Spring see-saw to deliver hottest September weather in years for south-east Australia

A rapid warming trend is set to bring the hottest September weather in years to south-east Australia this weekend, with temperatures soaring up to 12 degrees Celsius above average.

The sudden change comes after a polar blast brought frigid air and snow to the region earlier in the week, with temperatures in some areas expected to drop just as quickly once another cold front moves in.

Warmest September weekend in years

Following a cold snap that saw temperatures drop as much as 10C below average and snow fall close to sea level in Tasmania, a north-westerly airstream is set to bring warm air to the region.

“The cold southerlies are now being replaced by a north-westerly airstream,” said a spokesperson. The warm air swept through Western Australia on Thursday and Friday and is expected to reach western South Australia on Saturday and the east on Sunday.

Several capitals are predicted to experience their warmest September day in years, with:

• Canberra expected to reach 25C on Sunday, its warmest September day in three years
• Hobart predicted to reach 27C on Sunday, its warmest September day in seven years
• Melbourne expected to reach 27C on Sunday, its warmest September day in three years
• Sydney city predicted to reach 28C on Saturday and Sunday, with western suburbs tipped to peak from 30C to 34C

Much of the south-east inland is also expected to reach the low-to-mid 30s this weekend, with some towns and cities, such as Mildura and Griffith, predicted to experience their highest September temperatures in years.

Spring weather volatility explained

The rapid change in temperature is due to the region's notoriously variable spring weather, with a greater disparity between tropical and polar temperatures during this time.

Northern Australia is already in the hot season by September, with daily maximums in the “heat engine” – the Pilbara and surrounding areas – nudging 40C.

When northerly winds develop over the interior, the large mass of hot air is transported to southern states, bringing temperatures above 30C as far south as Hobart.

“The difference in temperature between northern Australia and the Southern Ocean reaches a peak in spring,” said a spokesperson.

First summer forecast revealed

Despite the current day-to-day fluctuations, the spring and summer temperature outlooks indicate that Australia is facing record challenging heat.

The medium range outlook is tipping temperatures up to 6C above average through the fourth week of September, with October and November also likely to be dominated by above-normal temperatures.

A hot summer is predicted by leading global models, with mean temperatures 1 to 2C above a recent baseline already affected by climate change.