Arpoador Swell Statistics, Autumn: Surf with Light or Offshore Winds
This image shows only the swells directed at Arpoador that coincided with light winds or offshore conditions through a typical southern hemisphere autumn. It is based on 6580 predictions, one every 3 hours. The direction of the spokes show where quality surf generating swell comes from. Five colours show increasing wave sizes. The smallest swells, less than 0.5m (1.5 feet), high are coloured blue. Green and yellow show increasing swell sizes and red illustrates the highest swells, greater than >3m (>10ft). In either graph, the area of any colour is proportional to how commonly that size swell happens.
The diagram implies that the prevailing swell direction, shown by the largest spokes, was SSE, whereas the the dominant wind blows from the NE. The chart at the bottom shows the same thing but without direction information. For example, swells larger than 1.5 feet (0.5m) coincided with good wind conditions 28% of the time, equivalent to 25 days. Open sea swells exceeding >3m (>10ft) are unlikely to arise in a normal southern hemisphere autumn but 6% of the time we expect swell in the range 2-3m (6.5-10ft) 6%, equivalent to (5 days). Taking into account the ratio of these swells that coincided with forecast offshore winds, and given the fact that Arpoador is slightly protected from open water swells, we think that that clean surf can be found at Arpoador about 28% of the time and that surf is blown out by onshore wind 16% of the time. This is means that we expect 40 days with waves in a typical southern hemisphere autumn, of which 25 days should be surfable.
IMPORTANT: Beta version feature! Swell heights are open water values from NWW3. There is no attempt to model near-shore effects. Coastal wave heights will generally be less, especially if the break does not have unobstructed exposure to the open ocean.