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Conditions at Rottnest Island in September
September: Big Spring Swell Meets a Returning Sea Breeze
September is the tail end of the big-swell season, and it can still produce outstanding waves. Average swell height is 8-9ft (2.6m) and period sits at 13.0s, with SW dominating at 35.9% and WSW adding 14.3% - a powerful, long-period combination. However, the atmosphere is changing. The subtropical ridge begins to shift south, and the classic S and SSW sea-breeze pattern returns: S winds (10.9%) and SSW winds (10.3%) become significant again, while ideal conditions drop to 12%. The offshore N/NW quadrant weakens considerably, and stronger SW/W/SW synoptic winds often alternate with clean offshore breaks. Water temperature falls to 18.9°C, air temperatures remain cool at 15.8°C, and rainfall is moderate at 2.56 mm/day. If you score a September morning with offshore N to NW winds and a solid SW groundswell, you are in for a memorable, powerful session - just do not expect it to last all afternoon.
Average Spot conditions at Rottnest Island in September
Swell history for September
Wind history for September
Swell quality
Analyze the groundswell consistency at Rottnest Island during September. Based on historical data, there is a % probability of groundswell occurring this month. The chart below provides a detailed breakdown of the average wave height distribution, offering deep insights into the swell quality and surf potential you can expect at Rottnest Island for your next trip in September.
Ground swell
Ground swell by size
Wind conditions
Evaluate the wind and swell alignment at Rottnest Island for September. Our analysis shows that favorable offshore or side-shore winds coincide with surfable swell approximately % of the time. The accompanying graph illustrates the average size distribution of waves during these optimal wind windows at Rottnest Island.