|NSW and southern Queensland are particularly prone to large hail, normally in association with severe thunderstorms that develop along low pressure troughs. Many such storms have hit Sydney, but none worse than that of Wednesday, 14th April 1999. The severe hailstorm that struck the eastern suburbs of Sydney caused extensive damage. The storm represents Australia's costliest natural disaster in terms of insured losses (in excess of $1.5b), with total losses considerably higher.|
During the late afternoon a thunderstorm developed north of Nowra. It moved to the north-east over the ocean, where it changed direction, moving parallel to the coast. The storm recrossed the coast near Helensburgh and cut a path of destruction through eastern Sydney. Huge hailstones, some the size of softballs (11cm in diameter), struck the city and suburbs (particularly in the east). The onslaught of ice, the worst since white settlement, badly damaged or destroyed many cars, partly destroyed many homes, and even damaged commercial aircraft. At least 35,000 buildings, mostly homes, suffered serious roof damage; in many cases roofs were totally destroyed.
The storm was highly unusual in regard to: the size of the hailstones in the eastern suburbs of Sydney (the largest ever recorded in the Sydney area); the duration of the storm (five and a half hours); its track (moving from land to sea, back to land, and then finally out to sea); the time of year (there was no record of giant hail in April in Sydney since 1795); and the time of day (there was a low probability of storms between 7 p.m. and 10 p.m.). It was a rare but unusually severe type of thunderstorm known as a 'supercell', the structure, intensity, movement and longevity of which are characteristically quite different from those of ordinary thunderstorms. Map 1.9 shows the path of the storm.
1.9 PATH OF THE THUNDERSTORM - 14 April 1999
Source: Bureau of Meteorology.