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Sydney's wettest September day in 146 years

Sydney, Canberra and Wollongong have all had their wettest day of 2025, while Sydney’s total of 122mm in the 24 hours to 9am Thursday was the city’s heaviest daily rainfall total for September since 1879.

Flood warnings have been issued for three rivers in the Sydney Basin – the Nepean, the Georges and the Cooks – as heavy rain continues into Thursday morning.

The combined radar and satellite loop below shows the intense rainfall swirling around a low pressure system centred over the Sydney region between 7pm Wednesday and 7am Thursday. 72mm of rainfall was recorded during that 12-hour period.

Image: 12 hour combined satellite and radar loop for NSW up until 7am on Thursday September 11, 2025.

While there were a few rumbles of thunder in the Sydney region on Wednesday evening, this was a night of persistent heavy rainfall rather than the intense but brief rainfall which tends to be associated with storms (although severe thunderstorms did occur in parts of NSW mostly west of the Great Divide).

READ MORE: Tornado observed near Young, NSW

The unstable low pressure system fed by abundant atmospheric moisture which drenched Sydney also brought very high 24-hour rainfall totals to areas south and southwest of the Sydney basin, including:

• 46mm in Canberra, which was the national capital’s highest daily fall of 2025 to date.
• More than 130mm at numerous coastal weather stations south of Sydney, including Kiama, Bellambi and Jervis Bay.
• The highest NSW reading of 144.8mm was in Ulladulla, which is having a very wet year with a year-to-date rainfall total which is approaching double its running average. Ulladulla also had the wettest day anywhere in Australia in July 2025 when 224mm fell on July 2.

This is a somewhat unseasonable weather system. September is typically the driest month of the year in Sydney, with a monthly rainfall average of 67.2mm which is almost exactly half that of the wettest month (March with 135.2mm).

Those with a long memory might recall how the Sydney 2000 Olympic Games – which ran during the last two weeks of September – were almost totally dry throughout.

The good news for sun-starved Sydneysiders is that fine weather will return by Friday and stick around all weekend and well into the new week.

Often, coastal low pressure systems will dampen the NSW coastline for up to a week, however the current system is expected to dissipate quickly, with only a few light showers persisting along the northern part of the NSW coast in coming days.

Please check the latest flood warnings and more on the Weatherzone warnings page.