BEAUFORT WIND SCALE

Admiral Sir Francis Beaufort (1774-1857) developed his scale in 1805 to
help sailors estimate wind speeds using visual observations. The speeds
are at a height of 10 metres above the ground.

FORCE MPH   KNOTS  DESCRIPTION      SPECIFICATIONS FOR USE ON LAND
        
0     0-1    0-1   Calm             Calm; smoke rises vertical.
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
                                    use 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        --



FORCE MPH   KNOTS  DESCRIPTION      SPECIFICATIONS FOR USE AT SEA

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.



