Sydney and much of NSW has swung from one weather extreme to another, with heavy falls and cooler temperatures snapping the sequence of heatwaves and an extended dry spell.

"There's a high potential for unsettled weather," Abrar Shabren, a Bureau of Meteorology duty forecaster, said.

More rain, including possible thunderstorms, is on the way for eastern NSW including Sydney. Credit:Isabella Porras

An upper level trough moving across the state will enhance the threat of severe, isolated thunderstorms from Sunday overnight into Monday.

"This system may bring large hail and damaging winds," Mr Shabren said, possibly affecting a wide swath of eastern NSW.