From flames to floods: Wet weather set to sweep the east coast

A dramatic shift in weather is set to bring widespread rain and thunderstorms to eastern Australia this week, following last week's intense heatwave and destructive bushfires.

The Bureau of Meteorology says a "sustained period of wet weather" will move across large parts of the east, easing immediate bushfire threats but increasing the risk of flash flooding in several regions.

Meanwhile, the remnants of ex-Tropical Cyclone Koji are continuing to generate heavy rainfall across tropical Queensland, while another tropical system is expected to develop over the Top End this weekend, raising renewed flood concerns and a low chance of cyclone formation.

Heavy rain and storms for NSW and Victoria

Eastern New South Wales and Victoria are bracing for their most significant rainfall in months as storm activity intensifies from Thursday.

Thunderstorms with heavy downpours and an elevated risk of flash flooding are forecast across Queensland, NSW, Victoria and the Australian Capital Territory, particularly around East Gippsland, the south-east corner of NSW, and areas along the northern slopes and ranges.

By Friday, the main thunderstorm zone is expected to shift over central eastern and north-eastern NSW, while steadier rain and isolated storms develop along the NSW south coast and across Gippsland.

Weather models suggest the heaviest rainfall band, accompanied by gusty winds, will gradually track north along the coast through the weekend. By Sunday, attention turns to the Illawarra, Sydney Basin and Hunter region, where flash flooding remains a concern.

While catchments are currently relatively dry - limiting the risk of major river flooding - the BoM warns that minor river rises are possible, particularly along the Illawarra and south coast.

Ex-tropical cyclone keeps the north wet

Flooding rain is also forecast across parts of northern Australia as ex-Tropical Cyclone Koji continues drifting north-west across Queensland.

Koji's remnants are expected to trigger further localised heavy falls and flash flooding from the Gulf Country to the Central Coast on Thursday, with thunderstorm downpours continuing into Friday. The BoM is forecasting more than 100 millimetres of rain across north-east Queensland and western parts of the Northern Territory over the coming week.

Flood watches remain active for 15 rivers and creeks across the Gulf Country, western and central Queensland, and Cape York.

The likelihood of Koji redeveloping into a cyclone remains low - around 15 per cent or less until at least next Wednesday - but as conditions ease in Queensland, a new tropical low is expected to form off the Top End.

Forecast models indicate the system may drift west offshore early next week, bringing about a 25 per cent chance of cyclone development off the north coast of Western Australia.