Arrifana Swell Statistics, Setembro: Surf with Light or Offshore Winds
This image shows only the swells directed at Arrifana that coincided with light winds or offshore conditions over a normal September and is based upon 2400 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 represent increasing swell sizes and red represents the highest swells, greater than >3m (>10ft). In both graphs, the area of any colour is proportional to how often that size swell was forecast.
The diagram indicates that the most common swell direction, shown by the largest spokes, was NW (which was the same as the dominant wind direction). 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 17% of the time, equivalent to 5 days. Open sea swells exceeding >3m (>10ft) are unlikely to occur in a normal September but 14% of the time you can expect swell in the range 1.3-2m (4-6.5ft) 14%, equivalent to (4 days). Taking into account the proportion of these swells that coincided with forecast offshore winds, and given the fact that Arrifana is slightly protected from open water swells, we think that that clean surf can be found at Arrifana about 17% of the time and that surf is blown out by onshore wind 27% of the time. This is means that we expect 13 days with waves in a typical September, of which 5 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.