What does a Small Craft Advisory Mean?

So what does this mean to the mariner when the National Weather Service issues a “[B]Small Craft Advisory[/B]”?

The National Weather Service has developed a multi-tier concept for forecasting hazardous weather which includes outlooks, watches, warnings and advisories. An outlook is issued to indicate that a hazardous weather or hydrologic event may occur over the next several days. A watch is issued whenever that risk has increased significantly but the occurrence, location or timing are still uncertain. A warning is issued when the hazardous condition or event is either occurring, imminent or likely.

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My understanding is that it means vessels under 65’ are expected to exercise extreme caution when at sea.

It means the water is about to splash out of your bath tub :^)

Seriously, web searchs can reveal a lot:

[B]SMALL CRAFT ADVISORY:[/B] An advisory issued by coastal and Great Lakes Weather Forecast Offices (WFO) for areas included in the Coastal Waters Forecast or Nearshore Marine Forecast (NSH) products. Thresholds governing the issuance of small craft advisories are specific to geographic areas. A Small Craft Advisory may also be issued when sea or lake ice exists that could be hazardous to small boats. There is no precise definition of a small craft. Any vessel that may be adversely affected by Small Craft Advisory criteria should be considered a small craft. Other considerations include the experience of the vessel operator, and the type, overall size, and sea worthiness of the vessel. There is no legal definition of “small craft”. The Small Craft Advisory is an advisory in Coastal Waters and Nearshore forecasts for sustained winds, frequent gusts, or sea/wave conditions, exceeding defined thresholds specific to geographic areas. A Small Craft Advisory may also be issued when sea or lake ice exists that could be hazardous to small boats.
Eastern (ME…SC, Lake Erie, Lake Ontario) - Sustained winds or frequent gusts ranging between 25 and 33 knots (except 20 to 25 knots, lower threshold area dependent, to 33 knots for harbors, bays, etc.) and/or seas or waves 5 to 7 feet and greater, area dependent.
Central (MN…OH) - Sustained winds or frequent gusts (on the Great Lakes) between 22 and 33 knots inclusive, and/or seas or waves greater than 4 feet.
Southern (GA…TX and Caribbean) - Sustained winds of 20 to 33 knots, and/or forecast seas 7 feet or greater that are expected for more than 2 hours.
Western (WA…CA) - Sustained winds of 21 to 33 knots, potentially in combination with wave heights exceeding 10 feet (or wave steepness values exceeding local thresholds).
Alaska (AK) - Sustained winds or frequent gusts of 23 to 33 knots. A small craft advisory for rough seas may be issued for sea/wave conditions deemed locally significant, based on user needs, and should be no lower than 8 feet.
Hawaii (HI), Samoa - Sustained winds 25 knots or greater and seas 10 feet or greater.
Guam and the Northern Mariana Islands - Sustained winds 22 to 33 knots and/or combined seas of 10 feet or more.
“Frequent gusts”are typically long duration conditions (greater than 2 hours). For a list of NWS Weather Offices by Region, refer to the following website: http://www.nws.noaa.gov/organization.php