Satellite image of a tropical cyclone.

Satellite image of a tropical cyclone off the coast of Australia.

Image: Jeff Schmaltz/NASA/GSFC

A massive storm called Typhoon Haiyan hit the Philippines earlier this month. One of the largest storms ever observed, it has caused widespread destruction in the island nation.

Typhoons, cyclones and hurricanes are all different names for the same thing: a particularly violent type of tropical storm. Which name it is given depends on where such a storm starts. If it starts around the Americas in the Atlantic and Northeast Pacific ocean, it’s a hurricane. Around Asia, they’re called typhoons. If they form in the South Pacific or Indian ocean they’re referred to as tropical cyclones.

These huge storms start with tropical waters close to the Equator. The warm water heats the air above it. As the air heats it expands in volume and its density decreases, making it rise higher. This creates what is called a low-pressure system.

The warm air cools as it rises. If it cools fast enough the low-pressure system encourages the formation of thunderstorms – a key cyclone ingredient. Still more things are needed, including the right amount of moisture in the air, and existing atmospheric disturbances. Sometimes, even when all these conditions are present, a cyclone still won’t form. The reasons why might not be obvious, and this makes predicting cyclones difficult.

Tropical cyclones are given a category, usually based on how strong their winds are. The Australian Bureau of Meteorology (BOM) uses five categories. The most dangerous tropical cyclones, called category 5, have wind gusts of more than 280 kilometres per hour. Other places will have slightly different systems.

Another thing about cyclones that sets them apart is the fact that they are given names. For Australian cyclones, BOM maintains a list of alternating male and female names. When a tropical cyclone forms, it is given the next name on the list. Other naming systems exist, which use things like animal and plant names as well. As cyclones move from one region to another, they might be given multiple names, based on the different systems.

Typhoon Haiyan, also known as Typhoon Yolanda, was a category 5 super typhoon – the worst category. Similarly powerful storms have also affected North America and Australia in recent years. No matter what you call them, cyclones have the potential to be devastating.

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