I know this stuff is easy to
look up but I think it's fun to see the descriptions which form the basis of the Beaufort Scale.
This was all formulated when there was no easy way of measuring wind speed, so the basis of the marks in the scale were determined by the observable change in the open sea state. What always tickles me is that the original scale didn't get beyond a 12, on the grounds that there was no discernible difference in the sea state however much more the wind blew. Or was it perhaps that no-one had been at sea in anything more than a 12 and survived.
0 Calm Sea like a mirror
1 Light air Ripples with the appearance of scales are formed, but without foam crests
2 Light breeze Small wavelets, still short but more pronounced; crests have a glassy appearance and do not break Wind felt on exposed skin.
3 Gentle breeze Large wavelets. Crests begin to break; scattered whitecaps
4 Moderate breeze Small waves with breaking crests. Fairly frequent whitecaps.
5 Fresh breeze Moderate waves of some length. Many whitecaps. Small amounts of spray.
6 Strong breeze Long waves begin to form. White foam crests are very frequent. Some airborne spray is present.
7 High wind Sea heaps up. Some foam from breaking waves is blown into streaks along wind direction. Moderate amounts of airborne spray.
8 Gale Moderately high waves with breaking crests forming spindrift. Well-marked streaks of foam are blown along wind direction. Considerable airborne spray.
9 Strong/severe gale High waves whose crests sometimes roll over. Dense foam is blown along wind direction. Large amounts of airborne spray may begin to reduce visibility.
10 Storm Very high waves with overhanging crests. Large patches of foam from wave crests give the sea a white appearance. Considerable tumbling of waves with heavy impact. Large amounts of airborne spray reduce visibility.
11 Violent storm Exceptionally high waves. Very large patches of foam, driven before the wind, cover much of the sea surface. Very large amounts of airborne spray severely reduce visibility.
12 Hurricane force Huge waves. Sea is completely white with foam and spray. Air is filled with driving spray, greatly reducing visibility.