Eastern Australia faces wet weather and flooding with 70% chance of third consecutive La Niña

How said the heavy rain forecast was a combination of climate drivers including a negative Indian Ocean Dipole (IOD) and warmer than average waters to the north of Australia.

"The bureau's three-month climate outlook shows a high chance of above average rainfall for most of the eastern two-thirds of the Australian mainland between September and November," he said.

"As many Australians in the east know, soils are still quite wet, rivers are running quite high and dams are full. So with this outlook of increased rainfall, it does bring elevated flood risk for much of eastern Australia."

The prediction for renewed rainfall comes after three major flooding events in New South Wales within a year and a widespread flooding event in Queensland that claimed the lives of 18 people.

"Australia's climate has warmed by around 1.47C for the 1910 to 2020 period," the BoM said. "Southern Australia has seen a reduction of 10% to 20% in cool season rainfall in recent decades.

"There has also been a trend towards a greater proportion of rainfall from high-intensity short duration rainfall events, especially across northern Australia."

Wetter than normal conditions have lingered in eastern Australia since 2020. Sydney had its wettest summer for 30 years in 2021-22 and its wettest March and July on record. As of August, it's already experiencing its wettest year on record.

Weather forecasting page Higgins Storm Chasing said Australia would be the "land meat" between an Indian and Pacific Ocean sandwich for the next six months.

"All latest global data is still saying above average rain," it said, pointing to a strong negative IOD event, which tends to bring more rain over southern and eastern Australia.

"Watch for very moist north-westerly winds to develop across the Indian [Ocean] and pile moisture in across the country.

The Indian Ocean Dipole index has been "very close" or within negative thresholds since early June, the BoM said, while the latest weekly value was "one of the strongest observed so far".

"All surveyed climate models indicate that negative IOD conditions are likely to continue into late spring."

A negative IOD means warmer ocean temperatures in the east, increasing the likelihood of low pressure systems in Australia's south-east and moistening the air.

"We've only seen that three times since the middle of last century," he said.

At the same time, Tasmania is likely to be drier during the spring months.

The Southern Annular Mode index is "neutral" and likely to be mostly positive for the coming three months, bringing lower than average rain in western Tasmania and a wetter influence for parts of eastern NSW and far eastern Victoria.