Meteorologist Grace Legge said that with Christmas still a week away, conditions may change.

"The heatwave that is forecast to stretch from the north-west of Western Australia all the way to central New South Wales later this week will still be making its presence felt, as hot, dry air lingers, bringing very high temperatures to many inland regions," she said.

"Heat will be dragged through much of the country for Christmas, though sea breezes may keep some coastal areas a little cooler than inland parts.

"Through southern Victoria and Tasmania temperatures are a little hard to predict with the timing of a cool southerly change that will determine the Christmas maximum."

Sydney is facing a mixed bag of weather over the six days leading up to the big day, with showers forecast every day until Sunday.