The word cyclone originates from the Greek "kukloma" meaning "a wheel". It can be defined as a closed circulation of air around a center of low pressure, clockwise in the southern hemisphere and anticlockwise in the northern hemisphere.

Meteorologists use the term cyclone for relatively large-scale storms, usually more than 80km in diameter. This excludes smaller-scale, but sometimes extremely violent storms like tornadoes, water-spouts and whirlwinds.

The most destructive larger-scale storms in the world are Tropical Cyclones, establishing several records for low pressures, high winds, and heavy rainfalls. They breed over warm tropical oceans where the sea surface temperatures are about 27 degrees Celsius. They occur frequently in the western Pacific north of the equator, but rarely if ever occur over the colder waters of the south Atlantic and the eastern part of the South Pacific. A regular supply of abundant water is required by tropical cyclones, and if it is cut off, they decay and die. These cyclones will quickly lose intensity when they move over land and over colder waters. When they move out of the tropics, they will either decay or change their characteristics.

Cyclones require warm waters because they are powered by the release of latent heat from the condensation of water vapor in the atmosphere. The latent heat that can be released in a tropical cyclone in one day is equivalent to the energy released by 400 twenty megaton hydrogen bombs, however, the energy from these cyclones is not as concentrated as in the hydrogen bomb and not released in as short a space of time.. Harnessed this energy would probably be able to met Australia's needs for energy for more than 5 years.

WARNING SYSTEMS

In years past, many cyclones hit the coast with little or no warning. Few observation were available from over the tropical oceans to forecasters, and sometimes cyclones would develop and not be detected from observations at coastal stations, and unless a ship or an aircraft happened to come into contact with one it's existence would be unknown. Even if known, tracking of it's path would be impossible. Satellites and radar have completely changed this situation, enabling forecasters to track and monitor cyclones while they are over the oceans, and as they move closer to the coast, they can be tracked and monitored closely by radar. This combination of satellite and radar has ensured that no major cyclone will go undetected and strike the coast without warning. Weather Bureaus have given high priority to the development of their cyclone warning systems.