Force 0 is the quiet end of the Beaufort wind force scale. Smoke rises vertically. At force 12, a hurricane blows at 119 to 220 kph (74 to 136 mph).
The scale links those extremes through numbers, usually 0 to 12. Sir Francis Beaufort, an officer in the British Royal Navy, devised the method in 1805. It described wind force according to the procedures for setting sails on a warship.
Beaufort was born in 1774 and died in 1857. National Geographic Education calls the scale “a descriptive table.” Its central work is to estimate wind power without a wind instrument. A sailor or meteorologist looks at smoke, flags, trees, or the sea and turns what is visible into a force number.
What the numbers show
Force 1 is light winds at 1-5 kph (1-3 mph). Smoke drift shows wind direction. Force 2 is a light breeze at 6-11 kph (4-7 mph); wind can be felt on the face, and flags ripple. By force 3, flags wave. Force 4, a gentle breeze at 20-28 kph (13-18 mph), scatters paper and leaves.
At force 5, a fresh breeze reaches 29-38 kph (19-24 mph). Small trees sway and whitecaps form on waves. Force 6 is a strong breeze at 39-49 kph (25-31 mph); umbrellas become hard to use. A moderate gale at force 7, 50-61 kph (32-38 mph), makes walking in the wind difficult. Force 8, a fresh gale at 62-74 kph (39-46 mph), snaps twigs and branches off trees.
Force 9 is a strong gale at 75-88 kph (47-54 mph); its marker is “Roof tiles blow off buildings.” Force 10, a whole gale at 89-102 kph (55-63 mph), carries the note “Trees are uprooted.” Force 11 is a storm at 103-118 kph (64-73 mph); the guide lists “Widespread damage to vegetation and buildings” and nearly no visibility at sea. Force 12, a hurricane at 119-220 kph (74-136 mph), is the scale’s top step in ordinary use; it matches a Category 1 hurricane or a Category 1 tornado, with widespread destruction.
Beyond twelve
The scale does not stop at 12. It goes to 17. The last five numbers apply only to tropical typhoons, and they are used only in the areas around China and Taiwan.
Hurricanes and typhoons are the same kind of storm. A hurricane is a tropical storm with wind speeds of at least 119 kilometers (74 miles) per hour, usually located in the Atlantic Ocean region. A typhoon has the same wind threshold but usually sits in the Pacific or Indian Ocean region.
