Storms are brewing across NSW with severe thunderstorm warning issued for regions around Dubbo and Lismore.
The Bureau of Meteorology is warning people in the Central West Slopes and Plains, and Northern Tablelands, to brace for large hailstones, damaging winds and heavy rainfall that may lead to flash flooding on Monday.
Tenterfield, Dubbo, Tabulam, Drake, Baryulgil and Narromine are in the path of a low-pressure system that's moving across the state, according to the BoM warning issued at 6.45am.
More than 100mm of rain is also due to hit Inverell.
The storm cell is expected to move south with up to 70mm of rain forecast to drench Sydney on Tuesday.
NSW SES spokesman Phil Campbell says emergency services are "quite concerned" about the "supercell thunderstorms".
"We're asking people up in that northeast part of the state and also inland around Tamworth and Moree just to make sure they're well prepared," he told AAP on Monday.
"At the moment, we've not had any calls for assistance, which is good news.
"We do have a number of weather models, according to the bureau, that are forecasting very heavy rain from the middle to late part of the week. We're just keeping an eye on that."
© AAP 2017