Iztapa Swell Statistics, Summer: All Swell – Any Wind
This chart illustrates the variation of swells directed at Iztapa through a typical northern hemisphere summer. It is based on 5802 NWW3 model predictions since 2006 (values every 3 hours). The wave model does not forecast surf and wind right at the coast so we have chosen the best grid node based on what we know about Iztapa. In the case of Iztapa, the best grid node is 52 km away (32 miles).
The rose diagram illustrates the distribution of swell sizes and directions, while the graph at the bottom shows the same thing without direction information. Five colours represent increasing wave sizes. Very small swells of less than 0.5m (1.5 feet) high are shown in blue. These happened only 0.1% of the time. Green and yellow show increasing swell sizes and red represents largest swells greater than >3m (>10ft). In both graphs, the area of any colour is proportional to how frequently that size swell occurs.
The diagram suggests that the dominant swell direction, shown by the longest spokes, was SSW, whereas the the most common wind blows from the E. Because the wave model grid is offshore, sometimes a strong offshore wind blows largest waves away from Iztapa and away from the coast. We lump these in 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 surfable at Iztapa, you can view an alternative image that shows only the swells that were forecast to coincide with glassy or offshore wind conditions. Over an average northern hemisphere summer, swells large enough to cause good for surfing waves at Iztapa run for about 100% 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.