Australia posted its fourth-warmest autumn by maximum temperatures on record, while NSW had its hottest and Victoria, its second-warmest. Rainfall was a third-below average for the season, while May alone was the third-driest in national records going back to 1910.

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During El Nino years, easterly equatorial trade winds slow or reverse. The Pacific Ocean also absorbs less heat from the atmosphere, adding a temperature kick to the background warming from climate change.

The impacts of El Ninos on Australia are typically worst when reinforced by a so-called positive Indian Ocean Dipole, when temperatures off north-western Australia are relatively cool compared with those off eastern Africa. So far, only one of the models used by the bureau point to a positive-IOD forming, Ms Duell said.

Globally, May was the fourth warmest on record, with the other three coming since 2014, according to international agencies such as NASA.