Wind Speed Is An Important Way Of Describing Winds
But Mixed Descriptive Terms And Measurement Systems Can Lead To Tragic Consequences
How Winds Are Described
We talk about breezes, winds, gales, tornadoes and hurricanes or cyclones,but when does a breeze become a wind, and when does wind reach gale force.
Classifying wind is not as easy as it sounds, because we have a number of systems in use, and not as much consistency between them as perhaps there should be. Here is a short article about when a wind is and isn't a wind.
The Categories of Wind- An informative article about the different kinds of winds
by Neisha Bjorklund
The speed at which the air current moves, and the direction from which it moves determines what the wind is named and also determines weather the wind is harmful or beneficial. A wind of 19 to 24 mile an hour is classified as a fresh breeze, and is not harmful. When the wind reaches a speed of 47 miles an hour, it is called a strong gale, and may cause some damage to fruit crops. At 64-75 miles an hour, it is considered a wind storm and dangerous to both crops and properties. Above 75 miles an hour, when it is classified as a hurricane, wind is devastating among its damage to crops, properties, and man himself.
The most dangerous wind of all winds is the tornado, a swirling movement of the wind in a counterclockwise direction, sometimes at more than 300 miles per house. The speed of a tornado has never been measures accurately, but the destruction is almost incredible.
In describing the force of wind, mariners use a scale drawn up in 1805 by Rear Admiral Sir Francis Beaufort, a famous British hydrographer. He developed a historic table of the strengths of winds based on the effect of wind on sailing ships.
- 0-1 MPH - Calm
- 1-2 MPH - Light Breeze
- 4-7 MPH - Slight Breeze
- 8-12 MPH - Gentle Breeze,
- 13-18 MPH - Moderate Breeze,
- 19-24 MPH - Fresh Breeze,
- 25-31 MPH - Strong Breeze,
- 32-38 MPH - Moderate Gale,
- 39-46 MPH - Fresh Gale,
- 47-54 MPH - Strong Gale,
- 55-63 MPH - Whole Gale,
- 64-75 MPH - Wind Storm,
- Above 75 MPH - Hurricane
Neisha Bjorklund is the webmaster for http://www.aweathervaneworld.com. To monitor your wind’s direction take a look at our large selection of quality rooftop and garden weathervane.
Neisha Borklund's article clarifies many of the difficulties people encounterwhen describing wind speed and effects. But not quite all.
For example, a hurricane is a weather system rather than a wind, and winds of75 mph (about 120 kph) or more can occur with quite a few other types of weather.Downbursts in thunderstorms, winds like chinooks (a type of foehn wind) when they are funnelled through a mountain pass, and subtropical storms can all produce winds in excess of 75mph.
Similarly there are sometimes problems with terms like gale and storm. In forecasting terms, a gale is a strong wind, but storm force winds are stronger, and fortunately less common.But this means that strong wind warnings may predict gale force winds, and the thought may lodge in our minds that this is the strongest type of wind we need to worry about (excluding hurricanes and tornadoes)
Conversely, many people restrict their understanding of the term storm to a thunderstorm. Thunderstorms may be quite gentle, and even at their full force they tend to pass on in a few hours.
Storms at sea are a different matter. They are always severe, and can last for days.
The Sydney - Hobart Ocean Race Disaster, 1998
Problems with definitions have arisen during ocean yacht races. Every Boxing Day a world class yacht race with a long history is sailed off the eastern Australian Coast. It is called the Sydney to Hobart race, and it includes the crossing of Bass Strait, which separates mainland Australia from the island state of Tasmania, where the race finishes.
The 1998 race was a disaster - 5 dead, 55 rescued and numerous yachts sunk or damaged. Despite storm warnings, many yachts attempted to race on instead of seeking shelter. The fleet sailed into a storm with 45-55 knot winds forecast. This is equivalent to 52-64 mph, or 83-102kph, and the actual windspeeds were probably more.
But what most sailors didn't realize was that the forecast was for sustained wind speeds, and gusts up to 40% stronger could be expected. Film taken during the rescue operations showed the conditions to be horrendous.
So what went wrong?
Firstly the disaster involved highly modified racing yachts with crews set on winning the race, or at least doing well. The yachts were not designed to handle the conditions which developed.
Secondly, although experienced mariners would have understood what a storm warning meant, it is likely that many of the skippers and crews did not. Some actually said that they believed a storm was less of a threat than a gale, which they believed they could handle. Many of these crews were not regular competitors, the Sydney - Hobart race being a holiday event.
Thirdly, many of those involved did not understand the weather reporting conventions - sustained wind of 55 knots also means gusts of almost 80 knots - over 90mph or 140 kph.
And finally, although the Australian Bureau of Meteorology provided special race forecasts, no special effort appears to have been made to emphasize the seriousness and danger of the forecast conditions.
Hopefully changes since the race will prevent a repetition of the misunderstandings of the forecasts, but the whole affair is a sad example of how poor definitions, inadequate preparation, and the use of different systems in describing weather and wind speeds can and did lead to tragedy.
Apart from weather systems like tornadoes and hurricanes, strong regular winds which regularly affect particular areas are given their own names, no matter what their speed is.
You can find out more about them in a series of articles beginning with an Introduction To Winds.
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Last update 05/28/2011