13th Beach • Statistics for September

September: Longest Periods of the Year, Spring Mixing

September is a transition month with a premium wave-quality ingredient: the longest average swell period of the entire year at 12.6s. These are pure, long-period Southern Ocean groundswells - the kind that wrap into the coast with real momentum and steepness. Average wave height is around 6ft (1.7m), with SW accounting for 45% of the wave energy, WSW 16% and SSW 10%. The wind balance is shifting toward spring: offshore N, NNE, NE and NNW winds remain robust at 27.3%, while the onshore SSE-SW component rises to 19.3%; ideal wind is still a solid 23% of the time. The first major spring storms can also generate some extremely large swells, occasionally pushing past 8ft (2.5m). Water temperature begins to recover slowly to 12.8°C, average air temps sit around 12.1°C, and the longer days help with comfort. September is a high-performance month: plenty of power, plenty of period, and still a high probability of clean offshore-groomed surf.