South Australians are bracing for a scorching heatwave this Christmas season ahead of potentially heavy rain from two tropical systems.

Adelaide’s first summer heatwave is forecast to begin with 36C on Friday, followed by 37C on Saturday, 40C on Christmas Day and Boxing Day and 37C on Tuesday.

Meanwhile the state’s North East Pastoral area is also set to bake, with 41C expected at Leigh Creek Christmas Eve and Christmas Day and in the Flinders Ranges at Hawker Christmas Day is forecast to reach 42C.

Melbourne also set to swelter

Victoria is set for a very hot Christmas, with the Bureau of Meteorology warning of severe heatwave conditions for much of the state on Friday and across the weekend.

After a cool day today, temperatures are forecast to rise on to 29C in Melbourne on Friday, before reaching 31C on Christmas Eve and hitting a top of 35C on Christmas Day.

“[It’ll be] a scorcher for Christmas Day, with winds tending around to the north and that’ll push the temperature up to the mid-30s, pretty warm conditions,” he said.

The bureau’s Chris Godfrey said despite a forecast change in conditions, the hot weather would continue throughout next week.

“It’s certainly going to be an uncomfortable night as we move into Boxing Day with temperatures across the majority of the state not really dropping below the mid-20s,” he said.

“However it does look like we are going to get a shallow trough that will move across the state during Monday, so that means that for Monday and Tuesday, at least in southern Victoria, the maximum temperatures will scale back somewhat to around the high 20s or 30s.

“But having said that, it will continue to be humid, so it’s not really true relief.”

In the state’s north-west, Mildura temperatures will reach 38 on Friday, ahead of weekend temperatures in the high 30s and early 40s.

Central and northern Victoria will also swelter with temperatures in the high 30s from Friday.

Despite the hot Christmas period, winds are forecast to be light, and the CFA has not yet declared a total fire ban for next four-day period.

Mr Godfrey said the Christmas period would be first stretch of unabating heat for the summer.

“Up until now — although a lot of people are saying that summer hasn’t really started — we have been getting the odd hot day,” he said.

What is different about this is this is the first period of sustained heat where it’s going to continue and we’re not really going to get very cool temperatures at night time to cool things off.