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Marine Wind & Sea Threat Level
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T hreat Level Descriptions
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Extreme
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"An Extreme Threat to Life and Property Aboard Marine Vessels, Especially Small Craft, from Marine Winds/Seas."
Storm-force prevailing winds with extreme combined seas. Sustained winds of 48 knots or greater (Beaufort Scale 10+) capable of driving seas of 32 feet or greater. At Beaufort Scale 10, very high waves with long overhanging crests. Visibility very seriously affected from dense blowing foam and spray. At Beaufort Scales greater than 10, small to medium sized ships may be lost to view behind the waves as conditions worsen. Bay and inland waters extremely rough. Small craft encouraged to seek safe harbor or stay in port as conditions support potential "Storm Warning".
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High
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"A High Threat to Life and Property Aboard Marine Vessels, Especially Small Craft, from Marine Winds/Seas."
Gale-force prevailing winds with very large combined seas. Sustained winds of 34 - 47 knots (Beaufort Scale 8 - 9) capable of driving seas of 19 - 32 feet. At Beaufort Scale 8, high waves of greater length form. Foam is blown in well marked streaks. At Beaufort Scale 9, high waves with the visibility becoming affected by blowing foam and spray. Bay and inland waters becoming extremely rough. Small craft encouraged to seek safe harbor or stay in port as conditions support potential "Gale Warning".
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Moderate
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"A Moderate Threat to Life and Property Aboard Marine Vessels, Especially Small Craft, from Marine Winds/Seas."
Strong prevailing winds and large combined seas. Sustained winds of 22 - 33 knots (Beaufort Scale 6 - 7) capable of driving seas of 10 - 18 feet. At Beaufort Scale 6, larger waves form. Spray is present with white foam crests everywhere. At Beaufort Scale 7, even larger waves form, but seas begin to heap up. White foam is present and blowing in streaks. Bay and inland waters becoming very rough. Conditions typical for a "Small Craft Advisory".
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Low
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"A Low Threat to Life and Property Aboard Marine Vessels, Especially Small Craft, from Marine Winds/Seas."
Prevailing winds and combined seas are moderate. Sustained winds of 17 - 21 knots (Beaufort Scale 5) capable of driving seas of 7 - 9 feet. Moderate waves but with a more pronounced long form. Bay and inland waters becoming rough. Conditions typical for a "Small Craft Advisory".
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Very Low
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" A Very Low Threat to Life and Property Aboard Marine Vessels, Especially Small Craft, from Marine Winds/Seas."
Prevailing winds and combined seas becoming moderate. Sustained winds around 14 - 16 knots (Beaufort Scale 4) capable of driving seas of 4 - 6 feet. Small to moderate waves but with a long form. Bay and inland waters becoming choppy. Conditions typical for "Small Craft To Exercise Caution".
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Non-Threatening
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" No Discernable Threat to Life and Property Aboard Marine Vessels, Especially Small Craft, from Marine Winds/Seas."
Prevailing winds and combined seas are non-threatening.
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| Note: Combined seas are the combination of wind waves and swells as they relate to sea height. The height (or significant wave height) is defined as the average height of the one third highest waves. |
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