Coastguards Swell Statistics, Winter: All Swell – Any Wind
The figure describes the range of swells directed at Coastguards through a typical northern hemisphere winter. It is based on 6363 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 most applicable grid node based on what we know about Coastguards. In the case of Coastguards, the best grid node is 21 km away (13 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 occurred only 57% of the time. Green and yellow illustrate 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 often that size swell was forecast.
The diagram indicates that the prevailing swell direction, shown by the longest spokes, was S, whereas the the dominant wind blows from the WNW. Because the wave model grid is offshore, sometimes a strong offshore wind blows largest waves away from Coastguards and away from the coast. We lump these in 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 clean enough to surf at Coastguards, you can view an alternative image that shows only the swells that were predicted to coincide with glassy or offshore wind conditions. Over an average northern hemisphere winter, swells large enough to cause surfable waves at Coastguards run for about 43% 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.