Facts on Severe Wind Gusts in NSW
Severe thunderstorms by definition produce wind gusts of at least 90 km/h or more, although peak winds may exceed 160 km/h in the most damaging storms. The strongest measured wind gust during a NSW thunderstorm is 174 km/h at Richmond on 3 December 2001.
Wind gusts are generated in thunderstorms when falling rain and hail drag the surrounding air downwards. Evaporation of the raindrops and hail cools the descending air, increasing the air's density, and accelerating the downward rush. The strong downdraft then spreads out once it reaches the ground, producing a cool, gusty wind that can cause damage. If the storm itself is moving quickly, or the atmospheric winds aloft are strong, the wind gusts at ground level may increase further.
Severe thunderstorm wind gusts can occur at any time of the year, however the most likely times are from August to December. Approximately 40% of all severe thunderstorms are associated with strong wind gusts.
The most damaging thunderstorm-related windstorm to date in Australian history occurred in Sydney's northern suburbs on the afternoon of 21 January 1991. Trees up to one metre in diameter were snapped or uprooted and 7,000 houses damaged, 20 so badly they had to be demolished. An inspection of damage following the event suggested winds at the height of the storm reached 230 km/h. The combination of extraordinary winds and hail up to 7cm in diameter saw an insurance payout of $219 million.
Recent examples of damaging wind gusts include: