This image shows only the swells directed at Watamu Bay that coincided with light winds or offshore conditions over a normal July. It is based on 1736 predictions, one every 3 hours. The direction of the spokes show where quality surf generating swell comes from. Five colours illustrate increasing wave sizes. Blue shows the smallest swells, less that 0.5m (1.5 feet) high. Green and yellow illustrate increasing swell sizes and red shows highest swells greater than >3m (>10ft). In either graph, the area of any colour is proportional to how often that size swell occurs.
The diagram indicates that the most common swell direction, shown by the largest spokes, was ESE, whereas the the dominant wind blows from the S. The chart at the bottom shows the same thing but without direction information. For example, swells larger than 1.5 feet (0.5m) coincided with good wind conditions 0.2% of the time, equivalent to 0 days. Open sea swells exceeding >3m (>10ft) are unlikely to happen in a normal July. Taking into account the proportion of these swells that coincided with predicted offshore winds, and given the fact that Watamu Bay is exposed to open water swells, we estimate that clean surf can be found at Watamu Bay about 0.2% of the time and that surf is spoilt by onshore wind 100% of the time. This is means that we expect 31 days with waves in a typical July, of which 0 days should be clean enough to surf.
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.