An international weather standard
A GRIB or GRIdded Binary file is a file format standardized by the World Meteorological Organization, WMO. These files were created to facilitate the exchange of numerical weather modeling data. For the nautical industry, it facilitates the reception on board of the boat to plan its weather and its navigation route.
The wind direction convention
In weather, the name of the wind always indicates the direction from which the wind comes. Thus, we speak of a north wind when the wind comes from there. It blows from North to South. And yet the arrow in a GRIB file indicates the direction the wind is blowing, its direction of propagation.
The lines at the end of the arrow, called barbs, indicate its strength: a short line counts as 5 knots, and a long one as 10 knots. In the example below, the expected wind is 15 knots.
In our example the arrow or shaft of the wind goes from right to left, from East to West. It represents an East wind, answer B.
