Sydneysiders may need to bring a brolly to their Christmas dinner, with clouds and some rain expected across the city late on Christmas Day after a warmer weekend.
North-westerly winds will build heat in central and western Sydney throughout the week, with a scorcher in the high 30s expected on Christmas Eve.
But relief will arrive around the same time as Santa, with temperatures dropping early on Christmas morning.
Craig McIntosh, a meteorologist at Weatherzone, said Sydney itself will have a top of 34 degrees on Christmas eve.
In the west, a lack of cooling sea breeze will see Penrith crack 40 degrees, while Liverpool and Richmond are forecast to reach 39 degrees.
When the cool change hits, Sydney will have a cloudy Christmas, with a maximum of 24 degrees in the city, 21 at Bondi and 28 at Penrith.