Residents between the NSW central and south coasts, including in Sydney, are being warned to brace for another rain event this week, with totals in excess of 300 millimetres predicted between Wednesday and Friday.
Flood watches have been issued for catchments in these areas, including minor to moderate flood watches for the Wollombi Brook and Lower Hunter River, Upper Nepean River, Nepean River, Hawkesbury and Lower Nepean River, and the Colo River.
Bureau of Meteorology senior hydrologist Ailsa Schofield said while there would be widespread high rainfall totals, there was also the potential for more localised, heavier falls.
"The catchments are very wet and it won't take much rainfall for us to see flash flooding and river rises," she said.
"We potentially expect dangerous road conditions and the potential for further landslips."
The bureau has forecast the development of the coastal trough on Wednesday, which is expected to intensify on Thursday with rain continuing on Friday.
It should then weaken by Saturday.
School holiday travellers urged to postpone plans
NSW SES Assistant Commissioner Dean Storey said people planning school holiday travel in the next few days should reconsider their plans, if those plans were within the areas that could be impacted.
"Know what you would do and where you would go if you need to evacuate.
"Avoid unnecessary travel and never drive through floodwaters."
The NSW SES is already working with communities to ensure homes are prepared, including providing sandbags to those in need.
Mr Storey said plans were also in place to establish evacuation centres if required.
The SES has received 31,400 calls for help across NSW during the past six weeks.
People who need SES assistance can call 132 500, or if it is a life-threatening emergency, dial 000.
