Subject: D2) How are Australian tropical cyclones ranked?
Cyclone Severity Categories – From the Australian Bureau of Meteorology FAQ
An estimate of cyclone severity is now included in all tropical cyclone advices. The table below provides information concerning effects due to wind which are typical of cyclones in the various categories. Remember that the system is not designed to give an exact statement of conditions at individual locations but will give a general idea of the expected worst conditions. Categories of cyclone severity range from ” 1 ” for weak cyclones to “5” for the most severe cyclones. Accordingly, the risk of property and crop damage, shore erosion and danger to life increases from low for a category 1 to very high for a category 5 cyclone. Using this severity scale, communities will be able to assess the degree of cyclone threat and take appropriate action. It must be emphasized that the category refers to the severity in the zone of maximum winds and therefore the effects felt at individual locations may not be exactly as described in the accompanying table.
Damage will vary from location to location depending upon factors such as:
* how far you are from the zone of maximum winds
* how exposed the location is
* building standards
* vegetation type
* resultant flooding
It should also be noted that the category does not refer to storm tides; if a storm tide is expected it will be mentioned separately in the cyclone warning.
|Categories||Strongest Gusts||Averaged Wind Speeds||Typical effects
|Category 1||< 125 km/h||63-88 km/h||Negligible house damage. Damage to some crops, trees and
caravans. Craft may drag moorings.
|Category 2||125 – 170 km/h||89 – 117 km/h||Minor house damage. Significant damage to signs, trees and
caravans. Heavy damage to some crops. Risk of power failure. Small craft
may break moorings.
|Category 3||170 – 225 km/h||118 – 159 km/h||Some roof and structural damage. Some caravans destroyed. Power
|Category 4||225 – 280 km/h||160 – 199 km/h||Significant roofing loss and structural damage. Many caravans
destroyed and blown away. Dangerous airborne debris. Widespread power failure.
|Category 5||> 280 km/h||> 200 km/h||Extremely dangerous with widespread destruction.||Cyclone Orson|
Note: Average wind speed is for 10-minute average. 1 km/h ~ .54 kt or .63 mph