The change means the chance of a La Nina occurring this year has increased to 70 per cent, roughly three times the normal likelihood.

The Bureau's Manager of Climate Operations, Dr Andrew Watkins, said La Nina typically results in above-average winter-spring rainfall for Australia, particularly across eastern, central and northern regions.

"It typically also brings cooler and cloudier days, more tropical cyclones, and an earlier onset of the first rains of the wet season across the north," Dr Watkins said.

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"The cooling of surface temperatures in the tropical Pacific Ocean and an increase in the strength of the Pacific Trade Winds indicates the chance of La Nina has risen.

"When these two changes occur at the same time, at this time of year, we see a greatly increased chance of a La Nina forming and persisting through spring."

The last significant La Nia event was in 2010-11, which was the Australia's wettest two-year period on record.

The last time the Pacific Ocean approached La Nina conditions was in late 2017, but thresholds were only briefly exceeded.

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For some crop farmers, the rain cannot come fast enough, with a dry June and July. Fortunately, the Bureau forecasted a wetter than average August.

At a recent webinar, Agriculture Victoria Seasonal Risk Agronomist Dale Grey said high-pressure systems were slowly being replaced by low-pressure systems.

"If La Nina is going to occur at all, that needs to keep going," he said.

For more information on La Nina and the impacts of past events, head to the Bureau's ENSO Outlook page.

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