Common Meteorological Terms and Their Meanings - Wind

Sometimes trying to understand what's happening with the weather is made difficult due to all the technical terms used. For example, what does "Expect warm temperatures today - it will be muggy with high humidity with a chance of showers in the evening. Light winds from the NW".

To kick things off, below you will see a screen shot from Weather Display - an application that allows you to take data from your weather station and publish it on the internet, or even just display and store it on a computer. There is plenty of alternative software around that will do the same job, but that's a discussion for another day.

Current Wind Speed

One way of thinking about wind speed is to imagine that you are standing still and see something being blown past you. You might want to know how fast that object is travelling. Assuming you don't have to take friction and a bunch of other assumptions into place, then this would be the current wind speed. Effectively it's a measurement at a point in time.

In the screen shot above wind speed is mentioned twice. Most commonly when people talk about wind speed, they actually mean current wind speed.

Average Wind Speed

Average wind speed is measured across a period of time. For example this might be the previous 10 mins. As an example, to calculate this you might take a measurement of current wind each minute for 10 mins. If you then added these up and divided by 10 you would get an average, roughly approximating the middle speed (but not exactly!). It's a useful measure in terms of removing gusts and lulls and provides a better picture of what the wind is doing over a period of time, especially of compared with other average wind readings (ie is the wind getting stronger or weaker).

Wind Direction

Of course any measurement of wind would be largely useless without a direction, and for expressing that we use the points on a compass. In the screen shot above the large dial on the left represents (current) wind speed, while the dial on the right represents the direction the wind is coming from. So in this case the wind comes from around halfway between the North and the West (so North west), but a little bit more north than west. This is described as North northwest or NNW for short. Below the dial you can see that stated and a number 328 degrees or 328°. Degrees is a measurement used to describe a position on a circle. A circle is divided up into 360 degrees in total and are numbered off starting at north and moving clockwise around the circle.

Units

Wind speed can be measured in knots, kilometers per hour (km/h), meters per second (m/s), or miles per hour (mph). Knots is an interesting measurement - it's used mainly in maritime, air and meteorology. 1 knot is equal to the speed of 1 nautical mile per hour. A nautical mile is larger than a normal mile, and in fact nautical miles are now defined in terms of metres, which further adds to confusion. To help, here are some useful conversions:

**Conversions between common units of speed**
	m/s	km/h	mph	knot
1 m/s =	1	3.6	2.236936*	1.943844*
1 km/h =	0.277778*	1	0.621371*	0.539957*
1 mph =	0.44704	1.609344	1	0.868976*
1 knot =	0.514444*	1.852	1.150779*	1

(* = approximate values)

Source: Wikipedia

You can find out more about knots on Wikipedia including how the measurement got it's name.

The Beaufort scale

Measuring wind can be difficult. Usually it's done using an instrument called an anemometer. These look like a 4 small cups that rotate around a central point. The speed of rotation is then used to calculate the wind speed.

When you don't have the right equipment at hand there is a good way of estimating wind strength, devised by Francois Beaufort in 1805. During this time weather observations from ships were being made, but there was no fixed description for these observations. One person might describe a wind as a gentle while the other might describe the same wind as strong. Francois Beaufort devised a scale which effectively solved this issue, and the descriptions are still often used today.

**Beaufort Scale**
Beaufort number	Description	Wind speed	Wave height	Sea conditions	Land conditions
0	Calm	< 1 knot < 1 mph < 2 km/h < 0.5 m/s	0 ft (0 m)	Sea like a mirror	Smoke rises vertically.
1	Light air	1–3 knots	0–1 ft	Ripples with appearance of scales are formed, without foam crests	Direction shown by smoke drift but not by wind vanes.
		1–3 mph	0–1 ft
		2–5 km/h	0–0.3 m
		0.5–1.5 m/s	0–0.3 m
2	Light breeze	4–6 knots	1–2 ft	Small wavelets still short but more pronounced; crests have a glassy appearance but do not break	Wind felt on face; leaves rustle; wind vane moved by wind.
		4–7 mph	1–2 ft
		6–11 km/h	0.3–0.6 m
		1.6–3.3 m/s	0.3–0.6 m
3	Gentle breeze	7–10 knots	2–4 ft	Large wavelets; crests begin to break; foam of glassy appearance; perhaps scattered white horses	Leaves and small twigs in constant motion; light flags extended.
		8–12 mph	2–4 ft
		12–19 km/h	0.6–1.2 m
		3.4–5.5 m/s	0.6–1.2 m
4	Moderate breeze	11–16 knots	3.5–6 ft	Small waves becoming longer; fairly frequent white horses	Raises dust and loose paper; small branches moved.
		13–18 mph	3.5–6 ft
		20–28 km/h	1–2 m
		5.5–7.9 m/s	1–2 m
5	Fresh breeze	17–21 knots	6–10 ft	Moderate waves taking a more pronounced long form; many white horses are formed; chance of some spray	Small trees in leaf begin to sway; crested wavelets form on inland waters.
		19–24 mph	6–10 ft
		29–38 km/h	2–3 m
		8–10.7 m/s	2–3 m
6	Strong breeze	22–27 knots	9–13 ft	Large waves begin to form; the white foam crests are more extensive everywhere; probably some spray	Large branches in motion; whistling heard in telegraph wires; umbrellas used with difficulty.
		25–31 mph	9–13 ft
		39–49 km/h	3–4 m
		10.8–13.8 m/s	3–4 m
7	High wind, moderate gale, near gale	28–33 knots	13–19 ft	Sea heaps up and white foam from breaking waves begins to be blown in streaks along the direction of the wind; spindrift begins to be seen	Whole trees in motion; inconvenience felt when walking against the wind.
		32–38 mph	13–19 ft
		50–61 km/h	4–5.5 m
		13.9–17.1 m/s	4–5.5 m
8	Gale, fresh gale	34–40 knots	18–25 ft	Moderately high waves of greater length; edges of crests break into spindrift; foam is blown in well-marked streaks along the direction of the wind	Twigs break off trees; generally impedes progress.
		39–46 mph	18–25 ft
		62–74 km/h	5.5–7.5 m
		17.2–20.7 m/s	5.5–7.5 m
9	Strong/severe gale	41–47 knots	23–32 ft	High waves; dense streaks of foam along the direction of the wind; sea begins to roll; spray affects visibility	Slight structural damage (chimney pots and slates removed).
		47–54 mph	23–32 ft
		75–88 km/h	7–10 m
		20.8–24.4 m/s	7–10 m
10	Storm whole gale	48–55 knots	29–41 ft	Very high waves with long overhanging crests; resulting foam in great patches is blown in dense white streaks along the direction of the wind; on the whole the surface of the sea takes on a white appearance; rolling of the sea becomes heavy; visibility affected	Seldom experienced inland; trees uprooted; considerable structural damage.
		55–63 mph	29–41 ft
		89–102 km/h	9–12.5 m
		24.5–28.4 m/s	9–12.5 m
11	Violent storm	56–63 knots	37–52 ft	Exceptionally high waves; small- and medium-sized ships might be for a long time lost to view behind the waves; sea is covered with long white patches of foam; everywhere the edges of the wave crests are blown into foam; visibility affected	Very rarely experienced; accompanied by widespread damage.
		64–72 mph	37–52 ft
		103–117 km/h	11.5–16 m
		28.5–32.6 m/s	11.5–16 m
12	Hurricane force	≥ 64 knots	≥ 46 ft	The air is filled with foam and spray; sea is completely white with driving spray; visibility very seriously affected	Devastation.

Source: Wikipedia

Maximum wind gust recorded

The maximum wind ever recorded was in 1996 on Barrow Island in Australia. Maximum wind gusts were 253 miles per hour (407 km/h) during Tropical Cyclone Olivia.

Previous to that the record was held by the Mount Washington Observatory in New Hampshire, in the United States of America. This occurred on April 12 1936 and was 236 miles per hour (379 km/h). Although the station no longer holds the record, you can read about what it was like to experience such a wind on their website.

If you have any questions or comments on this article, or you think something might be missing, feel free to post your comments below. Otherwise enjoy the other articles in this series

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