Sydney’s Spring weather is can be very changeable. It’s the beginning of the storm season. Winter-style cold fronts still get through. We get cold outbreaks in September, October, even November. It has snowed in the Blue Mountains in mid October a couple of times in recent years. We get outbreaks of heat. Near the coast, the hottest day of the season might be in November, even October. It’s just the nature of the beast.
EDIT: just started raining fairly heavily.
Perfect example of that is last November. Coldest temp was 15.6, hottest was two back to back days above 40 (40.8, 40.5) which was the first time that had happened in any month since the 30s. Those days above 40 were also the hottest days for the whole summer for Sydney. Rest of Summer, particularly December, was was wet, warm and bordering on mild for some parts.