Haast Beach • Statistics for September

September: Big Swells, Changeable Winds

September is the transitional month where winter's biggest swells meet spring's instability. The average swell height rises to 5ft (1.5m) - the highest of the year - and the period remains long at 11.4s, so the ocean has serious power. W is again the primary swell source at 36%, but WNW jumps to 22%, NW at 12.5%, and NNW at 11.4%; WSW drops to 11%. The size distribution is the most energetic of the year, with large portions of 3-5ft (1-1.5m) and 5-6.5ft (1.5-2m), plus 9% in the 6.5-8ft (2-2.5m) range. The problem is wind: ideal conditions fall to 33%, and the N/NW onshore sector begins to reestablish itself as spring systems alternate with the last winter fronts. Still, when a large WNW swell coincides with a SW/SSW/S offshore wind, Haast will be world-class. Water temp is 12.2°C, air averages 7.9°C, and rainfall peaks at 6.99 mm/day.