Mangahume Swell Statistics, August: All Swell – Any Wind
This picture shows the combination of swells directed at Mangahume over a normal August. It is based on 1984 NWW3 model predictions since 2006 (values every 3 hours). The wave model does not forecast surf and wind right at the shore so we have chosen the optimum grid node based on what we know about Mangahume. In the case of Mangahume, the best grid node is 37 km away (23 miles).
The rose diagram describes the distribution of swell sizes and directions, 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 occurred only 20% of the time. Green and yellow represent increasing swell sizes and red represents the biggest swells, greater than >3m (>10ft). In each 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 biggest spokes, was WSW, whereas the the prevailing wind blows from the WNW. Because the wave model grid is offshore, sometimes a strong offshore wind blows largest waves away from Mangahume and away from the coast. We group these with the no surf category of the bar chart. To keep it simple we don't show these in the rose diagram. Because wind determines whether or not waves are good for surfing at Mangahume, you can select a similar diagram that shows only the swells that were expected to coincide with glassy or offshore wind conditions. During a typical August, swells large enough to cause clean enough to surf waves at Mangahume run for about 80% 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.