Hailstorms in history – Lessons in Hailstorm Forecasts
The worst hailstorm in history in terms of damage occurred on the 14th April 1999. During the late afternoon as a change began to encroach Wollongong, it was sufficient forcing to break the cap that had kept convection from erupting. Once the cell took off it developed into tall towers. An upper trough of cooling was accompanying the change and assisted in hail production with hail the size of golf balls being reported in the region near Shell Harbour. The Bureau of Meteorology failed to issued a severe thunderstorm warning due to not taking seriously one warning and obvious radar echoes. It was thought the storm was heading off the coast southeast of Sydney.
Unfortunately, the supercell was able to back build onto the Royal National Park and the storm literally exploded probably resulting with the arrival of the coldest air with the upper level trough. Giant hailstones the size of grape fruits pummelled vehicles and punctured holes in household roofs. Finally as the storm was near the city CBD, a warning was issued for hailstones. It was unfortunately too late and the storm had created hundreds of millions of damage. The storm drifted over the northern suburbs and off the coast off the Central Coast. A second storm followed almost in the same path and though with substantially smaller hailstones and affected more of the eastern suburbs and the eastern portions of areas already affected by the giant hailstones!
The estimated cost of this hailstorm was calculated at 1.6 billion dollars making it the costliest hailstorm in Australia’s history! The lack of warning of this natural disaster saw some policy changes and improvements in the Bureau of Meteorology’s severe thunderstorm warning system.