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Hurricane Glossary


Barometric Pressure: The weight of the column of air that extends from the ground (or water's surface) to the top of the atmosphere. It is also called air pressure. Barometric pressure is very low in a hurricane.

Convective Organization: The patterns of wind flow that work together to create conditions in which severe weather can form.

Cyclone: A closed, rotating wind. Cyclones rotate counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.

Doppler Radar: A radar that compares in frequency, up or down from the original signal, echoes returned from weather systems to create highly-accurate measurements of the weather system's velocity.

Extratropical Cyclone: A storm that forms outside the tropics, sometimes as a tropical storm or hurricane changes.

Eye: The low pressure center of a hurricane. 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.

Hurricane: A tropical cyclone with winds of 74 mph or more.

Knot: Measure of speed. It is one nautical mile per hour.

Landfall: The intersection of the surface center of a tropical cyclone with a coastline.

Low-Pressure Trough: An extended area of relatively-lower atmospheric pressure that can be the extension of a cyclone and is generally associated with severe weather.

Major Hurricane: A hurricane that is classified as Category 3 or higher.

Millibar: A measurement of air pressure.

Remnant Low: Used for systems no longer having the sufficient convective organization required of a tropical cyclone.

Small Craft Advisory: A warning of sustained surface winds between roughly 25mph and 38mph, predicted or occurring not directly associated with tropical cyclones.

Squall Line: A line of severe thunderstorms that can form along or ahead of a cold front. The line contains heavy precipitation, and often hail, frequent lightning, strong straight-line winds and possibly tornadoes and waterspouts.

Storm Surge: The dome of water that builds as a hurricane moves over water.

Storm Tide: A combination of storm surge and the normal tide.

Sustained Winds: The wind speed defined by the average wind measurement recorded over a one-minute period.

Tropical Cyclone: A low-pressure weather system in which the center of the storm is warmer than the surrounding atmosphere.

Tropical Depression: A tropical cyclone with maximum sustained winds of less than 39 mph.

Tropical Disturbance: The earliest stages of a tropical cyclone, with winds less than 30 mph.

Tropical Wave: A bend in the normally straight flow of surface air in the tropics which forms a low pressure trough and showers and thunderstorms. This can develop into a tropical cyclone.

Typhoon: A hurricane in the north Pacific-west of the International Date Line.

Upper Level Low: An area of cold air aloft that is rotating counter-clockwise.

Waterspout: A waterspout is a tornado that passes over water. It is a funnel-shaped formation of wind, water and ocean spray.

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