Sydneysiders will shake off the coldest December in 51 years this week, with soaring temperatures marking the beginning of a sizzling summer in the city.

The temperature in the city is expected to peak at 31 degrees on Wednesday, about five degrees above average, and up to 36 degrees in the western suburbs, Weatherzone senior meteorologist Alex Zadnik said.

"You can see right there that it's a return to more typical summer weather for the Sydney region," Mr Zadnik said.

North-west winds were bringing summer to Sydney, he said.

"Those north-west winds transport heat from inland parts of NSW into the Sydney Basin and that's a reason for the rising temperatures.