Southerly Busters, also known to Sydneysiders as Southerly Bursters, are fierce winds that roar up the coast of New South Wales between October and February. Gusts are greater than 29 knots or 89 kph. Within an hour, the temperature drops by 10 to fifteen degrees.
A roll cloud like the one seen in the picture is not always a precursor to these winds. Often they come with little or no warning. About five of these hit Sydney every year, usually showing up in late afternoon or early evening.
Typically, Busters are between thirty and a hundred kilometers wide and depths can reach a thousand metres. In 1948, a spectacular Buster brought winds gusting to 113 kph. Along with violent squalls, Busters bring thunder and lightning.