Seldom experienced inland trees uprooted considerable structural damage. High waves dense streaks of foam crests of waves begin to topple, tumble and roll over spray may affect visibility. Slight structural damage occurs -roofing dislodged larger branches break off. Moderately high waves of greater length edges of crests begin to break into spindrift foam is blown in well-marked streaks along the direction of the wind. Twigs break off trees progress generally impeded. Sea heaps up and white foam from breaking waves begins to be blown in streaks along direction of wind. Whole trees in motion inconvenience felt when walking against wind. Large waves begin to form the white foam crests are more extensive with probably some spray Large branches in motion whistling heard in telephone wires umbrellas used with difficulty. Moderate waves, taking a more pronounced long form many white horses are formed - a chance of some spray Small trees in leaf begin to sway crested wavelets form on inland waters Small waves - becoming longer fairly frequent white horses. Raises dust and loose paper small branches are moved. Small wavelets, ripples formed but do not break: A glassy appearance maintained. Wind felt on face leaves rustle ordinary vanes moved by wind. The table below describes what can be expected for each level of the scale and the relationship to the forecast average wind speed values. Although the system is old (first developed in 1805 by Sir Francis Beaufort), it remains a widely used system to measure wind speed today. The Beaufort wind scale measures wind speed according to the impact the wind has on the land and sea. Read the six things you need to know about wind warnings for more information about wind warnings. Check your local forecasts carefully for mention of thunderstorms or squalls before you go out and be prepared to change your plans. Gusts from thunderstorms may also come from a different direction than the average wind direction. Remember, wind gusts can be stronger still in the vicinity of thunderstorms and squalls. Cliffs and other landscape features will affect winds near the shore.Ĭhecking wind conditions is one of the five vital weather safety checks everyone should complete before heading out on the water.īased on the 40 per cent rule of thumb, the table below shows the potential gust you could expect for different forecast average wind speeds and associated wind warning category. Wind speed and direction can be influenced significantly by the local environment. For example, a northerly wind is blowing from the north towards the south. The wind direction is based on true north orientation and is the direction the wind is blowing from. Wind speed usually increases with height above the sea-surface, so winds at the surface are not typically as strong as they are at 10 metres, where wind is measured and forecast by the Bureau.Ī wind forecast range (for example, 10 to 15 knots) may be given when the wind speed is expected to vary significantly within a coastal area. Thunderstorm and squalls may produce even stronger gusts. For example, when the average wind speed is 25 knots, it is normal to experience gusts of 35 knots and lulls of lighter winds. The gusts during any 10-minute period are typically 40% higher than the average wind speed. The Bureau's forecasts of wind speed and direction are the average of these gusts and lulls, measured over a 10-minute period at a height of 10 metres above sea level.
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