The Beaufort, Saffir-Simpson, & Fujita Scales That which no canvas could withstand. hurricane No sail can stand even when running The Beaufort Scale has become the standard method of judging wind force. It is not the oldest, since rating the strength of wind by number and/or assigning names to the ratings had been done for some time. In 1806 Francis Beaufort (later Admiral and Sir) wrote out a numerical scale in his log. This was evidently copied from a British Admiralty pamphlet. Beaufort, however, refined and specified the scale, and in 1838 it was officially adopted by the Admiralty. In 1906 a report further refined the scale with corresponding wind speeds and descriptions of effects on land. Beaufort himself had specified the sailing conditions that went with each rating, as seen in the chart at right. Separate wind scales for tornadoes and hurricanes did not come until the 1970's. The Fujita (or Fujita-Pearson) Scale for tornadoes was proposed in 1971 by T. Theodore Fujita and Allen Pearson.

Soon thereafter, the Saffir-Simpson Scale for hurricanes was formulated by Herbert Saffir and Robert Simpson. Thus, the movie Twister was anachronistic when it had Helen Hunt's father warn, in 1965, that they might have an F5 tornado headed toward them. The scale had not been invented yet. There has been some recent revision of some of these systems. I have not yet updated the presentation here. The complete Beaufort Scale has thirteen divisions, as shown above (starting with zero ). Beaufort grouped these into 5 categories of winds, or finely divided using five "breezes," four "gales," and four other designations. light strong whole Breezes and gales both use the same simple scale of adjectives in the table at left. It always seemed a little odd to me that the designations jumped directly from "breezes" to "gales." One might expect an intermediate category, like simple "winds." Indeed, Beaufort himself grouped "strong breeze" and "moderate gale" as "strong winds" [ note ]. The Fujita and Saffir-Simpson scales are almost entirely subdivisions of hurricane force winds.

Only the F0 tornado merely has gale force winds. The complete table below gives wind speeds, the appearance of objects affected by the wind (as described in 1906), the kinds of damage to be expected from tornadoes and hurricanes, and other details, like barometric pressure, for hurricanes. Gale force winds mean that a "tropical depression" becomes a "tropical storm," which is then given a name by the appropriate authorities. Warning flags for water craft are also given. At the left of the table, the Beaufort, Fujita, and Saffir-Simpson Scales are given B, F, and S numbers, respectively. Note that severe hurricanes are often attended with tornadoes as well. Hurricanes in the Western Pacific are called "Typhoons," and those in the Indian Ocean, "Cyclones." Tornadoes used to often be called "Cyclones" also. Modern terminology is that all low pressures systems, which includes hurricanes, tornadoes, and less severe phenomena, are "cyclones." In 1927, a German captain, Petersen, provided "State-of-Sea" descriptions for each wind force. These are given at right.

The term "white horses" is not familiar to me, at least from American usage. This seems to mean simply "whitecaps." B0 261-318 mph strongly built homes are completely blown away My introduction to meteorology came with the Life Science Library book Weather, by Philip D. Thompson, Robert O'Brien, and "the Editors of LIFE" [Time Incorported, 1965], which I acquired, about the time it was published, when I was in Junior High School. Some of the descriptions here are still drawn from that volume. I did have an actual meterology class at the University of New Mexico in 1968, but I got less out of it than I might have and failed to hold on to any class materials. Now, however, complete background to all of this can be found at The Weather Channel website. The following descriptions have been taken from that source, from Everything Weather, The Weather Channel's CD-ROM, and from other sources, web and print, that I have lost track of.

A detailed history of the Beaufort Scale is now to be found in Defining the Wind, The Beaufort Scale, and How a 19th-Century Admiral Turned Science into Poetry by Scott Huler [Three Rivers Press, New York, 2004]. I was unaware of the sailing condition descriptions, or indeed of the history of the Scale, until finding this book. The Petersen State-of-Sea descriptions can be found at the British Met(erological) Office . 12 hurricane It may be silly, but it bugs me that the Beaufort terminology should jump directly from a "breeze" to a "gale." As I use the words, "wind" can refer to all movement of air, but the very same word also denotes something that is rather more than a "breeze" but still less than a "gale." I don't think of a breeze as much of a wind at all, while a gale is something quite strong and unusual, at least on land, or apart from a winter storm. A breeze is pleasant, and will not cause any inconvenience or rearrange any objects, except the lightest.

A real wind, however, many be annoying, render some activities unpleasant, and will move some things around, even if only leaves, that will require attention. But then a gale: no outside activities will be pleasant, and the wind can cause some damage. I remedy this with the additions at left. Here we simply would have three "breezes," three "winds," and three "gales." This is how it might be done in Chinese, where many things, like rank, are divided into "high," , "middle" , and "low" , degrees. I expect that the exclusive use of "breeze" and "gale," without using "wind" for specific forces, might be to avoid ambiguity. In the traditional Beaufort Scale "wind" is not used with two meanings, the general and the specific. That is quite reasonable. My proposal then, would certainly not be for any usage where ambiguity might cause some inconvenience or danger. The table simply represents my intuition about ordinary usage and meaning, that a breeze is not quite a wind, while a gale is much more than just a wind. Return to Text Clouds Clouds are the mountains of the sky.

They can, indeed, be taller than any mountains of the earth, reaching up to 40,000 feet or, rarely, even to 60,000 feet, far beyond Everest. On the other hand, they exist on a vastly different time scale. The tallest clouds can develop and disappear in less than a day, while earthly mountains grow and erode over millions of years. In Los Angeles, there is usually not much to be seen in the way of interesting clouds. Much of the weather is simply clear, and in the spring and summer a marine layer of fog and stratus clouds moves in. Occasionally in the summer, thunderheads develop over the San Gabriel mountains and the storms may, though sometimes not for several years, move over the Los Angeles basin. Winter storms off the Pacific, usually lasting no more than a day or two, are responsible for most of the average rainfall of 15 inches. Growing up in Los Angeles, I didn't feel like I saw much in the way of cloud variety until I lived in New Mexico, Lebanon, Hawaii, and Texas.

New Mexico was especially noteworthy for the colors that would play on the clouds: The setting sun could fill the same sky with yellow, pink, orange, and cherry red on different clouds. In Hawaii , where clouds would build up over the windward mountains daily in the rainy season, one striking memory is of the full moon shining on the towering, isolated thunderheads. There was, however, limited thunder from those clouds, which would drop some rain in the valleys and foothills and then disperse, often not even getting Waikiki wet. More violent weather came with the occasional winter storm (a "kona" storm, since the wind may blow from leeward, against the trade winds), or with the rare hurricane. Clouds are classified by form and by altitude. The basic forms, with symbols, are ("heaped up," in Latin), ("spread out," the neuter form of which is stratum, used for extensive layers of similar rock in geology), and ("lock" or "curl" of hair) . Cumulus clouds tend to form from rising air, from 6,000 feet on up, and so are classified as "vertically developing" clouds.

Stratus clouds, below 8,000 feet, may be rather like an elevated fog bank; or, altenatively, fog can be thought of as a stratus cloud at ground level. While cumulus clouds mean that air has risen to an elevation where the temperature is at the dew point , so that the water condenses, with stratus clouds the temperature of the air itself may have fallen to the dew point. Cirrus clouds are ice crystals at high altitude, from 18,000 to 40,000 feet; their whispy structure comes from scattering by the wind. Besides stratus, low level clouds can include (between 3,000 and 10,000 feet), from which rain falls (nimbus simply means "cloud," or "raincloud") and (below 8,000 feet), where cumulus clouds stretch out in a solid layer, showing a lot more structure than stratus clouds, whose outlines can be very indistinct.

At high altitudes (18,000 to 40,000), cirrus clouds can form a fairly solid layer, becoming , or they can take on a lumpy structure, with grains or ripples (a "mackerel sky"), suggestive of cumulus clouds, becoming . At middle altitudes, from 6,000 to 18,000 feet, too low to freeze into cirrus but higher than ordinary stratus, are (above 15,000 feet) and . The "alto-" element is from Latin "altus," which originally meant "grown" but came also to mean "high," as it is used in these names. Altocumulus can be part of the development of cumulus and cumulonimbus clouds. The highest -- all the way up to 60,000 feet -- most spectacular, and most violent clouds result when the air, rising to form cumulus clouds, continues to rise, drawing moisture to high altitudes and generating extreme conditions. This makes a cumulonimbus cloud. The swelling top spreads out into a characteristic anvil shape, which then may be blown away by high level winds.

Because of freezing air at those altitudes, the streaming clouds from the anvil will often take a cirrus form. Freezing air can also cause hail to form, as ice crystals begin to fall and then are lifted back up again and again to grow larger and larger. When the hail finally falls, descriptions of its size are borrowed from the produce counter and from sports: Small hail is described as "pea" sized, whence we move up to "grape" sized, "ping-pong ball" sized, "golf ball" sized, "baseball" sized, and, most devastating of all, "grapefruit" sized. Baseball and grapefruit sized hail can break any window, ruin a car, flatten a field of crops, or even kill somebody. The movement of wind, water, and ice up and down the column of clouds also generates differentials in electrical charge, which are then discharged as lightning. Isolated thunderstorms, generated by summer heating, may pass over with a minimum of damage.

Spring cold fronts, however, pushing still cold air from the north under warm moist Gulf air, as in Texas, can produce massive squall lines of thunderstorms, stretching for hundreds of miles, filling the sky with vast gray clouds, rain, wind, hail, lightning, and, worst of all, tornadoes. These conditions get called, with charming understatement, "severe weather." Short of hurricane force winds, or actual tornadoes, nature provides no more awesome weather. During one overnight thunderstorm and flash flood that I witnessed in Austin, Texas, on the eve of Memorial Day in 1981 , where serious flooding and deaths occurred, the flashes of lightning were so frequent that they were right on top of each other and the night was literally without darkness. I also see other cloud symbols, such as the altostratus plus cirrus symbol at left. I have yet to see exactly what this would look like in the sky, but I like how this looks. Copyright (c) 1998, 2015 Kelley L. Ross, Ph.D. All Rights Reserved Note on Dew Point The dew point tells us the absolute humidity.

The more commonly used "relative humidity" is the percentage to which the air is saturated with moisture. The dew point is simply the temperature at which the air would be saturated, would have 100% relative humidity. Warmer air can hold more moisture, so that air that would be saturated at 75oF, with 100% relative humidity, would only have about 50% relative humidity if the temperature rises to 95oF without any moisture being added. While people complaining of summer humidity often say that both the temperature and the relative humidity must both be 90 or more, this really does not happen and would be deadly if it did. Typical summer dew points in Texas are around 75oF, as in the example just cited. The highest dew point I've ever heard of was 80o, reported by The Weather Channel at places in eastern Pennsylvania and New Jersey as a line of thunderstorms was arriving in June 1998 (I was nearby in New Jersey -- it was humid). Typical summer dew points in Los Angeles are in the 50's. Extremely humid summer conditions in Los Angeles usually only mean dew points in the 60's.

Autumn arrives in Los Angeles in October, when dry air (and sometimes a Santa Ana wind) arrives with the first cold front, dropping the dew point precipitously. October 20, 1996, the dew point in Van Nuys was reported at 37o, the 21st at 14o, and the 22nd at 9o. October 7, 1997, the dew point was reported at 39o and the 15th at 25o. October 5, 1998, the dew point was reported at 13o and the 17th at 19o. Although understanding the dew point in abstraction, its real connection to the feel of the air was not obvious to me until I began seeing dew point isotherm maps on The Weather Channel in the 1980's. Since air can hold about twice as much moisture for every 20 degrees Fahrenheit, this may be used to write very simple equations for the dew point.

In the following equations, D is the dew point in degrees Fahrenheit, T is the air temperature, and H is the relative humidity written as a whole number percentage (i.e. "50" instead of "0.5" for "50%"). The first equation gives the dew point for the temperature and relative humidity, which is usually what one can easily determine, while the second equation gives the relative humidity from the temperature and dew point. D = T - 20*((2 - log H)/log 2) log H = 2 - ((log 2*(T-D))/20) C = 5*(F - 32)/9 C = (5*(F + 40)/9) - 40 F = (9*C/5) + 32 F = (9*(C + 40)/5) - 40 A more precise value for the dew point can be derived from the equations below. For the main equation, the value "X" must be calculated first, based on the relative humidty. The temperature and dew point here will be in degrees Celsius (or centigrade).

Celsius and Fahrenheit can be converted back and forth with the equations in the box at right. (Note that the equations that add and subtract 40, in precisely the same way, may be easier to remember than the more traditional conversion equations.) X = 1 -(.01*H) D = T - (14.55+.114*T)*X - ((2.5+.007*T)*X)3 - (15.9+.117*T)*X14 If we have a temperature of 73oF (22.8oC) at 24% relative humidity, the Fahrenheit equation gives us a dew point of 3l.8oF. The Celsius equation gives us a dew point of 1.1oC, or 34.0oF. An error of 2.2oF, or 1.2oC, is not bad, especially considering how much easier the Fahrenheit equation is to use. My favorite personal experience with dew point was when I drove from Austin, Texas, to Tularosa, New Mexico, in June 1982.

A cold drink in Texas causes a large amount of moisture to condense on a glass. It "sweats"; and the water collects on the table or in a coaster, sometimes so much that it makes it seem like the glass is leaking. Arriving in New Mexico at my aunt and uncle's place, the next day I had a glass of iced tea sitting on the broad arm of a wooden chair. After half an hour, I checked the glass to make sure that there wasn't any condensing water that might damage the wood. There wasn't. At an elevation of over 4000 feet, far from the Gulf Coast, the relative humidity might only have about 5% or so. Copyright (c) 1998 Kelley L. Ross, Ph.D. All Rights Reserved Snow, Sleet, Ice, and Rain The temperatures of the air produce different phenomena of precipitation. The most familiar are snow and rain. In the former, ice crystals fall through air that is below freezing from the clouds to the surface. Snow then accumulates in drifts on the ground. The water content of snow can vary, so that some times it is dry, light, and fluffy, other times wet, heavy, and dense.

Wet snows can adhere, so that drifts can appear to flow or sag without breaking apart. With rain, water droplets fall through air that is above freezing. Puddles accumulate on the ground, or the water flows away. Other forms of precipitation occur when the air temperature changes from above freezing to below between the clouds and the surface. If the boundary occurs high enough, there is time for rain droplets to freeze before hitting the ground. This is sleet. As solid little ice pellets, sleet will tend to fall faster than snow and will hit surfaces with some noise. A snow fall is silent. Sleet can sound like small hail. When it accumulates on the ground, sleet can look a bit like snow, but the consistency and the color will look a bit different. If the boundary between the air above freezing and below freezing is close enough to the surface, we get freezing rain. This is one of the rarer of these phenomena, and its effects are striking and dangerous. Rain drops hit surfaces and freeze. This produces a glaze of ice on amost anything and a surface of "black" ice on streets. An accumulation of ice becomes heavy.

Branches, trees, and power lines can easily be brought down in an ice storm. Driving is treacherous. In the daylight after an ice storm, everything looks like it is wrapped in glass. This can be extraordinarily beautiful, but it may be purchased at a terrible price in damage and even lives. Hail is produced when updrafts carry rain drops high into clouds, and into freezing air at altitude, even during warm times of the year. The rain drop freezes and may fall, or it may be carried up into the clouds again and receive a further coating of ice. This can happen over and over again, producing ever larger hail stones. Hail is thus usually characterized by its size, ranging from pea sized to grapefruit sized. The latter, of course, can cause sever damage or injury when it finally falls to the ground. The Beaufort Wind Force Scale ≥14 ≥46 Huge waves. Sea is completely white with foam and spray. Air is filled with driving spray, greatly reducing visibility. Considerable and widespread damage to vegetation, a few windows broken, structural damage to mobile homes and poorly constructed sheds and barns. Debris may be hurled about.

In the United States, winds of Beaufort 6 or 7 result in the issuance of a small craft advisory, with force 8 or 9 winds bringing about a gale warning, 10 or 11 a storm warning (or "tropical storm warning" for 8 to 11 if related to a tropical cyclone), and anything to 12 a hurricane warning. In the Indian Ocean and South China Sea, this scale is extended by the addition of Numbers 13 through 17 because of the frequency of extremely forceful Typhoons in those areas. Wind speed can be approximated using the Beaufort Force Scale. Originally, the Beaufort Scale was developed to provide a scale based on visual observations of the sea surface, you can get a very rough equation of wind speed by subtracting 1 from the number of the Beaufort Force and multiplying that by 5. The resultant number will be a rough approximation of wind speed in knots. (i.e.: Force 8 is about 35 knots +/- ((8-1) x 5 = 35). What is the Beaufort scale? | The Weather Guys What is the Beaufort scale?

Posted on September 17, 2012 by Weather Guys Editor The Beaufort scale is a method of estimating wind speed based on the general condition of the surface of a large body of water with respect to wind waves and swell. This scale allows sailors to estimate the wind speed just by observing the state of the sea surface. The scale has a long history, but was finalized in 1805 by Rear Admiral Sir Francis Beaufort, an Irish hydrographer in the British Royal Navy. It was officially first used during the voyage of Charles Darwin on HMS Beagle. The Beaufort scale can also be applied to conditions on land, but it is most often associated with the sea state. The modern day Beaufort scale consists of 13 numbers ranging from 0 to 12. A Beaufort force 0 is assigned to calm winds where the water surface is smooth. A Beaufort force 12 occurs with waves greater in height than 46 feet and the sea is completely white with foam and spray with greatly reduced visibility. Such conditions are associated with wind speeds of greater than 74 mph, which are hurricane-force winds.

The National Weather Service defines sustained wind speeds of 39-54 mph as a gale, and forecasters typically issue gale warnings when winds of this strength are forecast. A Beaufort force 6 is a near gale with wind speeds between 25-30 mph and includes white foam from breaking waves that begins to be blown in streaks along the wind direction. A Beaufort force in the range of 6 to 7 is designated as strong winds; 8 to 9 as gale force winds; and 10 to 11 as storm force winds. Weather Doctor's Weather People and History: The Weather Legacy of Admiral Sir Francis Beaufort The Weather Legacy of Admiral Sir Francis Beaufort Admiral Robert Fitzroy of H.M.S. Beagle fame wrote of Admiral Sir Francis Beaufort, "All honor to Beaufort, who used and introduced this succinct method of approximation by scale..." The method to which Fitzroy refers, one of Beaufort's many accomplishments during his distinguished naval career, is the Wind Force Scale, still in widespread use today by men of the sea.

Francis Beaufort was born in 1774, in County Meath, Ireland, the son of the Reverend Daniel Augustus Beaufort, the Rector of Navan. At the tender age of 13, he began his nautical career as a cabin boy in the British Navy. Three years after going to sea, Francis Beaufort recognized the value of being weatherwise and began keeping a meteorological journal in the form of brief comments on the general weather scene, a practice he would continue until his death. At 22, he had risen to the rank of lieutenant, serving aboard H.M.S. Phaeton. In 1805, Beaufort was given his first command, H.M.S. Woolwich, and assigned to conduct a hydrographic survey of the Rio de la Plata region of South America. During these early years of command, he developed the first versions of his Wind Force Scale and Weather Notation coding, which he was to use in his journals for the remainder of his life.

Injury Leads to New Career Beaufort's assignment during the years 1811 and 1812 led him to the Eastern Mediterranean off Asia Minor for a combined hydrographic study and patrol mission against the pirates operating out of the Levant. In June, 1812, Beaufort sent a survey party ashore to make astronomical observations. When the party encountered armed hostilities from the local pashas, Beaufort himself led the rescue. As they were rowing back to H.M.S. Fredrikssteen, Beaufort was struck in the groin by sniper fire. The ball fractured Beaufort's hip, and he subsequently spent several months convalescing aboard ship. By the end of the year, however, it was obvious that both ship and commander were in great need of repair, and they were ordered home by the Admiralty. Francis Beaufort would never again return to active sea duty although he would remain in the British Navy until he was 81. In 1829, Beaufort was appointed Hydrographer to the Admiralty. From this post, he outlined the hydrographic studies for many British expeditions including that of H.M.S.

Beagle, commanded by his protégé Robert Fitzroy. In 1838, Beaufort's Wind Force Scale was introduced for use by the British fleet for all log entries, joining his Weather Notation, which had been prescribed for use five years earlier. The Admiralty promoted Beaufort to Rear Admiral in 1846. Beaufort was bestowed the title Knight Commander of the Bath two years later. In 1855, after 68 years of service, Sir Francis retired from the Admiralty. He died in 1857, but his life's work continued to receive recognition and honor. Of his many achievements, Admiral Beaufort is remembered today most for the Wind Force Scale which now bears his name. The scale, which he conceived in 1805 and the British Navy adopted in 1838, however, underwent major changes in the 100 years following it initial adaptation.

Rigging of a British Frigate circa 1830 Frigates as Wind Sensors -- The Beaufort Wind Force Scale In his journal for January of 1806, then-Commander Beaufort wrote, "From now on I shall evaluate the force of the wind in accordance with the following scale, since nothing gives a more indefinite representation of the wind and the weather than the previously used expressions like moderate wind or cloudy weather." Originally, the Wind Force Scale consisted of 13 degrees of wind strength, from calm to hurricane, and was based upon the effects of various wind strengths upon the amount of canvas carried by the fully rigged frigates of the period. In the days before elaborate meteorological instruments, Beaufort had chosen for his wind sensor the prime ship of the British fleet. The 1831 version of the wind scale as outlined in a memorandum to Commander Robert Fitzroy could be divided into three sections. The first five states (Forces 0-4) described a ship's speed with all sails set and clean full, and in smooth water. The next five (Forces 5-9) concerned the ship's mission, the chase, and its sail-carrying ability.

For example, in a fresh gale (Force 8), a well-conditioned man-of-war could just carry in chase, full and by, treble-reefed topsails, etc. The final three Forces (10-12) referred to a ship's ability to survive whole gale, storm, or hurricane. In 1838, the British Admiralty officially prescribed the Scale and made its use mandatory for all ship's log entries, for, as ir was defined, the Scale had no ambiguities for the sailors and officers of the day. But the winds of change move ever onward, and like Beaufort himself, the frigate eventually passed from the scene as the prime ship of the British Navy. Thus, when the Permanent Committee of the First Meteorological Congress met to adopt the Beaufort Wind Scale for international use in meteorological telegrams, changes were needed. Beaufort Wind Force Scale TCFAQ D10) Why do hurricane force winds start at 64 knots ? Subject: D10) Why do hurricane force winds start at 64 knots ?

Contributed by Neal Dorst (HRD) In 1805-06, Commander Francis Beaufort RN (later Admiral Sir Francis Beaufort) devised a descriptive wind scale in an effort to standardize wind reports in ship's logs. His scale divided wind speeds into 14 Forces (soon after pared down to thirteen) with each Force assigned a number, a common name, and a description of the effects such a wind would have on a sailing ship. And since the worst storm an Atlantic sailor was likely to run into was a hurricane, that name was applied to the top Force on the scale. During the 19th Century, with the manufacture of accurate anemometers, actual numerical values were assigned to each Force level, but it wasn't until 1926 (with revisions in 1939 and 1946) that the International Meteorological Committee (predecessor of the WMO) adopted a universal scale of wind speed values. Since the scale was originally nautical in nature, and that most wind reports at that time were in nautical miles per hour (or converted to them), these numerical values were given in knots.

It was a progressive scale with the range of speed for Forces increasing as you go higher. Thus Force 1 is only 3 knots in range (1 kt - 3 kt), while the Force 11 is eight knots (56 kt - 63 kt) in range. So Force 12 [Hurricane] starts out at 64 knots (74 mph, 33 m/s). There is nothing magical in this number, and since hurricane force winds are a rare experience, chances are the committee which decided on this number didn't do so because of any real observations during a hurricane. Indeed, the Smeaton-Rouse wind scale in 1759 pegged hurricane force at 70 knots (80 mph, 36 m/s). Just the same, when a tropical cyclone has maximum winds of approximately these speeds we do see the mature structure (eye, eyewall, spiral rainbands) begin to form, so there is some utility with setting hurricane force in this neighborhood.

References Hamblyn, Richard "The Invention of Clouds : How an Amateur Meteorologist Forged the Language of the Skies", (2001) Farrar, Straus, and Giroux New York, NY DeBlieu, Jan "Wind : How the Flow of Air Has Shaped Life, Myth, and the Land" (1998) Houghton Mifflin Co. New York, NY Last updated August 13, 2004 Beaufort scale : definition of Beaufort scale and synonyms of Beaufort scale (English) 5 External links History The scale was devised in 1805 by Francis Beaufort (later Rear Admiral Sir Francis Beaufort), an Ireland Irish -born Royal Navy officer, while serving on HMS Woolwich . The scale that carries Beaufort's name had a long and complex evolution, from the previous work of others, including Daniel Defoe the century before, to when Beaufort was a top administrator in the Royal Navy in the 1830s when it was adopted officially and first used during Charles Darwin Darwin’s voyage on Template:HMS eagle .

[1] In the early 19th century, naval officers made regular weather observations, but there was no standard scale and so they could be very subjective — one man's "stiff breeze" might be another's "soft breeze". Beaufort succeeded in standardizing the scale. Sir Francis Beaufort The initial scale of thirteen classes (zero to twelve) did not reference wind speed numbers but related qualitative wind conditions to effects on the sails of a man-of-war , then the main ship of the Royal Navy , from "just sufficient to give steerage" to "that which no canvas sails could withstand". [2] At zero, all sails would be up; at six, half of the sails would have been taken down; and at twelve, all sails would be stowed away. [3] The scale was made a standard for ship's log entries on Royal Navy vessels in the late 1830s and was adapted to non-naval use from the 1850s, with scale numbers corresponding to cup anemometer rotations. In 1916, to accommodate the growth of steam power, the descriptions were changed to how the sea, not the sails, behaved and extended to land observations.

Rotations to scale numbers were standardized only in 1923. George Simpson , C.B.E. (Later Sir George Simpson), Director of the UK Meteorological Office , was responsible for this and for the addition of the land-based descriptors. [1] the measure was slightly altered some decades later to improve its utility for meteorologist s. Today, many countries have abandoned the scale and use the metric system metric -based units m/s or km/h instead, Template:Citation needed date=January 2008 but the severe weather warnings given to the public are still approximately the same as when using the Beaufort scale. The Beaufort scale was extended in 1946, when forces 13 to 17 were added. [4] However, Forces 13 to 17 were intended to apply only to special cases, such as tropical cyclones. Nowadays, the extended scale is only used in Taiwan and mainland China, which are often affected by typhoons. Wind speed on the 1946 Beaufort scale is based on the empirical relationship empirical formula :< ref> Tom Beer (1997). Environmental Oceanography. CRC Press.

</ref> v = 0.836 B3/2 m/s Where v is the equivalent wind speed at 10 meters above the sea surface and B is Beaufort scale number. For example, B = 9.5 is related to 24.5 m/s which is equal to the lower limit of "10 Beaufort". Using this formula the highest winds in hurricanes would be 23 in the scale. Today, hurricane force winds are sometimes described as Beaufort scale 12 through 16, very roughly related to the respective category speeds of the Safire–Simpson Hurricane Scale , by which actual hurricanes are measured, where Category 1 is equivalent to Beaufort 12. However, the extended Beaufort numbers above 13 do not match the Safire–Simpson Scale. Category 1 tornadoesq . on the Fujita and TORRO scales also begin roughly at the end of level 12 of the Beaufort scale but are indeed independent scales -although the TORRO scale wind values are based on the 3/2 power law relating wind velocity to Beaufort force.

[5] Note that wave heights in the scale are for conditions in the open ocean , not along the shore. Modern scale ≥ 46 ft ≥ 32.7 m/s The scale is used in the Shipping Forecasts broadcast on BBC Radio 4 in the United Kingdom , and in the Sea Area Forecast from Met Éireann , the Irish Meteorological Service. Met Éireann issues a "Small Craft Warning" if winds of Beaufort force 6 (mean wind speed exceeding 22 knots) are expected up to 10 nautical miles offshore.

Other warnings are issued by Met Éireann for Irish coastal waters, which are regarded as extending 30 miles out from the coastline, and the Irish Sea or part thereof: "Gale Warnings" are issued if winds of Beaufort force 8 are expected; "Strong Gale Warnings" are issued if winds of Beaufort force 9 or frequent gusts of at least 52 knots are expected.; "Storm Force Warnings" are issued if Beaufort force 10 or frequent gusts of at least 61 knots are expected; "Violent Storm Force Warnings" are issued if Beaufort force 11 or frequent gusts of at least 69 knots are expected; "Hurricane Force Warnings" are issued if winds of greater than 64 knots are expected. This scale is also widely used in the Netherlands , Greece , China , Taiwan , Hong Kong , and Macau , however with some differences between them. Taiwan uses the Beaufort scale with the extension to 17 noted above.

China also switched to this extended version without prior notice on the morning of 15 May 2006, [7] and the extended scale was immediately put to use for Typhoon Chanchu . Hong Kong and Macau however keep using force 12 as the maximum. In the United States , winds of force 6 or 7 result in the issuance of a small craft advisory , with force 8 or 9 winds bringing about a gale warning , force 10 or 11 a storm warning ("a tropical storm warning " being issued instead of the latter two if the winds relate to a tropical cyclone ), and force 12 a hurricane force wind warning (or hurricane warning if related to a tropical cyclone). A set of red warning flags (daylight) and red warning lights (night time) is displayed at shore establishments which coincide with the various levels of warning. In Canada , maritime winds forecast to be in the range of 6 to 7 are designated as "strong"; 8 to 9 "gale force"; 10 to 11 "storm force"; 12 "hurricane force".

Appropriate wind warnings are issued by Environment Canada's Meteorological Service of Canada: strong wind warning, gale (force wind) warning, storm (force wind) warning and hurricane force wind warning. These designations were standardized nationally in 2008, whereas "light wind" can refer to 0 to 12 or 0 to 15 knots and "moderate wind" 12 to 19 or 16 to 19 knots, depending on regional custom, definition or practice. Prior to 2008, a "strong wind warning" would have been referred to as a "small craft warning" by Environment Canada, similar to US terminology. (Canada and the USA have the Great Lakes in common.) However, there being no generally accepted definition of "small craft", and to have consistency between wind speed ranges and their associated warnings, the phrase "strong wind warning" has become the national Canadian norm. See also

Question: What number is a hurricane-force storm on the conventional Beaufort Wind Force Scale?
Answer: 12