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Tropical storm
Tropical cyclone with winds of 39 to 74 mph.
Tropical wave
A kink or bend in the normally straight flow of surface air in the tropics which forms a low pressure trough, or pressure boundary, showers and thunderstorms. Can develop into a tropical cyclone.
Tropical cyclone
A low-pressure weather system in which the central core is warmer than the surrounding atmosphere. The term "tropical cyclone" is also used in the Indian Ocean and around the Coral Sea off northeastern Australia to describe storms called "hurricanes" and "typhoons" in other areas.
Tropical depression
A tropical cyclone with maximum sustained winds near the surface of less than 39 mph.
Hurricane
A tropical cyclone with winds of 74 mph or more. Normally applied to such storms in the Atlantic Basin and the Pacific Ocean east of the International Date Line.
Tropical Storm Alert
Tropical storm conditions (34-73 mph) are expected within 72 hours.
Tropical Storm Watch
Tropical storm conditions (34-73 mph) are expected within 48 hours.
Tropical Storm Warning
Tropical storm conditions (34-73 mph) are expected within 36 hours.
Tropical Storm All Clear
This means that the storm has left the area, but caution should prevail.
Storm surge
The dome of water that builds up as a hurricane moves over water. As the water comes ashore with the storm, it causes flooding that is usually a hurricane's biggest killer.
Eye
The low pressure centre of a tropical cyclone. Winds are normally calm and sometimes the sky clears.
Eye wall
The ring of thunderstorms that surrounds a storm's eye. The heaviest rain, strongest winds and worst turbulence are normally in the eye wall.
Knot
A measure of speed. It is one nautical mile per hour. Never refer to "knots per hour" unless you want to describe acceleration. A nautical mile is one minute of one degree of longitude and is slightly longer than the ordinary, or statute, mile used in the US. To convert nautical miles to miles or knots to miles per hour, multiply by 1.15. To convert miles to nautical miles or mile per hour to knots, divide by 1.15.
Millibar
A metric measurement of air pressure.
Barometric Pressure
defined as atmospheric pressure, i.e., the force exerted on a surface of unit area caused by the weight of the air column above, normally at 1013.2 millibars at sea level. It indicates the presence and movement of weather patterns and affects many physical measurements.
North Atlantic Basin (sometimes called the Atlantic Basin)
The Atlantic Ocean north of the equator, the Caribbean Sea, and the Gulf of Mexico.

Last Updated: 2010-08-15