South-east Queensland will be gripped by widespread 40-degree heat on Friday and Saturday before relief by as much as 8 degrees arrives on Sunday thanks to a southerly wind change.

Fire danger ratings are expected to rise back to severe again across many south-eastern fire districts, with 46 bushfires still burning on Wednesday following last month's state emergency.

Weatherzone meteorologist Craig McIntosh said warm winds and an inland trough would push the mercury up, with slightly cooler conditions on Wednesday before the spike would begin on Thursday.

"What’s driving the heat at the moment is the winds are generally offshore and that is bringing inland heat to the south-east coast," he said.