| The Beaufort Scale
The
Beaufort Wind Scale
Devised
in 1805 by the Irish hydrographer Francis Beaufort.
For
the full history, see the American NWS, Chicago web
page on the topic at http://taiga.geog.niu.edu/nwslot/beaufort.html
Wind
Speed & Observed Effects
|
Force |
Knots |
Mph |
Kph |
Sea
Term |
Sea
Conditions |
On-land
Appearance |
|
0 |
<1 |
<1 |
<1 |
Calm |
sea like
a mirror |
smoke
rises vertically |
|
1 |
1-3 |
1-3 |
1-6 |
Light
air |
ripples
with appearance of scales: no foam crests |
smoke
drifts and leaves rustle |
|
2 |
4-6 |
4-7 |
7-11 |
Light
breeze |
small
wavelets: crests of glassy appearance, not breaking |
wind felt
on face |
|
3 |
7-10 |
8-12 |
12-19 |
Gentle
breeze |
large
wavelets: crests begin to break: scattered whitecaps |
flags
extended, leaves move |
|
4 |
11-16 |
13-18 |
20-30 |
Moderate
breeze |
small
waves, becoming longer: numerous whitecaps |
dust and
small branches move |
|
5 |
17-21 |
19-24 |
31-39 |
Fresh
breeze |
moderate
waves, taking longer form: many whitecaps: some spray |
small
trees begin to sway |
|
6 |
22-27 |
25-31 |
40-50 |
Strong
breeze |
larger
waves forming: whitecaps everywhere: some spray |
large
branches move, wires whistle |
|
7 |
28-33 |
32-38 |
51-61 |
Near
gale |
sea
heaps: white foam from breaking waves begins to be blown in streaks |
trees
in motion, resistance felt when walking |
|
8 |
34-40 |
39-46 |
62-74 |
Gale |
moderately
high waves of greater length: edges of crests begin to break into spindrift:
foam is blown in well-marked streaks |
walking
impeded |
|
9 |
41-47 |
47-54 |
75-87 |
Strong
gale |
high
waves: sea begins to roll: dense streaks of foam: spray may reduce visibility |
structural
damage may occur |
|
10 |
48-55 |
55-63 |
88-102 |
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 |
trees
uprooted, structural damage likely |
|
11 |
56-63 |
64-72 |
103-117 |
Violent
Storm |
exceptionally
high waves: sea covered with white foam patches: visibility still more
reduced |
damage
to structures wide spread |
|
12 |
>63 |
>72 |
>117 |
Hurricane |
air
filled with foam: sea completely white with driving spray: visibility
greatly reduced |
severe
structural damage to buildings, wide spread devastation, flooding |
|
