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| Meteorological Information
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The Tropical cyclone warning system
General Description The Bureau of Meteorology is responsible for detecting, tracking and issuing warnings of tropical cyclones in the Australian region. The warning system is based on three Tropical Cyclone Warning Centres (TCWCs) located in regional offices in Brisbane Darwin and Perth. The centres receive data from radar-equipped weather stations at strategic locations around the coastline, and at Willis Island in the Coral Sea, a series of automatic weather stations on off-shore reefs, a network of several hundred cooperative observers and reports from ships, aircraft, off-shore oil rigs and satellites. During the cyclone season a continuous surveillance is maintained to ensure early detection of possible cyclone development. Whenever the occurrence of a tropical cyclone is expected in the TCWC's area of responsibility, the TCWC is fully activated and manned around the clock by expert tropical cyclone meteorologists supported by specialist technical staff. The meteorologists examine all incoming data, determine the cyclone's position and intensity, and issue advices accordingly.
Warning Advices A Tropical Cyclone Advice is the general name given to cyclone watch and cyclone warning messages. The TCWCs issues the cyclone watch and warning advices and liaises with the police, State or Territory Emergency Services and the media. A tropical cyclone or developing depression that does not threaten any coastal community will be mentioned only in the Bureau's weather notes and in warnings to shipping and aviation. Immediately it is recognised that a cyclone may endanger life or property of coastal communities within 48 hours, the public advice system is activated and a Cyclone Watch is issued. Cyclone Watches are issued whenever the tropical cyclone is expected to cause winds above gale force (63 km/h) on the coast within 48 hours but not within 24 hours. The message contains details of the cyclone's location, intensity and movement, and identifies the coastal areas that could be affected. Cyclone Watches are issued every six hours. A Cyclone Warning is issued as soon as a tropical cyclone is expected to cause gales or stronger winds at coastal or island communities within 24 hours. It identifies the communities being threatened, contains the cyclone's name and category, its location, intensity (including maximum wind gusts), and its movement. Forecasts of heavy rainfall, flooding and abnormally high tide are included when necessary. Communities under threat are also advised to take precautions necessary to safeguard their lives and property. Cyclone Warnings are issued every three hours. When a cyclone is under radar surveillance close to the coast and poses a major threat, Hourly Advices are issued. A tropical cyclone advice is prefixed FLASH when it is the first warning to a community not previously alerted by a cyclone watch. This prefix is also used when major changes are made to the previous warnings, for example due to unexpected movement towards the coast or rapid intensification.
Tropical Cyclone Severity Categories An estimate of tropical cyclone severity is included in all Tropical Cyclone Advices. Categories of cyclone severity range from 1 for a cyclone just reaching cyclone strength to 5 for the most severe cyclones. Accordingly, the risk of property and crop damage, shore erosion and danger to life increase from low for a category 1 to high for a category 5 cyclone. It should be kept in mind that the typical effects described in the table below refer to the expected worst conditions near the cyclone centre.
Tropical Cyclone Severity Categories
Source: Bureau of Meteorology 1992
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