Summer holidays are just around the corner! Many of you may have started planning already. As summer approaches, Japan also enters annual typhoon season. In this article, let us talk about the typhoon season in Japan.
When is the typhoon season in Japan?
Typhoon season in Japan is typically from July to October, partially overlapping the rainy season. As we saw in our previous article “What is the rainy season like in Japan?”, typhoons are actually generated throughout the year, but they approach Kanto and Koshin Regions (including Tokyo) starting from June/July to October.
▼30-year average number of typhoons that approached Kanto and Koshin Regions (since 1991) (Source: Japan Meteorological Agency)
How is a typhoon formed?
Typhoons are generated in the tropical seas south of Japan, where the seawater temperature is high and the sun shines down. The combination of high seawater temperature and strong sunshine makes the water evaporate, creating ascending air current. As the water vapor rises, it is cooled and turns into water and ice and forms clouds, in the course of which releases heat and warms itself up, making the air current even stronger. Since warmed air is lighter, the atmospheric pressure becomes lower than the surrounding air. And since air flows from high pressure to low pressure, air flows in from the surrounding seawater surface bringing more vapor with it. Slowly the air starts to swirl counterclockwise, due to the force of the earth’s rotation. This is a start of a tropical cyclone. The bigger the swirl gets, the stronger a tropical cyclone becomes. Typhoon is a name for tropical cyclones generated in the Northwestern Atlantic Ocean and South China Sea and the maximum wind speed near the center is 17m/s or faster.
(Source: Nikkei4946)
How to read a typhoon tracking chart
When a typhoon is approaching Japan, you will often see this chart below shown on TV or internet. This chart shows the past and future trajectory of a typhoon. By checking this chart, you will be able to see more or less the location of the typhoon.
(Source: Japan Meteorological Agency)
First, the mark X shows the current location of the center of a typhoon. The blue line is the trajectory followed by the typhoon.
The red small circle shows the range of wind speed 25m/s or more, while the yellow circle shows the range of wind speed 15m/s. The thin red line shows the area where the storm of wind speed 25m/s possibly hits. And the white circles with dotted line show the estimated range wherein the center of a typhoon may come with 70% of chance.
At first sight, the dotted white circles may look like the estimated size of the typhoon as it moves. But after you understand how to read the chart, it sure is not as terrifying as the size of the dotted white circles look.
You may also notice weathercasters use different terms to refer to a typhoon. Japan Meteorological Agency (JMA) calls a typhoon according to the following manner depending on its size and strength.
▼Size of a Typhoon
▼Designation of a Typhoon by its Intensity
The energy source of a typhoon is water vapor supplied by warm seawater. Therefore, a typhoon usually weakens as it goes northward where the seawater temperature is lower, and eventually disappears after turning into a tropical cyclone or an extratropical cyclone.
What should we watch out for?
However, a typhoon does bring strong wind and heavy rain, and it is important to know the risks.
For example, according to the website of JMA, when a wind speed is 15m/s, we will find it very hard to walk against the wind, and some people may easily fall. With a wind speed of 25m/s, we can barely stand without holding onto something, or if you are driving a car, it becomes difficult to drive at a normal speed. If the wind gets even stronger, tree branches or skinny trees may break or fall and street signs and other objects not firmly fixed or installed may fly. You can see it is extremely dangerous to be outside.
We also need to stay vigilant for the massive rainfall. Typhoons bring large amounts of rainfall over a wide area in a short period of time from a few hours to several days. This can cause rivers to rise and levees to break, resulting in inundation and flooding. Intensive rainfall upstream of a river can cause the water to rise suddenly, rushing downstream and causing flood damage even though there has been no rainfall in the downstream area. Rain can also cause landslides, as the ground becomes loose with the rainwater.
Summer is a perfect season for outdoor activities. Whether going to the mountains or to the beach, please keep an eye on the weather forecast so you can take the necessary precautions. We wish you all a safe and fun summer!
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