At this stage, the storm is expected to hit inland, skimming the Newcastle coastline.

Severe thunderstorms are predicted to produce damaging winds, heavy rain, and large hail. 

The thunderstorms have developed and are likely over many parts of the state, as warm humid air feeds into a trough that lies about the western plains, combined with an upper low pressure system entering the far southwest.

The State Emergency Service advises that people should: 

* Move your car under cover or away from trees. 

* Secure or put away loose items around your house, yard and balcony. 

* Keep at least eight metres away from fallen power lines or objects that may be energised, such as fences. 

* Report fallen power lines to either Ausgrid on 131 388, or Endeavour Energy on 131 003 or Essential Energy on 132 080, as shown on your power bill. 

* Keep clear of creeks and storm drains. 

* Don't walk, ride your bike or drive through flood water. 

* If you are trapped by flash flooding, seek refuge in the highest available place and ring 000 if you need rescue. 

* Unplug computers and appliances. 

* Avoid using the phone during the storm. 

* Stay indoors away from windows, and keep children and pets indoors as well. 

* For emergency help in floods and storms, ring the SES (NSW and ACT) on 132 500.