A large chunk of Australia's east coast is heading for a drenching from today, with warnings of falls up to 150mm for some areas.
Residents in New South Wales and Queensland should expect widespread rain and thunderstorms for the early part of this week, the Bureau of Meteorology says.
The late winter drenching is being driven by an upper trough system interacting with deep moisture from the Coral Sea.
The bureau early today issued a severe weather warning for the NSW Northern Rivers area, following heavy rain overnight.
The town of Byron Bay received 89mm, while other nearby communities recorded falls of 100mm or more.
The State Emergency Service warned residents there may be water and flood debris on roads today.
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"When leaving for work, school etc this morning- be vigilant and drive to conditions.
"If you come across a flooded road - turn around. Maintain a safe speed and drive to conditions. Turn your headlights on."
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In an update early today, the bureau says six-hourly rainfall totals of 40mm to 80 mm are likely with isolated totals up to 150mm possible.
Meanwhile, large parts of central and southeastern Queensland can falls of 25mm to 50mm today, but there could be a much heavier soaking in some areas if the weather system slows, the bureau says.
"(They could) be up around 100-150mm, and possibly even higher than that," meteorologist Dean Narramore said.
The wet weather is forecast to weaken from Thursday.