Intense, torrential rain with thunderstorms have the potential to cause flash flooding in parts of the NSW Central Coast and the Hunter region, the Bureau of Meteorology says.

While rain is forecast for Sydney, the weather bureau says the city will escape the worst of the weather.

The bureau has issued a severe weather warning and a severe thunderstorm warning on Wednesday morning for the Hunter region and the lower Mid North Coast, including Taree, Newcastle, Nelson Bay, Barrington Tops and Dungog.

“Most of those areas will experience really persistent showers, so more of a steady increase of rain throughout today and tomorrow,” meteorologist Rose Barr said.