Matosinhos Swell Statistics, August: All Swell – Any Wind
The rose diagram describes the combination of swells directed at Matosinhos through an average August, based on 2422 NWW3 model predictions since 2006 (values every 3 hours). The wave model does not forecast wind and surf right at the coast so we have chosen the most applicable grid node based on what we know about Matosinhos. In this particular case the best grid node is 32 km away (20 miles).
The rose diagram illustrates the distribution of swell sizes and swell direction, while the graph at the bottom shows the same thing without direction information. Five colours show increasing wave sizes. The smallest swells, less than 0.5m (1.5 feet), high are coloured blue. These were forecast only 11% of the time. Green and yellow illustrate increasing swell sizes and highest swells greater than >3m (>10ft) are shown in red. In each graph, the area of any colour is proportional to how frequently that size swell was forecast.
The diagram suggests that the most common swell direction, shown by the longest spokes, was WNW, whereas the the dominant wind blows from the NW. Because the wave model grid is offshore, sometimes a strong offshore wind blows largest waves away from Matosinhos and away from the coast. We lump these in with the no surf category of the bar chart. To avoid confusion we don't show these in the rose graph. Because wind determines whether or not waves are good for surfing at Matosinhos, you can view an alternative image that shows only the swells that were forecast to coincide with glassy or offshore wind conditions. In a typical August, swells large enough to cause clean enough to surf waves at Matosinhos run for about 89% 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.