If wind speeds are expected to be sustained between 21 and 33 knots, a "Small Craft Advisory" will be issued. There's no legal definition of "small craft" but the Coast Guard generally recommends boats smaller than 33 feet should avoid being on the water, but it depends on the experience of the crew.
If winds are expected between 34-47 knots sustained, a "Gale Warning" will be issued. "Storm Warnings" will be issued for any sustained wind speeds higher than 48 knots in the Northwest. However, "Hurricane Warnings" will be issued along the Atlantic Seaboard and Gulf Coast for higher wind speeds with approaching hurricanes.