Millions of Australians on the east coast could sweat through 40C-plus temperatures as extreme weather event brings scorching end to summer

You’re not imagining it if you live on Australia’s east coast– it has not been a very hot season by the numbers.

In fact, December 2022 was a remarkably cold month for the eastern seaboard, with much of NSW shivering at times through mean maximum temperatures that were among the lowest 10 per cent of historical observations since 1910.

Victorians and Tasmanians have had their coats on hand the whole season, as each cool change since November has brought with it howling winds, plummeting temperatures, wintry hailstorms, and alpine snow.

The reason for the rather sluggish rise in temperatures over the past few months has primarily been due to the continued presence of our third La Niña in as many years.

With the Pacific climate driver on its last legs, it comes as no surprise that La Niña not only brings relentless rain to eastern Australia, but also increased cloud cover – keeping daytime temperatures mild.

Fewer are familiar with the other climate driver which is bringing the rain – a positive Southern Annular Mode (SAM).

This occurs when the ring of westerly winds that swirl the Antarctic are hugged closer against the south pole, and often goes hand in hand with La Niña.

The SAM has been in a positive state all summer, favouring more rainfall than usual in the east, and reducing the chances of extreme heat.

But as the season draws to a close, all signs are pointing to both La Niña and the SAM reverting to neutral.

With that comes rising temperatures, and it starts with scorching sunshine over outback Western Australia.

The Pilbara region in outback WA is known as Australia’s “heat engine”.

In the hotter months of the year, constant sunshine and clear skies means the vast desert landscape can become a furnace, and any weather system pushing from west to east in the southern parts of the nation can push up the thermostat in those regions.

While the tropics have once again become more active with lows and cyclones spinning up in the oceans, the Pilbara looks to remain dry and very hot, and this heat is forecast to push across the country twice in the next two weeks. 

Without the recent quenching effects of rain and cloud for the east coast, the spread of dry heat across Australia increases the risk of stifling heatwave conditions at day and night over the next fortnight.

A heatwave is defined as a period of three days or more where temperatures at day and night are significantly above average for a specific location.

The hot nights of a heatwave can make these events lethal, reducing one’s ability to recover from the heat, and as temperatures rise quicker the next day, this increases the risk of heat-related injury or stress, including heat exhaustion and heat stroke.

Heatwaves, while normal in summer, are Australia’s worst natural hazard apart from epidemics.

Heatwaves have killed more Australians than any other natural disaster; a nine day heatwave in early 2009 in south-eastern Australia sparked the Black Saturday bushfires and is attributed to the deaths of 374 people.

This weekend, these type of extreme conditions will be in effect on both sides of Australia as a broad low pressure trough stretches from the Pilbara to NSW, dragging the heat coast to coast.

Brisbane will see a return to the uncomfortable humid nights they experienced last week.

While some relief will arrive early next week with showers and a drop in temperatures for the east coast, the heat engine barrelling over from the west is expected to remain cloud free and be followed by another round of extreme temperatures late next week – first for central and south Australia and then for the east coast.

A large part of the nation could exceed 40C from January 16 onwards, including the east coast.

While forecasts beyond seven days should be treated with some caution, most models agree this extreme heat event could happen next week.

Australians should keep up to date with their local forecast and heatwave risk in the coming days.

Viewers looking for more information about how and when you may be impacted can tune into Sky News Weather on Foxtel Channel 601.