The Bureau of Meteorology is expecting a floodwater peak of 10.7 metres at Menindee in the state's far west on Monday, above the 1976 record of 10.46 metres.
It follows a year of flooding for the small town with the latest a result of waters rushing through the Darling River.
In South Australia, the Murray River hit forecast peaks with multiple flood emergency warnings at riverside towns along the waterway.
Floodwaters had peaked at Berri near the SA/NSW border on New Year's Eve and were expected to remain high for weeks.
The floodwaters are expected to arrive in Blanchetown, west of Berri before the weekend.
In the Top End, Darwin's New Year's plans were cancelled as wild weather hit the Northern Territory capital.
The monsoon is expected to remain over the NT for the rest of the weekend, and is also sparking flood warnings in Western Australia.
Authorities issued initial flood warnings for the West Kimberley region as heavy rains hit the areas.
Large thunderstorms will be the price of a cool change in Tasmania and Victoria, with the weather to sour on Monday.
Tasmania State Emergency Service assistant director Leon Smith told people on the Apple Isle to prepare for 5cm-diameter hail, up to 90 km/h wind gusts and heavy localised rain.
"I urge everyone to be prepared before a significant change in the current fine weather conditions tomorrow," Mr Smith said.
Melburnians are in for a maximum of 31C on Monday before the storms bring hail and heavy rain.
12°C