TurtleIsland Swell Statistics, September: All Swell – Any Wind
This chart describes the combination of swells directed at TurtleIsland over a normal September. It is based on 2160 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 optimum grid node based on what we know about TurtleIsland. In this particular case the best grid node is 11 km away (7 miles).
The rose diagram shows the distribution of swell directions and swell sizes, 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 occurred only 0.1% of the time. Green and yellow show increasing swell sizes and highest swells greater than >3m (>10ft) are shown in red. In either graph, the area of any colour is proportional to how commonly that size swell occurs.
The diagram implies that the dominant swell direction, shown by the largest spokes, was SSW, whereas the the dominant wind blows from the NW. Because the wave model grid is offshore, sometimes a strong offshore wind blows largest waves away from TurtleIsland and away from the coast. We lump these in with the no surf category of the bar chart. To keep it simple we don't show these in the rose plot. Because wind determines whether or not waves are clean enough to surf at TurtleIsland, you can load a different image that shows only the swells that were expected to coincide with glassy or offshore wind conditions. During a typical September, swells large enough to cause surfable waves at TurtleIsland run for about 100% 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.