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Usami Swell Statistics, October: All Swell – Any Wind

The graph shows the variation of swells directed at Usami through an average October and is based upon 2976 NWW3 model predictions since 2006 (values every 3 hours). The wave model does not forecast wind and surf right at the shore so we have chosen the optimum grid node based on what we know about Usami. In the case of Usami, the best grid node is 77 km away (48 miles).

The rose diagram describes 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 54% of the time. Green and yellow illustrate increasing swell sizes and red represents biggest swells greater than >3m (>10ft). In either graph, the area of any colour is proportional to how frequently that size swell happens.

The diagram suggests that the most common swell direction, shown by the largest spokes, was E, whereas the the prevailing wind blows from the NE. Because the wave model grid is offshore, sometimes a strong offshore wind blows largest waves away from Usami and away from the coast. We combine these with the no surf category of the bar chart. To avoid confusion we don't show these in the rose diagram. Because wind determines whether or not waves are clean enough to surf at Usami, you can load a different image that shows only the swells that were forecast to coincide with glassy or offshore wind conditions. In a typical October, swells large enough to cause surfable waves at Usami run for about 8% 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.