 |
The Beaufort Scale
1 Knot = 2025 yards, 1.85 km, 1.15 miles |
In 1805, the British Admiral Sir Francis Beaufort devised an observation scale for measuring winds at sea on
a scale of 1-12, was extended to Force 17 by the US Weather Bureau in the 1950's.
Each scale number represents a certain
strength or velocity of wind at 10m (33ft) above ground in the open. |
| Force |
m.p.h. |
Knots |
Description |
State of Sea |
Waves |
| 0 |
0-1 |
0-1 |
Calm |
Like a mirror
Farmers complain. Minister for drought appointed |
0 |
| 1 |
1-3 |
1-3 |
Light Air |
Ripples like scales are formed
Rising smoke drifts. Weather vane does not move |
0m |
| 2 |
4-7 |
4-6 |
Light Breeze |
Small Wavelets, still short but more pronounced, not breaking
Wind felt on face. Leaves rustle |
0.1m |
| 3 |
8-12 |
7-10 |
Gentle Breeze |
Large wavelets, crests begin to break; a few white horses
Leaves in constant motion. Flag extends |
0.4m |
| 4 |
13-18 |
11-16 |
Moderate Breeze |
Small waves growing longer, fairly frequent white horses
Paper blown about. Small branches moved |
1m |
| 5 |
19-24 |
17-21 |
Fresh Breeze |
Moderate waves, taking more pronounced form, many white horses, perhaps some spray
Small trees in leaf sway. Flag waves
vigorously |
2m |
| 6 |
25-31 |
22-27 |
Strong Breeze |
Large waves forming; white foam crests more extensive; probably some spray
Large tree branches move. Telephone wires
whistle. Umbrellas difficult to control. Farmers complain about the apple crop. |
3m |
| 7 |
32-38 |
28-33 |
Near Gale |
Sea heaps up; white foam from breaking waves begins to blow in streaks
Large trees sway. Difficult to walk |
4m |
| 8 |
39-46 |
34-40 |
Gale |
Moderately high waves of great length; edge of crests break into spindrift; foam blown in well marked streaks
Twigs
and small branches broken from trees |
5.5m |
| 9 |
47-54 |
41-47 |
Strong Gale |
High waves with tumbling crests; dense streaks of foam; spray may affect visibility
Slight damage to buildings, tiles
blown off roofs |
7m |
| 10 |
55-63 |
48-55 |
Whole Gale |
Very high waves with long overhanging crests; dense streams of foam make surface of sea white. Heavy tumbling sea; visibility
affected
Large trees uprooted. Considerable building damage. Met Office roof blown off. Jimmy Young starts appeal fund. |
9m |
| 11 |
64-72 |
56-63 |
Storm |
Exceptionally high waves; sea completely covered with long white patches of foam; edges of wave crests blown into froth.
Visibility affected.
Expensive widespread damage. |
11m |
| 12 |
73-82 |
64-71 |
Hurricane |
Air filled with foam and spray; sea completely white with driving spray; visibility very seriously affected
Extreme
destruction |
14m |
| 13 |
83-92 |
72-80 |
- |
|
- |
| 14 |
93-103 |
81-89 |
- |
|
- |
| 15 |
104-114 |
90-99 |
- |
|
- |
| 16 |
115-125 |
100-108 |
- |
|
- |
| 17 |
126-136 |
109-118 |
- |
|
- |
