A typhoon is a powerful tropical cyclone born over tropical seas, bringing heavy rain and strong winds to Japan from summer through autumn.
Basic Knowledge
A typhoon is a tropical cyclone that forms in the northwestern Pacific (west of 180° east longitude) and reaches a maximum wind speed of 17.2m/s (34 knots) or more. Near its center, winds blow counterclockwise inward, and the central “eye” may have clear weather because of descending air currents.
The typhoon's energy source is the latent heat of condensation of water vapor from warm seawater (approximately 26–27℃ or higher), and it develops more strongly as the seawater temperature rises. When it reaches a cold front or land, its supply of water vapor is cut off and it weakens.
Near the equator, its path is carried westward by the trade winds. As it moves north, it turns eastward after entering the prevailing westerlies. When approaching Japan, it often follows a parabolic path toward the northeast.
Tropical cyclone (a low-pressure system that forms over tropical seas; it has no fronts)
Typhoon (a tropical cyclone with a maximum wind speed of 17.2m/s or more)
Eye of a typhoon (an area of weak winds and clear weather at the center; several tens of km in diameter)
Storm and gale-force wind areas (the storm area has winds of 25m/s or more; the gale-force wind area has winds of 15m/s or more)
Storm surge (a rise in sea level caused by the typhoon's low pressure effect + strong winds)
Dangerous semicircle and navigable semicircle (the right side in the direction of movement is the dangerous semicircle, where winds are stronger)
Further Study (Background and Significance)
A typhoon's energy comes from the latent heat of condensation of water vapor, and its energy release in one day is sometimes said to equal that of tens of thousands of large hydrogen bombs. As seawater temperatures rise due to global warming, typhoon intensity and water volume are expected to increase, and extremely powerful storms called “super typhoons” have become more common in recent years.
Examples of typhoons that caused major damage in Japan include Isewan Typhoon (1959) (5,098 dead or missing) and the Reiwa 1 East Japan Typhoon (2019, Typhoon No. 19) (more than 140 victims).
On the right side in the direction of movement, the typhoon's own winds and its forward-motion winds combine. This side is called the dangerous semicircle and has stronger winds. Ships evacuate by choosing the left side (the navigable semicircle).
- Typhoon = tropical cyclone + wind speed of 17.2m/s or more
- Forms in the northwestern Pacific and has no fronts
- Energy source = latent heat of condensation of water vapor
- Develops at seawater temperatures of 26–27℃ or higher
- Initially moves west with trade winds → turns east with prevailing westerlies
- Passes near Japan along a parabolic path
- Right side in the direction of movement = dangerous semicircle (stronger winds)
Points of Caution (Easily Confused)
① A typhoon (northwestern Pacific), hurricane (northeastern Pacific to Atlantic), and cyclone (Indian Ocean to South Pacific) are regional names for the same type of tropical cyclone. ② Typhoons have no fronts, unlike extratropical cyclones. ③ The dangerous semicircle is the right side in the direction of movement. ④ A storm surge is the combination of sea-level rise caused by falling air pressure + wind-driven water piling up.
Practice
- What seawater temperature, approximately, is needed for a typhoon to develop?
- What is the name of the region near a typhoon's center where the weather may be clear?
- Which is the dangerous semicircle, the right or left side in the direction of movement?