The maximum sustained wind associated with a

tropical cyclone A tropical cyclone is a rapidly rotating storm system with a low-pressure area, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain and squalls. Depending on its locat ...

is a common indicator of the intensity of the storm. Within a mature tropical cyclone, it is found within the eyewall at a certain distance from the center, known as the radius of maximum wind, or RMW. Unlike gusts, the value of these winds are determined via their sampling and averaging the sampled results over a period of time. Wind measuring has been standardized globally to reflect the winds at above

mean sea level A mean is a quantity representing the "center" of a collection of numbers and is intermediate to the extreme values of the set of numbers. There are several kinds of means (or "measures of central tendency") in mathematics, especially in statist ...

, and the maximum sustained wind represents the highest average wind over either a one-minute (US) or ten-minute time span (see the definition, below), anywhere within the tropical cyclone. Surface winds are highly variable due to friction between the atmosphere and the Earth's surface, as well as near hills and mountains over land. Over the ocean,

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imagery Imagery is visual symbolism, or figurative language that evokes a mental image or other kinds of sense impressions, especially in a literary work, but also in other activities such as. Imagery in literature can also be instrumental in conveying ...

is often used to estimate the maximum sustained winds within a tropical cyclone. Land, ship, aircraft reconnaissance observations, and

radar Radar is a system that uses radio waves to determine the distance ('' ranging''), direction ( azimuth and elevation angles), and radial velocity of objects relative to the site. It is a radiodetermination method used to detect and track ...

imagery can also estimate this quantity, when available. This value helps determine the damage potential of a tropical cyclone, through use of such scales as the

Saffir–Simpson scale The Saffir–Simpson hurricane wind scale (SSHWS) is a tropical cyclone intensity scale that classifies hurricanes—which in the Western Hemisphere are tropical cyclones that exceed the intensities of tropical depressions and tropical sto ...

Definition

The maximum sustained wind normally occurs at a distance from the center known as the radius of maximum wind, within a mature tropical cyclone's eyewall, before winds decrease at farther distances away from a tropical cyclone's center. Most weather agencies use the definition for sustained winds recommended by the

World Meteorological Organization The World Meteorological Organization (WMO) is a List of specialized agencies of the United Nations, specialized agency of the United Nations responsible for promoting international cooperation on atmospheric science, climatology, hydrology an ...

(WMO), which specifies measuring winds at a height of for 10 minutes, and then taking the average. However, the United States

National Weather Service The National Weather Service (NWS) is an Government agency, agency of the Federal government of the United States, United States federal government that is tasked with providing weather forecasts, warnings of hazardous weather, and other weathe ...

defines sustained winds within tropical cyclones by averaging winds over a period of one minute, measured at the same height. This is an important distinction, as the value of the highest one-minute sustained wind is about 14% greater than a ten-minute sustained wind over the same period.

Estimation and measurement

In most tropical cyclone basins, use of the satellite-based

Dvorak technique The Dvorak technique (developed between 1969 and 1984 by Vernon Dvorak) is a widely used system to estimate tropical cyclone intensity (which includes tropical depression, tropical storm, and hurricane/typhoon/intense tropical cyclone intensities ...

is the primary method used to estimate a tropical cyclone's maximum sustained winds. The extent of spiral banding and difference in temperature between the

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and eyewall is used within the technique to assign a maximum sustained wind and pressure. Central pressure values for their centers of low pressure are approximate. The tracking of individual clouds on minutely satellite imagery could be used in the future in estimating surface winds speeds for tropical cyclones. Ship and land observations are also used, when available. In the Atlantic as well as the Central and Eastern Pacific basins, reconnaissance aircraft are still utilized to fly through tropical cyclones to determine flight level winds, which can then be adjusted to provide a fairly reliable estimate of maximum sustained winds. A reduction of 10 percent of the winds sampled at flight level is used to estimate the maximum sustained winds near the surface, which has been determined during the past decade through the use of GPS dropwindsondes.Franklin, James L., Michael L. Black, and Krystal Valde.
GPS dropwindsonde wind profiles in hurricanes and their operational implications.
Retrieved on 2008-07-04.

Doppler weather radar A weather radar, also called weather surveillance radar (WSR) and Doppler weather radar, is a type of radar used to locate precipitation, calculate its motion, and estimate its type (rain, snow, hail etc.). Modern weather radars are mostly pu ...

can be used in the same manner to determine surface winds with tropical cyclones near land.

Variation

Friction between the atmosphere and the Earth's surface causes a 20% reduction in the wind at the surface of the Earth. Surface roughness also leads to significant variation of wind speeds. Over land, winds maximize at hill or mountain crests, while sheltering leads to lower wind speeds in valleys and lee slopes. Compared to over water, maximum sustained winds over land average 8% lower. More especially, over a city or rough terrain, the wind gradient effect could cause a reduction of 40% to 50% of the

geostrophic wind In atmospheric science, geostrophic flow () is the theoretical wind that would result from an exact balance between the Coriolis force and the pressure gradient force. This condition is called '' geostrophic equilibrium'' or ''geostrophic balanc ...

speed aloft; while over open water or ice, the reduction is between 10% and 30%.

Relationship to tropical cyclone strength scales

In most basins, maximum sustained winds are used to define the category of a tropical cyclone on each basin's tropical cyclone scale. In the Atlantic and northeast Pacific oceans, the

is used. This scale can be used to determine possible storm surge and damage impact on land. In most basins, the category of the tropical cyclone (for example, tropical depression, tropical storm, hurricane/typhoon, super typhoon, depression, deep depression, intense tropical cyclone) is determined from the cyclone's maximum sustained wind over one minute.

Notes

References

{{DEFAULTSORT:Maximum Sustained Wind Wind

Tropical cyclone meteorology The tropics are the regions of Earth surrounding the equator, where the sun may shine directly overhead. This contrasts with the temperate or polar regions of Earth, where the Sun can never be directly overhead. This is because of Earth's ax ...