Issued at 10:49 am Wednesday, 21 March 2018.

The Bureau of Meteorology warns that, at 10:45 am, severe thunderstorms were detected on the weather radar. Thunderstorms are moving towards the northwest. They are forecast to affect Nelson Bay, Anna Bay and Lemon Tree Passage by 11:15 am and Williamtown, Medowie and Karuah by 11:45 am.

Heavy rainfall that may lead to flash flooding is likely.

The State Emergency Service advises that people should:

• 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.

The next warning is due to be issued by 11:50 am.

A more general severe thunderstorm warning is also current for parts of the Mid North Coast and Hunter districts.

Warnings are also available through TV and Radio broadcasts, the Bureau's website at www.bom.gov.au or call 1300 659 218. The Bureau and State Emergency Service would appreciate warnings being broadcast regularly.