Beaufort Wind Force Scale and Sea State



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The Beaufort scale is an empirical measure for the intensity of the wind based mainly on sea-state or wave conditions.




BEAUFORT WIND FORCE SCALE:
Specifications and equivalent speeds for use at sea


FORCE

Equivalent

Speed

Wave

Height

Description

Map

U.S. Advisory

SPECIFICATIONS FOR USE AT SEA


miles/hr

knots

m

ft


Symbols

Flags


0

0-1

0-1

0

0

Calm



Sea like a mirror

1

1-3

1-3

.1

.33

Light Air



Ripples with the appearance of scales are formed, but without foam crests.

2

4-7

4-6

.2

.66

Light Breeze



Small wavelets, still short, but more pronounced. Crests have a glassy appearance and do not break.

3

8-12

7-10

.6

2

Gentle Breeze



Large wavelets. Crests begin to break. Foam of glassy appearance. Perhaps scattered white horses.

4

13-18

11-16

1

3.3

Moderate Breeze



Small waves, becoming larger; fairly frequent white horses.

5

19-24

17-21

2

6.6

Fresh Breeze



Moderate waves, taking a more pronounced long form; many white horses are formed. Chance of some spray.

6

25-31

22-27

3

9.9

Strong Breeze


Small Craft Advisory

Large waves begin to form; the white foam crests are more extensive everywhere. Probably some spray.

7

32-38

28-33

4

13

Near Gale



Sea heaps up and white foam from breaking waves begins to be blown in streaks along the direction of the wind.

8

39-46

34-40

5.5

18

Gale


Gale Warning

Moderately high waves of greater length; edges of crests begin to breakinto spindrift. The foam is blown in well-marked streaks slong the direction of the wind.

9

47-54

41-47

7

23

Severe Gale



High waves. Dense streaks of foam along the direction of the wind. Crests of waves begin to topple, tumble and roll over. Spray may affect visibility.

10

55-63

48-55

9

30

Storm


Storm Warning

Very high waves with long over-hanging crests. The resulting foam, in great patches, is blown in dense white streaks along the direction of the wind. On the whole the surface of the sea takes on a white appearance. The 'tumbling' of the sea becomes heavy and shock-like. Visibility affected.

11

64-72

56-63

11.5

38

Violent Storm



Exceptionally high waves (small and medium-size ships might be for a time lost to view behind the waves). The sea is completely covered with long white patches of foam lying along the direction of the wind. Everywhere the edges of the wave crests are blown into froth. Visibility affected.

12

73-83

64-71

14+

46+

Hurricane


Hurricane Warning

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

"The scale was created in 1806 by Sir Francis Beaufort, a British naval officer. The initial scale did not have wind speeds, but listed a set of qualitative conditions from 0 to 12 by how a naval vessel would act under them - from 'just sufficient to give steerage' to 'that which no canvas could withstand'. The scale was made a standard part of log entries for Royal Navy vessels in the late 1830s." From Wikepedia


Force 0
Sea like a mirror



Force 1
Ripples with the appearance of scales are formed, but without foam crests.



Force 2
Small wavelets, still short, but more pronounced. Crests have a glassy appearance and do not break.



Force 3
Large wavelets. Crests begin to break. Foam of glassy appearance. Perhaps scattered white horses.



Force 4
Small waves, becoming larger; fairly frequent white horses.



Force 5
Moderate waves, taking a more pronounced long form; many white horses are formed. Chance of some spray.



Force 6
Large waves begin to form; the white foam crests are more extensive everywhere. Probably some spray.



Force 7
Sea heaps up and white foam from breaking waves begins to be blown in streaks along the direction of the wind.



Force 8
Moderately high waves of greater length; edges of crests begin to breakinto spindrift. The foam is blown in well-marked streaks slong the direction of the wind.



Force 9
High waves. Dense streaks of foam along the direction of the wind. Crests of waves begin to topple, tumble and roll over. Spray may affect visibility.



Force 10
Very high waves with long over-hanging crests. The resulting foam, in great patches, is blown in dense white streaks along the direction of the wind. On the whole the surface of the sea takes on a white appearance. The 'tumbling' of the sea becomes heavy and shock-like. Visibility affected.



Force 11
Exceptionally high waves (small and medium-size ships might be for a time lost to view behind the waves). The sea is completely covered with long white patches of foam lying along the direction of the wind. Everywhere the edges of the wave crests are blown into froth. Visibility affected.



Force 12
The air is filled with foam and spray. Sea completely white with driving spray; visibility very seriously affected.

Pictures provided by N.O.A.A.

Pierson - Moskowitz Sea Spectrum vs Beaufort Force
(Sea State Table)
Force
Sea State
Significant Wave (Ft)
Significant Range of Periods (Sec)
Average Period (Sec)
Average Length of Waves (FT)
1
0
<.5
.5 - 1
1
2
2
1
0.5
1 - 2.5
1.5
9.5
3
2
2
1.5 - 5
3
26
4
3
3.5
2 - 6.5
4
50
5
4
6
2.5 - 8.5
5
80
6
5
8
3 - 10
6-7
130
7
6
18
4 - 13
8-9
220
8
7
32
5.5 - 17
10-12
400
9
8
52
7.5 - 23
13-15
650
10
11
12
9
60-100
9 - 28.5
16-19
800-1200


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