The rose diagram illustrates the range of swells directed at Vila Praia de Ancora through an average northern hemisphere autumn. It is based on 5144 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 most applicable grid node based on what we know about Vila Praia de Ancora, and at Vila Praia de Ancora the best grid node is 23 km away (14 miles).
The rose diagram illustrates the distribution of swell sizes and swell direction, 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 occurred only 7% of the time. Green and yellow show increasing swell sizes and red represents the largest 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 most common swell direction, shown by the longest spokes, was WNW, whereas the the most common wind blows from the N. Because the wave model grid is out to sea, sometimes a strong offshore wind blows largest waves away from Vila Praia de Ancora and offshore. We combine these with the no surf category of the bar chart. To keep it simple we don't show these in the rose plot. Because wind determines whether or not waves are surfable at Vila Praia de Ancora, you can select a similar diagram that shows only the swells that were predicted to coincide with glassy or offshore wind conditions. In a typical northern hemisphere autumn, swells large enough to cause good for surfing waves at Vila Praia de Ancora run for about 93% 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.