Meteorologist Jonathan How said the east's forecast is for hot and wet conditions while the west is forecast to experience scorching conditions of up to 49C during a Bureau of Meteorology severe weather update.

Parts of Victoria and New South Wales, including capital cities, are forecast for their "hottest day so far this summer" on Saturday, which will also bring severe fire dangers.

"On Saturday, that will be the peak day across the South East, with Canberra, Melbourne and Sydney all set to peak above 30 degrees even to the high twenties across Hobart," Dr How said.

"So with all this heat and instability, we are expecting to see quite a few storms pop up as well, mainly affecting the East Coast over the next few days."

"We could see some warnings issued, but thankfully nothing quite as severe or significant as what we've seen over the past few days."

Weather in the South East is set to cool down due to a cold front on Sunday, which could see rainfall and potential storms in both NSW, Victoria and Tasmania.

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Meanwhile, western pasts of the country are already in the midst of a severe heatwave.

"On Thursday, maximum temperatures well into the forties for large parts of Western Australia, the Northern Territory and western Queensland as well, and into the high thirties across southern WA and South Australia," Dr How said.

"On Friday, the heat builds across South Australia and Adelaide is expected to see its hottest day since February."

Dr How said the heatwave become even stronger and reach "extreme levels" in the Cape York Peninsula and northern WA over the coming days.

Marble Bar in the Pilbara is forecast for 49C on Sunday while other parts of WA are also forecast for temperatures well above 40C.

Dr How said the heatwave will pose a health risk to all communities, including healthy people, who need to take health precautions to avoid heat stroke or dehydration.

The meteorologist said there will be "severe to catastrophic" fire danger conditions through inland parts of WA on Thursday due to gusty winds and maximum temperatures well into the forties.

"Thankfully, there across the south west, we aren't seeing dangers. Fire weather conditions which where communities have been impacted by bushfires quite recently, particularly across the Margaret River area," he said.

"On Friday, severe fire danger said parts of South Australia, including the Mount Lofty Ranges.

"So with heat and fire dangers increasing over the next few days, be sure to take the proper precautions, don't forget your pets and please stay safe."