Cyclone season extends from 1 November to 30 April. When a cyclone approaches you should listen to your local radio station or monitor your television for cyclone information.
Disaster can strike anywhere and at anytime, with or without warning and may be either of natural or man-made causes. Such disasters include cyclones, earthquakes, flooding, fire, lost or missing persons, trapped persons (building collapse), major motor car, truck or bus accident and aircraft crash.
The threats which may affect the Shire of Roebourne have been identified by the Local Emergency Management Committee and are documented in the Shire's Local Emergency Management Arrangements.
Tropical cyclones are a seasonally occurring natural hazard that cause considerable loss of life and material damage. In Australia, Cyclone Tracy caused the loss of 55 lives in Darwin on Christmas Day 1974. Five lives were lost when Cyclone Alby passed close to the south-west of WA in April 1978 and the most recent loss of life 97) occurred at Onslow during Cyclone Bobby in 1995.
The strongest cyclone ever to cross into Australia (Severe Tropical Cyclone Vance) narrowly missed Karratha and Dampier in March 1999 but caused millions of dollars worth of damage to Onslow and Exmouth. Fortunately, there was no loss of life.
Definition and Occurrence
A tropical cyclone is a circular rotating storm of tropical origin in which the mean wind speed exceeds 63 km/h (gale force). Gale force is the threshold speed at which a cyclone is named. Wind speeds in excess of 100km/h are common by the time a cyclone crosses the coast and higher wind speeds frequently occur. Tropical cyclones can occur at any time of the year, but they are very rare outside the cyclone "season" from the beginning of November to the end of April. They are usually most frequent in February and March.
Once they cross the coast, cyclones tend to decay within 24 to 48 hours and the strong central winds die away. Dangerous flooding can occur as heavy rain falls from the decaying system.
Cyclones threaten life and property in 3 ways:
- Fluctuating wind pressure can weaken and possibly cause the collapse of buildings and other structures.
- Loose objects, such as patio furniture, rubbish bins, dog kennels or building material, become lethal wind borne projectiles that can cause severe structural damage to homes and kill or injure people in their path.
- Flooding, due to an abnormal rise in the level of the ocean (storm surge) caused by the cyclone or as a result of heavy rainfall in river catchments.
As cyclones often adopt an erratic course, or suddenly change speed, it is important that you be aware of any changes at the earliest possible time. In order to do this, keep your radio tuned to the ABC or your local commercial station, WA/FAM, and listen for the most up-to-date cyclone information which is broadcast at regular intervals.