Thunderstorms coupled with heavy rain occurred in the Sydney metropolitan area late 9 Apri 1998 and into the following day. Much of the reported damage was due to flash flooding. Hundreds of SES staff and volunteers worked to protect homes around the Narrabeen Lake area as water levels rose to a 15 year high.

Three houses were evacuated as they were threatened by stormwater at the rear of their properties. Approximately 5,000 homes lost power after the heavy rains. One person drowned after being swept away in a swollen creek. Avalon and Belrose recorded rainfall levels in excess of 200 mm. The Bureau of Meteorology advised the event was caused by an upper level system interacting with warm, moist onshore flow lifted by a trough off the coast.

The Insurance Council of Australia estimated the 1998 damage at $10 million, with the 2017 estimated normalised cost of $36.7 million