Marine weather forecast – Wind speed, direction and Sea state

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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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