Wind is the movement of air across the Earth’s surface, driven by differences in atmospheric pressure. It flows from areas of high pressure to areas of low pressure. Because wind affects everything from aviation and navigation to construction and safety, a standardized method for measuring its speed is necessary. Without a consistent scale, descriptions of wind speed would remain subjective, making the term “fast wind” meaningless for practical applications.
The Standard Measure for Wind Speed
The primary international standard for classifying wind speed is the Beaufort Wind Force Scale, devised in 1805 by Admiral Sir Francis Beaufort. Beaufort’s original scale was a descriptive measure, focusing on the qualitative effect of wind rather than instrument readings. This system provided a standardized way for naval officers to record weather conditions consistently.
The scale ranges from Force 0 (calm conditions) up to Force 12 (hurricane-force winds). Over time, the scale was adapted for use on land and at sea, correlating the visual effects of the wind with specific numerical speeds and quantitative measurements.
Classifying Wind Speeds: What Defines “Fast”
The point at which wind transitions to a condition requiring caution begins at Force 6 on the Beaufort scale. This level, known as a “Strong Breeze,” is the lowest classification where the wind’s effects become noticeably disruptive. A Strong Breeze corresponds to sustained speeds of 25 to 31 MPH (39 to 49 KPH), or 22 to 27 knots, the unit commonly used in maritime and aviation contexts.
These speeds make controlling an umbrella difficult and result in large tree branches being in constant motion. Force 7, or a “Near Gale,” solidifies the definition of fast wind as a potentially hazardous condition. Near Gale winds reach a sustained speed of 32 to 38 MPH (50 to 61 KPH, or 28 to 33 knots).
At this intensity, walking directly against the wind becomes inconvenient, and whole trees are observed moving. The threshold for a true “Gale,” or Force 8, is crossed when sustained winds reach 39 to 46 MPH (62 to 74 KPH, or 34 to 40 knots). This is the point where the wind can snap small branches and twigs from trees, significantly impeding outdoor progress.
Real-World Impacts of High Wind Speeds
Winds at Force 6 and above produce distinct and escalating physical consequences on both land and sea. On land, a Strong Breeze makes noise by whistling in wires and causes large branches to sway continuously. When wind speeds climb to the Near Gale range, the force is sufficient to create streaks of white foam on the water surface, and the sea begins to heap up.
The most immediate danger is often posed by wind gusts, which are sudden, brief increases in speed lasting only a few seconds. Gusts deliver a powerful surge of force that frequently exceeds the sustained wind speed. This concentrated burst of energy is responsible for structural damage, such as tearing off roof shingles or pushing over weakened trees.
As wind speeds approach the Gale level, impacts become more severe, sometimes causing slight structural damage, such as the removal of chimney pots or slates from roofs. At sea, the waves grow considerably high, and dense white streaks of foam cover the water surface, making navigation extremely challenging.
In response to these wind thresholds, weather services issue specific warnings to ensure public safety. A Wind Advisory is issued when sustained non-thunderstorm winds are expected to be between 31 and 39 MPH, or when gusts are forecast to be between 46 and 57 MPH. A more severe High Wind Warning is issued once sustained winds are expected to reach 40 MPH or higher, or gusts are predicted to hit 58 MPH or higher.