Temperatures will climb above 40C in South Australia and Victoria on Thursday and Friday and an ex-tropical cyclone could re-form off the coast of Queensland.

After a couple of milder days in parts of southern Australia, the Bureau of Meteorology is forecasting a resurgence of the high temperatures seen throughout the Christmas period, with possible severe to extreme fire danger over the next two days.

A broad area of the country will have temperatures 10 to 16 degrees above average for January. Adelaide is expected to reach 41C on Thursday and Melbourne 42C on Friday.

Parts of inland Victoria will have temperatures that climb into the mid 40s over the next two days: Mildura in the state’s northwest is forecast to reach 41C on Thursday and 46C on Friday.

A summer scorcher expected on Friday! Temperatures 44 to 46 deg in the north, 40 -42 in the south. A gusty southwest change late Friday leading to a cooler weekend. Check the forecast here: https://t.co/UFa3a5T6My #MelbWeather pic.twitter.com/5sZ2bAqr3i — Bureau of Meteorology, Victoria (@BOM_Vic) January 1, 2019

Hobart is expected to reach 35C on Friday and above-average temperatures in Tasmania could be accompanied by extreme fire danger for parts of that state.

The Bureau said the heat in South Australia and Victoria could trigger warnings of severe fire danger over the next two days.

“We’ve seen a couple of cooler days for southern Australia, still above average for this time of year but cooler than we’ve seen,” meteorologist Sarah Fitton said. “But we’ve still just had that heat sitting through central Australia which hasn’t gone away.

“We’re going to see north-westerly winds again and that’s going to drive that heat that’s been sitting in central Australia back across the southern states.”

Melbourne’s extreme highs on Friday are expected to be followed by a drop of 18C to a top of 24C on Saturday, before warming up again into next week.

New South Wales, which has experienced a long stretch of warm days, has no forecast relief from above-average temperatures.

The heatwave follows a year of above-average temperatures for the country.

The BOM, which will release its final data sometime in January, expects 2018 will register as one of the five warmest years on record for Australia overall and one of the third warmest in terms of maximum temperatures.

It said nighttime minimum temperatures were also warmer than average for most of the country through 2018.

On Wednesday, ex-tropical cyclone Penny was moving eastwards back over the Coral Sea after bringing heavy rains and some flooding when it made landfall in Queensland on Tuesday.

But Fitton said it could redevelop into a category 1 or 2 cyclone again and the bureau was monitoring whether it would move back towards the coast.

“Over the next few days, it’s not expected to affect mainland parts of Queensland but as we head into Friday and Saturday it might start to re-curve towards the Queensland coast in a south-westerly direction,” she said.

“From late on the weekend and into early next week, there’s a chance it could reach the central Queensland coast.”

She said there was still a lot of uncertainty about the system’s movements.

“It may only be a tropical low when it reaches the coast but despite that, there’s an increasing chance of some heavy rainfall, damaging rains and flooding,” she said.