Confused by all the jargon….? This might be useful.
In meteorology, a tropical cyclone is a type of low-pressure system which generally forms in the tropics. The cyclone is accompanied by thunderstorms, and a circulation of winds near the Earth’s surface, which is clockwise in the Southern hemisphere and counter-clockwise in the Northern hemisphere.
Tropical cyclones are classified into three main groups, tropical depressions, tropical storms, and a third group whose name depends on the region. A tropical depression is an an organized system of clouds and thunderstorms with a defined surface circulation and maximum sustained winds of less than 17 metres a second (33 knot or 38 mph). A tropical storm is an organized system of strong thunderstorms with a defined surface circulation and maximum sustained winds between 17 and 33 metres a second (34-63 knot or 39-73 mph). The term used to describe tropical cyclones with maximum sustained exceeding 33 metres a second, varies depending on region, as follows:
hurricane in the North Atlantic Ocean, North Pacific Ocean east of the dateline, and the South Pacific Ocean east of 160°E
typhoon in the Northwest Pacific Ocean west of the dateline
severe tropical cyclone in the Southwest Pacific Ocean west of 160°E or Southeast Indian Ocean east of 90°E
severe cyclonic storm in the North Indian Ocean
tropical cyclone in the Southwest Indian Ocean
(This terminology is defined in WMO/TC-No. 560, Report No. TCP-31, World Meteorological Organization; Geneva, Switzerland; available online from http://www.bom.gov.au/bmrc/pubs/tcguide/globa_guide_intro.htm)
The definition of sustained winds recommended by the WMO is that of a ten-minute average, and that definition is adopted by most countries. However, a few countries use different definitions: the United States, for example, defines sustained winds based on a 1-minute average wind measured at about 10 metres (33 ft) above the surface.
The ingredients for a tropical cyclone include a pre-existing weather disturbance, warm tropical oceans, moisture, and relatively light winds aloft. If the right conditions persist long enough, they can combine to produce the violent winds, incredible waves, torrential rains, and floods we associate with this phenomenon.
There is also a polar counterpart to the tropical cyclone, called an arctic cyclone.
Tropical cyclones with winds exceeding 33 metres a second are given names. These names are taken from lists which vary from region to region. The lists are decided upon either by national meteorological organizations, or by committees of the World Meteorological Organization. The names on the list are reused; however, tropical cyclones which cause major death or destruction have their names retired.
Atlantic names were originally assigned by the U.S. National Hurricane Centre, and are now maintained by the WMO. Other sets of names are used in the Eastern North Pacific, Central North Pacific, and the Western North Pacific (maintained by who?). The Australian Bureau of Meteorology maintains three lists of names, one for the Western Australian region, one for the Northern Australian region, and one for the Eastern Australian region. There are also Fiji region and Papua New Guinea region names (maintained by who?). The Seychelles Meteorological Service maintains a list for the Southwest Indian Ocean.
The category five storm is the worst cyclone to ever hit Australia. Here are some facts about the massive weather system:
Size: 310 miles wide
Winds: up to 186mph
Storm surge: up to 20ft high
Rainfall: 27 inches
Eye: measures 20 miles wide
Expected to hit at 10pm local time (1200 GMT) close to the town of Innisfail
Area on high alert: 400-mile stretch of coast from Cairns to Mackay
Homes at risk of flooding: more than 10,000
Number of people likely to be affected: 350,000
Number of people evacuated from the cyclone’s path: 30,000
The last large cyclone to hit Queensland was Cyclone Larry in 2006. Larry was a category four storm. It destroyed hundreds of homes in Innisfail and caused $1.5bn worth of damage. One person was killed. Cyclone Yasi is twice the size of Larry.
The worst most deadly cyclone to hit Australia was Cyclone Tracy, which devastated the Northern Territory capital of Darwin in 1974, killing 71 people.
IF you’re struggling to grasp the magnitude of Tropical Cyclone Yasi, consider this: it is so large it would almost cover the United States, most of Asia and large parts of Europe.
Most of the coverage about the scale of Yasi has tried to compare it with storms of the past – it’s bigger than Larry, more powerful than Tracy.
But just as powerful is this comparison, showing this storm is continental in size. The main bloc of the cyclone is 500km wide, while its associated activity, shown above in a colour-coding to match intensity, stretches over 2000km.
The storm’s scale of destruction is as shocking as it is inevitable. In the map above, the United States from Pennsylvania in the east to Nevada in the west, from Georgia in the south to Canada in the north and well into Mexico would be battered with 300km/h winds and up to one metre of rain.
The economic impact would be felt around the world.