Ala Moana Swell Statistics, Autumn: Surf with Light or Offshore Winds
The rose diagram shows only the swells directed at Ala Moana that coincided with light winds or offshore conditions through a typical southern hemisphere autumn. It is based on 6580 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 represent increasing swell sizes and biggest swells greater than >3m (>10ft) are shown in red. In either graph, the area of any colour is proportional to how often that size swell occurs.
The diagram indicates that the dominant swell direction, shown by the longest spokes, was SSW, whereas the the prevailing 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 8% of the time, equivalent to 7 days. Open sea swells exceeding >3m (>10ft) are unlikely to happen in a normal southern hemisphere autumn but 3% of the time we expect swell in the range 2-3m (6.5-10ft) 3%, equivalent to (3 days). Taking into account the ratio of these swells that coincided with predicted offshore winds, and given the fact that Ala Moana is exposed to open water swells, we calculate that clean surf can be found at Ala Moana about 8% of the time and that surf is spoilt by onshore wind 92% of the time. This is means that we expect 91 days with waves in a typical southern hemisphere autumn, of which 7 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.