This picture describes the variation of swells directed at Sidi Kaouki through a typical northern hemisphere autumn and is based upon 5144 NWW3 model predictions since 2006 (values every 3 hours). The wave model does not forecast surf and wind right at the coastline so we have chosen the best grid node based on what we know about Sidi Kaouki. In this particular case the best grid node is 18 km away (11 miles).
The rose diagram describes 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 1.3% of the time. Green and yellow show increasing swell sizes and highest swells greater than >3m (>10ft) are shown in red. In both graphs, the area of any colour is proportional to how often that size swell happens.
The diagram indicates that the prevailing swell direction, shown by the longest spokes, was NW, whereas the the dominant wind blows from the N. Because the wave model grid is offshore, sometimes a strong offshore wind blows largest waves away from Sidi Kaouki 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 plot. Because wind determines whether or not waves are surfable at Sidi Kaouki, you can load a different image that shows only the swells that were predicted to coincide with glassy or offshore wind conditions. Over an average northern hemisphere autumn, swells large enough to cause good for surfing waves at Sidi Kaouki run for about 99% 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.