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BE PREPARED: What they mean when they say


BE PREPARED: What they mean when they say

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ON THE APPROACH of a tropical storm, hurricane, or any weather system that can cause significant damage, you listen to the advisories being broadcast on the local radio and television stations.

Sometimes we don’t understand the terms used, so below is an explanation of some of those terms.

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, and showers and thunderstorms. Can develop into a tropical cyclone.

Tropical depression: A tropical cyclone with maximum sustained winds near the surface of less than 39 mph.

Tropical storm: Tropical cyclone with winds of 39 to 74 miles per hour.

Tropical storm alert: Tropical storm conditions (34 to 73 miles per hour) are expected within 48 hours.

Tropical storm watch: Tropical storm conditions (34 to 73 miles per hour) are expected within 36 hours.

Tropical storm warning: Tropical storm conditions (34 to 73 miles per hour) are expected within 24 hours.

Tropical storm all-clear: This means that the storm has left the area, but caution should prevail.

Hurricane: A tropical cyclone with winds of 74 miles per hour or more. Normally applied to such storms in the Atlantic Basin and the Pacific Ocean east of the International Date Line.

Hurricane alert: Hurricane conditions are possible (winds greater than 73 miles per hour) within 48 hours.

Hurricane watch: Hurricane conditions are possible and may threaten land within 36 hours.

Hurricane warning: Hurricane conditions are expected to make landfall within 24 hours.

Hurricane all-clear: This means that the hurricane has left the area, but caution should prevail.

Storm surge: The dome of water that builds up as a hurricane moves over water. As this water comes ashore with the storm, it causes flooding (usually a hurricane’s biggest killer).

Eye: The low pressure centre of a hurricane. Winds are normally calm and sometimes the sky clears.


Eye wall: The ring of thunderstorms that surrounds a hurricane’s eye. The heaviest rain, strongest winds, and worst turbulence are normally in the eye wall.

Knot: A measure of speed. To convert nautical miles to miles or knots to miles per hour, multiply by 1.15. To convert miles to nautical miles or miles per hour to knots, divide by 1.15.

Millibar: A metric measurement of air pressure.

Barometric Pressure: The force exerted on a surface of unit area caused by the weight of the air column above, atmospheric pressure. It indicates the presence and movement of weather patterns and affects many physical measurements.

North Atlantic Basin/Atlantic Basin): The Atlantic Ocean north of the equator, the Caribbean Sea, and the Gulf of Mexico.