Kahului Harbor Swell Statistics, August: All Swell – Any Wind
This image describes the combination of swells directed at Kahului Harbor over a normal August and is based upon 2232 NWW3 model predictions since 2006 (values every 3 hours). The wave model does not forecast wind and surf right at the coastline so we have chosen the best grid node based on what we know about Kahului Harbor, and at Kahului Harbor the best grid node is 11 km away (7 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 show increasing wave sizes. The smallest swells, less than 0.5m (1.5 feet), high are coloured blue. These occurred only 38% of the time. Green and yellow represent increasing swell sizes and red shows the highest swells, greater than >3m (>10ft). In either graph, the area of any colour is proportional to how often that size swell was forecast.
The diagram indicates that the most common swell direction, shown by the longest spokes, was NE, whereas the the dominant wind blows from the E. Because the wave model grid is away from the coast, sometimes a strong offshore wind blows largest waves away from Kahului Harbor and out to sea. We group 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 good for surfing at Kahului Harbor, 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 August, swells large enough to cause clean enough to surf waves at Kahului Harbor run for about 62% 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.