A low pressure system that brought heavy rains and damaging winds to southern and western NSW is expected to push further east.
It comes amid widespread flooding across the state as extended heavy rains fall in areas where the ground is saturated and rivers already high.
Australia is on track for its wettest spring in a decade and some regions in NSW have already received more than three times their normal rainfall for November.
The Bureau of Meteorology on Friday morning warned severe thunderstorms are likely to bring damaging winds and more heavy rain to parts of the Hunter, mid north coast and northwest slopes and plains regions.
Flash flooding is possible, with towns including Newcastle, Gosford, Maitland, Tamworth, Gunnedah and Narrabri on high alert.
Other regional and remote towns are facing the prospect of isolation, with floodwaters cutting off major road corridors.
The Kamilaroi Highway in northern NSW is closed between Curlewis and Breeza, between Gunnedah and Boggabri, and between Wee Waa and Narrabri.
In the Hunter flooding has closed the Golden Highway near Singleton, and Denman Road between Denman and Muswellbrook.
Henry Lawson Way between Forbes and Grenfell is closed in the central west along with the Cobb Highway between Ivanhoe and Wilcannia, and the Silver City Highway between Broken Hill and Queensland.
Many other local roads are affected and the risk of flash flooding from heavy rain could close more.
Riverine flooding is threatening many towns across the state, with the rainfall causing a bevvy of inland rivers to surge.
Major flooding is still underway on the Lachlan River in the state's central west, with floodwaters currently coursing through Jemalong on their way to Condobolin.
However, Forbes residents have now been given the all clear to return home after the river in the town fell below minor flood levels.
During the height of floods in Forbes earlier this month, close to 2000 residents were ordered to evacuate and the river peaked at 10.54 metres, near major levels but below the peak during flooding in 2016.
The Castlereagh River, also in the state's central west, has reached moderate flood levels, with Mendooran and Gilgandra expected to feel the impact.
Floodwaters have crept into Molong, with the creek in the town at moderate flood levels, and similar levels are expected along the Bell River at Wellington from midday.
Minor flooding continues along the Macquarie River at Wellington Bridge.
In the New England region, major flooding is occurring along the Namoi River at Wee Waa, which has been cut off from other towns.
The river has fallen in nearby Gunnedah, but moderate flooding is still underway.
Minor flooding is occurring at Narrabri, with the river expected to exceed moderate flood levels on Friday.
Many of the areas impacted by the deluge in recent weeks have been farmland, with growers watching paddocks disappear underwater and their crops destroyed after many years of drought conditions.
That has prompted the NSW Farmers Association to call for a statewide natural disaster declaration so relief funds can be accessed.
The rainy weather is not likely to ease significantly any time soon, with the BOM's outlook for the summer in NSW predicting ongoing wet conditions.
