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Last Updated: Feb 7th, 2010 - 09:52:29 

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Sea vs Swells
By Cynthia Kirkeby
May 27, 2004, 12:27



The news often reports seas of certain heights and swells of certain heights. What is the difference between 'seas' and 'swells'?

norm

Dear Norm-

Swells refer to the actual size of the ocean waves. If there are swells of 10-12 feet, then there are large non-breaking waves that measure an average of 10-12 feet from the bottom of the trough to the top of the swell.

Seas usually refers to the overall conditions in the ocean, such as calm seas or heavy seas. Rough seas are some combination of high swells and high winds. Rough seas include the following warning levels:

Small Craft Advisory: Observed or forecast winds of 18 to 33 knots - Small Craft Advisories may also be issued for hazardous sea conditions or lower wind speeds that may affect small craft operations. Issued up to 12 hours ahead of conditions. (There is no legal definition of the term "small craft".)

Gale Warning: Observed or forecast winds of 34 to 47 knots.

Storm Warning: Observed or forecast winds of 48 knots or greater.

Tropical Storm Warnings: Observed or forecast winds of 34 to 63 knots associated with a tropical storm.

Hurricane Warning: Observed or forecast winds of 64 knots or higher associated with a hurricane.

Special Marine Warning: Observed or forecast winds of 34 knots or more associated with a squall or thunderstorm and expected to last for 2 hours or less.

Source: US Coast Guard


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