Tropical cyclones keep making headlines worldwide. With wind speeds of up to 195 kilometers per hour, Cyclone Idai broke through southeastern Africa in March, leaving a picture of devastation. While the Southeast African country of Moçambique was hit again by a tropical cyclone shortly thereafter, recent hurricane “Dorian” in the Bahamas made for sad headlines. Although the terms “cyclone” and “hurricane” are likely to be familiar to most, when asked what is the difference between a hurricane, a cyclone, and a typhoon, many are likely to falter.
Are the three terms one and the same weather phenomenon or are there serious differences? The most important questions and answers at a glance:
Cyclone, Hurricane, Typhoon: What are the differences?
Hurricanes, typhoons and cyclones are all tropical cyclones and nothing more than different terms for one and the same weather phenomenon. Whether a tropical cyclone is called a cyclone, hurricane or typhoon depends on which region the storm is occurring.
- As hurricanes, tropical cyclones are called, which occur in the North Atlantic, the Caribbean and the Gulf of Mexico, as well as those in central and eastern North Pacific.
- The same weather phenomenon is called typhoon in the western North Pacific.
- Cyclones, in turn, occur in the Indian Ocean and the western South Pacific.
What are tropical cyclones?
A tropical cyclone is a low pressure area with organized vertical air movements – called convection in meteorology, heavy thunderstorms and a closed bottom wind circulation around the center. Usually they arise only in the tropics and subtropics.
The so-called Coriolis force causes tropical cyclones to rotate cyclically, and it also determines which direction a storm will turn. Because of the earth’s rotation, trade winds are deflected to the right in the northern hemisphere, and trade winds on the southern hemisphere to the left. As a result, tropical cyclones turn clockwise in the southern hemisphere and counterclockwise in the northern hemisphere.
When is a storm a hurricane, typhoon or cyclone?
To be classified as a hurricane, typhoon or cyclone, a storm near its center must reach wind speeds of at least 119 kilometers per hour. If a hurricane reaches a wind speed of 179 kilometers per hour, this is called a “strong hurricane”. A typhoon with a wind speed of 241 kilometers per hour is called “Supertaifun”.
On the Beaufort scale, the world’s most widely used system for describing wind speeds, a storm is called a hurricane, typhoon or cyclone when its wind force is more than 11.
On the Saffir-Simpson hurricane scale , hurricane strength varies between category 1 and 5. While category 1 hurricanes reach wind speeds of 119 to 153 kilometers per hour, wind speeds in a hurricane of level 5 are more than 249 kilometers per hour.
The wind speed has nothing with the speed of movement to do the storm, which is much deeper and is only 15 to 30 kilometers per hour.
How do such storms arise?
Prerequisite for the emergence of a tropical cyclone are strongly heated, moist air masses. Therefore, such storms can form only in intense sunlight above the sea at a water temperature of over 26 degrees Celsius. Such conditions are usually found only in the tropics and subtropics.
Emergence of tropical cyclones
Due to strong sunlight, the seawater heats up and evaporates. From at least 26.5 degrees Celsius, the conditions for the formation of a tropical cyclone are given. Warm, humid air rises and cools upwards.
Finally, more and more air rises through the storm clouds upwards, whereby the suction of the low pressure area is getting bigger. The incoming air is thereby accelerated. The rotation of the earth produces the Coriolis force. It deflects the movement of air in the thunderstorms so that a whirlwind arises from it.
How are tropical cyclones structured?
At the center of a cyclone depression is the so-called eye. It is free of cloud and wind and usually 20 to 60 kilometers wide. The clouds of a cyclone low turn around the eye and form a cloud wall of 12 to 16 kilometers in height. The cloud wall is the most active thunderstorm zone of a hurricane. Wind speeds can reach over 200 kilometers per hour and rainfall over 100 millimeters per hour.
At what time of year do tropical cyclones develop?
- In the Caribbean and America, the hurricane season lasts from
1 June to 30 November. The highlight of the season takes place in August and September.
- The typhoon season in the western North Pacific usually extends from May to November.
- The cyclone season in the Southwest Pacific and Australia usually lasts from November to April. In the Bay of Bengal and the Arabian Sea, on the other hand, the tropical cyclones usually occur from April to June and from September to November. The eastern coast of Africa is usually hit by cyclones from November to April.
Which regions are the hardest hit?
Because of the favorable water temperatures there, most tropical cyclones occur within a zone that lies around the equator between the southern and the northern latitude 30 degrees. The Coriolis force, the distracting force of the Earth’s rotation, however, is strong enough to initiate a rotational movement of the cyclones only from 5 degrees north and south latitude. Therefore, the equatorial area is practically excluded as a tropical tropics storm zone.
Around two-thirds of all tropical cyclones form in the northern hemisphere. They are most common in the Western Atlantic, the Eastern North Pacific, the Western North Pacific, the Northern and Southern Indian Ocean, and the Southwest Pacific off Australia. There are virtually no tropical cyclones in the South Atlantic and Southeast Pacific, where the sea surface temperature is too low.
The hurricanes of the North Atlantic are particularly dangerous for the Caribbean, Central America and the southern United States. The typhoons in the Northwest Pacific often have an impact on China, Japan, South Korea, Southeast Asia and numerous islands in Oceania. Cyclones in the Indian Ocean mainly hit India, Bangladesh, Sri Lanka, Burma and Pakistan as well as eastern Africa. Cyclones in the Pacific pose a threat especially to Australia and the islands in Oceania.
How long does a tropical cyclone survive?
The lifetime of a tropical cyclone can be several days or weeks. Important for the survival of the storm is the supply of warm, moist air. This supply is interrupted as soon as the cyclone low hits land or a cool ocean current. If the cloud vortex hits land, it is additionally slowed down by the soil friction. As a result, the low pressure area weakens and finally dissolves.
What were the strongest tropical cyclones in the recent past?
The strength of a tropical cyclone can be measured in several ways, such as with the highest wind speeds reached or with the low air pressure caused. The record for the highest ever measured wind speed outside a tornado is held by the cyclone “Olivia”, which sailed over Western Australia in 1996. The record speed of 408 kilometers per hour, measured on Barrow Island off the Australian west coast, was later reviewed and confirmed by scientists.