This image shows the variation of swells directed at San Juan del Sur through an average northern hemisphere summer and is based upon 5080 NWW3 model predictions since 2006 (values every 3 hours). The wave model does not forecast wind or surf right at the coast so we have chosen the optimum grid node based on what we know about San Juan del Sur. In this particular case the best grid node is 31 km away (19 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 illustrate increasing wave sizes. Blue shows the smallest swells, less that 0.5m (1.5 feet) high. These happened only 3% of the time. Green and yellow represent increasing swell sizes and red represents biggest swells greater than >3m (>10ft). In both graphs, the area of any colour is proportional to how commonly that size swell was forecast.
The diagram implies that the dominant swell direction, shown by the longest spokes, was SSW, whereas the the prevailing wind blows from the ENE. Because the wave model grid is out to sea, sometimes a strong offshore wind blows largest waves away from San Juan del Sur and offshore. We group 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 clean enough to surf at San Juan del Sur, 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 northern hemisphere summer, swells large enough to cause surfable waves at San Juan del Sur run for about 97% 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.