Forecasting Terms and the Beaufort Scale.

The Beaufort Scale is just one of the forecasting terms still in use by marine forecasters today.

This scale and a number of other terms are used to convey specific, concise, meanings to help sailors estimate the wind speed and strength, sea state and forecast predictions

The Beaufort Wind Force Scale.

The Beaufort Scale was created by Admiral Sir Francis Beaufort in 1805, his wind strength and sea state numbers are among the forecasting terms still in use today.

Wind Speed Kts)
Wind Speed km/hour
Sea State
0 / Calm
Sea like a mirror, Wave Height 0 ft.
1 / Light Air
Ripples but without foam crests Wave Height > 0.25 ft.
2 / Light Breeze
6 – 12
Small wavelets. Crests have a glassy appearance and do not break, Wave Height: >0.5 ft
3 / Gentle Breeze
13 – 20
Large wavelets. Some whitecaps Wave Height >2 ft
4 / Moderate Breeze
21 – 30
Small waves, Fairly frequent white caps, Wave Height >4 ft.
5 / Fresh Breeze
31 – 40
Moderate waves, many white caps, Chance of some spray, Wave Height >6 ft.
6 / Strong Breeze
41 - 50
Large waves begin to form; the white foam crests are more extensive everywhere. Probably some spray, Wave Height >10 ft.
7 / Near Gale
Sea heaps up and white foam from breaking waves blown in streaks in the direction of the wind. Wave Height >14 ft.
8 / Gale
Moderately high waves of greater length, Crests begin to break into spindrift, In the tropics categorized as a Tropical Storm, Wave Height >18 ft.
9 / Strong Gale
High waves. Dense foam streaks along the direction of the wind. Crests of waves begin to topple and roll over. Spray may affect visibility, Wave Height >23 ft.
10 / Storm
Very high waves with long overhanging crests. Foam is blown in dense white streaks, The surface of the sea takes on a white appearance. The tumbling of the sea becomes heavy, Visibility affected. Wave Height >29 ft.
11 / Violent Storm
Exceptionally high waves, The sea is completely covered with long white patches of foam lying along the direction of the wind, Wave crests are blown into froth, Visibility, Wave Height >37 ft.
12 / Hurricane
The air is filled with foam and spray. Sea completely white with driving spray. Visibility very seriously affected. Equal to a Category 1 Hurricane on the Saffir-Simpson Scale, Wave Height 45 ft.

Wind descriptions.

Marine Weather Forecasting Terms used to describe how the wind is forecast to behave.

This is always the direction from which wind is blowing.
Wind becoming cyclonic
A rapid change in direction, usually associated with frontal system
Wind direction changing in a clockwise direction, eg. S to SW to W etc.
Wind direction changing in an anti-clockwise direction, eg. E to NE to N etc.

Forecasting Terms for Visibility.

These Forecasting Terms are used to describe viability quite specifically.

Down to less than 1000 Meters, 0.6 nautical miles.
Between 1000 Meters and 2 nautical miles
Between 2 and 5 nautical miles
More than 5 nautical miles

Time periods.

Expected within 6 hours of time of issue or broadcast.
Expected within 6 to 12 hours of time of issue or broadcast.
Expected more than 12 hours from time of issue or broadcast.

Pressure tendency.

Rising / Falling More Slowly.
The pressure is rising or falling at a slower rate through the previous three hours.
Rising / Falling slowly.
A pressure change of 0.1 to 1.5 0 hPa/mb in the preceding three hours.
Rising / Falling.
Pressure change of 1.6 to 3.5 0 hPa/mb in the preceding three hours.
Rising / Falling quickly.
Pressure change of 3.6 to 6.0 0 hPa/mb in the preceding three hours.
Rising / Falling V. Rapidly.
Pressure change of more than 6.0 hPa/mb in the preceding three hours.
Now Rising / Falling.
Pressure has been Rising / Falling or steady in the preceding three hours, but at the time of observation was definitely beginning to Rise / Fall.

Speed of pressure systems movement.

These Forecasting Terms are used to describe the predicted movements of pressure systems.

Moving at less than 15 Knots
Moving at 15 to 25 Knots
Moving at 25 to 35 Knots
Moving at 35 to 45 Knots
Very Rapidly
Moving at more than 45 Knots

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