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Tasmania is home to some of the windiest places in the country. This is why

By Belinda House, Wednesday November 18, 2020 - 15:35 EDT
ABC image
The highest wind gust recorded in Tasmania was similar to a category three cyclone. - ABC

As a small, mountainous island Tasmania has many exposed coastal sites and elevated terrain.

It is at these locations that the windiest conditions are experienced.

So what are the highest wind gusts measured in Tasmania?

And how does Tasmania's terrain affect winds across the island?



What drives Tasmania's winds?

Tasmania's wind and weather are dominated by a persistent belt of westerly winds that extend across the state throughout the year.

The strength of these westerly winds varies between the seasons, determined by the north-south movement of a band of high pressure, known as the sub-tropical ridge, over Australia.

During the cooler months, the sub-tropical ridge sits over the Australian continent.

Strong cold fronts cross Tasmania bringing a shift from relatively warm north-westerly winds originating from mainland Australia to colder, south-westerly winds drawn up from Antarctica.



During summer the sub-tropical ridge shifts to the south of the continent.

High pressure systems become more dominant over Tasmania, as the belt of westerly winds also shifts southwards.

And while summer still sees the intrusion of the occasional cold front, winds associated with them tend not to be as strong.

Local effects

While Tasmania's prevailing winds are westerly during summer, when these winds tend to weaken, onshore winds becoming more dominant in the form of sea breezes.



Warming over the land under the summer sun causes air to rise, which draws in air from adjacent waters resulting in an onshore air-flow known as a sea breeze.

Sea breezes are not purely a summer-time phenomenon but they are strongest during summer, with late afternoon the strongest time of day.

Tasmania's mountainous terrain also affects wind strength and direction.

Generally speaking, winds are stronger higher up in the atmosphere than lower down, so mountain peaks are likely to experience greater wind strength.

Winds in the lee of mountains can also be affected — sometimes enhancing wind strength, sometimes lowering it — and even changing the wind's direction.

An example of this can be seen when strong westerly winds blowing over a mountain encounter a stable layer in the atmosphere just above ridge top.

These winds can be redirected down the mountain, producing gusty conditions at the surface.

If the winds aloft are particularly strong the air-flow can become turbulent, producing winds of varying speeds and directions.



Wind observations

kunanyi/Mount Wellington, in the state's south, with an elevation of 1,260 metres, has a highest recorded wind gust of 200 kilometres per hour — similar to a category three cyclone.

The highest wind gust on Maatsuyker Island, the state's southern most island, was 185kph.

Other notable wind gusts, all in excess of 150kph, are listed in the table below:

Highest wind gusts recorded in Tasmania


Location

(elevation, metres)

Maximum wind gust

(kph) Date
kunanyi/Mount Wellington (1,260 m) 200 March 1998
Maatsuyker Island (147 m) 185 June 2015
Tasman Island (240 m) 161 September 2003
Cape Grim (94 m) 161 August 2013
Scotts Peak (408 m) 159 July 2014
Mount Read (1,120 m) 156 August 2007
Bushy Park (27 m) 154 April 2004
Hobart (51 m) 150 September 1965

Source: Bureau of Meteorology



Wind warnings

The Bureau of Meteorology issues warnings for potentially hazardous wind.

Severe Weather Warnings are issued for land areas and warn of the risk of damaging or destructive winds.



Severe winds in Tasmania are most often associated with the passage of vigorous cold fronts or deep low-pressure systems, with the strongest winds aligned to the prevailing westerly direction.

In Tasmania, damaging winds are defined as sustained winds of 63 km/h or more or wind gusts of 100 km/h, and destructive wind gusts are defined as wind gusts of 125 km/h or more.

However, in situations where the winds are not the prevailing westerly, winds of a lower strength may still be hazardous.

An example of this is when deep low-pressure systems form over the Tasman Sea, bringing strong easterly winds to Tasmania.

It is observed that trees are more susceptible to falling in less prevalent wind conditions, especially if the ground is saturated, and it may be appropriate to consider lower wind strength thresholds — Severe Weather Warnings reflect this.

The Marine Wind Warning Service complements the Bureau of Meteorology's local and coastal waters forecasts and is designed to alert marine users to strong winds, defined as 26 knots or more, or stronger.

Understandably, the Marine Wind Warning is a common feature on the daily Tasmanian Warnings Summary.

Belinda House is a meteorologist with the Bureau of Meteorology


- ABC

© ABC 2020

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