Every state and territory will bake through a heatwave on Monday with meteorologists saying soaring temperatures will last for days in some parts.
The Bureau of Meteorology said hot days were expected in January but multiple days in a row of temperatures above 40 degrees were unusual.
"Particularly northern South Australia, they're looking at maybe five days in a row above 45 and normally they might only get five or 10 a year," meteorologist Dean Narramore told AAP on Sunday.
Low intensity heatwave conditions have been forecast across parts of central Western Australia to southern parts of the Northern Territory, southwestern Queensland and across NSW, Victoria, Tasmania and South Australia on Monday.
Some regions won't be affected at all while more severe and extreme heat conditions are expected across each state, moving into east and northeastern NSW and southern Queensland by mid to late week.
Sydney will see highs of 31C on Tuesday, 32C on Wednesday, 33C on Thursday and 33 on Friday followed by a hot 36 on Saturday.
Melbourne will see a high of 32C on Monday, 35C on Tuesday, 32C on Wednesday followed by 31C on Thursday and Friday.
Brisbane will see highs of 32C on Monday and Tuesday, 33C on Wednesday, 32 on Thursday and Friday before hitting 33C on Saturday.
This comes off the back of heatwave conditions over the Christmas and New Year period, with inland areas being hit hardest.
Holidaymakers and those getting back to work in Melbourne can expect to see a few days in the mid to high 30s, while a sea breeze will shield Sydney city.