Arrifana Swell Statistics, December: All Swell – Any Wind
The figure shows the variation of swells directed at Arrifana through an average December, based on 2457 NWW3 model predictions since 2006 (values every 3 hours). The wave model does not forecast wind and surf right at the shore so we have chosen the best grid node based on what we know about Arrifana. In this particular case the best grid node is 26 km away (16 miles).
The rose diagram describes the distribution of swell sizes and swell direction, while the graph at the bottom shows the same thing but without direction information. Five colours illustrate increasing wave sizes. Blue shows the smallest swells, less that 0.5m (1.5 feet) high. These happened only 8% of the time. Green and yellow illustrate increasing swell sizes and red represents 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. Because the wave model grid is offshore, sometimes a strong offshore wind blows largest waves away from Arrifana and away from the coast. We lump these in with the no surf category of the bar chart. To simplify things we don't show these in the rose plot. Because wind determines whether or not waves are surfable at Arrifana, you can select a similar diagram that shows only the swells that were expected to coincide with glassy or offshore wind conditions. In a typical December, swells large enough to cause good for surfing waves at Arrifana run for about 77% of the time.
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.