Arrifana Swell Statistics, Autumn: All Swell – Any Wind
The graph describes the variation of swells directed at Arrifana through an average northern hemisphere autumn. It is based on 7252 NWW3 model predictions since 2006 (values every 3 hours). The wave model does not forecast wind or surf right at the coast so we have chosen the optimum grid node based on what we know about Arrifana. In the case of Arrifana, the best grid node is 26 km away (16 miles).
The rose diagram illustrates the distribution of swell sizes and directions, while the graph at the bottom shows the same thing but without direction information. Five colours represent increasing wave sizes. Very small swells of less than 0.5m (1.5 feet) high are shown in blue. These happened only 4% of the time. Green and yellow represent increasing swell sizes and red represents the highest swells, greater than >3m (>10ft). In each graph, the area of any colour is proportional to how frequently that size swell happens.
The diagram suggests that the dominant swell direction, shown by the biggest spokes, was WNW, whereas the the dominant wind blows from the NNW. Because the wave model grid is out to sea, sometimes a strong offshore wind blows largest waves away from Arrifana and offshore. We lump these in with the no surf category of the bar chart. To keep it simple we don't show these in the rose diagram. Because wind determines whether or not waves are good for surfing at Arrifana, you can load a different image that shows only the swells that were forecast to coincide with glassy or offshore wind conditions. In a typical northern hemisphere autumn, swells large enough to cause clean enough to surf waves at Arrifana run for about 64% 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.