Dec 08 2014

What is a Super-typhoon

What is a Super-typhoon?

This is a term utilized by the U.S. Joint Typhoon Warning Center for typhoons that reach maximum sustained 1-minute surface winds of at least 240 kph or 150 mph.

This is the equivalent of a strong Saffir-Simpson category 4 or category 5 hurricane in the Atlantic basin or a category 5 severe tropical cyclone in the Australian basin (Australia: winds with typical gusts over open flat land of more than 280 km/h.).

Wind Speed Definitions:

Gusts are just a few seconds, for example the maximum speed sustained for about 3 to 5 seconds.

Maximum sustained wind is normally taken over a ONE, TWO or TEN minute period, to get a value for a sustained wind peak.

Winds are measured at 10 metres (33 ft) above the Earth’s surface.

Differences in Measurement of Maximum sustained winds

The United States National Weather Service defines sustained winds within tropical cyclones by averaging Maximum sustained winds over a period of ONE minute.

The World Meteorological Organization (WMO), defines sustained winds within tropical cyclones by averaging Maximum sustained winds over a period of TEN minutes.

Tropical Cyclone Intensity from an Australian perspective

Tropical cyclone intensity is defined by the maximum mean wind speed over open flat land or water. This is sometimes referred to as the maximum sustained wind and will be experienced around the eye-wall of the cyclone.

Mean Winds and Gusts

Mean Wind: In most of the world the mean wind speed is defined as the wind speed averaged over a period of 10 minutes. It should be measured at 10 m above the surface. The major exception is the USA where they use a 1-minute average.

Wind Gust: In most of the world the wind gust speed is defined as the wind speed averaged over 2 or 3 seconds (in Australia we use 3 seconds).

Typically gusts over open land will be about 40% greater than the mean wind and gusts over the ocean will be 25 – 30% greater than the mean wind. It is often the stronger gusts that cause the most significant damage to buildings.

http://www.bom.gov.au/cyclone/about/intensity.shtml

Saffir–Simpson hurricane wind scale

Category Wind speeds kmh Wind speeds mph
Five over 251 over 156
Four 209 to 251 130 to 156
Three 178 to 208 111 to 129
Two 154 to 177 96 to 110
One 119 to 153 74 to 95
Tropical Storm 63 to 118 39 to 73
Tropical Depression under 63 under 39

Tropical Cyclone Category System

CATEGORY 1 (tropical cyclone)

Negligible house damage. Damage to some crops, trees and caravans. Craft may drag moorings.
A Category 1 cyclone’s strongest winds are GALES with typical gusts over open flat land of 90 – 125 km/h.
These winds correspond to Beaufort 8 and 9 (Gales and strong gales).

CATEGORY 2 (tropical cyclone)

Minor house damage. Significant damage to signs, trees and caravans. Heavy damage to some crops. Risk of power failure. Small craft may break moorings.
A Category 2 cyclone’s strongest winds are DESTRUCTIVE winds with typical gusts over open flat land of 125 – 164 km/h. These winds correspond to Beaufort 10 and 11 (Storm and violent storm).

CATEGORY 3 (severe tropical cyclone)

Some roof and structural damage. Some caravans destroyed. Power failures likely.
A Category 3 cyclone’s strongest winds are VERY DESTRUCTIVE winds with typical gusts over open flat land of 165 – 224 km/h.
These winds correspond to the highest category on the Beaufort scale, Beaufort 12 (Hurricane).

CATEGORY 4 (severe tropical cyclone)

Significant roofing loss and structural damage. Many caravans destroyed and blown away. Dangerous airborne debris. Widespread power failures.
A Category 4 cyclone’s strongest winds are VERY DESTRUCTIVE winds with typical gusts over open flat land of 225 – 279 km/h.
These winds correspond to the highest category on the Beaufort scale, Beaufort 12 (Hurricane).

CATEGORY 5 (severe tropical cyclone)

Extremely dangerous with widespread destruction.
A Category 5 cyclone’s strongest winds are VERY DESTRUCTIVE winds with typical gusts over open flat land of more than 280 km/h.
These winds correspond to the highest category on the Beaufort scale, Beaufort 12 (Hurricane).

The Beaufort scale

0: Under 1 km/h – Calm
1: 1 to 5 km/h – Light Air
2: 6 to 11 km/h – Light breeze
3: 12 to 19 km/h – Gentle breeze
4: 20 to 28 km/h – Moderate breeze
5: 29 to 38 km/h – Fresh breeze
6: 39 to 49 km/h – Strong breeze
7: 50 to 61 km/h – Near gale
8: 62 to 74 km/h – Gale
9: 75 to 88 km/h – Strong gale
10: 89 to 102 km/h – Storm
11: 103 to 117 km/h – Violent storm
12: 118 and over km/h – Hurricane

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