One 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 Beaufort scale:
For use on landFor use at sea
FORCE EQUIVALENT SPEED DESCRIPTION SPECIFICATIONS FOR USE ON LAND
10 m above ground
miles/hour 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 --
For use on landFor use at sea Top of page
FORCE EQUIVALENT SPEED DESCRIPTION SPECIFICATIONS FOR USE AT SEA
10 m above ground
miles/hour 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.
For use on landFor use at sea Top of page
Extracted from the Observers Handbook, Met Office
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Last Updated: 7th November 1997
Dave Wheeler weatherman@zetnet.co.uk
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