Wind is simply the movement of air, but the terms used to describe its speed can be confusing to the average person tracking a weather report. Meteorologists use two distinct measurements to characterize the force of this air movement: sustained wind speed and wind gusts. While both are reported in units like miles per hour or knots, they represent fundamentally different aspects of the atmosphere’s dynamic flow. Understanding this distinction is necessary for correctly interpreting weather forecasts and assessing potential hazards.
Defining Sustained Wind Speed
Sustained wind speed measures the consistent force of the wind over a specific period. This value is calculated by averaging the wind speed measured over an extended time frame, typically two minutes for the U.S. National Weather Service. This average represents the steady pressure the wind exerts against objects. Sustained speed is the metric used to categorize the intensity of large weather systems, such as hurricanes, which are classified based on their maximum sustained wind speeds. Because sustained wind smooths out momentary fluctuations, it offers a baseline for wind forecasts.
Defining Wind Gusts
A wind gust is a sudden, brief surge in wind speed that exceeds the sustained wind speed, usually lasting less than 20 seconds. They are caused by atmospheric turbulence, where irregular air motion transports higher-momentum air down toward the surface. A peak in wind speed is officially classified as a gust when it exceeds the sustained wind speed by a specified threshold. This abrupt acceleration and deceleration of air flow makes gusts feel like a sudden, powerful shove. Gusts are often observed near obstacles like buildings and trees, or they can result from intense weather phenomena like thunderstorms and squall lines.
How Wind Data Is Measured and Reported
Both sustained wind speed and wind gusts are measured using instruments called anemometers, typically mounted at a standardized height of 10 meters above the ground. These devices continuously record the wind speed to capture the atmosphere’s rapid fluctuations. Meteorological services process this raw data to extract the two distinct values for reporting. Sustained wind speed is calculated by averaging all recorded measurements over the set two-minute period. Conversely, the reported wind gust is the maximum instantaneous speed, typically a three-second average, recorded during a longer observation window. Official weather reports communicate both figures, for example, stating “Winds 15 mph, gusting to 25 mph.”
Real World Impacts of Wind Speed Versus Gusts
The distinction between sustained wind speed and gusts is important because each measurement predicts a different type of physical effect. Sustained wind determines the constant stress applied to large structures and objects. This steady pressure causes prolonged swaying in trees, creates a constant drag on vehicles, and contributes to the long-term load on buildings. Wind gusts, however, deliver a concentrated burst of energy. The dynamic load from a gust can push an object past its breaking point almost instantly, even if the sustained wind speed is low. Gusts are a major hazard for aviation, causing unexpected turbulence, and for maritime activities, where a sharp burst of wind can quickly capsize a small boat.