On the 8 November 1984, thunderstorms caused extremely heavy rain over a sizeable area near the centre of Sydney. Observatory Hill recorded 196 mm in three hours. Due to large expanses of urban areas being paved, much of the rainfall became flood run-off, causing damage to homes along the Harbour. Vehicles were swept off roads or buried in mud.

Thousands of homes were flooded, and hundreds of people evacuated.

The Insurance Council of Australia estimated the 1984 damage at $80 million, with the 2011 estimated normalised cost of $578 million.