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National

Wet autumn outlook for parts of eastern Australia as the BOM predicts above average rainfall

It's a gloomy day at Sydney's Collaroy Beach, as a hazardous surf warning remains in place for parts of the NSW coastline into Saturday. (ABC News: Jake Lapham)

For anyone looking for an end to the wet weather soaking Australia's east coast, the news isn't good — above average rainfall is set to continue.

That's the latest message from senior hydrologist Paul Feikema in the Bureau of Metrology's (BOM) climate and water outlook video, which looks at what to expect over the next three months.

He said April to June was likely to have above median rainfall for northern and eastern Australia.

It means the risk of widespread flooding persists across many parts of eastern Australia, which already have full catchments and wet soils.

It has been a soggy, record-breaking few months. Australia had its wettest November, January saw high rainfall totals and it was Sydney's rainiest March ever.

The Bureau of Meteorology's rainfall outlook for April to June. (Supplied: Bureau of Meteorology)

So what's the cause? Well, one major factor is La Niña, a weather pattern which could continue.

"Waters around Australia remain warmer than average while in the Pacific, the 2021-22 La Niña persists," Dr Feikema said.

Experts say this La Niña pattern is moderate compared with 2010-11, despite breaking rainfall and flooding records.

Australia is now in its second consecutive La Niña year.

A third is not out of the question — the last time we saw that happen was 1998–2001.

But Dr Feikema said models suggest the event has passed its peak and is likely to return to neutral levels — neither La Niña or El Niño — later this autumn.

Some experts say it's too early to tell whether Australia will experience a third consecutive year of La Niña. (AAP: Darren England)

Climate scientist Agus Santoso, from the University of NSW, said the La Niña was "dying off slowly" though it was too early to tell whether a three-peat would occur.

"It's not as rapidly as we would expect so it's still lingering around," Dr Santoso said.

"There is an autumn predictability period for El Niño and La Niña … which means we cannot predict for sure what's going to happen towards the end of the year.

Meteorologist Milton Speer, visiting fellow at the University of Technology Sydney, said global warming could be expected to affect the impacts of La Niña climate phases in eastern Australia, through the increased heat and moisture that results.

"That means even for moderate La Niñas, such as just experienced, there is more potential for larger rainfall totals in future, especially as cooler, drier air from Southern Ocean frontal systems can be expected less likely to penetrate north along the east coast," he said.

Other factors at play

Dr Santoso reiterated that the La Niña was not the only factor that influenced south-eastern rainfall.

"There is Southern Annular Mode, which has been in a positive phase recently, which means it allows more air flowing towards eastern Australia … so that brings in more moisture," he said.

A range of factors influence Australia's climate including the Indian Ocean Dipole, which can impact rainfall. (ABC News: Alice Pavlovic)

The BOM said that was expected to return to neutral levels in the coming days and remain so for the coming fortnight.

"There's also Indian Ocean Dipole (IOD)," Dr Santoso said.

The IOD refers to annual changes of tropical sea temperatures in the Indian Ocean, which can affect rainfall.

It is currently in a neutral phase, but according to the BOM, the outlooks show it could swing into negative IOD territory by August – though it notes predictions have low accuracy beyond autumn's 'neutral' reading.

"When you have a negative phase, the eastern part of the Indian Ocean actually warms and that can cause higher than normal rainfall over south-eastern Australia," Dr Santoso said.

While parts of Australia want to see the end of sodden lawns and grey skies, there are others that want rain.

There hasn't been enough of it in western Queensland where graziers are feeling the effects of an absent wet season.

The usually wet western Tasmania is also in a dry spell and the BOM is predicting below median rainfall there for the next three months.

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