A surface trough and a developing East Coast Low is expected to bring heavy rainfall to central parts of the NSW coast from the Lower Hunter to the South Coast and parts of the Central West during the weekend and into Monday.

A message posted by the Bureau of Meteorology said: "This heavy rain may cause minor to moderate riverine flooding along parts of the Wollombi Brook, Central Coast, Greater Sydney, South Coast and Central West. Major flooding is possible in the Hawkesbury Nepean Valley from Sunday, with minor flooding expected from late Saturday.

"This weekend's rainfall is expected to cause localised flash flooding. Rainfall is expected to continue into the new week and may cause additional river rises and flooding along the NSW coast."

The weather system is expected to cause riverine flooding for the catchments listed from Saturday. Flood classes (minor, moderate, major) are only defined for catchments where the Bureau provides a flood warning service.

MAKING NEWS:

The Macquarie River to Bathurst catchment area was listed as a "minor flooding" risk.

As of 4pm on Saturday, 9.2mm of rain had been recorded at Orange Airport.

FloodSafe advice is available at www.ses.nsw.gov.au. For emergency assistance call the SES on telephone number 132 500. For life threatening emergencies, call 000 immediately.

Across NSW the federal government approved Australian Defence Force support, with 100 troops also available from Sunday onwards, Emergency Management Minister Murray Watt said.

Two Australian Defence Force helicopters will be available to assist with rescues as areas of NSW brace for intense rainfall and possible flooding.

"I want to assure people that the federal government ... is 100 per cent prepared for what might lie ahead," Mr Watt said from Brisbane on Saturday.

"One of the things that we've learned over the last couple of years is that when we don't have a federal government that takes responsibility and isn't proactive, bad things can happen."

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