HURRICANE ALLEY
The following is a glossary of terms typically found in tropical cyclone advisories and information sources.
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BACKSHORE
Upper shore zone beyond the reach of ordinary waves and tides, landward from the beach crest.
BACKWASH
The seaward return of flood waters that have accumulated inland due to a tropical cyclone tide.
BAR
The outer limit of the central cloud mass, where a transition to hurricane clouds, rain, and winds often takes place suddenly.
CENTRAL PRESSURE
The minimum surface pressure at the cyclone center. Used as a measure of the cylone's strength.
CLIMATOLOGICAL TRACK
An average of histroical tracks, usually computed on a monthly or seasonal basis.
CYCLONE
A low-pressure system in which winds move counterclockwise around the pressure center in the Northern Hemisphere, clockwise in the Southern Hemisphere; usually attended by foul weather and strong wind speeds.
DISTURBANCE
A disruption of the normal or prevailing flow or circulation; usually associated with abnormal cloudiness and precipitation.
EXTRATROPICAL CYCLONE
Any synoptic-scale cyclone that is not a tropical cyclone. It usually originates in middle or higher latitudes in a baroclinic environment. Its foul weather and strong winds affect a much broader area than those of a tropical cyclone, with worst conditions occurring at a greater distance from the low-pressure center.
HURRICANE
A regional name for tropical cyclones with maximum winds over 63 kt in the Atlantic and eastern North Pacific Oceans.
INVERSE BAROMETER
The component of rise in sea level resulting from pressure gradients in a storm system.
ISOBAR
A line of constant pressure on a weather map.
ISOTACH
A line of constant wind speed on a weather map.
ISOTHERM
A line of constant temperature on a weather map.
LANDFALL (OF A HURRICANE)
The position at a seacoast where the center of the hurricane passes from sea to land.
LONGSHORE CURRENT
A shoal-water current moving essentially parallel to the coastline: generally caused by waves breaking along a line at an acute angle to the coast.
MACROSCALE EVENT
A circulation system or disturbance whose dimensions exceeds 1,000 km.
MERIDIONAL
Directed north-south, usually positive in the northern hemisphere.
MESOSCALE EVENT
A circulation system or disturbance whose dimensions are less than 100 km.
MIXING LENGTH
The mean travel distance over which an air eddy maintains its identity.
MIXING RATIO (ATMOSPHERIC)
The amount of water vapor in a given mass of dry air.
MODEL
A numerical scheme for describing the properties of an atmospheric circulation system - usually a disturbance or cyclone - its development and/or movement. A dynamical model is based upon the fundamental physics that govern the changes in properties or movement; a statistical model is based upon a statistical evaluation of the behavior in historic cases.
MONSOON
A wind whose direction reverses seasonally, typically over the south China Sea and the eastern Indian Ocean. A process in which the monsoon wind blows generally from an atmospheric cold source to a warm source.
OROGRAPHIC
Related to, or caused by, terrain variations.
PROBABILITY ELLIPSE
A statistically derived elliptical area inside of which an uncertain event will have a probability of occurring equal to that assigned to the ellipse.
RADAR (RADIO DETECTION AND RANGING)
In meteorology, used to detect and display distributions and intensity of precipitation. Pulse Doppler is a radar system that measures the speed with which precipitation targets approach or recede from the radar antenna and, thereby, the wind component transporting the precipitation.
RADIOSONDE
A balloon-borne atmospheric sounding device for measuring vertical profiles of pressure, temperature, and humidity.
RAWINSONDE
A radiosonde also equipped to measure vertical profiles of the horizontal wind velocity.
RECURVATURE (OF A HURRICANE)
Usually, the change from movement toward the west, under the influence of trade winds, to a north or northeastward movement, under the influence of westerlies from higher latitudes.
RIDGE
An area of pronounced anticyclonic flow where pressure generally reaches a maximum.
SHEAR LINE A synoptic-scale line across which wind velocity components parallel to the line change discontinuously in the cyclonic sense.STABILITY
A general property of atmospheric systems that forces the return to an equilibrium state after a disturbance is imposed. Thermal Stability requires that a parcel of air, displace vertically, return to its initial position.STORM SURGE
A superelevation of sea level due to a combination of direct wind-driven water and an uplift induced by the pressure drop.SUBTROPICS
The intermediate region between tropical and middle latitudes, generally in the latitude of 25o-35o, that varies with sesaon and by region.TRADE WINDS
Steady easterly winds blowing across the subtropical and tropical oceans, generally with an equatorward component.TRAJECTORY, OR TRACK (OF A HURRICANE)
(a) The path taken by the center of a tropical cyclone; (b) the path of individual air particles spiraling about the cyclone center.TROPICAL CYCLONE
A synoptic-scale near-circular cyclone generally originating over tropical oceans, distinguished by torrential rains and damaging winds that reach a maximum very near the pressure center.TROPICS
The latitude belt in which weather typical of the tropics occurs. Geographically, it is the global region between the tropics of Cancer and Capricorn; its weather is variable with geographic season and region.TROUGH
The counterpart of a ridge; an area of pronounced cyclonic flow where pressure generally reaches a minimum.TYPHOON
The regional term for a tropical cyclone in the weatern North Pacific Ocean.VORTICITY
The local rotation of air about a discrete center; may be reflected in the cyclonic or anticyclonic turning of streamlines or by wind shear perpendicular to an axis of rotation. Absolute vorticity is the sum of the local or relative vorticity and that due to the earth's rotation.WIND SHEAR
The change in wind velocity relative to a horizontal or vertical axis; e.g., vertical shear of the horizontal wind, the change in wind velocity with height.