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Advisory:

Official information issued by tropical cyclone warning centersdescribing alltropical cyclone watches andwarnings in effect along with details concerning tropical cyclonelocations, intensity and movement, and precautions that should betaken. Advisories are also issued to describe: (a)tropical cyclones prior to issuance of watches andwarnings and (b)subtropicalcyclones.

Best Track:

A subjectively-smoothed representation of atropical cyclone's location, intensity, type, and size over its lifetime. The best track contains the cyclone's latitude, longitude, maximum sustained surface winds, minimum sea-level pressure, stage (e.g., tropical, extratropical, remnant low, etc.), and size (e.g., radius of maximum winds, hurricane-force winds, 50-kt winds, and tropical storm-force winds) at 6-hourly intervals and at landfall for tropical storms and hurricanes. These best track attributes, based on a post-storm assessment of all available data, may differ from values contained in system advisories. The best track locations also generally will not reflect the erratic motion implied by connecting individualcenter fix positions.

Center:

Generally speaking, the vertical axis of atropical cyclone,usually defined by the location of minimum wind or minimum pressure.The cyclone center position can vary with altitude. Inadvisoryproducts, refers to the center position at the surface.

Center / Vortex Fix:

The location of the center of atropical orsubtropical cycloneobtained byreconnaissance aircraft penetration, satellite, radar, or synoptic data.

Central Dense Overcast:

A dense mass of clouds that covers the eyewall or the most tightly curved inner bands of a tropical cyclone.

Central North Pacific Basin:

The region north of the Equator between 140W and theInternational Dateline. TheCentral Pacific Hurricane Center (CPHC) inHonolulu, Hawaii is responsible for trackingtropical cyclones in thisregion.

Cyclone:

An atmospheric closed circulation rotating counter-clockwise inthe Northern Hemisphere and clockwise in the SouthernHemisphere.

Direct Hit:

A close approach of atropical cyclone to a particular location.For locations on the left-hand side of a tropical cyclone's track(looking in the direction of motion), a direct hit occurs when thecyclone passes to within a distance equal to the cyclone'sradius ofmaximum wind. For locations on the right-hand side of the track, adirect hit occurs when the cyclone passes to within a distance equalto twice the radius of maximum wind. Compareindirect hit,strike.

Eastern North Pacific Basin:

The portion of the North Pacific Ocean east of 140W. The NationalHurricane Center in Miami, Florida is responsible for trackingtropicalcyclones in this region.

Eye:

The roughly circular area of comparatively light winds thatencompasses the center of a severetropical cyclone. The eye iseither completely or partially surrounded by theeyewall cloud.

Eyewall / Wall Cloud:

An organized band or ring of cumulonimbus clouds that surroundthe eye, or light-wind center of atropicalcyclone. Eyewall and wallcloud are used synonymously.

Extratropical:

A term used in advisories and tropical summaries to indicate thata cyclone has lost its "tropical" characteristics. The term impliesboth poleward displacement of the cyclone and the conversion of thecyclone's primary energy source from the release of latent heat ofcondensation to baroclinic (the temperature contrast between warm andcold air masses) processes. It is important to note that cyclones canbecome extratropical and still retain winds ofhurricane ortropical storm force.

Extratropical Cyclone:

A cyclone of any intensity for which the primary energy source is baroclinic, that is, results from the temperature contrast between warm and cold air masses.

Fujiwhara Effect:

The tendency of two nearbytropical cyclones to rotate cyclonically about each other.

Gale Warning:

A warning of 1-minute sustained surface winds in the range 34 kt(39 mph or 63 km/hr) to 47 kt (54 mph or 87 km/hr) inclusive, eitherpredicted or occurring and not directly associated withtropical cyclones.

High Wind Warning:

A high wind warning is defined as 1-minute average surface windsof 35 kt (40 mph or 64 km/hr) or greater lasting for 1 hour or longer,or winds gusting to 50 kt (58 mph or 93 km/hr) or greater regardlessof duration that are either expected or observed overland.

Hurricane / Typhoon:

Atropical cyclone in which the maximum sustained surface wind(using the U.S. 1-minute average) is 64 kt (74 mph or 119 km/hr) ormore. The term hurricane is used for Northern Hemisphere tropicalcyclones east of the International Dateline to the Greenwich Meridian.The term typhoon is used for Pacific tropical cyclones north of theEquator west of the International Dateline.

Hurricane Local Statement:

A public release prepared by localNational Weather Service offices in or near a threatened area giving specific details for itscounty/parish warning area on (1) weather conditions, (2) evacuationdecisions made by local officials, and (3) other precautions necessaryto protect life and property.

Hurricane Season:

The portion of the year having a relatively high incidence ofhurricanes. The hurricane season in the Atlantic, Caribbean, and Gulfof America runs from June 1 to November 30. The hurricane season in theEastern Pacific basin runs from May 15 to November 30. The hurricaneseason in theCentral Pacific basin runs from June 1 to November 30.

Hurricane Warning:

An announcement that sustained winds of 64 knots (74 mph or 119 km/hr) or higher areexpected somewhere within the specified area in association with atropical,subtropical, orpost-tropical cyclone. Because hurricane preparedness activities become difficult once winds reachtropical storm force, the warning is issued 36 hours in advance of the anticipated onset of tropical-storm-force winds. The warning can remain in effect when dangerously high water or a combination of dangerously high water and waves continue, even though winds may be less thanhurricane force.

Hurricane Watch:

An announcement that sustained winds of 64 knots (74 mph or 119 km/hr)or higher arepossible within the specified area in association with atropical,subtropical, orpost-tropical cyclone. Because hurricane preparedness activities become difficult once winds reachtropical storm force, the hurricane watch is issued 48 hours in advance of the anticipated onset of tropical storm force winds.

Indirect Hit:

Generally refers to locations that do not experience a direct hitfrom atropical cyclone, but do experiencehurricane force winds(either sustained or gusts) or tides of at least 4 feet above normal.

Inter-Tropical Convergence Zone:

A zonally elongated axis of surface wind confluence of northeasterly and southeasterly trade winds in the tropics.

Invest:

A weather system for which a tropical cyclone forecast center (NHC, CPHC, or JTWC) is interested in collecting specialized data sets (e.g., microwave imagery) and/or running model guidance. Once a system has been designated as an invest, data collection and processing is initiated on a number of government and academic web sites, including the Naval Research Laboratory (NRL) and the University of Wisconsin Cooperative Institute for Meteorological Satellite Studies (UW-CIMSS). The designation of a system as an invest does not correspond to any particular likelihood of development of the system into a tropical cyclone; operational products such as the Tropical Weather Outlook or the JTWC/TCFA should be consulted for this purpose.

Inundation:

The flooding of normally dry land, primarily caused by severe weather events along the coasts, estuaries, and adjoining rivers. These storms, which include hurricanes and nor'easters, bring strong winds and heavy rains. The winds drive large waves and storm surge on shore, and heavy rains raise rivers. (A tsunami — a giant wave caused by earthquakes or volcanic eruptions under the sea or landslides into the sea — is another kind of coastal inundation, but should not be confused with storm surge.)

Landfall:

The intersection of the surfacecenter of atropical cyclone with a coastline. Because thestrongest winds in a tropical cyclone are not located precisely at thecenter, it is possible for a cyclone's strongest winds to beexperienced over land even if landfall does not occur. Similarly, itis possible for a tropical cyclone to make landfall and have itsstrongest winds remain over the water. Comparedirect hit,indirect hit, andstrike.

Major Hurricane:

Ahurricane that is classified as Category 3 or higher.

Maximum Sustained Surface Wind:

The standard measure of a tropical cyclone's intensity. When the term is applied to a particular weather system, it refers to the highest one-minute average wind (at an elevation of 10 meters with an unobstructed exposure) associated with that weather system at a particular point in time.

Monsoon:

A large-scale, seasonally-reversing surface wind circulation in the tropics accompanied by large amplitude seasonal changes in precipitation.

Monsoon Trough:

A surface trough in association with amonsoon circulation. This is depicted by a lineon a weather map showing the location of minimum sea level pressure coinciding with the maximum cyclonic turningof the surface winds, with southwesterly or northwesterly flow prevailing equatorward and northeasterly flow prevailing poleward of the typically zonally oriented trough axis.

National Geodetic Vertical Datum of 1929 [NGVD 1929]:

A fixed reference adopted as a standard geodetic datum for elevations determined by leveling. The datum was derived for surveys from a general adjustment of the first-order leveling nets of both the United States and Canada. In the adjustment, mean sea level was held fixed as observed at 21 tide stations in the United States and 5 in Canada. The year indicates the time of the general adjustment. A synonym for Sea-level Datum of 1929. The geodetic datum is fixed and does not take into account the changing stands of sea level. Because there are many variables affecting sea level, and because the geodetic datum represents a best fit over a broad area, the relationship between the geodetic datum and local mean sea level is not consistent from one location to another in either time or space. For this reason, the National Geodetic Vertical Datum should not be confused with mean sea level.

Post-storm Report:

A report issued by a local National Weather Service officesummarizing the impact of atropical cycloneon its forecast area.These reports include information on observed winds, pressures, stormsurges, rainfall, tornadoes, damage and casualties.

Post-tropical Cyclone:

A former tropical cyclone. This generic term describes a cyclone that no longer possesses sufficient tropical characteristics to be considered atropical cyclone. Post-tropical cyclones can continue carrying heavy rains and high winds. Note that former tropical cyclones that havebecome fullyextratropical...as well asremnant lows...are two classes of post-tropical cyclones.

Potential Tropical Cyclone:

A term used in NWS advisory products to describe a disturbance that is not yet atropical cyclone, but which poses the threat of bringingtropical storm orhurricane conditions to land areas within 72 hours.

Preliminary Report:

Now known as the "Tropical Cyclone Report". A report summarizingthe life history and effects of an Atlantic or eastern Pacifictropical cyclone. It contains a summary of the cyclone life cycle andpertinent meteorological data, including the post-analysisbest track(six-hourly positions and intensities) and other meteorologicalstatistics. It also contains a description of damage and casualtiesthe system produced, as well as information on forecasts and warningsassociated with the cyclone. NHC writes a report on every tropicalcyclone in its area of responsibility.

Present Movement:

The best estimate of the movement of thecenter of atropicalcyclone at a given time and given position. This estimate does notreflect the short-period, small scale oscillations of the cyclonecenter.

Radius of Maximum Winds:

The distance from thecenter of atropical cyclone to the location of the cyclone'smaximum winds. In well-developedhurricanes,the radius of maximum winds is generally found at the inner edge oftheeyewall.

Rapid Intensification:

An increase in the maximum sustained winds of atropical cyclone of at least 30 kt in a 24-h period.

Relocated:

A term used in anadvisoryto indicate that a vector drawn fromthe preceding advisory position to the latest known position is notnecessarily a reasonable representation of the cyclone'smovement.

Remnant Low:

Apost-tropical cyclone that no longer possesses the convective organization required of atropical cyclone...and has maximum sustained winds of less than 34 knots. The term is most commonly applied to the nearly deep-convection-free swirls of stratocumulusin the eastern North Pacific.

Saffir-Simpson Hurricane Wind Scale:

The Saffir-Simpson Hurricane Wind Scale is a 1 to 5 categorization based on the hurricane's intensity at the indicated time. The scale provides examples of the type of damage and impacts in the United States associated with winds of the indicated intensity. The following table shows the scale broken down by winds:

Category	Wind Speed (mph)	Damage
1	74 - 95	Verydangerous winds will produce some damage
2	96 - 110	Extremelydangerous winds will cause extensive damage
3	111 - 129	Devastatingdamage will occur
4	130 - 156	Catastrophicdamage will occur
5	> 156	Catastrophicdamage will occur

A detailed description of the Saffir-Simpson Hurricane Wind Scale is available athttp://www.nhc.noaa.gov/aboutsshws.php.

Storm Surge:

An abnormal rise in sea level accompanying ahurricane or otherintense storm, and whose height is the difference between the observedlevel of the sea surface and the level that would have occurred in theabsence of the cyclone. Storm surge is usually estimated bysubtracting the normal or astronomic high tide from the observed stormtide.

Storm Surge Warning:

The danger of life-threatening inundation from rising water moving inland from the shoreline somewhere within the specified area, generally within 36 hours, in association with an ongoing orpotential tropical cyclones, asubtropical cyclone or apost-tropical cyclone.The warning may be issued earlier when other conditions, such as the onset oftropical-storm-force winds are expected to limit the time available to take protective actions forsurge (e.g., evacuations). The warning may also be issued for locations not expected to receive life-threatening inundation but which could potentially be isolated by inundation in adjacent areas.

Storm Surge Watch:

The possibility of life-threatening inundation from rising water moving inland from the shoreline somewhere within the specified area,generally within 48 hours, in association with an ongoing orpotential tropical cyclones, asubtropical cyclone or apost-tropical cyclone.The watch may be issued earlier when other conditions, such as the onset oftropical-storm-force winds are expected to limit the time available to takeprotective actions forsurge (e.g., evacuations). The warning may also be issued for locations not expected to receivelife-threatening inundation but which could potentially be isolated by inundation in adjacent areas.

Storm Tide:

The actual level of sea water resulting from the astronomic tidecombined with thestorm surge.

Storm Warning:

A warning of 1-minute sustained surface winds of 48 kt (55 mph or88 km/hr) or greater, either predicted or occurring, not directlyassociated withtropical cyclones.

Strike:

For any particular location, ahurricanestrike occurs if that location passes within the hurricane's strikecircle, a circle of 125 n mi diameter, centered 12.5 n mi to the rightof the hurricanecenter (looking in thedirection of motion). This circle is meant to depict the typicalextent of hurricane force winds, which are approximately 75 n mi tothe right of the center and 50 n mi to the left.

Subtropical Cyclone:

A non-frontal low-pressure system that has characteristics of both tropical and extratropical cyclones. Like tropical cyclones, they are non-frontal, synoptic-scale cyclones that originate over tropical or subtropical waters, and have a closed surface wind circulation about a well-defined center. In addition, they have organized moderate to deep convection, but lack a central dense overcast. Unlike tropical cyclones, subtropical cyclones derive a significant proportion of their energy from baroclinic sources, and are generally cold-core in the upper troposphere, often being associated with an upper-level low or trough. In comparison totropical cyclones, these systems generally have a radius of maximum winds occurring relatively far from the center (usually greater than 60 n mi), and generally have a less symmetric wind field and distribution of convection.

Subtropical Depression:

Asubtropical cyclone in which the maximum sustained surface windspeed (using the U.S. 1-minute average) is 33 kt (38 mph or 62 km/hr)or less.

Subtropical Storm:

Asubtropical cyclone in which the maximum sustained surface windspeed (using the U.S. 1-minute average) is 34 kt (39 mph or 63 km/hr)or more.

Synoptic Track:

Weather reconnaissance mission flown to provide vitalmeteorological information in data sparse ocean areas as a supplementto existing surface, radar, and satellite data. Synoptic flightsbetter define the upper atmosphere and aid in the prediction oftropical cyclone development and movement.

Tropical Cyclone:

A warm-core non-frontal synoptic-scale cyclone, originating overtropical or subtropical waters, with organized deep convection and aclosed surface wind circulation about a well-definedcenter. Onceformed, a tropical cyclone is maintained by the extraction of heatenergy from the ocean at high temperature and heat export at the lowtemperatures of the upper troposphere. In this they differ fromextratropical cyclones, which derive their energy from horizontaltemperature contrasts in the atmosphere (barocliniceffects).

Tropical Cyclone Plan of the Day:

A coordinated mission plan that tasks operationalweather reconnaissance requirements during the next 1100 to 1100 UTC day or asrequired, describes reconnaissance flights committed to satisfy bothoperational and research requirements, and identifies possiblereconnaissance requirements for the succeeding 24-hourperiod.

Tropical Depression:

Atropical cyclone in which the maximum sustained surface windspeed (using the U.S. 1-minute average) is 33 kt (38 mph or 62 km/hr)or less.

Tropical Disturbance:

A discrete tropical weather system of apparently organizedconvection -- generally 100 to 300 nmi in diameter -- originating in thetropics or subtropics, having a nonfrontal migratory character, andmaintaining its identity for 24 hours or more. It may or may not beassociated with a detectable perturbation of the windfield.

Tropical Storm:

Atropical cyclone in which the maximum sustained surface wind speed (using the U.S. 1-minute average) ranges from 34 kt (39 mph or 63 km/hr) to 63 kt (73 mph or 118 km/hr).

Tropical Storm Warning:

An announcement that sustained winds of 34 to 63 knots (39 to 73 mph or 63 to 118 km/hr) areexpected somewhere within the specified area within 36 hours in association with atropical,subtropical, orpost-tropical cyclone.

Tropical Storm Watch:

An announcement that sustained winds of 34 to 63 knots (39 to 73 mph or 63 to 118 km/hr) arepossible within the specified area within 48 hours in association with atropical,subtropical, orpost-tropical cyclone.

Tropical Wave:

A trough or cyclonic curvature maximum in the trade-windeasterlies. The wave may reach maximum amplitude in the lower middletroposphere.

US Dept of Commerce
National Oceanic and Atmospheric Administration
National Hurricane Center
11691 SW 17th Street
Miami, FL, 33165
nhcwebmaster@noaa.gov

Central Pacific Hurricane Center
2525 Correa Rd
Suite 250
Honolulu, HI 96822
W-HFO.webmaster@noaa.gov

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