This picture illustrates the variation of swells directed at Mount Maunganui through a typical January. It is based on 1728 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 best grid node based on what we know about Mount Maunganui. In the case of Mount Maunganui, the best grid node is 32 km away (20 miles).
The rose diagram illustrates the distribution of swell sizes and directions, while the graph at the bottom shows the same thing but lacks direction information. Five colours illustrate increasing wave sizes. Blue shows the smallest swells, less that 0.5m (1.5 feet) high. These happened only 18% of the time. Green and yellow represent increasing swell sizes and largest swells greater than >3m (>10ft) are shown in red. In both graphs, the area of any colour is proportional to how often that size swell happens.
The diagram indicates that the most common swell direction, shown by the largest spokes, was NE, whereas the the most common wind blows from the NW. Because the wave model grid is out to sea, sometimes a strong offshore wind blows largest waves away from Mount Maunganui and offshore. 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 surfable at Mount Maunganui, you can select a similar diagram that shows only the swells that were forecast to coincide with glassy or offshore wind conditions. Over an average January, swells large enough to cause good for surfing waves at Mount Maunganui run for about 24% 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.