Force |
Wind
(Knots) |
WMO
Classification |
Appearance
of Wind Effects |
On
the Water |
On
Land |
0 |
Less than 1 |
Calm |
Sea surface smooth and mirror-like |
Calm, smoke rises vertically |
1 |
1-3 |
Light Air |
Scaly ripples, no foam crests |
Smoke drift indicates wind
direction, still wind vanes |
2 |
4-6 |
Light Breeze |
Small wavelets, crests glassy, no
breaking |
Wind felt on face, leaves rustle,
vanes begin to move |
3 |
7-10 |
Gentle Breeze |
Large wavelets, crests begin to
break, scattered whitecaps |
Leaves and small twigs constantly
moving, light flags extended |
4 |
11-16 |
Moderate Breeze |
Small waves 1-4 ft. becoming longer,
numerous whitecaps |
Dust, leaves, and loose paper
lifted, small tree branches move |
5 |
17-21 |
Fresh Breeze |
Moderate waves 4-8 ft taking longer
form, many whitecaps, some spray |
Small trees in leaf begin to sway |
6 |
22-27 |
Strong Breeze |
Larger waves 8-13 ft, whitecaps
common, more spray |
Larger tree branches moving,
whistling in wires |
7 |
28-33 |
Near Gale |
Sea heaps up, waves 13-20 ft, white
foam streaks off breakers |
Whole trees moving, resistance felt
walking against wind |
8 |
34-40 |
Gale |
Moderately high (13-20 ft) waves of
greater length, edges of crests begin to break into spindrift,
foam blown in streaks |
Whole trees in motion, resistance
felt walking against wind |
9 |
41-47 |
Strong Gale |
High waves (20 ft), sea begins to
roll, dense streaks of foam, spray may reduce visibility |
Slight structural damage occurs,
slate blows off roofs |
10 |
48-55 |
Storm |
Very high waves (20-30 ft) with
overhanging crests, sea white with densely blown foam, heavy
rolling, lowered visibility |
Seldom experienced on land, trees
broken or uprooted, "considerable structural damage" |
11 |
56-63 |
Violent Storm |
Exceptionally high (30-45 ft) waves,
foam patches cover sea, visibility more reduced |
|
12 |
64+ |
Hurricane |
Air filled with foam, waves over 45
ft, sea completely white with driving spray, visibility greatly
reduced |
|