Martinhal Swell Statistics, April: All Swell – Any Wind
The graph shows the variation of swells directed at Martinhal through a typical April. It is based on 2160 NWW3 model predictions since 2007 (values every 3 hours). The wave model does not forecast surf and wind right at the shore so we have chosen the best grid node based on what we know about Martinhal. In the case of Martinhal, the best grid node is 38 km away (24 miles).
The rose diagram illustrates the distribution of swell sizes and directions, while the graph at the bottom shows the same thing without direction information. Five colours illustrate increasing wave sizes. Blue shows the smallest swells, less that 0.5m (1.5 feet) high. These occurred only 80% of the time. Green and yellow represent increasing swell sizes and red represents the biggest swells, greater than >3m (>10ft). In both graphs, the area of any colour is proportional to how frequently that size swell occurs.
The diagram suggests that the most common swell direction, shown by the longest spokes, was WSW, whereas the the prevailing wind blows from the NNW. Because the wave model grid is out to sea, sometimes a strong offshore wind blows largest waves away from Martinhal and offshore. We group these 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 Martinhal, you can load a different image that shows only the swells that were forecast to coincide with glassy or offshore wind conditions. Over an average April, swells large enough to cause clean enough to surf waves at Martinhal run for about 4% 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.