| Force |
Wind
(mph) |
WMO*
Classification |
Appearance
of Wind Effects |
| On Land |
On the Water |
| 0 |
Less than 1 |
Calm |
Calm, smoke rises vertically |
Sea surface smooth and mirror-like |
| 1 |
1-3 |
Light Air |
Smoke drift indicates wind direction, still wind vanes |
Scaly ripples, no foam crests |
| 2 |
4-7 |
Light Breeze |
Wind felt on face, leaves rustle, vanes begin to move |
Small wavelets, crests glassy, no breaking |
| 3 |
8-12 |
Gentle Breeze |
Leaves and small twigs constantly moving, light flags extended |
Large wavelets, crests begin to break, scattered whitecaps |
| 4 |
13-18 |
Moderate Breeze |
Dust, leaves, and loose paper lifted, small tree branches move |
Small waves 1-4 ft. becoming longer, numerous whitecaps |
| 5 |
19-24 |
Fresh Breeze |
Small trees in leaf begin to sway |
Moderate waves 4-8 ft taking longer form, many whitecaps, some spray |
| 6 |
25-31 |
Strong Breeze |
Larger tree branches moving, whistling in wires |
Larger waves 8-13 ft, whitecaps common, more spray |
| 7 |
32-38 |
Near Gale or Moderate Gale |
Whole trees moving, resistance felt walking against wind |
Sea heaps up, waves 13-20 ft, white foam streaks off breakers |
| 8 |
39-46 |
Fresh Gale or Gale |
Whole trees in motion, resistance felt walking against wind |
Moderately high (13-20 ft) waves of greater length, edges of crests
begin to break into spindrift, foam blown in streaks |
| 9 |
47-54 |
Strong Gale |
Slight structural damage occurs, slate blows off roofs |
High waves (20 ft), sea begins to roll, dense streaks of foam, spray may
reduce visibility |
| 10 |
55-63 |
Whole Gale or Storm |
Seldom experienced on land, trees broken or uprooted, "considerable
structural damage" |
Very high waves (20-30 ft) with overhanging crests, sea white with
densely blown foam, heavy rolling, lowered visibility |
| 11 |
64-74 |
Violent Storm |
Very rarely experienced, accompanied by widespread damage |
Exceptionally high (30-45 ft) waves, foam patches cover sea, visibility
more reduced |
| 12 |
75+ |
Hurricane |
Devastation occurs |
Air filled with foam, waves over 45 ft, sea completely white with
driving spray, visibility greatly reduced |