It’s gonna be a scorcher! Three-day 40C heatwave in Sydney to be the hottest end of December in 50 YEARS Sydney is on track to swelter through its hottest end to a year in over 50 years, with forecasts of a three-day heatwave bringing temperatures in the high 30s to low 40s. The Bureau of Meteorology predicts perfect summer weather for Sydney on Tuesday and Wednesday, with temperatures tipped to reach 30 degrees with cloud coverage.