A tropical storm watch (TRA) is issued when tropical storm conditions, including winds from 39 to 73 mph (35 to 64 knots, 63 to 117 km/h) pose a possible threat to a specified coastal area within 36 hours.
Tropical Storm Warning
A tropical storm warning (TRW) is issued when tropical storm conditions (as above) are expected in a specified coastal area within 24 hours or less.
A hurricane watch (HWA) is issued for a specified area for which a hurricane or a hurricane-related hazard is a possible threat within 36 hours.
A hurricane warning (HWW) is issued when a hurricane with sustained winds of 74 mph (65 knots, 118 km/h) or higher is expected in a specified coastal area in 24 hours or less. Maritime flags indicate this with two square red flags with a black square in the middle of each.
A hurricane warning can remain in effect when dangerously high water or a combination of dangerously high water and exceptionally high waves continues, even though the winds may have subsided below hurricane intensity.
Where the intensity or track of a forecast cyclone are uncertain (such as a tropical storm bordering hurricane intensity or on the edge of a track), a Tropical Storm Warning and a Hurricane Watch are often in effect at the same time on parts of the coast.