Despite a brief cool spell early in the month which included Sydney’s wettest September day in 146 years, the harbour city has recorded its second-warmest September since records were first kept in 1858.

In September 2025:

• Sydney’s average maximum was 23.5°C, which was around 3.3°C above the long-term average of 20.2°C.
• Sydney’s average minimum was 13.1°C, which was around 1.9°C above the long-term average of 11.2°C.

Only September 2013 was warmer than September 2025 in Sydney for both maximums and minimums, while 2023 was slightly hotter than this year for maximums.

Why was September 2025 so warm?

In addition to the underlying influence of the warming climate, Sydney’s weather was also impacted by the Sudden Stratospheric Warming (SSW) over Antarctica.

The SSW is a weakening of the polar vortex which in turn leads to a negative Southern Annual Mode (SAM). This tends to produce more frequent spells of warm, windy conditions on the NSW coast.

Image: Forecast minimums and maximums for Sydney on the Weatherzone app.

What about Sydney temperatures and rainfall in other months this year?

Rainfall:

• Sydney has had a wet year thus far in 2025, with seven of the nine months seeing above-average rainfall.
• August was exceptionally wet with 389.6mm (nearly five times the long-term monthly average). It rounded out the city’s wettest winter in 18 years.
• Sydney exceeded its long-term annual rainfall average of 1222.6mm during the soggy 2025 August.
• Five of the last six years have now seen above-average rainfall in Sydney, including the record-breaking year of 2022.

Temperatures:

• Wet weather tends to go hand-in-hand with slightly cooler-than-average days, but despite its relatively high rainfall, Sydney has seen above-average maximums in each month of 2025 to date.
• Sydney’s minimums have been above average in eight of the nine months so far this year. The exception was June, when overnight lows were around half a degree below average.

Meanwhile fans can expect a very warm afternoon with a top of 31°C at Sydney Olympic Park ahead of the NRL Grand Final between the Melbourne Storm and the Brisbane Broncos, which kicks off at 7:30pm this Sunday evening, October 5, at Accor Stadium.

While the men’s match should be played in the cool of the evening, the women’s grand final between the Roosters and the Broncos commences at 4pm, which will be close to the hottest part of the day.