Force

Speed

(Knots)

Sea Condition

1

Sea like a mirror.  

2

Ripples but without foam crests.

3

Small wavelets. Crests do not break.  

4

Large Wavelets. Perhaps scattered white horses.

5

Moderate waves, many white horses.  

6

Large waves begin to form; white foam crests, probably spray.  

7

Sea heaps up and white foam blown in streaks along the direction of the wind.  

8

Moderately high waves, crests begin to break into spindrift.  

9

High waves. Dense foam along the direction of the wind. Crests of waves begin to roll over. Spray may affect visibility.  

10

Very high waves with long overhanging crests. The surface of the sea takes a white appearance. The tumbling of the sea becomes heavy and shock like. Visibility affected.  

11

Exceptionally high waves. The sea is completely covered with long white patches of foam lying in the direction of the wind. Visibility affected.  

12

The air is filled with foam and spray. Sea completely white with driving spray. Visibility very seriously affected.