The graph illustrates how commonly and how strongly the wind blows from different directions through a typical September. The biggest spokes point in the directions the wind most commonly blows from and the shade of blue indicates the strength, with the strongest winds shown by deep blue. It is based on 1680 NWW3 forecasts of wind since since 2006, at 3hr intervals, for the closest NWW3 model node to Ile de Noirmoutier - Barbatre, located 24 km away (15 miles). There are not enough recording stations world wide to use actual wind data. No doubt some coastal places have very localized wind effects that would not be predicted by NWW3.
According to the model, the prevailing wind at Ile de Noirmoutier - Barbatre blows from the W. If the rose plot shows a nearly round shape, it means there is no strong bias in wind direction at Ile de Noirmoutier - Barbatre. Converseley, dominant spokes illustrate favoured directions, and the more deep blue, the stronger the wind. Spokes point in the direction the wind blows from. Over an average September, the model suggests that winds are light enough for the sea to be glassy (the lightest shade of blue) about 11% of the time (3 days each September) and blows offshore 39% of the time (10 days in an average September). In a typical September wind stronger than >40kph (25mph) was forecast for only a single days at Ile de Noirmoutier - Barbatre
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.