A warning means that hurricane conditions are expected whereas a watch means that conditions are possible.
Hurricane warnings indicate that hurricane conditions (sustained winds of 74 mph or higher) are expected somewhere within the specified area. Because hurricane preparedness activities become difficult once winds reach tropical storm force (sustained winds of 39 to 73 mph), the hurricane warning is issued 36 hours in advance of the anticipated onset of tropical-storm-force winds to allow for important preparation.
During a hurricane warning, complete storm preparations and immediately leave the threatened area if directed by local officials.
A hurricane watch means that hurricane conditions (sustained winds of 74 mph or higher) are possible within the specified area. A hurricane watch is issued 48 hours in advance of the anticipated onset of tropical-storm-force winds in an area.
During a hurricane watch, prepare your home and review your plan for evacuation in case a hurricane or tropical storm warning is issued. Listen closely to instructions from local officials.
For more information:
National Hurricane Center
Original article: What is the difference between a hurricane watch and a warning?