The rose diagram describes how frequently and how strongly the wind blows from different directions over a normal year. The biggest spokes point in the directions the wind most commonly blows from and the shade of blue suggests the strength, with the strongest winds shown by dark blue. It is based on 20068 NWW3 forecasts of wind since since 2006, at 3hr intervals, for the closest NWW3 model node to Upolu Point, located 29 km away (18 miles). There are insufficient 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 prevailing wind at Upolu Point blows from the NNW. If the rose graph shows a fairly circular pattern, it means there is no strong bias in wind direction at Upolu Point. Converseley, dominant spokes represent favoured directions, and the more the darkest shade of blue, the stronger the wind. Spokes point in the direction the wind blows from. During a typical year, the model suggests that winds are light enough for the sea to be glassy (the lightest shade of blue) about 3% of the time (11 days each year) and blows offshore just 5% of the time (22 days in an average year). Over an average year wind stronger than >40kph (25mph) was predicted for only a single days at Upolu Point
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.