A fire crew works to contain fires near Bungendore on Wednesday ... The restorative justice process in the ACT allows those affected by fires to tell arsonists how they have been hurt.

Battling fires ... more heat is on the way. Photo: Rohan Thomson

The mercury is on the way up again in fire-threatened regions of south-eastern Australia, with the return of hotter temperatures likely to add to the burdens of those fighting blazes.

Also troubling for fire authorities and the public is a re-intensification of severe heat over regions of Western Australia, which will lift the temperatures back to extreme levels in some inland regions.

Melbourne should reach 37 degrees on Friday before cooler weather brings moderate temperatures for the next five days, according to current forecasts from the Bureau of Meteorology. A day of total fire ban has been declared for New South Wales and Victoria for tomorrow.

Sydney's temperatures are predicted to climb to 33 and 35 on Friday and Saturday, respectively, before an expected cool change brings relief on Saturday afternoon. Regions to the west, such as Penrith, though, can expect to swelter with peaks of 41 and 42 on those two days.

As authorities battle fires in both states, the impending weather pattern appears to be less threatening than earlier this week. "Winds are not expected to be as strong as last Tuesday's," Julie Evans, a senior meteorologist at the bureau, said.

New record

Records, though, continue to be broken, with Leonora in central Western Australia yesterday posting the highest temperature during the current heatwave, which began late last year.

Leonora hit 49 degrees, breaking its previous record set for the location just a day earlier at 48.3. The 47.8 level reached on Monday matched a high that had stood for about 55 years.

Inland regions of NSW, such as Tibooburra, will come close to those levels, with 48 predicted for Sunday. Victorian towns such as Mildura and Swan Hill, meanwhile, may see peaks of 42 during the next ramp-up on Friday.

"It's these big blocking highs pushing the cold fronts south," Melissa MacKellar, a meteorologist with Weatherzone, said. "The heat just keeps recycling."

The bureau earlier this week drew international attention after it added additional colour to its forecast charts – adding a deep purple and a pink to extend the range from 50 to 50-52 and 52-54 degrees.

The first eight days of 2013 have all made it into the top 20 hottest days for Australia in more than a century and the massive heat cell over the continent shows little sign of budging.

The region around Eucla, for instance, on the Nullarbor Plain, may approach 50 degrees on Tuesday, according to the bureau's forecast charts.

"One big question is what's going to happen to the monsoonal trough," said Aaron Coutts-Smith, NSW manager of climate services at the bureau. "It's been a relatively late start to the monsoon."

The weak monsoonal conditions mean northern regions aren't getting the cloud cover and rainfall that would normally sap some of the heat collecting in the interior.

"That can really put a lid on extreme temperatures," he said.

Average or below-average temperatures on Wednesday across much of Victoria, Tasmania and parts of NSW saw the run of exceptionally hot average national maximums broken. Wednesday's average maximum came in at 38.36 degrees.

Before that, the first eight days of 2013 were all in the top 20 hottest ever days, with Monday's 40.33 degrees setting a new peak.