The Bureau of Meteorology has warned that thunderstorms, rain and hail are on the way for NSW and the ACT.
BoM manager Agata Inielska said wet weather will peak in NSW's Northeast, Northwest, South Coast and Mid North Coast as well as Sydney and Canberra on Wednesday and Thursday.
"We are expecting a low pressure system to develop and deepen over the south coast of New South Wales, and that really bringing some very heavy rainfall to the region over the next couple of days, particularly Thursday being a key concern," Ms Inielska said.
"With that heavy rainfall in the South Coast we are likely to see potential for riverine flooding, but also flash flooding. So this particular system will produce that heavier rainfall that can really change road conditions quite rapidly."
Ms Inielska also warned of rainfall for the nation's capital.
"It will be a pretty wet couple of days for Canberra as well and they will also have that potential of thunderstorms as well. So it will be broadly a wet period over the next couple of days," she said.
The rain may impact already saturated catchments such as the Namoi, Gwydir, Macintyre and Macquarie Rivers, which were recently affected by moderate to major flooding.
Rainfall is expected to clear for both NSW and the ACT going into the weekend.
"Peak conditions are really Wednesday and Thursday. Friday we'll still see a bit of rainfall in the southeast of the state. But conditions will really improve into the weekend, however, as that low moves offshore n this condition scope, we might still see some hazardous conditions on the weekend," Ms Inielska said.
But Ms Inielska said rain may still persist after the weekend as the La Nina pattern continues to bring wet weather to Australia's east coast.
'This severe weather season, really, it's not a sprint, it's a marathon," she said.