This picture shows how often and how strongly the wind blows from different directions through a typical September. The largest spokes point in the directions the wind most commonly blows from and the shade of blue indicates the strength, with the darkest shade of blue showing the strongest winds. It is based on 1680 NWW3 forecasts of wind since since 2006, at 3hr intervals, for the closest NWW3 model node to La Tranche sur Mer, located 44 km away (27 miles). There are not enough recording stations world wide to use actual wind data. Invevitably some coastal places have very localized wind effects that would not be predicted by NWW3.
According to the model, the dominant wind at La Tranche sur Mer blows from the W. If the rose graph shows a fairly circular pattern, it means there is no strong bias in wind direction at La Tranche sur Mer. Converseley, dominant spokes show favoured directions, and the more the darkest shade of 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 12% of the time (4 days each September) and blows offshore 45% of the time (12 days in an average September). In a typical September wind stronger than >40kph (25mph) was forecast for only a single days at La Tranche sur Mer
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.