A negative IOD typically increases the chance of winter and spring rainfall over much of southern and eastern Australia, along with warmer days than usual in northern Australia.

In its latest three-month outlook, the BOM also notes there is a high chance (greater than 80 per cent) of above median August to October rainfall for much of the eastern two-thirds of the mainland, with chances reducing gradually in the west, and tending to below median for western Tasmania and an area of south-western Western Australia.

Most of the eastern two-thirds of the mainland has more than double the normal chance of unusually high rainfall (in the wettest 20 per cent of all August-October periods over 1981-2018) rising to over triple the normal chance for parts of the tropics and scattered parts of the south-east.

The BOM's head of long-range forecasting, Dr Andrew Watkins, said that the Bureau's three-month climate outlook is for above average rainfall for much of Australia, particularly for the central and eastern states.

"With wet soils, high rivers and full dams, and the outlook for above average rainfall, elevated flood risk remains for eastern Australia," Dr Watkins said.