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
|  |
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
| | |
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
|  | ||
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
|  | |
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
|  | ||
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
|  |
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
|  |
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
|  | ||
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
|  |
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
|  | ||
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
|  |
11
|
Violent storm
|
56-63
|
104-117
|
28.5-32.5
|
Widespread structural damage.
|
Exceptionally high waves.
|
11.5
|
37.7
|  | ||
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+
|  |
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
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