Arrifana Swell Statistics, Julho: All Swell – Any Wind
The figure shows the combination of swells directed at Arrifana over a normal July, based on 2480 NWW3 model predictions since 2006 (values every 3 hours). The wave model does not forecast surf and wind right at the shore so we have chosen the optimum 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 illustrates the distribution of swell directions and swell sizes, while the graph at the bottom shows the same thing but lacks direction information. Five colours show increasing wave sizes. The smallest swells, less than 0.5m (1.5 feet), high are coloured blue. These occurred only 1.0% of the time. Green and yellow represent 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 frequently that size swell happens.
The diagram suggests that the most common swell direction, shown by the longest spokes, was NW, whereas the the prevailing wind blows from the NNW. 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 clean enough to surf at Arrifana, you can select a similar diagram that shows only the swells that were forecast to coincide with glassy or offshore wind conditions. During a typical July, swells large enough to cause surfable waves at Arrifana run for about 48% 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.