| 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 (1-3 mph) |
Light Air |
Scaly ripples, no foam crests |
Smoke drift indicates wind direction, still wind vanes |
| 2 |
4-6(4-7 mph) |
Light Breeze |
Small wavelets, crests glassy, no breaking |
Wind felt on face, leaves rustle, vanes begin to move |
| 3 |
7-10(8-2 mph) |
Gentle Breeze |
Large wavelets, crests begin to break, scattered whitecaps |
Leaves and small twigs constantly moving, light flags extended |
| 4 |
11-16(13-18 mph) |
Moderate Breeze |
Small waves 1-4 ft. becoming longer, numerous whitecaps |
Dust, leaves, and loose paper lifted, small tree branches move |
| 5 |
17-21(19-24 mph) |
Fresh Breeze |
Moderate waves 4-8 ft taking longer form, many whitecaps, some spray |
Small trees in leaf begin to sway |
| 6 |
22-27(25-31 mph) |
Strong Breeze |
Larger waves 8-13 ft, whitecaps common, more spray |
Larger tree branches moving, whistling in wires |
| 7 |
28-33(32-38 mph) |
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(39-46 mph) |
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(47-64 mph) |
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(55-63 mph) |
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(64-75 mph) |
Violent Storm |
Exceptionally high (30-45 ft) waves, foam patches cover sea, visibility more reduced |
|
| 12 |
64+(>75mph) |
Hurricane |
Air filled with foam, waves over 45 ft, sea completely white with driving spray, visibility greatly reduced |
|
www.weather.gov 
