The Beaufort scale // is an empirical measure that relates wind speed to observed conditions at sea or on land. Its full name is the Beaufort wind force scale.
The scale was devised in 1805 by the Irish hydrographer Francis Beaufort (later Rear Admiral Sir Francis Beaufort), a 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 Hydrographer of the Navy in the 1830s when it was adopted officially and first used during the voyage of HMS Beagle under Captain Robert FitzRoy who was later to set up the first Meteorological Office (Met Office) in Britain giving regular weather forecasts. – one man's "stiff breeze" might be another's "soft breeze". Beaufort succeeded in standardising the scale.In the 18th century, naval officers made regular weather observations, but there was no standard scale and so they could be very subjective
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 frigate, then the main ship of the Royal Navy, from "just sufficient to give steerage" to "that which no canvas sails could withstand".
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 1853, the Beaufort scale was accepted as generally applicable at the First International Meteorological Conference in Brussels.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, CBE (later Sir George Simpson), director of the UK Meteorological Office, was responsible for this and for the addition of the land-based descriptors. The measures were slightly altered some decades later to improve its utility for meteorologists. Nowadays, meteorologists typically express wind speed in kilometers per hour or miles per hour, but Beaufort scale terminology is still used for weather forecasts for shipping and the severe weather warnings given to the public.
The Beaufort scale was extended in 1946 when forces 13 to 17 were added.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. Internationally, WMO Manual on Marine Meteorological Services (2012 edition) defined the Beaufort Scale only up to force 12 and there was no recommendation on the use of the extended scale.
Wind speed on the 1946 Beaufort scale is based on the empirical relationship:
Where v is the equivalent wind speed at 10 metres 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 Saffir–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 Saffir–Simpson scale. F1 tornadoes on the Fujita scale and T2 TORRO scale also begin roughly at the end of level 12 of the Beaufort scale, but are independent scales – although the TORRO scale wind values are based on the 3/2 power law relating wind velocity to Beaufort force.
Wave heights in the scale are for conditions in the open ocean, not along the shore.
|Beaufort number||Description||Wind speed||Wave height||Sea conditions||Land conditions||Sea conditions (photo)||Associated warning flag|
|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.|
|2–5 km/h||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.|
|6–11 km/h||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.|
|12–19 km/h||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.|
|20–28 km/h||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.|
|29–38 km/h||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.|
|39–49 km/h||3–4 m|
|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.|
|50–61 km/h||4–5.5 m|
|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.|
|62–74 km/h||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).|
|75–88 km/h||7–10 m|
|10|| Storm, |
|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.|
|89–102 km/h||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.|
|103–117 km/h||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.|
|≥ 73 mph|
|≥ 118 km/h||≥ 14 m|
|≥ 32.7 m/s|
The Beaufort scale is not an exact nor an objective scale; it was based on visual and subjective observation of a ship and of the sea. The corresponding integral wind speeds were determined later, but the values in different units were never made equivalent.
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, Germany,Greece, China, Taiwan, Hong Kong, Malta, and Macau, although 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, and the extended scale was immediately put to use for Typhoon Chanchu. Hong Kong and Macau retain 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.)
The Saffir–Simpson hurricane wind scale (SSHWS), formerly the Saffir–Simpson hurricane scale (SSHS), classifies hurricanes – Western Hemisphere tropical cyclones – that exceed the intensities of tropical depressions and tropical storms – into five categories distinguished by the intensities of their sustained winds.
A gale is a strong wind, typically used as a descriptor in nautical contexts. The U.S. National Weather Service defines a gale as 34–47 knots of sustained surface winds. Forecasters typically issue gale warnings when winds of this strength are expected. In the United States, a gale warning is specifically a maritime warning; the land-based equivalent in National Weather Service warning products is a wind advisory.
A small craft advisory is a type of wind warning issued by the National Weather Service in the United States. In Canada a similar warning is issued by Environment Canada. It is issued when winds have reached, or are expected to reach within 12 hours, a speed marginally less than gale force. A Small Craft Advisory may also be issued when sea or lake ice exists that could be hazardous to small boats.
Tropical cyclone warnings and watches are two levels of alert issued by national weather forecasting bodies to coastal areas threatened by the imminent approach of a tropical cyclone of tropical storm or hurricane intensity. They are notices to the local population and civil authorities to make appropriate preparation for the cyclone, including evacuation of vulnerable areas where necessary. It is important that interests throughout the area of an alert make preparations to protect life and property, and do not disregard it on the strength of the detailed forecast track. Tropical cyclones are not points, and forecasting their track remains an uncertain science,
Weather services issue a gale warning for maritime locations currently or imminently experiencing winds of Gale Force on the Beaufort scale. Gale warnings allow mariners to take precautionary actions to ensure their safety at sea or to seek safe anchorage and ride out the storm on land. Though usually associated with deep low-pressure areas, winds strong enough to catalyze a gale warning can occur in other conditions too, including from anticyclones, or high-pressure systems, in the continental interior. The winds are not directly associated with a tropical cyclone.
This article describes severe weather terminology used by the National Weather Service (NWS) in the United States. The NWS, a government agency operating as an arm of the National Oceanic and Atmospheric Administration (NOAA) branch of the United States Department of Commerce (DoC), defines precise meanings for nearly all of its weather terms.
Tropical cyclones are ranked on one of five tropical cyclone intensity scales, according to their maximum sustained winds and which tropical cyclone basin(s) they are located in. Only a few scales of classifications are used officially by the meteorological agencies monitoring the tropical cyclones, but some alternative scales also exist, such as accumulated cyclone energy, the Power Dissipation Index, the Integrated Kinetic Energy Index, and the Hurricane Severity Index.
Cyclone Percy was the seventh named storm of the 2004–05 South Pacific cyclone season and the fourth and final severe tropical cyclone to form during the 2004–05 South Pacific cyclone season. Cyclone Percy originated as a tropical disturbance on February 23. Over the course of the next few days, the system organized while moving east-southeastward, before intensifying into a Category 1 tropical cyclone on the Australian region scale on February 26. The system quickly intensified, reaching Category 4 status later that day. On the next day, Percy was steered southward by a blocking ridge of high pressure, while stretched out the structure of the storm into an elliptical shape, weakening it back to Category 3 status. Afterward, the storm rapidly reintensified, reaching its peak intensity as a Category 5 tropical cyclone on March 2. Afterward, Percy encountered increasing wind shear and weakened once again, turning southeastward on the next day. On March 5, Percy transitioned into an extratropical storm, before dissipating soon afterward.
Tropical cyclone windspeed climatology is the study of wind distribution among tropical cyclones, a significant threat to land and people. Since records began in 1851, winds from hurricanes, typhoons and cyclones have been responsible for fatalities and damage in every basin. Major hurricanes usually cause the most wind damage. Hurricane Andrew for example caused $45 billion in damage, most of it wind damage.
The 2005–06 Australian region cyclone season was an above average tropical cyclone season. It began on 1 November 2005 and ended on 30 April 2006. The regional tropical cyclone operational plan also defines a tropical cyclone year separately from a tropical cyclone season, which runs from 1 July 2005 to 30 June 2006.
Severe Tropical Cyclone Daman was the strongest cyclone of the 2007–08 South Pacific cyclone season. Cyclone Daman was the fourth tropical depression and the first severe tropical cyclone to form east of longitude 180° during the 2007–08 South Pacific cyclone season. Due to the severity of the storm, the name Daman was retired and replaced with Denia.
The following is a glossary of tropical cyclone terms.
Severe Tropical Cyclone Ofa was considered to be the worst tropical cyclone to affect Polynesia since Cyclone Bebe. The system was first noted on January 27, 1990, near Tuvalu, as a shallow tropical depression that had developed within the South Pacific Convergence Zone. The cloud pattern slowly organized, and on January 31, while located east of Tuvalu, Ofa attained cyclone intensity. Moving slowly southeast, Ofa developed storm-force winds. It attained hurricane-force winds on February 2. Cyclone Ofa reached peak intensity on February 4. Shortly after, its peak Ofa began to weaken over a less favourable environment. Ofa was declared an extratropical cyclone on February 8, though the system was still tracked by meteorologists until February 10.
Severe Tropical Cyclone Ernie was one of the quickest strengthening tropical cyclones on record. Ernie was the first Category 5 severe tropical cyclone in the Australian region since Cyclone Marcia in 2015, and also the strongest tropical cyclone in the Australian region since Cyclone Ita in 2014. Ernie developed from a tropical low into a cyclone south of Indonesia in the northeast Indian Ocean on 6 April 2017, and proceeded to intensify extremely rapidly to a Category 5 severe tropical cyclone. A few days later, on 10 April, the system was downgraded below cyclone intensity following a period of rapid weakening, located southwest of its original position. Ernie had no known impacts on any land areas.
Tropical cyclones by year. Since the year 957, there have been at least 11,982 recorded tropical or subtropical cyclones in the Atlantic, Pacific, and Indian Oceans, which are known as basins. Collectively, tropical cyclones caused more than US$1.2 trillion in damage, unadjusted for inflation, and have killed more than 2.6 million people. Most of these deaths were caused by a few deadly cyclones, including the 1881 Haiphong typhoon, the 1931 Shanghai typhoon, the 1970 Bhola cyclone, Typhoon Nina in 1975, the 1991 Bangladesh cyclone, and Cyclone Nargis in 2008.
Throughout 2020 so far, 34 tropical or subtropical cyclones have formed in bodies of water known as tropical cyclone basins. Of these, 20 have been named, including a subtropical cyclone in the South Atlantic, by various weather agencies when they attained maximum sustained winds of 35 knots. The strongest storm of the year so far is Cyclone Harold in the South Pacific Ocean.
Tropical Cyclone Ann was a small and relatively weak off-season tropical cyclone that brought minor impacts to the Solomon Islands, Far North Queensland and coastal regions of the Northern Territory's Top End during May 2019. Ann was the twenty-fifth tropical low, eleventh tropical cyclone, ninth Category 2 tropical cyclone and second off-season tropical cyclone of the 2018–19 Australian region cyclone season. The system developed from a tropical low that formed on 7 May in the South Pacific cyclone region. The low gradually intensified while moving southwards, and strengthened into a tropical cyclone on 11 May. The storm then turned to the west-northwest and continued to strengthen over the Coral Sea. Ann reached peak intensity on 12 May as a Category 2 tropical cyclone on the Australian scale, with ten-minute sustained winds of 95 km/h (60 mph) and a central barometric pressure of 993 hPa (29.32 inHg). One-minute sustained winds of 100 km/h (65 mph) made Ann equivalent to a strong tropical storm on the Saffir-Simpson hurricane wind scale. The storm began to decay soon afterwards, and weakened to a gale-force tropical low on 14 May. Ann made landfall near Lockhart River on Cape York Peninsula on 15 May, before re-emerging over water a few hours later. Ann maintained a steady west-northwestwards track for several days before dissipating as a tropical low near East Timor on 18 May.
|Wikimedia Commons has media related to Beaufort Scale .|
|Wikisource has the text of the 1911 Encyclopædia Britannica article Beaufort Scale .|