On 24 October 1999, severe thunderstorms affected the mid-north coast and northern rivers districts of New South Wales. Twenty three yachts on Sydney Harbour were damaged and lightning cut power across parts of Sydney. Strong winds brought down trees in many Sydney suburbs. At Kendall in the mid-north coast, 5.5 cm diameter hail was reported. It dented cars, broke windows and skylights, and destroyed gardens. The Illawarra Escarpment received the heaviest rainfall in this event with Wattamolla (Tamol) recording 340 mm over two days.

The Insurance Council of Australia estimated the 1999 damage at $45 million, with the 2017 estimated normalised cost of $129 million.