Heavy rainfall across parts of NSW expected

While most of the NSW coast has experienced a wet week those conditions will sharpen when a developing inland trough in the state's far west drifts towards the coast, according to the Bureau of Meteorology.

"What we have seen as spotty, intermittent shower activity across the coast is really going to fill in and become persistent rainfall," senior meteorologist Angus Hines said.

BoM said some parts of NSW's north and central inland may see isolated 24 hour totals of 40-70 millimetres of rainfall with thunderstorms.

"The coastal trough will deepen on Sunday, with the focus of rainfall shifting to the state's central east on Sunday where moderate to locally heavy falls are possible especially in the Illawarra," Mr Hines said.

"Illawarra and Shoalhaven may see widespread 24 hour totals of 40 to 70 millimetres with isolated totals exceeding 100 millimetres possible on Sunday."

There is a risk of flash flooding in the Illawarra and Shoalhaven.

The Sydney metropolitan and Port Macquarie region should also experience significant rainfall between 25-50 millimetres.

NSW SES acting assistant commissioner Allison Flaxman said they were monitoring conditions across the state.

"Isolated rainfall in excess of 100 millimetres in some coastal areas is not out of the question, but we are well positioned to respond to any calls for assistance," he said.

Next week should bring an easing of conditions.

"West of the Divide will see dry weather during the first half of the new week, but showers will still continue east of the Divide with persistent onshore airstream," Mr Hines said.

"However, the risk of moderate to heavy falls will easy early next week with northward movement of the coastal trough."