Sydney’s soggiest August weekend in nearly three decades adds onto an already well above average month of rain as moist onshore winds stream into eastern NSW.

Image: Radar imagery showing rainfall moving across the metropolitan region on Sunday, August 10, 2025.

A moist south-to-southeasterly airstream has gripped Sydney since Friday evening, delivering periods of heavy rain. Showers moving from over a very warm Tasman Sea onto land brought just over 80 mm of rain last weekend, including:

• 42 mm in the 24 hours to 9am Saturday
• 38.2 mm in the 24 hours to 9am Sunday
• 80.2 mm across both days
• 79.9 mm is Sydney’s average rainfall across August

Image: DTN Quantitative Precipitation Estimate (QPE) showing widespread rainfall accumulations of 40-80mm across the greatermetropolitan region on Saturday and Sunday, August 9-10, 2025.

Saturday and Sunday’s rainfall totals make it the wettest August weekend since 1998, when 136 mm fell on Saturday, August 8th, 1998, and 8.2 mm on the following Sunday, for a total of 144.2 mm. It was also the wettest weekend (any month) since the start of June 2024. Unfortunately, this weekend coincided with the City2Surf run, which saw drizzly conditions and slippery road conditions.

Sydney’s wettest start to August since 1998

This weekend’s rainfall (plus 16.6 mm in the 24 hours to 9am on Monday) adds onto nearly 100 mm accumulated in the first 8 days of the month, bringing the total up to 194.8 mm, over double the monthly average. This makes it the wettest first 11 days of August since 1998, and the city’s 5th wettest start to August in 168 years of records.

Image: Sydney’s Observations History on the Weatherzone App showing the wet start to August the city has been experiencing.

Even only a third into the month, this is already Sydney’s wettest August since 2014 — which saw a total of 215 mm,  and the 16th wettest August on record.

Why this intense August rainfall?

As mentioned in Friday’s story, abnormally warm Sea Surface Temperatures (SST) off Sydney’s coastline helped provide increased atmospheric moisture feeding this soggy weekend rainfall. SST off the NSW coast of 19 to 22°C are about 2 to 3°C warmer than average, causing more evaporation over the ocean surface and fueling heavy rainfall.

Image: SST off NSW’s coast on Saturday, August 9, 2025, showing a tongue of warm water sitting off the coast. Source: IMOS

These warm SST have been tapped into by persistent onshore winds feeding this August rainfall. A positive Southern Annular Mode (SAM) emerged last week, driving higher than average pressure across southeast Australia and the Tasman Sea, promoting this persistent pattern of moist onshore winds over eastern NSW.

Showery periods should remain over the coming days, although much less intense than the past weekend, with drier conditions returning from Friday. Hints of another positive SAM signal could develop into next week, suggesting the potential for further August rainfall topping up an already very wet month.

Image: Sydney’s 28-Day Rainfall Calendar on the Weatherzone App showing the potential for more wet weather next week.