The weather bureau says a huge cloudband over Australia is expected to bring “a whole lot of rain” to NSW and Qld in coming days.
Severe storms could hit NSW — including Sydney — on Tuesday and Wednesday as the system moves east.
Hail, thunder and possible flash flooding could occur as the moisture-laden blanket smothers the state.
However BOM meteorologist Sarah Skully said dry air would move in on Thursday and clear up the rain.
The wet weather could instead be experienced in south-east Queensland as it contracts north.
The cloudband which stretches across Australia has been drenching Western Australia this week.
In a slightly different prediction, weatherzone.com.au says there will be two such blankets of cloud sweeping the country, bringing rain to every state and territory.
Such so-called north-west cloudbands typically stretch from the far north-west of Australia towards the south-east corner.
They are caused by moisture-laden air from the Indian Ocean and usually produce widespread rain over Australia between autumn and spring.
“Two north-west cloudbands will pass over Australia as streams of Indian Ocean moisture move south and interact with a series of cut-off upper-level lows passing over the nation’s southern states,” Weatherzone wrote on Tuesday.
Over the next seven days, the two “pulses” of airborne moisture will spread across Australia.
“Rain will fall over much of every state and territory this week, with some places also likely to see thunderstorms,” Weatherzone said.
“Pockets of heavy rain will produce areas of flooding, both with and independent of thunderstorms.”
There were already flood warnings for Queensland and NSW on Tuesday.
