Both the arrows and the letters show the direction the wind is blowing. In keeping with meteorological standards, the letters indicate the direction the wind is blowing from, while the arrows point in the direction the wind is moving toward. The orientation of the arrows is based on the directions on most maps, where north is upward.
For example, an arrow pointing upwards indicates that the wind blows from south to north; it will be accompanied by the letter S (south). An arrow pointing right means the wind blows from west to east; it will be accompanied by the letter W (west).
The flags (feathers) or pennants at the tail end of each arrow represent the wind speed.
- Each half-flag (small notch) depicts 5 knots (9.3 km/h; 5.8 mph).
- Each full flag (full notch) depicts 10 knots (19 km/h; 12 mph).
- Each pennant (filled triangle) depicts 50 knots (93 km/h; 58 mph).
- A circle depicts no wind.
Where an arrow features multiple symbols, they have to be added up to calculate the wind speed. For example, an arrow with 2 full flags and a half-flag means that the wind speed is 25 knots.
The values for wind speed are rounded to the nearest whole unit.