NSW and Queensland are poised to receive unusually high September-November rainfall ranking in the top 20% of all springs on record, the Bureau of Meteorology says.

A negative Indian Ocean dipole, which is associated with wetter than average conditions over Australia, means much of the eastern half of Australia has an increased chance of above average spring rainfall, senior climatologist Lynette Bettio says.

“We also see a developing La Nina event,” Dr Bettio said. “La Nina, as we've seen in recent years, is also associated with wetter than average conditions over Australia.”

The Bureau says the chance of a La Niña returning this spring is 70%. Four of seven models suggest La Nina thresholds are likely to be met by early to mid-spring while the other three are neutral.

The Bureau last week issued an alert that a third La Nina in a row is likely to develop this year.

The Spring 2022 Climate and Water Outlook comes just months after Australia’s costliest ever floods, which devasted northern NSW and parts of Queensland and racked up more than $5 billion in insured losses.

Where soils and catchments are wet, and stream flows are high, further rainfall this spring will increase the risk of flooding for eastern Australia, Dr Bettio says.

The first rains of the wet season are likely earlier than normal for much of Queensland and the Northern Territory this year. Dr Bettio says a positive Southern Annular Mode (SAM) is also likely, which pushes weather systems south, bringing wetter easterly winds to NSW and fewer cold fronts to western Tasmania.

Parts of WA and western Tasmania are likely to experience below average rainfall this spring, while almost all of Australia is likely to experience warmer than average nights, with cooler days likely for large parts of the mainland except the tropical north.

The negative IOD is likely to persist throughout spring, upping the chance of warmer days and nights for northern Australia.

Sea surface temperatures are currently warmer than average around much of Australia, contributing to the wetter outlook.