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In case of natural disasters |
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2-2 Typhoons
Typhoons occur between July and October, bringing torrential rain and extremely strong winds. Landslides and flooding can occur due to typhoons. There is also a risk of injuries due to fragments that have been blown about, and flood tides.
(1) Typhoons
Tropical cyclones occurring at a longitude of 100-180 degrees east in the Pacific Ocean or East China Sea with minimum wind speed of 17.2m/s near the center are called "typhoons." They are the same as hurricanes and cyclones. Caution is necessary, because typhoons can cause a great deal of damage.
The mean pressure of the surrounds of Japan is 1013hPa (Hectopascal); when a typhoon approaches, the air pressure goes down. The lower the air pressure, the stronger the wind and rain tend to become.
The winds of a typhoon in Japan blows in an anticlockwise direction. Moving towards the right-hand side in the direction of the typhoon, this side is even stronger than the left-hand side because the wind which is generated by the typhoon itself blows in the same direction as the wind which is moving the typhoon. The extent of the damage varies considerably depending on the path which the typhoon takes, so you should prepare for typhoons by measures such as watching the weather forecast.
It is essential to be careful of flood tides around the coastline due to rises in sea levels and strength of the wind caused by the low air pressure. Sea levels go up 1cm for every 1hPa that air pressure drops, and grows higher by square in proportion to the power of the wind speed. When the effect of the high water levels is added to high tide, this can result in serious damage; you should avoid going near the sea at such times.
(2) Strength of typhoons
The strength of the winds of a typhoon are measured primarily in terms of maximum wind speed, with reference to the center of the typhoon and air pressure.
| Type of strength |
Air pressure at the center (hPa) |
Maximum wind speed |
| Low-level typhoon |
990～ |
17.2～25m |
| Regular typhoon |
950～989 |
25～33m |
| Strong typhoon |
930～949 |
33～45m |
| Very strong typhoon |
900～929 |
45～50m |
| Extreme typhoon |
～900 |
Over 50m |
(3) Level of typhoons (size)
The size of typhoons is shown as follows. The term "area affected by strong winds" refers to the area where wind speed reaches 15m/s. Areas where winds are stronger than this are referred to as the "storm area."
| Level |
Scope of the area affected by strong winds |
| (No phrase) |
Under 500km |
| Moderately large/Large |
Over 500km, under 800km |
| Very large/Extremely large |
Over 800km |
(4) Strength of winds
The winds of typhoons and the damage forecast are as follows.
| Average wind speed |
Effect on people/ damage to buildings etc. |
| Wind speed of 10m/s |
People cannot put up umbrellas. Signs and corrugated sheeting that have not been put up properly start to be blown about. |
| Wind speed of 15m/s |
Plastic greenhouses start to experience breakage. Signs and corrugated sheeting start to be blown about. |
| Wind speed of 20m/s |
Children are almost blown off their feet. People cannot stand without leaning at an angle of about 30 degrees. |
| Wind speed of 25m/s |
Branches are broken. Steel shutters begin to experience breakage. Window glass is broken by objects being blown about. Roof tiles are blown about, and television aerials and chimneys fall over. Brick walls are broken, and external fittings on buildings that have not been properly attached are torn off, and blown about. |
| Wind speed of 30m/s |
Weather-proof shutters come loose, roofs begin to be blown off and wooden houses begin to be destroyed. Electricity poles sometimes fall over. |
| Wind speed of 35m/s |
Passenger cars of train sometimes fall over. |
| Wind speed of 40m/s |
People cannot stand without leaning at an angle of about 45 degrees. Small rocks are blown about. |
| Wind speed of 50m/s |
Most wooden houses fall over. Trees are torn up by the roots and blown over. |
| Wind speed of 60m/s |
Steel towers are bent. |
(5) Indications of levels of precipitation
The levels of precipitation and actual situations caused by typhoons are as follows.
| Levels of precipitation per hour |
Actual situation |
| 5～10mm |
Puddles form. The sound of rain can be heard clearly. |
| 10～20mm |
Conversation may not be heard due to the sound of the rain. Disaster warnings become necessary should this rain continue for a long time. |
| 20～30mm |
Drain overflow, and small rivers can flood. There is a risk of landslides. |
| Over 30mm |
Torrential rain, as though buckets of water were being overturned. Prepare for evacuation, and evacuate on your own initiative if you think there is a danger. |
(6) When a typhoon occurs
1 If you have weather-proof shutters or ordinary shutters, close them. |
2 If the wind is strong, do not go outside. |
3 Frequently check the latest weather information. Notwithstanding point (a), evacuate promptly if an evacuation advisory is given. |
4 Keep away from broken electricity poles or electricity cable that are hanging down. |
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