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The Beaufort Scale or
Beaufort Wind Force Scale is a system for estimating wind strengths without
the use of instruments, based on the effects wind has on the physical
environment. The behaviour of smoke, waves, trees, etc., is rated on a 13
point scale of 0 (calm) to 12 (hurricane).
The Beaufort
system was
introduced around the early 19th Century, 1805, by British Navy
Rear-Admiral, Sir Francis Beaufort, Knight Commander of the Bath who was
born in Ireland in 1774. In the summer of 1805 Commander devised his wind
force scale as a mean of estimating wind effect on a fully rigged man-of-war
sailing vessel. It was later extended to include descriptions of effects on
land features as well. Beaufort later served as Hydrographer to the
Admiralty. He died in 1857 two years after his retirement.
International
practice today is to report wind speed in knots (1 knot = approx. 1.85 km,
or 1.15 mph). |
| |
|
Land Beaufort
Scale |
| Force
|
Speed
|
Land
Conditions |
| knots
|
mph
|
| 0
|
<1
|
<1
|
Calm, smoke rises
vertically |
| 1
|
1-3
|
1-3
|
Light air, direction of
wind shown by smoke drift only |
| 2
|
4-6
|
4-7
|
Light breeze, wind felt on
face, leaves rustle, vanes moved by wind |
| 3
|
7-10
|
8-12
|
Gentle breeze, leaves in constant motion, wind extends light flag
|
| 4
|
11-16
|
13-18
|
Moderate breeze, raises
dust, loose paper, small branches move |
| 5
|
17-21
|
19-24
|
Fresh breeze, small trees
in leaf begin to sway |
| 6
|
22-27
|
25-31
|
Strong breeze, large
branches in motion, umbrellas used with difficulty |
| 7
|
28-33
|
32-38
|
Near gale, whole trees in
motion, resistance felt against the wind
|
| 8
|
34-40
|
39-46
|
Gale, breaks twigs off
trees, impedes progress |
| 9
|
41-47
|
47-54
|
Strong gale, slight
structural damage occurs |
| 10
|
48-55
|
55-63
|
Storm, trees uprooted,
considerable damage occurs |
| 11
|
56-63
|
64-73
|
Violent storm, widespread
damage |
| 12
|
64+
|
74+
|
Hurricane, extreme
destruction |
|
| |
|
Marine Beaufort Scale |
| Force
|
Speed
|
Marine
Conditions |
| knots
|
mph
|
| 0
|
<1
|
<1
|
Calm, sea like a mirror.
|
| 1
|
1-3
|
1-3
|
Light air, ripples only.
|
| 2
|
4-6
|
4-7
|
Light breeze, small
wavelets (0.2m). Crests have a glassy appearance. |
| 3
|
7-10
|
8-12
|
Gentle breeze, large
wavelets (0.6m), crests begin to break. |
| 4
|
11-16
|
13-18
|
Moderate breeze, small
waves (1m), some white horses. |
| 5
|
17-21
|
19-24
|
Fresh breeze, moderate
waves (1.8m), many white horses. |
| 6
|
22-27
|
25-31
|
Strong breeze, large waves
(3m), probably some spray. |
| 7
|
28-33
|
32-38
|
Near gale, mounting sea
(4m) with foam blown in streaks downwind. |
| 8
|
34-40
|
39-46
|
Gale, moderately high
waves (5.5m), crests break into spindrift. |
| 9
|
41-47
|
47-54
|
Strong gale, high waves
(7m), dense foam, visibility affected. |
| 10
|
48-55
|
55-63
|
Storm, very high waves
(9m), heavy sea roll, visibility impaired.
|
| 11
|
56-63
|
64-73
|
Violent storm,
exceptionally high waves (11m), visibility poor. |
| 12
|
64+
|
74+
|
Hurricane, 14m waves, air
filled with foam and spray, visibility bad. |
|
| |
| |
| Source:
NCDC |
Updated
February 20, 2007. |
|
