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Tropical Cyclones

While tropical cyclones are relatively uncommon in New South Wales, over the past 55 years they have caused significant damage and killed over 30 people.  The effects of tropical cyclones include flooding, destructive winds, storm surges and loss of life.  Communities in at-risk areas should be aware of the risk and be prepared for the possibility of a tropical cyclone impact.

   TC Nancy 1990 Thumbnail
Track of Tropical Cyclone Nancy (1990)

Definition of a tropical cyclone

Tropical Cyclones are low pressure systems. They form over warm tropical waters and have gale force winds near their centre. Technically they are defined as a non-frontal low pressure system of synoptic scale developing over warm waters having organised convection and a maximum mean wind speed of 34 knots or greater extending more than half-way around near the centre and persisting for at least six hours.

The gale force winds can extend hundreds of kilometres from the cyclone centre. If the sustained winds around the centre reach 118 km/h (gusts in excess 165 km/h). then the system is called a severe tropical cyclone. These are referred to as hurricanes or typhoons in other countries.

The circular eye or centre of a tropical cyclone has light winds and often clear skies. The eye is surrounded by a dense ring of cloud about 16 km high known as the eye wall which marks the belt of strongest winds and heaviest rainfall.

Tropical cyclones derive their energy from the warm tropical oceans and do not form unless the sea-surface temperature is above 26.5°C, although once formed, they can persist over lower sea-surface temperatures. Tropical cyclones can persist for many days and may follow quite erratic paths. They usually dissipate over land or colder oceans.

Management of tropical cyclones in New South Wales

In New South Wales the State Emergency Service is responsible for the management of the response to a tropical cyclone. The SES is also responsible for the education of people regarding their risk from tropical cyclones, and ways in which they can prepare themselves and their property.

Tropical cyclone warnings

The Bureau of Meteorology has further information on tropical cyclones in New South Wales, including detailed warning information on how people in New South Wales will be advised if a cyclone is expected to impact New South Wales territory. This information is available at the Bureau of Meteorology Current Tropical Cyclones page.

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