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The Beaufort Scale

The Beaufort Wind Force Scale currently in use was developed by Admiral Francis Beaufort in 1805. The initial scale was from 0 to 12 only and they described qualitatively the sea conditions without defining quantitatively the wind speed. It was extended in 1946 to include Forces 13 to 17, and they are normally used in adverse weather conditions, e.g. tropical cyclones.

Beaufort Number
Description used by HKO
General Description
Wind Speed
TC strength
Land conditions

Sea
conditions

Wave Height
Image
knots
km/h
m/s
m
ft
0

Calm
(無風)

Calm
0
0-1
0-0.2
(N/A)
Calm. Smoke rises vertically.
Flat.
0
0
Force 0
1
Light
(輕微)
Light air
1-3
2-6
0.3-1.5
Wind motion visible in smoke.
Ripples without crests.
0.1
0.33
Force 1
2
Light breeze
4-6
7-11
1.6-3.3
Wind felt on exposed skin. Leaves rustle.
Small wavelets. Crests of glassy appearance, not breaking.
0.2
0.66
Force 2
3
Moderate
(和緩)
Gentle breeze
7-10
12-19
3.4-5.4
Leaves and smaller twigs in constant motion.
Large wavelets. Crests begin to break; scattered whitecaps.
0.6
2
Force 3
4
Moderate breeze
11-15
20-29
5.5-7.9
Dust and loose paper raised. Small branches begin to move.
Small waves.
1
3.3
Force 4
5
Fresh
(清勁)
Fresh breeze
16-21
30-39
8.0-10.7
LPA
Smaller trees sway.
Moderate (1.2 m) longer waves. Some foam and spray.
2
6.6
Force 5
6
Strong
(強風)
Strong breeze
22-27
40-50
10.8-13.8
TD
Large branches in motion. Whistling heard in overhead wires. Umbrella use becomes difficult.
Large waves with foam crests and some spray.
3
9.9
Force 6
7
Near gale
28-33
51-62
13.9-17.1
Whole trees in motion. Effort needed to walk against the wind.
Sea heaps up and foam begins to streak.
4
13.1
Force 7
8
Gale
(烈風)
Gale
34-40
63-75
17.2-20.7
TS
Twigs broken from trees. Cars veer on road.
Moderately high waves with breaking crests forming spindrift. Streaks of foam.
5.5
18
Force 8
9
Severe gale
41-47
76-87
20.8-24.4
Light structure damage.
High waves (2.75 m) with dense foam. Wave crests start to roll over. Considerable spray.
7
23
Force 9
10
Storm
(暴風)
Storm
48-55
88-103
24.5-28.4
STS
Trees uprooted. Considerable structural damage.
Very high waves. The sea surface is white and there is considerable tumbling. Visibility is reduced.
9
29.5
Force 10
11
Violent storm
56-63
104-117
28.5-32.5
Widespread structural damage.
Exceptionally high waves.
11.5
37.7
Force 11
12
Hurricane
(颶風)
Hurricane
64-71/ 64+
118-132/ 118+
32.6-36.6/ 32.6+
TY CAT. 1
Considerable and widespread damage to structures.
Huge waves. Air filled with foam and spray. Sea completely white with driving spray. Visibility greatly reduced.
14+
46+
Force 12+
13
(Not used by HKO)
(Not used except Taiwan and China)
72-80
133-149
36.7-41.3
Not generally seen on land. Catastrophic damage otherwise.
14
81-89
150-166
41.4-46.1
TY CAT. 2
15
90-99
167-183
46.2-50.8
16
100-108
184-201
50.9-55.8
TY CAT. 3 & above
17
109+
202+
55.9+

Source of the images (last column): http://www.stormfax.com/beaufort.htm

Last Accessed: Tue Oct 24 2017 19:14:21 HKT
Last Modified: Tue Dec 24 2013

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