The rose diagram shows the variation of swells directed at La Tranche sur Mer over a normal February and is based upon 1584 NWW3 model predictions since 2007 (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 La Tranche sur Mer. In this particular case the best grid node is 44 km away (27 miles).
The rose diagram shows 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 were forecast only 5% of the time. Green and yellow illustrate increasing swell sizes and biggest swells greater than >3m (>10ft) are shown in red. In either graph, the area of any colour is proportional to how often that size swell happens.
The diagram indicates that the most common swell direction, shown by the longest spokes, was WSW, whereas the the prevailing wind blows from the N. Because the wave model grid is offshore, sometimes a strong offshore wind blows largest waves away from La Tranche sur Mer and away from the coast. We group these with the no surf category of the bar chart. To simplify things we don't show these in the rose plot. Because wind determines whether or not waves are surfable at La Tranche sur Mer, you can select a similar diagram that shows only the swells that were predicted to coincide with glassy or offshore wind conditions. During a typical February, swells large enough to cause good for surfing waves at La Tranche sur Mer run for about 95% 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.