Japan Typhoon Season: How to Prepare for a Disaster

Earthquakes aren't the only natural disasters to be aware of in Japan. In recent years, rising sea surface temperatures due to global warming have caused typhoons to form closer to Japan and become more intense.

Tropical storms, which develop from tropical depressions, are known as “typhoons” in Japan and East Asia. In other parts of the world, they are called “hurricanes” (in North and Central America) or “cyclones” (in the South Pacific and Indian Ocean).

Read on to learn how to detect when a typhoon is approaching—and how to stay safe until it passes.

You can check the latest typhoon information on the Japan Meteorological Agency's website or the Joint Typhoon Warning Center (JTWC) website. On the JTWC site, click on the “TC Warning Graphic” for the specific typhoon to view detailed information.

Image source: Japan Meteorological Agency

Image source: Joint Typhoon Warning Center (JTWC), U.S. Navy

Typhoon Categories by Wind Speed and Knots

The classification of a typhoon is based on its maximum sustained wind speed, typically expressed in miles per hour (mph), meters per second (m/s), or knots (kt).

In Japan, a tropical system with a maximum wind speed of 39 mph (17 m/s or 34 kt) or more is classified as a “Typhoon (Taifū / 台風). Internationally, the term “Typhoon” is used for tropical cyclones in the Northwest Pacific with wind speeds of 74 mph (64 kt or 33 m/s) or higher—comparable to a hurricane or cyclone in other regions.

 

Maximum Wind Speed (mph)	Categorization in Japan	International Categorization
〜 38 mph (〜17 m/s)  〜 33 knots	Tropical Depression (Nettai Teikiatsu / 熱帯低気圧)	Tropical Depression (TD)
39 - 54 mph (18 - 24 m/s) 34 - 47 knots	Taifū (台風)	Tropical Storm (TS)
56 - 73 mph (25 - 32 m/s) 48 - 63 knots	Taifū （台風）	Severe Tropical Storm (STS)
74 - 97 mph (33 - 43 m/s) 64 - 84 knots	Strong Taifū (Tsuyoi Taifu / 強い台風 )	Typhoon / Hurricane
98 - 120 mph (44 - 53 m/s) 85 - 104 knots	Very Strong Taifū (Hijōni Tsuyoi Taifū /非常に強い台風)	Typhoon / Hurricane
Over 120 mph (54 m/s+) 105 knots+	Violent Taifū ( Mōretsuna Taifū / 猛烈な台風)	Typhoon / Hurricane

On news and weather forecasts, typhoons are often described with terms like “a large and very strong typhoon.”
When the Japan Meteorological Agency issues a warning ("Keihō") or an advisory ("Chūihō"), be sure to stay alert and take appropriate precautions.

Types of Typhoon Warnings

Major warnings can be expected at the time of a typhoon, especially with the sea nearby. Look out for the following types of warnings that can result from a strong typhoon.

Type of Alarms
Heavy Rain Warning Ōame Keihō	It announced when there is a risk of severe disasters due to heavy rain. Such disasters include severe inundation (flood) and major mudslides (landslides).
Flood warning Kōzui Keihō	It is announced when there is a risk of severe disasters because river water levels rising due to heavy rain, continual rain, snow melting, etc. Such disasters include the rise of overflow of the river, damages or breakages of the dike, etc.
Storm Warning (Gale Warning) Bōfū Keihō	It is announced when there is a risk of severe disasters due to violent wind.
High Surf Warning Harō Keihō	It is announced when there is a risk of severe disasters due to high surf. The "high surf" totally differs from a "Tsunami" that would appear after earthquakes.
High Tide Warning Takashio Keihō	It is announced when there is a risk of severe disasters due to the sea level rise caused by a typhoon or low atmospheric pressure.

From Japan Meteorological Agency (converted from m/s to mph), here are some guidelines to measure the hazardous conditions brought on by strong winds from a Typhoon:

• 45mph wind speed: People cannot easily stand straight up, and driving a car can be dangerous.
• 50mph wind speed: Trees can be pulled up from the roots and knocked over.

Weather warnings and alarms for the Kanto region (English)

What to Do When a Typhoon Warning or Advisory is Announced

There are five rules of thumb to remember to take the appropriate action in the event of a Typhoon.

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1. Prepare the Outside the House

Shut all the windows and shutters. Secure items that might fall or be blown away, and clean out all areas with poor drainage.

2. Prepare Inside the House

Check emergency supplies, and affix tape over glass to prevent shattering, which can lead to dangerous shards.

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3. Pay Attention to Storm/Flood Information

Staying informed is the best way to ensure the safety and survival of your family. Listen to the latest weather warnings, alarms and evacuation information from the television and radio.

4. Evacuate at the Early Stages of a Typhoon Disaster

Do not delay in evacuating when an evacuation advisory is issued or you feel in immediate danger. Check the advised evacuation method in your area. Also be sure to check the location of an evacuation site in advance as they vary depending on local administrative offices.

* This year many people may think of evacuating via private cars to safer areas rather than to crowded shelters in order avoid the risk of catching the new coronavirus. As a precaution, we highly recommend that you double check the amount of fuel in your vehicle in advance.

5. Do Not Approach Dangerous Places

Do not approach places where the riverbed is high, or where a flood or landslide may occur.

Dangerous Places to Avoid During a Typhoon

It is recommended to stay indoors whenever possible during a typhoon, but if you must be outside, avoid venturing out into these areas at all costs.

Shallow Beaches, Harbor Areas, River Mouth Areas at High Tide

Shallow beaches where water can deepen quickly and areas around harbors are vulnerable to high water conditions.

Stay away from coastal areas that are below average sea level at full tide. Levee breaks may cause serious disaster.

Alluvial Areas Pose a Flood Risk

Exercise extreme caution because deltas (made of sediment carried by the river and deposited at the mouth of a river) and floodplains (area made of deposited sand carried by consistent floods) can flood easily.

River basins and dry riverbeds can also present a serious danger of flooding during downpours.

Developed Land, Alluvial Cones, and Mountain Ranges May Result in Sliding

Developed land that was made by breaking up hillsides may contain unstable soil and terrain. These areas may slide when downpours loosen the ground.

Torrential downpours may cause mountain landslides, and alluvial cones at the foot of a mountain may receive a direct hit. Steep sloping lands of greater than 30° angles and heights of more than 5m may experience a landslide when there is rain. There is an increased danger of mudslides at treeless mountains.

Most Importantly, Stay Safe

Japan typhoon season is a natural phenomenon that should be taken seriously, but if you follow the steps above and keep yourself informed, you should be able to ride out the storm with ease.