The State Emergency Service is warning Hunter residents heavy rain forecast for later today has the potential to cause flash flooding.
A coastal trough, cradled between two high-pressure systems will develop along parts of the coast over the next 24-hours.
The weather bureau is forecasting up to 20mm of rain on Tuesday and up to 120mm on Wednesday with no sign of stopping until Friday.
Rachel Squires from the SES said the weather is unpredictable and residents should be prepared now.
"Clean out your gutter, make sure anything lying around in your yard is secure and keep on top of information that comes through," she said.
"You can follow [the SES] on our Facebook page, or you can follow the Bureau of Meteorology on the web - they provide information and updates on rainfall and river heights."
The SES advises people who find themselves trapped by flash flooding to seek refuge in the highest available place and ring your local SES Unit on 132 500 in emergencies.
