Matosinhos Swell Statistics, August: All Swell – Any Wind
The figure shows the combination of swells directed at Matosinhos over a normal August and is based upon 2480 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 Matosinhos, and at Matosinhos the best grid node is 32 km away (20 miles).
The rose diagram shows the distribution of swell sizes and swell direction, while the graph at the bottom shows the same thing but lacks 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 10% of the time. Green and yellow represent increasing swell sizes and biggest 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 occurs.
The diagram suggests that the prevailing swell direction, shown by the longest spokes, was WNW, whereas the the prevailing wind blows from the NW. Because the wave model grid is out to sea, sometimes a strong offshore wind blows largest waves away from Matosinhos and offshore. We combine these 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 surfable at Matosinhos, you can view an alternative image that shows only the swells that were expected to coincide with glassy or offshore wind conditions. During a typical August, swells large enough to cause good for surfing waves at Matosinhos run for about 90% 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.