| Advisory |
Official information issued by tropical cyclone warning centers describing all tropical cyclone watches and warnings in effect along with details concerning tropical cyclone locations, intensity and movement, and precautions that should be taken. Advisories are also issued to describe: (a) tropical cyclones prior to issuance of watches and warnings and (b) subtropical cyclones. |
| Best Track |
A subjectively smoothed path, versus a precise and very erratic fix-to-fix path, used to represent tropical cyclone movement. It is based on an assessment of all available data. |
| Center |
The vertical axis or core of a tropical cyclone. It is usually determined by cloud vorticity patterns, wind, and/or pressure distributions. |
| Center/Vortex Fix |
The location of the center of a tropical or subtropical cyclone obtained by reconnaissance aircraft penetration, satellite, radar, or synoptic data. |
| Central North Pacific Basin |
The region north of the equator between 140° west and the international date line. The Central Pacific Hurricane Center (CPHC) in Honolulu, Hawaii, is responsible for tracking tropical cyclones in this region. |
| Cyclone |
An atmospheric closed circulation rotating counter-clockwise in the northern hemisphere and clockwise in the southern hemisphere. |
| Eastern North Pacific Basin |
The region north of the equator east of 140W. The National Hurricane Center in Miami, Florida is responsible for tracking tropical cyclones in this region. |
| Eye |
The relatively calm center of the tropical cyclone that is more than one half surrounded by wall cloud. |
| Eye Wall/Wall Cloud |
An organized band of cumuliform clouds immediately surrounding the center of a tropical cyclone. Eye wall and wall cloud are used synonymously. |
| Explosive Deepening |
A decrease in the minimum sea-level pressure of a tropical cyclone of 2.5 mb/hr for at least 12 hours or 5 mb/hr for at least 6 hours. |
| Extratropical |
A term used in advisories and tropical summaries to indicate that a cyclone has lost its 'tropical' characteristics. The term implies both poleward displacement of the cyclone and the conversion of the cyclone's primary energy source from the release of latent heat of condensation to baroclinic (the temperature contrast between warm and cold air masses) processes. It is important to note that cyclones can become extratropical and still retain winds of hurricane or tropical storm force. |
| Fujiwhara Effect |
A binary interaction where tropical cyclones within a certain distance of each other begin to rotate about a common midpoint. |
| Gale Warning |
A warning of 1-minute sustained surface winds in the range 34 knot (63 km/h or 39 mph) to 47 knot (87 km/h or 54 mph) inclusive, either predicted or occurring not directly associated with tropical cyclones. |
| High Wind Warning |
A high wind warning is defined as 1-minute average surface winds of 35 knot (64 km/h or 40 mph) or greater lasting for 1 hour or longer, or winds gusting to 50 knot (93 km/h or 58 mph) or greater regardless of duration that are either expected or observed over land. |
| Hurricane/Typhoon |
A warm-core tropical cyclone in which the maximum sustained surface wind (using the U.S. 1-minute average) is 64 knot (119 km/h or 74 mph) or more. The term hurricane is used for northern hemisphere cyclones east of the international dateline to the Greenwich meridian. The term typhoon is used for Pacific cyclones north of the equator west of the international dateline. |
| Hurricane Local Statement |
A public release prepared by local National Weather Service offices in or near a threatened area giving specific details for its county/parish warning area on (1) weather conditions, (2) evacuation decisions made by local officials, and (3) other precautions necessary to protect life and property. |
| Hurricane Season |
The portion of the year having a relatively high incidence of hurricanes. The hurricane season in the Atlantic, Caribbean, and Gulf of Mexico runs from June 1 to November 30. The hurricane season in the eastern Pacific basin runs from May 15 to November 30. The hurricane season in the central Pacific basin runs from June 1 to November 30. |
| Hurricane Warning |
A warning that sustained winds 64 knot (119 km/h or 74 mph) or higher associated with a hurricane are expected in a specified coastal area in 24 hours or less. A hurricane warning can remain in effect when dangerously high water or a combination of dangerously high water and exceptionally high waves continue, even though winds may be less than hurricane force. |
| Hurricane Watch |
An announcement of specific coastal areas that a hurricane or an incipient hurricane condition poses a possible threat, generally within 36 hours. |
| Post-storm Report |
A report issued by a local National Weather Service office summarizing the impact of a tropical cyclone on it's forecast area. These reports include information on observed winds, pressures, storm surges, rainfall, tornadoes, damage and casualties. |
| Preliminary Report |
A report summarizing the life history and effects of an Atlantic or eastern Pacific tropical cyclone. It contains a summary of the cyclone life cycle and pertinent meteorological data, including the post-analysis best track (six-hourly positions and intensities) and other meteorological statistics. It also contains a description of damage and casualties the system produced, as well as information on forecasts and warnings associated with the cyclone. NHC writes a preliminary report on every tropical cyclone in its area of responsibility. |
| Present Movement |
The best estimate of the movement of the center of a tropical cyclone at a given time and given position. This estimate does not reflect the short-period, small scale oscillations of the cyclone center. |
| Probability of Tropical Cyclone Conditions |
The probability, in percent, that the cyclone center will pass within 80 km (50 mi) to the right or 120 km (75 mi) to the left of the listed location within the indicated time period when looking at the coast in the direction of the cyclone's movement. |
| Rapid Deepening |
A decrease in the minimum sea-level pressure of a tropical cyclone of 1.75 mb/hr or 42 mb for 24 hours. |
| Relocated |
A term used in an advisory to indicate that a vector drawn from the preceding advisory position to the latest know position is not necessarily a reasonable representation of the cyclone's movement. |
| Storm Surge |
An abnormal rise in sea level accompanying a hurricane or other intense storm, and whose height is the difference between the observed level of the sea surface and the level that would have occurred in the absence of the cyclone. Storm surge is usually estimated by subtracting the normal or astronomic high tide from the observed storm tide. |
| Storm Tide |
The actual level of sea water resulting from the astronomic tide combined with the storm surge. |
| Storm Warning |
A warning of 1-minute sustained surface winds of 48 knot (88 km/h or 55 mph) or greater, either predicted or occurring, not directly associated with tropical cyclones. |
| Subtropical Cyclone |
A low pressure system that develops over subtropical waters that initially has a non-tropical circulation but in which some elements of tropical cyclone cloud structure are present. Subtropical cyclones can evolve into tropical cyclones. Subtropical cyclones are generally of two types: |
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(1) An upper level cold low with circulation extending to the surface and maximum sustained winds generally occurring at a radius of about 160 km (100 mi) or more from the pressure center. |
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(2) A mesoscale cyclone originating in or near a frontolyzing zone of horizontal wind shear, with radius of maximum sustained winds generally less than 50 km (30 mi). The entire circulation sometimes encompasses an area initially no more than 160 km (100 mi) in diameter. These generally short-lived, marine cyclones may vary in structure from cold to warm core. |
| Subtropical Depression |
A subtropical cyclone in which the maximum sustained surface wind speed (using the U.S. 1-minute average) is 33 knot (62 km/h or 38 mph) or less. |
| Subtropical Storm |
A subtropical cyclone in which the maximum sustained surface wind speed (using the U.S. 1-minute average) is 34 knot (63 km/h or 39 mph) or more. |
| Synoptic Track |
Weather reconnaissance mission flown to provide vital meteorological information in data sparse ocean areas as a supplement to existing surface, radar, and satellite data. Synoptic flights better define the upper atmosphere and aid in the prediction of tropical cyclone development and movement. |
| Tropical Cyclone |
A warm-core, nonfrontal low pressure system of synoptic scale that develops over tropical or subtropical waters and has a definite organized surface circulation. |
| Tropical Depression |
A tropical cyclone in which the maximum sustained surface wind speed (using the U.S. 1-minute average) is 33 knot (62 km/h or 38 mph) or less. |
| Tropical Disturbance |
A discrete tropical weather system of apparently organized convection originating in the tropics or subtropics, having a nonfrontal migratory character, and maintaining its identity for 24 hours or more. It may or may not be associated with a detectable perturbation of the wind field. |
| Tropical Storm |
A tropical cyclone in which the maximum sustained surface wind speed (using the U.S. 1-minute average) ranges from 34 knot (63 km/h or 39 mph) to 63 knot (118 km/h or 73 mph). |
| Tropical Storm Warning |
A warning for tropical storm conditions including sustained winds within the range of 34 to 63 knot (63 to 118 km/h or 39 to 73 mph) that are expected in a specified coastal area within 24 hours or less. |
| Tropical Storm Watch |
An announcement that a tropical storm poses or tropical storm conditions pose a threat to coastal areas generally within 36 hours. A tropical storm watch should normally not be issued if the system is forecast to attain hurricane strength. |
| Tropical Wave |
A trough or cyclonic curvature maximum in the trade-wind easterlies. The wave may reach maximum amplitude in the lower middle troposphere. |
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