WITH Cyclone Debbie bearing down on much of Central and North Queensland, there are plenty who perhaps have heard the sirens and the warnings but know little about what they're facing.
With the help of the Bureau of Meteorology, here are a bunch of answers to questions you were too embarrassed to ask while hunkering down at your nearest storm shelter.
WHAT IS A TROPICAL CYCLONE?
A tropical cyclone is low pressure weather system that grows over warm waters, and must have an average wind speed of 34 knots or higher for at least six hours.
Every cyclone is unique varying according to a number of factors including life cycle, intensity, movement, size and impact (wind, storm surge and flooding).
WHAT DO THE CATEGORIES MEAN?
Negligible house damage. Damage to some crops, trees and caravans. Craft may drag moorings
Strongest wind gusts: less than 125kmh (Damaging winds)
Minor house damage. Significant damage to signs, trees and caravans. Heavy damage to some crops. Risk of power failure. Small craft may break moorings.
Strongest gusts: 125-164kmh (Destructive winds)
Some roof and structural damage. Some caravans destroyed. Power failures likely. (e.g. Winifred)
Strongest gusts: 165-224kmh (Very destructive winds)
Significant roofing loss and structural damage. Many caravans destroyed and blown away. Dangerous airborne debris. Widespread power failures. (e.g. Tracy, Olivia)
Strongest gusts: 225-279kmh (Very destructive winds)
Extremely dangerous with widespread destruction. (e.g. Vance)
Strongest gusts: more than 279kmh (Very destructive winds)
WHAT IS THE DIFFERENCE BETWEEN A STORM SURGE AND STORM TIDE?
The combination of storm surge and astronomical tide is known as 'storm tide'. The worst impacts occur when the storm surge arrives on top of a high tide.
When this happens, the storm tide can reach areas that might otherwise have been safe.
A storm surge is a "mound" of water that hits the coast as the cyclone makes landfall.
HOW MUCH DAMAGE IS DONE AS WIND SPEED INCREASES?
Would a cyclone with wind gusts of 280 km/h cause twice the damage of a similar sized cyclone with wind gusts of 140 km/h? No - it would cause hundreds of times more damage.
As wind speed increases the power of the wind to do damage increases exponentially.
Hence a category 5 severe tropical cyclone (with wind gusts > 280 km/h) has the potential to do around 250 times the damage of a Category 3 severe tropical cyclone (with wind gusts of 165 km/h).
HOW DOES THE BOM MEASURE THE INTENSITY OF A CYCLONE?
Winds are measured by "anemometers" from observing sites, although whatever speeds they record is an underestimate.
- The "Dvorak Technique" has been used to measure cyclone intensity, based on infra-red and visible cloud patterns, which are then matched to wind speed.
- Scatterometers measure the roughness of the ocean to estimate wind speeds, but their accuracy is not so great when smashed by heavy winds and rains that come when a cyclone tops Category 2.
- Microwave instruments aboard weather satellites show extra information by "seeing through" high clouds that hide the centre of the storm. Aircraft observation, computer alorithms and computer modelling also play a role.
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