Millions braced for a deluge on Saturday as flood warnings rolled out across much of South Australia and threatened western reaches of NSW and Victoria.
The system is not letting up, with severe weather warnings across parts of all three states in place.
The rain came early to the South Australia's west coast and Eyre Peninsula, with Ceduna and Wudinna recording record falls into Saturday morning.
Isolated falls exceeded 100 mm in surrounding towns, the most rain seen in months.
After receiving just 3.6 millimetres of rain so far this year, Adelaide was told to expect falls of up to 50mm on Sunday.
Widespread rain, severe thunderstorms, flash flooding and possible riverine flooding were forecast across the state and western parts of NSW and Victoria from late Saturday into Sunday.
"For some locations, the rainfall could be heavy enough to cause inundation of homes, properties, businesses and agricultural land," senior Bureau of Meteorology forecaster Dean Narrimore said.
The downpour came as a shock to South Australia, after forecasters tipped the state's first dry summer since 2019, the eighth since records began.
As the system swept south on Saturday, South Australian Premier Peter Malinauskas warned residents to prepare for risks in the days ahead.
Senior Bureau of Meteorology forecaster Jon Fischer said the slow-moving tropical low - which had sat over the Simpson Desert in the southeast Northern Territory for a week - was highly unusual.
"We've all seen images of roads being washed away, impacts to the rail line and usually dry creeks turning into torrents," Mr Fischer said.
For many farmers, some rain is welcome but forecasters warn that benefits will turn to risk as totals push beyond 50-80 mm.
The low was expected to weaken as it pushes east early next week, with rain clearing from South Australia from Monday night.
Until then, authorities are urging people to stay across warnings and avoid floodwaters.
Flood warnings remain for large parts of central Australia, with much of the water flowing into Kati Thanda-Lake Eyre and possibly affecting river systems further south.
Parts of Victoria more than doubled seasonal averages on Friday night, with heavy showers forecast from late Sunday and into Monday.
Cumulative rainfall totals of 50 to 100 mm are in store across Victoria with isolated falls exceeding 150 mm.
Consistent falls in Sydney, meanwhile, prompted warnings of increased bull shark activity in Sydney Harbour and estuaries along the NSW coast after recent heavy rain.
Rich run-off can attract baitfish and, in turn, bull sharks.
