Conditions at Ondarreta in September
September: The Season's First Real Pulse
September is where the North Atlantic starts to wake up. Average wave height climbs to 1.3m (4ft) and the average period lengthens to 10.4s, moving back into the powerful long-period category. The swell direction is still overwhelmingly NW (53.5%) with WNW (21.0%) and NNW (14.5%) close behind. More importantly, the proportion of meaningful waves increases: 21.1% of all waves are in the 1-1.5m (3-5ft) class and another 9.9% in the 1.5-2m (5-6.5ft) class.
Winds are still transitioning. The ideal-wind percentage is 38%, better than summer but still not winter-level. NNW winds (11.7%) are the most frequent, with WNW (10.2%) and NW (8.6%) also present; however, S winds at 7.7% and SSE at 6.6% become more common as low pressures begin to track farther south. Water remains warm at 20.9°C and air temps average 19.0°C, so September can deliver the first proper surf of the season without the winter chill. It is a strong transitional month for early groundswell.
Average Spot conditions at Ondarreta in September
Swell history for September
Wind history for September
Swell quality
Analyze the groundswell consistency at Ondarreta 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 Ondarreta for your next trip in September.
Ground swell
Ground swell by size
Wind conditions
Evaluate the wind and swell alignment at Ondarreta 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 Ondarreta.