Force 0/Calm - winds under 1 knot (<1 style=""> Open Sea: The surface of the water is smooth or mirror-calm . Land: Smoke rises vertically and appears undisturbed by the wind. Tree leaves do not move.
Force 1/Light Air - winds of 1-3 knots (1-3 mph/1-5 kph). Open Sea: The water surface has scaly ripples without crests. Land: Wind direction is indicated in the drift of smoke. However, the wind is not strong enough to move a weather vane.
Force 2/Light Breeze - winds of 4-6 knots (4-7 mph/6-11 kph). Open Sea: Small wavelets are observed with crests that take on a glassy appearance but still do not break. Land: Wind can be felt on the face or exposed skin. Tree leaves rustle and weather vanes begin to move. Light flags may wave slightly.
Force 3/Gentle Breeze - winds of 7-10 knots (8-12 mph/12-19 kph). Open Sea: Large wavelets are observed. Crests begin to break and there are scattered whitecaps. Land: Leaves and twigs are in constant motion while the wind will extend light flags.
Force 4/Moderate Breeze - winds of 11-16 knots (13-18 mph/20-29 kph). Open Sea: Small waves of 1-4 feet in length are observed and whitecaps are more numerous. Land: The wind will raise dust, leaves, and loose paper. Small branches in trees begin to move.
Force 5/Fresh Breeze - winds of 17-21 knots (19-24 mph/30-38 kph). Open Sea: Moderate waves of 4-8 feet are observed with many whitecaps and some spray and foam. Land: Smaller trees in leaf begin to sway.
Force 6/Strong Breeze - winds of 22-27 knots (25-31 mph/39-50 kph). Open Sea: Larger waves of 8-13 feet are observed. Whitecaps are now common with more foam and spray. Land: Large tree branches move, the wind whistles in overhead wires, and the use of an umbrella becomes difficult.
Force 7/Near Gale - winds of 28-33 knots (32-38 mph/51-61 kph). Open Sea: The surface heaps up with waves of 13-20 feet and white foam streaks can be observed off breakers. Land: Whole trees are moving in the wind while walking becomes affected by the wind.
Force 8/Gale - winds of 34-40 knots (39-46 mph/62-74 kph). Open Sea: Waves are moderately high at 13-20 feet and of greater length. Breaking crests begin to form spindrift and foam is blown in streaks. Land: Whole trees are in motion with twigs being broken from them. Walking in the wind becomes very difficult and cars veer on the road due to wind.
Force 9/Strong Gale - winds of 41-47 knots (47-54 mph/75-86 kph). Open Sea: High waves consistently 20 feet or more are observed. The sea begins to roll and has dense streaks of foam while considerable spray may reduce visibility. Land: Light structural damage will occur such as the removal of slate or shingles from roof tops. Tree branches break due to wind force.
Force 10/Storm - winds of 48-55 knots (55-63 mph/87-101 kph). Open Sea: Very high waves of 20-30 feet with overhanging crests are observed. The sea is white with densely blown foam and is rolling heavily. Visibility is lowered. Land: Trees are broken or uprooted. Structural damage is considerable.
Force 11/Violent Storm - winds of 56-63 knots (64-74 mph/102-120 kph). Open Sea: Waves are 30-45 feet in height and the sea is covered with white foam patches. Visibility is further reduced. Land: Structural damage is widespread and considerable.
Force 12/Hurricane - winds in excess of 64 knots (75+ mph/120+ kph). Open Sea: Waves exceed 45 feet, the air is filled with foam and the sea is completely white with driving spray. Visibility is greatly reduced. Land: Structural damage is severe and extensive.
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