There is a committee at the World Meteorological Organisation in Geneva that decides the names many years in advance. They have a list of names for each region in the world that is responsible for identifying and classifying a tropical cyclone.
Importantly they never use the names of previous cyclones again in case some members of the public think Cyclone Tracy or Hurricane Katrina, for example, have come back. That is impossible, of course, but some may fear a cyclone with the same name might have the same impact. We acknowledge Aboriginal and Torres Strait Islander peoples as the First Australians and Traditional Custodians of the lands where we live, learn, and work.
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Popular Now 1. The formation of a tropical cyclone requires a number of favourable environmental conditions and one of them is a suitable latitude. Almost all tropical cyclones form over regions more than 5 degrees of latitude away from the Equator and very few occur near the Equator.
To explain why this happens, we need to first understand which forces in the atmosphere are critical to the formation of tropical cyclones. There are three such forces including the frictional force, pressure gradient force and Coriolis force due to the Earth's rotation. The characteristics of these three forces are introduced below:. We all know that the air pressure decreases as we move towards the centre of an area of low pressure. If there were only pressure gradient force and frictional force in the atmosphere, the air would just flow from the surroundings of higher pressure to the centre of the low pressure without any rotation see Figure 3.
However, in the presence of Coriolis force, the air will not just move from the surroundings towards the centre of the low pressure, but will also be deflected leading to the formation of a vortex see Figure 4 , which is favourable to tropical cyclone formation.
Skip Content. The characteristics of these three forces are introduced below: Frictional force: generated when the air molecules move and rub against ambient substances for example, the ground surface. Frictional force causes the air molecules to lose kinetic energy and slow down. Pressure gradient force: arising from the pressure difference between two places.
The air molecules are pushed from an area of higher pressure towards an area of lower pressure. A tropical cyclone has so many of these, they form huge, circular bands. Air from surrounding areas with higher air pressure pushes in to the low pressure area. Then that "new" air becomes warm and moist and rises, too. As the warm air continues to rise, the surrounding air swirls in to take its place.
As the warmed, moist air rises and cools off, the water in the air forms clouds. The whole system of clouds and wind spins and grows, fed by the ocean's heat and water evaporating from the surface.
Storms that form north of the equator spin counterclockwise. Storms south of the equator spin clockwise. This difference is because of Earth's rotation on its axis. As the storm system rotates faster and faster, an eye forms in the center. It is very calm and clear in the eye, with very low air pressure. Higher pressure air from above flows down into the eye. If you could slice into a tropical cyclone, it would look something like this. The small red arrows show warm, moist air rising from the ocean's surface, and forming clouds in bands around the eye.
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