HERETROPICAL DISTURBANCE
Rotary circulation slight or absent at surface, but sometimes better developed aloft, no closed isobars (lines of equal atmospheric pressure) and no strong wind – a common phenomenon in the tropics.

TROPICAL DEPRESSION
One or more closed isobars and some rotary circulation at the surface, highest wind speed 38 mph (33 knots).

TROPICAL STORM
Closed isobars, distinct rotary circulation, wind speeds of 39-73 mph (34-63 knots).

HURRICANE
Closed isobars, strong and very pronounced rotary circulation, winds of 74 mph (64 knots) or more.

TROPICAL STORM WATCH
An announcement for specific areas that a tropical storm or an incipient tropical storm condition poses a possible threat to coastal areas generally within 36 hours.

TROPICAL STORM WARNING
A warning that tropical storm conditions including possible sustained winds within the range of 39 to 73 mph a re expected in specific coastal areas in 24 hours or less.

HURRICANE WATCH
An announcement for specific areas that a hurricane or an incipient hurricane condition poses a possible threat to coastal areas generally within 36 hours.

HURRICANE WARNING
A warning that sustained winds of 74 mph or higher associated with a hurricane are expected in a specific coastal area in 24 hours or less. When a hurricane warning is issued, all precautions should be taken immediately. If the hurricane’s path is unusual or erratic, the warnings may be issued only a few hours before the beginning of hurricane conditions.

SMALL CRAFT ADVISORY
When a hurricane moves within a few hundred miles on the coast, advisories warn small-craft operators to take precautions and not to venture into open ocean.