the Beaufort scale: For use at sea For use on land
THE BEAUFORT WIND SCALEOne of the first scales to estimate wind speeds and the effects was created by Britain's Admiral Sir Francis Beaufort (1774-1857). He developed the scale in 1805 to help sailors estimate the winds via visual observations. The scale starts with 0 and goes to a force of 12. The Beaufort scale is still used today to estimate wind strengths. the scales history is here on wikipedia.orgthe Beaufort scale: For use at sea For use on land beaufort table view
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FORCE EQUIVALENT SPEED DESCRIPTION SPECIFICATIONS FOR USE AT SEA
mph knots
0 0-1 0-1 Calm Sea like a mirror
1 1-3 1-3 Light air Ripples with the appearance of
scales are formed, but without
foam crests.
2 4-7 4-6 Light Breeze Small wavelets, still short,
but more pronounced. Crests
have a glassy appearance and
do not break.
3 8-12 7-10 Gentle Breeze Large wavelets. Crests begin
to break. Foam of glassy
appearance. Perhaps scattered
white horses.
4 13-18 11-16 Moderate Breeze Small waves, becoming larger;
fairly frequent white horses.
5 19-24 17-21 Fresh Breeze Moderate waves, taking a more
pronounced long form; many
white horses are formed.
Chance of some spray.
6 25-31 22-27 Strong Breeze Large waves begin to form; the
white foam crests are more
extensive everywhere.
Probably some spray.
7 32-38 28-33 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 Gale Moderately high waves of greater
length; edges of crests begin to
breakinto spindrift. The foam is
blown in well-marked streaks
along the direction of the wind.
9 47-54 41-47 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 Storm 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 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 Hurricane The air is filled with foam and
spray. Sea completely white with
driving spray; visibility very
seriously affected.
the Beaufort scale: For use at sea For use on land
note: 10 m above ground
FORCE EQUIVALENT SPEED DESCRIPTION SPECIFICATIONS FOR USE ON LAND
mph knots
0 0-1 0-1 Calm Calm; smoke rises verticall.
1 1-3 1-3 Light air Direction of wind shown by
smoke drift, but not by wind
vanes.
2 4-7 4-6 Light Breeze Wind felt on face; leaves
rustle; ordinary vanes moved
by wind.
3 8-12 7-10 Gentle Breeze Leaves and small twigs in
constant motion; wind extends
light flag.
4 13-18 11-16 Moderate Breeze Raises dust and loose paper;
small branches are moved.
5 19-24 17-21 Fresh Breeze Small trees in leaf begin to
sway; crested wavelets form on
inland waters.
6 25-31 22-27 Strong Breeze Large branches in motion;
whistling heard in telegraph
wires; umbrellas used with
difficulty.
7 32-38 28-33 Near Gale Whole trees in motion;
inconvenience felt when walking
against the wind.
8 39-46 34-40 Gale Breaks twigs off trees;
generally impedes progress.
9 47-54 41-47 Severe Gale Slight structural damage occurs
(chimney-pots and slates removed).
10 55-63 48-55 Storm Seldom experienced inland; trees
uprooted; considerable structural
damage occurs.
11 64-72 56-63 Violent Storm Very rarely experienced;
accompanied by wide-spread damage.
12 73-83 64-71 Hurricane --
return to the top
| Force | Speed | Name | Conditions at Sea |
Conditions on Land |
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Calm | Sea like a mirror. | Smoke rises vertically. |
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Light air | Ripples only. | Smoke drifts and leaves rustle. |
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Light breeze | Small wavelets (0.2 m). Crests have a glassy appearance. | Wind felt on face. |
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8-11 | Gentle breeze | Large wavelets (0.6 m), crests begin to break. | Flags extended, leaves move. |
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Moderate breeze | Small waves (1 m), some whitecaps. | Dust and small branches move. |
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Fresh breeze | Moderate waves (1.8 m), many whitecaps. | Small trees begin to sway. |
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Strong breeze | Large waves (3 m), probably some spray. | Large branches move, wires whistle, umbrellas are difficult to control. |
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Near gale | Mounting sea (4 m) with foam blown in streaks downwind. | Whole trees in motion, inconvenience in walking. |
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Gale | Moderately high waves (5.5 m), crests break into spindrift. | Difficult to walk against wind. Twigs and small branches blown off trees. |
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Strong gale | High waves (7 m), dense foam, visibility affected. | Minor structural damage may occur (shingles blown off roofs). |
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Storm | Very high waves (9 m), heavy sea roll, visibility impaired. Surface generally white. | Trees uprooted, structural damage likely. |
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Violent storm | Exceptionally high waves (11 m), visibility poor. | Widespread damage to structures. |
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Hurricane | 14 m waves, air filled with foam and spray, visibility bad. | Severe structural damage to buildings, wide spread devastation. |
| Beaufort number (force) | Wind Speed | Wave height (feet) | WMO* description | Effects observed on the sea | Effects observed on land | |
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| knots | mph | |||||
| 0 | under 1 | under 1 | - | Calm | Sea is like a mirror |  |
| 1 | 1 - 3 | 1 - 3 | 0.25 | Light air | Ripples with appearance of scales; no foam crests | |
| 2 | 4 - 6 | 4 - 7 | 0.5 - 1 | Light breeze | Small wavelets; crests of glassy appearance, not breaking |  |
| 3 | 7 - 10 | 8 - 12 | 2 - 3 | Gentle breeze | Large wavelets; crests begin to break; scattered whitecaps |  |
| 4 | 11-16 | 13-18 | 3½ - 5 | Moderate breeze | Small waves, becoming longer; numerous whitecaps |  |
| 5 | 17-21 | 19-24 | 6 - 8 | Fresh breeze | Moderate waves, taking longer form; many whitecaps; some spray |  |
| 6 | 22-27 | 25-31 | 9½-13 | Strong breeze | Larger waves forming; whitecaps everywhere; more spray |  |
| 7 | 28-33 | 32-38 | 13½-19 | Near gale | Sea heaps up; white foam from breaking waves begins to be blown in streaks |  |
| 8 | 34-40 | 39-46 | 18-25 | Gale | Moderately high waves of greater length; edges of crests begin to break into spindrift; foam is blown in well-marked streaks |  |
| 9 | 41-47 | 47-54 | 23-32 | Strong gale | High waves; sea begins to roll; dense streaks of foam; spray may begin to reduce visibility |  |
| 10 | 48-55 | 55-63 | 29-41 | Storm | Very high waves with overhanging crests; sea takes white appearance as foam is blown in very dense streaks; rolling is heavy and visibility is reduced |  |
| 11 | 56-63 | 64-72 | 37-52 | Violent storm | Exceptionally high waves; sea covered with white foam patches; visibility further reduced |  |
| 12 | 64 and over | 73 and over | 45 and over | Hurricane | Air filled with foam; sea completely white with driving spray; visibility greatly reduced |  |
| * World Meteorological Organization | ||||||
Extracted from the Observers Handbook, Met Office and other various places
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