Wind Speed

The rate at which air is moving horizontally past a given point. It may be a 2-minute average speed (reported as wind speed) or an instantaneous speed (reported as a peak wind speed, wind gust, or squall). The following table is a way of estimating wind speed:

Force	Speed		Name	Conditions at Sea/Land
	knots	mph
12	64+	74+	Hurricane	14 m waves, air filled with foam and spray, visibility bad. Severe structural damage to buildings, wide spread devastation.
11	56-63	64-73	Violent storm	Exceptionally high waves (11 m), visibility poor. Widespread damage to structures.
10	48-55	55-63	Storm	Very high waves (9 m), heavy sea roll, visibility impaired. Surface generally white. Trees uprooted, structural damage likely.
9	41-47	47-54	Strong gale	High waves (7 m), dense foam, visibility affected. Minor structural damage may occur (shingles blown off roofs).
8	34-40	39-46	Gale	Moderately high waves (5.5 m), crests break into spindrift. Difficult to walk against wind. Twigs and small branches blown off trees.
7	28-33	32-38	Near gale	Mounting sea (4 m) with foam blown in streaks downwind. Whole trees in motion, inconvenience in walking.
6	22-27	25-31	Strong breeze	Large waves (3 m), probably some spray. Large branches move, wires whistle, umbrellas are difficult to control.
5	17-21	19-24	Fresh breeze	Moderate waves (1.8 m), many whitecaps. Small trees begin to sway.
4	11-16	12-18	Moderate breeze	Small waves (1 m), some whitecaps. Dust and small branches move.
3	7-10	8-11	Gentle breeze	Large wavelets (0.6 m), crests begin to break. Flags extended, leaves move.
2	4-6	5-7	Light breeze	Small wavelets (0.2 m). Crests have a glassy appearance. Wind felt on face.
1	1-3	1-4	Light air	Ripples only. Smoke drifts and leaves rustle.
0	<>	<>	Calm	Sea like a mirror. Smoke rises vertically.