Q: Is that why the September typhoons are powerful?
A: Yes, typhoons tend to get stronger in September due to rising sea water temperatures during the summer and therefore can cause significant damage when they make landfall. Since the Heisei era (1988-2019), eight typhoons have killed at least 40 people each in Japan. All of them made landfall or approached the Japanese archipelago between September and October. Because these typhoons can boost fall rain fronts and cause downpours, you should be wary of them.
Q: Do typhoons occur most often in the fall?
A: According to the Japan Meteorological Agency, over the 30-year period to 2020, August saw the highest average number of typhoons with 5.7, followed by 5 in September and 3.7. in July. However, the average number of typhoons that made landfall in Japan was 1 in September, followed by 0.9 in August and 0.6 in July. The figure is highest in September due to the effects of high pressure systems.
Q: How do high pressure systems affect the path of typhoons?
A: After a typhoon occurs in the tropical atmosphere over the Pacific Ocean, it moves along the anticyclonic system, blown by trade winds eastward around the equator. Because Japan is often covered by an anticyclonic system in the summer, typhoons are more likely to move in the direction of the Korean Peninsula at this time of year. In the fall, however, the high pressure system weakens to cover fewer countries, increasing the chances of typhoons making landfall in Japan.
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