The earth is about 3.5 million miles closer to the sun in early January than in early July. North of the Tropic of Cancer that effect is overriden by the tilt of the earth and the length of days and how high the sun goes in the sky. Still, considering that Sydney is right by the Pacific Ocean this is unusually hot for Sydney. They must be getting the weather coming in from the hot interior.
Just as LA can get winds from Nevada and New York can get winds from the Gulf,I'm sure that Sydney can get winds from the Outback.Years ago I visited a town called Broken Hill which is very much in the Outback.My two days there (in March,the end of their summer) featured 105 degrees and not a cloud to be seen.IIRC Broken Hill is just about due west of Sydney.