The aim of this post is to make you aware how wind speed at sea decides the sea state. Generally, higher the wind speed, higher the sea state and rougher the sea.
Weather forecasts are extremely important for ships to ensure comfort and safety. Operators can route ships to avoid severe weather, reducing the risk of injury and damage.
The shipping forecast contains a number of unusual terms, used to convey specific meanings that are given below:
Gales
Gale warning | Beaufort | Wind speed (Knots) |
Gale | 8 | 34 – 40 |
Severe gale | 9 | 41 – 47 |
Storm | 10 | 48 – 55 |
Violent storm | 11 | 56 – 63 |
Hurricane | 12 | 64 – 71 |
Time periods
Imminent | expected within 6 hours of time of issue |
Soon | expected within 6 to 12 hours of time of issue |
Later | expected more than 12 hours from time of issue |
Speed of movement – pressure systems
Description | Speed (Knots) |
Slowly | Moving at less than 15 |
Steadily | Moving at 15 to 25 |
Quickly | Moving at 25 to 35 |
Rapidly | Moving at 35 to 45 |
Very Rapidly | Moving at more than 45 |
Wind descriptions
Description | Meaning |
Direction | Direction from which wind is blowing |
Wind becoming cyclonic | Rapid change in direction, usually associated with frontal system |
Veering | Wind direction changing in a clockwise direction – S to SW to W etc. |
Backing | Wind direction changing in an anti-clockwise direction – E to NE to N etc. |
Wind direction
Abbreviation | Wind direction | Degrees |
N | North | 0° |
NNE | NorthNorthEast | 22.5° |
NE | NorthEast | 45° |
ENE | EastNorthEast | 67.5° |
E | East | 90° |
ESE | EastSouthEast | 112.5° |
SE | SouthEast | 135° |
SSE | SouthSouthEast | 157.5° |
S | South | 180° |
SSW | SouthSouthwest | 202.5° |
SW | Southwest | 225° |
WSW | WestSouthwest | 247.5° |
W | West | 270° |
WNW | WestNorthwest | 292.5° |
NW | Northwest | 315° |
NNW | NorthNorthwest | 337.5° |
Visibility
Description | Meaning |
Fog | Less than 1000m (approx 0.6 nautical miles) |
Poor | Between 1000 and 2 nautical miles |
Moderate | Between 2 and 5 nautical miles |
Good | More than 5 nautical miles |
The Beaufort Sea State Scale (wind speed)
- Sea State 0 (Under 1 Knot)
- Sea State 1 (1 – 3 Knots)
- Sea State 2 (4 – 6 Knots)
- Sea State 3 (7 – 10 Knots)
- Sea State 4 (11 – 16 Knots)
- Sea State 5 (17 – 21 Knots)
- Sea State 6 (22 – 27 Knots)
- Sea State 7 (28 – 33 Knots)
- Sea State 8 (34 – 40 Knots)
- Sea State 9 (41 – 47 Knots)
- Sea State 10 (48 – 55 Knots)
- Sea State 11 (56 – 63 Knots)
- Sea State 12 (64+ Knots)
Sea State 0:
Description: Calm
Conditions: Sea like a mirror.
Wind Speed: Under 1 knot
Wave Height: 0 feet
Sea State 1:
Description: Light Air
Conditions: Ripples but without foam crests.
Wind Speed: 1 – 3 knots
Wave Height: 0.25 feet
Sea State 2:
Description: Light Breeze
Conditions: Small wavelets. Crests do not break.
Wind Speed: 4 – 6 knots
Wave Height: 0.5 feet
Sea State 3:
Description: Gentle Breeze
Conditions: Large wavelets. Perhaps scattered white caps.
Wind Speed: 7 – 10 knots
Wave Height: 2 feet
Sea State 4:
Description: Moderate Breeze
Conditions: Small waves. Fairly frequent white caps.
Wind Speed: 11 – 16 knots
Wave Height: 4 feet
Sea State 5:
Description: Fresh Breeze
Conditions: Moderate waves, many white caps.
Wind Speed: 17 – 21 knots
Wave Height: 6 feet
Sea State 6:
Description: Strong Breeze
Conditions: Large waves begin to form; white foam crests, probably spray.
Wind Speed: 22 – 27 knots
Wave Height: 10 feet
Sea State 7:
Description: Near Gale
Conditions: Sea heaps up and white foam blown in streaks along the direction of the wind. Wind Speed: 28 – 33 knots
Wave Height: 14 feet
Sea State 8:
Description: Gale
Conditions: Moderately high waves, crests begin to break into spindrift.
Wind Speed: 34 – 40 knots
Wave Height: 18 feet
Sea State 9:
Description: Strong Gale
Conditions: High waves. Dense foam along the direction of the wind. Crests of waves begin to roll over. Spray may affect visibility.
Wind Speed: 41 – 47 knots
Wave Height: 23 feet
Sea State 10:
Description: Storm
Conditions: Very high waves with long overhanging crests. The surface of the sea takes a white appearance. The tumbling of the sea becomes heavy and shock like. Visibility affected.
Wind Speed: 48 – 55 knots
Wave Height: 29 feet
Sea State 11:
Description: Violent Storm
Conditions: Exceptionally high waves. The sea is completely covered with long white patches of foam lying in the direction of the wind. Visibility affected.
Wind Speed: 56 – 63 knots
Wave Height: 37 feet
Sea State 12:
Description: Hurricane
Conditions: The air is filled with foam and spray. Sea completely white with driving spray. Visibility very seriously affected.
Wind Speed: 64+ knots
Wave Height: 45 feet
No Image available
* Photographs from National Weather Service Observing Handbook No. 1, US National Weather Service.
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