Wind is a fundamental measurement in meteorology, but not all wind is measured or reported in the same way. The air flow we experience is often turbulent, fluctuating in speed from one moment to the next. To provide a consistent and meaningful value for weather reporting and hazard assessment, meteorologists rely on a standardized measurement called “sustained wind.” This specific metric helps to differentiate the general force of a weather system from its momentary spikes in speed. Understanding the definition and application of sustained winds is necessary to accurately interpret weather forecasts and warnings.
Defining the Measurement
Sustained wind is officially defined as the average speed of the wind measured over a specific time interval. This measurement is not an instantaneous reading but a calculated mean, designed to smooth out the minor atmospheric turbulence that causes rapid, short-term fluctuations in wind speed.
The exact time interval for calculating the average speed varies depending on the region and the agency reporting the data. The United States National Weather Service (NWS) typically defines sustained wind within tropical cyclones by averaging the wind speed over a period of one minute. However, the World Meteorological Organization (WMO) standard, adopted by many international agencies, uses a longer ten-minute averaging period. This difference is significant, as a one-minute sustained wind speed is generally about 14% greater than a ten-minute sustained wind speed for the same event.
For accurate and comparable data, wind speed is also measured at a standardized height above the ground. Global meteorological standards require that the measurement be taken at an elevation of 10 meters, or approximately 33 feet, above the surface. This height is chosen to minimize the effect of surface friction from terrain, buildings, and trees, which can dramatically slow down or disrupt the air flow closer to the ground. An unobstructed exposure at this height ensures that the reported speed reflects the true force of the wind field.
The Difference Between Sustained Winds and Gusts
The distinction between sustained winds and wind gusts is a primary source of confusion for the general public, yet they describe fundamentally different atmospheric phenomena. Sustained wind represents the steady, continuous force exerted by the air flow over a longer period, while a wind gust is a sudden, temporary burst of higher speed. Gusts are essentially short, sharp peaks of wind speed that are superimposed upon the overall sustained wind speed.
A wind gust is typically defined as the highest instantaneous wind speed observed, often lasting for only a few seconds, generally less than 20 seconds. These short, violent surges are caused by the turbulent nature of the atmosphere, often resulting from air moving over rough ground, buildings, or from intense convection within a thunderstorm.
A helpful way to visualize the difference is to imagine the wind as a continuous push against an object. The sustained wind is the steady pressure you feel, which persists for minutes at a time. The gust, by contrast, is a sudden, momentary slap of air that hits with greater intensity. Gust speeds are almost always higher than the reported sustained wind speed for the same event, sometimes exceeding the sustained speed by as much as 50%.
This difference in speed and duration means they present different types of hazards. Sustained winds exert a constant, long-term strain on structures, while gusts are responsible for sudden actions like snapping tree branches or making driving momentarily difficult. The short duration of a gust means its destructive power is localized and brief, whereas the continuous force of sustained wind can lead to structural fatigue and failure.
Why Sustained Winds Determine Storm Severity
The sustained wind speed is the metric meteorologists use to classify the intensity of major weather systems, such as tropical depressions, tropical storms, and hurricanes or typhoons. This is because the overall intensity and destructive potential of a storm is best represented by the constant, continuous force it applies to the environment. Scales like the Saffir-Simpson Hurricane Wind Scale categorize the storm based on its maximum one-minute sustained wind speed.
The sustained force represents the continuous pressure exerted on structures, which is the key factor in structural failure and long-term damage. When a building is subjected to a steady, powerful push over many minutes, the structure experiences prolonged stress that can lead to catastrophic failure, such as the complete loss of a roof or exterior walls. A gust, while momentarily stronger, does not last long enough to cause this structural collapse.
For a tropical cyclone to be classified as a hurricane, for example, its maximum sustained wind speed must reach at least 74 miles per hour (119 kilometers per hour). This sustained speed is used to estimate potential property damage across the five categories of the Saffir-Simpson scale and forms the basis for official warnings and evacuation decisions.