The Bureau of Meteorology now says up to 120mm of rain could fall in Penrith tomorrow, sparking concerns of flash flooding and dangerous conditions on the roads.
Commuters are even being warned to work from home if possible, with expectations that the public transport system will struggle to cope with the major downpour.
Up to 60mm could fall on Thursday while heavy rainfall will continue all the way until early next week.
Warragamba Dam is currently at 99 per cent of capacity and will spill in the coming days.
The NSW State Emergency Service says minor to major flooding is possible in the lower Nepean River area.
Earlier today, Prime Minister Scott Morrison said Sydney needed to prepare for what was a “significant” weather event.
“We will see it come into the Central Coast and Sydney. We are already experiencing elements of that right now, and particularly over the next 24 hours, we will then see that extend further into the South Coast of NSW,” he said.
“We need to be continuing to be preparing ourselves for the impacts in those regions.”
Premier Dominic Perrottet said the flood emergency impacting parts of New South Wales was a “one in 1000 year disaster”.
Troy Dodds is the Weekender’s Managing Editor and Senior Writer. He has more than 20 years experience as a journalist, working with some of Australia’s leading media organisations.