Wind effects observed on sea
WMO description
Wind effects observed on land
Sea surface smooth and mirror-like.
| 0 |
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< 1 knot < 1 mph < 1 km/h < 0.5 m/s |
|
Calm |
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Calm; smoke rises vertically. |
Ripples with the appearance of scales are formed, but without foam crests.
| 1 |
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1--3 knots 1--3 mph 1--5 km/h 0.5--1.5 m/s |
|
Light air |
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Direction of wind shown by smoke drift, but not by wind vanes. |
Small wavelets, still short, but more pronoun- ced; crests have a glassy appearance and do not break.
| 2 |
|
4--6 knots 4--7 mph 6--11 km/h 1.6--3.0 m/s |
|
Light breeze |
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Wind felt on face, leaves rustle, vanes begin to move. |
Large wavelets; crests begin to break; foam of glassy appearance; perhaps some scattered whitecaps (white foam crests).
| 3 |
|
7--10 knots 8--12 mph 12--19 km/h 3.1--5.1 m/s |
|
Gentle breeze |
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Leaves and small twigs in constant motion; wind extends light flag. |
Small waves (1-4 ft), becoming longer; fairly frequent whitecaps.
| 4 |
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11--16 knots 13--18 mph 20--28 km/h 5.2--8.2 m/s |
|
Moderate breeze |
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Dust, leaves, and loose paper lifted, small tree branches move. |
Moderate waves (4-8 ft), taking a more pronoun- ced long form; many whitecaps; some spray.
| 5 |
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17--21 knots 19--24 mph 29--38 km/h 8.3--10.8 m/s |
|
Fresh breeze |
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Small trees in leaf begin to sway; crested wavelets form on inland waters. |
Larger waves (8-13 ft) begin to form; whitecaps common; more spray.
| 6 |
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22--27 knots 25--31 mph 39--49 km/h 10.9--13.9 m/s |
|
Strong breeze |
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Large tree branches in motion; whistling heard in telegraph wires; umbrellas used with difficulty. |
Sea heaps up; waves of ~13 ft; white foam from breaking waves begins to be blown in streaks along the direction of the wind
| 7 |
|
28--33 knots 32--38 mph 50--61 km/h 14.0--17.0 m/s |
|
Near gale |
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Whole trees in motion; resistance felt when walking against the wind. |
Moderately high (13-20 ft) waves of greater length; edges of crests begin to break into spindrift; foam is blown in well-marked streaks along the direction of the wind.
| 8 |
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34--40 knots 39--46 mph 62--74 km/h 17.1--20.5 m/s |
|
Gale |
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Breaks twigs off trees; generally impedes motion against wind. |
High waves (20 ft); crests of waves begin to topple, tumble and roll over; dense streaks of foam along the direction of the wind; spray may reduce visibility.
| 9 |
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41--47 knots 47--54 mph 75--88 km/h 20.6--24.2 m/s |
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Strong gale (Severe gale) |
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Slight structural damage occurs, chimney-pots and slate blows off roofs. |
Very high (20-30 ft) waves with overhanging crests; sea surface takes white appearance as foam is blown in very dense streaks along the direction of the wind; tumbling (rolling) of the sea becomes heavy and shock like; lowered visibility.
| 10 |
|
48--55 knots 55--63 mph 89--102 km/h 24.3--28.3 m/s |
|
Storm |
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Seldom experienced on land, trees broken or uprooted, considerable structural damage occurs. |
Exceptionally high (30-45 ft) waves; small and medium-size ships might be for a time lost to view behind the waves; sea completely covered with long white patches of foam lying along the direction of the wind; edges of the wave crests blown into froth; visibility further reduced.
| 11 |
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56--63 knots 64--72 mph 103--117 km/h 28.4--32.4 m/s |
|
Violent storm |
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Very rarely experienced on land; accompanied by wide-spread damage. |
Air filled with foam and spray; waves over 45 ft; sea completely white with driving spray; visibility greatly reduced
| 12 |
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>= 64 knots >= 73 mph >= 118 km/h >= 32.5 m/s |
|
Hurricane |
UPDATED : 2004-11-07
WEBSITE EDITOR : Krešimir J. Adamić