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Usami Swell Statistics, January: All Swell – Any Wind

This image describes the range of swells directed at Usami over a normal January. It is based on 2620 NWW3 model predictions since 2007 (values every 3 hours). The wave model does not forecast wind or surf right at the coastline 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 shows the distribution of swell directions and swell sizes, while the graph at the bottom shows the same thing 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 88% 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 often that size swell occurs.

The diagram indicates that the dominant swell direction, shown by the largest spokes, was E, 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 Usami 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 graph. Because wind determines whether or not waves are surfable at Usami, 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 January, swells large enough to cause good for surfing waves at Usami run for about 3% 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.