'Heat engine' brings hottest weather in years across southern states of Australia

A heatwave stretching across western and southern Australia is bringing the hottest weather in years and is likely to intensify further for southern states next week.

The prolonged spell of hot weather is due to an activation of Australia's 'heat engine', the term used to describe northern WA during periods when monsoon rains are absent, leading to an extended period of sunshine and the formation of a very hot air mass.

The hot air from the north west expanded south and east this week and has now engulfed a massive region from the north west coast of WA to eastern NSW.

Hottest weather in years for south east

This week has already brought maximum temperatures as much as 17 above average, including Edithburgh on Yorke Peninsula where the maximum reached 41.9 degrees Celsius on Thursday, the town's hottest day in two years.

While the South Australian coast welcomed a cool south-west change on Friday, many towns in Tasmania, Victoria and western NSW were sweating in their highest temperature from one to three years, including to 3:30pm on Friday:

• Laverton 42.0C - 16 above average and hottest day in 3 years

• Melbourne's 40.5C - 15 above average and hottest day in 3 years

• Geelong 40.3.C - 15 above average and hottest day in 3 years

• Mildura 42.8C - 11 above average and hottest day in 2 years

• Ballarat 38.5C - 13 above average and hottest day in 3 years

• Hay 42.5C - 9 above average and hottest day in 14 months

• Hobart 36.1C - 14 above average and hottest day in 2 years

The cool change will move east bringing a temporary pause to the heatwave in Victoria and Tasmania on Saturday, but ahead of the change most of NSW will swelter in the hottest weather in about a year, including Sydney where the highest maximum so far this summer near the CBD has only been 30.6C.

While the south-east states are feeling the impacts of a low intensity heatwave, much of WA has passed severe heatwave thresholds as maximums climb into the mid 40s. This weekend promises to deliver even hotter weather to the west, potentially into the high 40s near the north-west coast.

Even hotter weather ahead next week The heatwave will continue across southern inland Australia through Monday and Tuesday, with daily maximus still climbing above 40C from north-west WA to Bourke.

By Wednesday a northerly airstream will carry 40-degree heat back to the southern coastline, including Adelaide, and as a result the Bureau of Meteorology is already warning of a severe heatwave next week for much of South Australia.

For the heatwave to finally end what's required is cooler air from the oceans surrounding Australia to blow into the interior.

For southern states that may not occur until next weekend, prolonging the spell of above average temperature for another week.

Fire threat increasing Along with the direct threat heatwaves bring to human health, the extended spell of hot and dry weather is also raising the risk of bushfires and grassfires.

Thankfully winds are currently not strong enough to cause catastrophic fire dangers, and only a handful of districts have passed the 'extreme' level.

Perhaps a more significant impact is the heat will dry-out vegetation and create the right ground conditions for a major bushfire outbreak if a burst of stronger winds accompany the latter days of the heatwave towards next weekend.

Story by ABC Meteorologist Tom Sanders

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