Arrifana Swell Statistics, December: 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 December. It is based on 2457 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 biggest 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 prevailing swell direction, shown by the largest spokes, was WNW, whereas the the prevailing 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 40% of the time, equivalent to 12 days. Open water swells exceeding >3m (>10ft) only occur 3% of the time in a typical December, equivalent to just one day but 18% of the time we expect swell in the range 2-3m (6.5-10ft) 18%, equivalent to (5 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 40% of the time and that surf is messed up by onshore wind 37% of the time. This is means that we expect 23 days with waves in a typical December, of which 12 days should be clean enough to surf.
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.