The BoM has forecast sky-high heat across the country

While Western Australia will bear the brunt of the unusual spring scorcher the Bureau of Meteorology (BoM) has forecast temperatures to soar across Perth, Sydney, Canberra, and Adelaide.

Temperatures are set to reach 10 to 16 degrees Celsius above average for September.

Senior meteorologist Sarah Scully said the heat will extend across northern Australia and reach down into northern parts of NSW by the end of the week.

"This high pressure system in the Great Australian Bite starts to dominate, bringing clear skies and allowing those temperatures to start to build, which is what we see particularly about the far western WA, pushing up into the mid-30s," she said.

"In fact, it's from Wednesday onwards and towards the end of the week that record-breaking heat may occur across WA."

AFL fans in Melbourne could expect 28 degrees Celsius on Saturday for the grand final.

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In Canberra temperatures are set to soar into the high 20s on Friday and extend into the weekend.

"It is really important slip, slop, and slap!" Ms Scully said.

She also advises people to remain up-to-date with the latest fire warnings.