The radius of maximum wind (RMW) is the distance between the center of a cyclone

Cyclone

In meteorology, a cyclone is an area of closed, circular fluid motion rotating in the same direction as the Earth. This is usually characterized by inward spiraling winds that rotate anticlockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere of the Earth. Most large-scale...

 and its band of strongest wind

Wind

Wind is the flow of gases on a large scale. On Earth, wind consists of the bulk movement of air. In outer space, solar wind is the movement of gases or charged particles from the sun through space, while planetary wind is the outgassing of light chemical elements from a planet's atmosphere into space...

s. It is a parameter in atmospheric dynamics and tropical cyclone forecasting

Tropical cyclone forecasting

Tropical cyclone forecasting is the science and art of forecasting where a tropical cyclone's center, and its effects, are expected to be at some point in the future. There are several elements to tropical cyclone forecasting: track forecasting, intensity forecasting, rainfall forecasting, storm...

. The highest rain

Rain

Rain is liquid precipitation, as opposed to non-liquid kinds of precipitation such as snow, hail and sleet. Rain requires the presence of a thick layer of the atmosphere to have temperatures above the melting point of water near and above the Earth's surface...

fall rates occur near the RMW of tropical cyclone

Tropical cyclone

A tropical cyclone is a storm system characterized by a large low-pressure center and numerous thunderstorms that produce strong winds and heavy rain. Tropical cyclones strengthen when water evaporated from the ocean is released as the saturated air rises, resulting in condensation of water vapor...

s. The extent of a cyclone's storm surge

Storm surge

A storm surge is an offshore rise of water associated with a low pressure weather system, typically tropical cyclones and strong extratropical cyclones. Storm surges are caused primarily by high winds pushing on the ocean's surface. The wind causes the water to pile up higher than the ordinary sea...

 and its maximum potential intensity can be determined using the RMW. As maximum sustained wind

Maximum sustained wind

The maximum sustained winds associated with a tropical cyclone are a common indicator of the intensity of the storm. Within a mature tropical cyclone, they are found within the eyewall at a distance defined as the radius of maximum wind, or RMW. Unlike gusts, the value of these winds are...

s increase, the RMW decreases. Recently, RMW has been used in descriptions of tornado

Tornado

A tornado is a violent, dangerous, rotating column of air that is in contact with both the surface of the earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud. They are often referred to as a twister or a cyclone, although the word cyclone is used in meteorology in a wider...

es. When designing building

Building

In architecture, construction, engineering, real estate development and technology the word building may refer to one of the following:...

s to prevent against failure from atmospheric pressure change, RMW can be used in the calculations.

Determination

The RMW is traditionally measured by reconnaissance aircraft in the Atlantic basin. It can also be determined on weather maps

Surface weather analysis

Surface weather analysis is a special type of weather map that provides a view of weather elements over a geographical area at a specified time based on information from ground-based weather stations...

 as the distance between the cyclone center and the system's greatest pressure gradient. Using weather satellite

Weather satellite

The weather satellite is a type of satellite that is primarily used to monitor the weather and climate of the Earth. Satellites can be either polar orbiting, seeing the same swath of the Earth every 12 hours, or geostationary, hovering over the same spot on Earth by orbiting over the equator while...

 data, the distance between the coldest cloud top temperature and the warmest temperatature within the eye

Eye (cyclone)

The eye is a region of mostly calm weather found at the center of strong tropical cyclones. The eye of a storm is a roughly circular area and typically 30–65 km in diameter. It is surrounded by the eyewall, a ring of towering thunderstorms where the second most severe weather of a cyclone...

, in infrared satellite imagery, is one method of determining RMW. The reason why this method has merit is that the strongest winds within tropical cyclone

Tropical cyclone

A tropical cyclone is a storm system characterized by a large low-pressure center and numerous thunderstorms that produce strong winds and heavy rain. Tropical cyclones strengthen when water evaporated from the ocean is released as the saturated air rises, resulting in condensation of water vapor...

s tend to be located under the deepest convection

Convection

Convection is the movement of molecules within fluids and rheids. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids....

, which is seen on satellite imagery as the coldest cloud tops. Use of velocity data from Doppler weather radar

Weather radar

Weather radar, also called weather surveillance radar and Doppler weather radar, is a type of radar used to locate precipitation, calculate its motion, estimate its type . Modern weather radars are mostly pulse-Doppler radars, capable of detecting the motion of rain droplets in addition to the...

 can also be used to determine this quantity, both for tornadoes and tropical cyclones near the coast.

Tornadoes

In the case of tornadoes, knowledge of the RMW is important as atmospheric pressure change (APC) within sealed buildings can cause failure of the structure. Most buildings have openings totaling one square foot per 1000 cubic feet (28.3 m³) volume to help equalize air pressure between the inside and outside of the structures. The APC is around one-half of its maximum value at the RMW, which normally ranges between 150 feet (45.7 m) and 500 feet (152.4 m) from the center (or eye) of the tornado. The widest tornado as measured by actual radar wind measurements was the Mulhall

Mulhall, Oklahoma

Mulhall is a town in Logan and Payne counties in the U.S. state of Oklahoma. The population was 239 at the 2000 census. It is part of the Oklahoma City Metropolitan Statistical Area.-History:...

 tornado in northern Oklahoma, part of the 1999 Oklahoma tornado outbreak, which had a radius of maximum wind of over 800 metres (2,624.7 ft).

Tropical cyclones

An average value for the RMW of 47 kilometres (29.2 mi) was calculated as the mean (or average) of all hurricanes with a lowest central atmospheric pressure

Atmospheric pressure

Atmospheric pressure is the force per unit area exerted into a surface by the weight of air above that surface in the atmosphere of Earth . In most circumstances atmospheric pressure is closely approximated by the hydrostatic pressure caused by the weight of air above the measurement point...

 between a pressure of 909 hectopascals (26.8 inHg) and 993 hectopascals (29.3 inHg). As tropical cyclones intensify, maximum sustained winds increase as the RMW decreases. The heaviest rainfall within intense tropical cyclones has been observed in the vicinity of the RMW.

The radius of maximum wind helps determine the direct strikes of tropical cyclones. Tropical cyclones are considered to have made a direct strike to a landmass when a tropical cyclone passes close enough to a landmass that areas inside the radius of maximum wind are experienced on land. The radius of maximum wind is used within the maximum potential intensity equation. The Emanuel equation for Maximum Intensity Potential relies upon the winds near the RMW of a tropical cyclone to determine its ultimate potential.

The highest storm surge is normally coincident with the radius of maximum wind. Because the strongest winds within a tropical cyclone lie at the RMW, this is the region of a tropical cyclone which generates the dominant waves near the storm, and ultimately ocean swell

Ocean Swell

Ocean Swell was a British Thoroughbred racehorse and sire. In a career that lasted from 1943 to 1945 he ran fifteen times and won six races. As a three-year-old 1944 he won the New Derby, a wartime substitute for the Epsom Derby run at Newmarket...

 away from the cyclone. Tropical cyclones mix the ocean water within a radius three times that of the RMW, which lowers sea surface temperatures due to upwelling

Upwelling

Upwelling is an oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water towards the ocean surface, replacing the warmer, usually nutrient-depleted surface water. The increased availability in upwelling regions results in high levels of primary...

.

Much is still unknown about the radius of maximum wind in tropical cyclones, including whether or not it can be predictable.