Typhoon

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.

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 blow 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.

Strength of typhoons

The strength of the winds of a typhoon is 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

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

Strength of winds

The winds of typhoons and the damage forecast 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.