Advisory: Official information provided by tropical cyclone warning centers describing all relevant watches, warnings, and details concerning storm locations, intensity, tracking movement, and precautionary measures to take. Advisories are issued also detailing tropical cyclones as well as Sub-tropical cyclones.
Storm Warning: A warning of 1-minute sustained surface winds of 48 knots (55 mph or 88 km/hr) or greater, either predicted or occurring, not directly associated with a 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) are possible within the specified area within 48 hours in association with tropic, sub-tropical, or post-tropical cyclone.
Tropical Storm Warning: An announcement that sustained winds of 34 to 63 knots (39 to 73 mph or 63 to 118 km/hr) are expected somewhere within the specified area within 36 hours in association with a tropical, sub-tropical, or post-tropical cyclone
Tropical Storm: A tropical cyclone in which the maximum sustained surface wind speed (using the U.S. 1-minute average) ranges from 34 knots (39 mph or 63 km/hr) to 63 knots (73 mph or 118 km/hr).
Hurricane Watch: An announcement that sustained winds of 64 knots (74 mph or 119 km/hr) or higher are possible within the specified area in association with a tropical, subtropical, or post-tropical cyclone. Because hurricane preparedness activities become difficult once winds reach tropical storm force, the hurricane watch is issued 48 hours in advance of the anticipated onset of tropical storm force winds.
Hurricane Warning: An announcement that sustained winds of 64 knots (74 mph or 119 km/hr) or higher are expected somewhere within the specified area in association with a tropical, subtropical, or post-tropical cyclone. Because hurricane preparedness activities become difficult once winds reach tropical 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 than hurricane force.
Hurricane/ Typhoon: A tropical cyclone in which the maximum sustained surface wind (using the U.S. 1-minute average) is 64 knots (74 mph or 119 km/hr) or more. The term hurricane is used for Northern Hemisphere tropical cyclones east of the International Dateline to the Greenwich Meridian. The term typhoon is used for Pacific tropical cyclones north of the Equatorand West of the International Dateline.
Algorithm– A computer program (or set of programs) which is designed to systematically solve a certain kind of problem. Ex. WSR-88D radars (NEXRAD) employ algorithms to analyze radar data and automatically determine storm motion, probability of hail, accumulated rainfall, and several other parameters.
Best Track- A subjectively-smoothed representation of a tropical cyclone’s location and intensity over its lifetime. The best track contains the cyclone’s latitude, longitude, maximum sustained surface winds, and minimum sea-level pressure at 6-hourly intervals. Best track positions and intensities, which are based on a post-storm assessment of all available data, may differ from values contained in storm advisories. They also generally will not reflect the erratic motion implied by connecting individual center fix positions.
Center- Generally speaking, the vertical axis of a tropical cyclone, usually defined by the location of minimum wind or minimum pressure. The cyclone center position can vary with altitude. In advisory products, refers to the center position at the surface.
Cyclone- An atmospheric closed circulation rotating counter-clockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.
Direct Hit- A close approach of a tropical 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 the cyclone passes to within a distance equal to the cyclone’s radius of maximum wind. For locations on the right-hand side of the track, a direct hit occurs when the cyclone passes to within a distance equal to twice the radius of maximum wind.
Doppler Radar- Radar that measures radial velocity.
Emergency- A serious, unexpected, and often dangerous situation requiring immediate action.
Evacuate- Remove someone from a place of danger to a safer place.
Eye- The roughly circular area of comparatively light winds that encompasses the center of a severe tropical cyclone. The eye is either completely or partially surrounded by the eyewall cloud.
Eyewall- An organized band or ring of cumulonimbus clouds that surround the eye, or light-wind center of a tropical cyclone. Eyewall and wall cloud are used synonymously.
Feeder Bands- Bands of low-level clouds that “feed” (move) into the updraft region of a thunderstorm.
Gale Warning- A warning of 1-minute sustained surface winds in the range 34 knots (39 mph or 63 km/hr) to 47 knots (54 mph or 87 km/hr) inclusive, either predicted or occurring and not directly associated with tropical cyclones.
Hail- Pellets of frozen rain, which fall in showers from cumulonimbus clouds.
Jet Stream- Relatively strong winds concentrated in a narrow stream in the atmosphere, normally referring to horizontal, high-altitude winds. The position and orientation of jet streams vary from day to day. General weather patterns (hot/cold, wet/dry) are related closely to the position, strength and orientation of the jet stream (or jet streams).
High Wind Warning- A high wind warning is defined as 1-minute average surface winds of 35 knots (40 mph or 64 km/hr) or greater lasting for 1 hour or longer, or winds gusting to 50 knots (58 mph or 93 km/hr) or greater regardless of duration that are either expected or observed over land.
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.
Indirect Hit- Generally refers to locations that do not experience a direct hit from a tropical cyclone, but do experience hurricane force winds (either sustained or gusts) or tides of at least 4 feet above normal.
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 surface center of a tropical cyclone with a coastline. Because the strongest winds in a tropical cyclone are not located precisely at the center, it is possible for a cyclone’s strongest winds to be experienced over land even if landfall does not occur. Similarly, it is possible for a tropical cyclone to make landfall and have its strongest winds remain over the water.
Lightning- The occurrence of a natural electrical discharge of very short duration and high voltage between a cloud and the ground or within a cloud, accompanied by a bright flash and typically also thunder.
Major Hurricane- A hurricane that is classified at a 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.
NHC- National Hurricane Center
NOAA- National Oceanic & Atmospheric Administration
NSSFC- National Severe Storm Forecast Center
NWS- National Weather Service
Post Storm Report- A report issued by a local National Weather Service office summarizing the impact of a tropical cyclone on its forecast area. These reports include information on observed winds, pressures, storm surges, rainfall, tornadoes, damage and casualties.
Preliminary Report- Now known as the “Tropical Cyclone 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 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.
Radius of Maximum Winds- The distance from the center of a tropical cyclone to the location of the cyclone’s maximum winds. In well-developed hurricanes, the radius of maximum winds is generally found at the inner edge of the eyewall.
Rapid Intensification- An increase in the maximum sustained winds of a tropical cyclone of at least 30 knots in a 24-h period.
Radial Velocity- Instantaneous component of motion paralleled to the radar beam (antennae essentially)
Relocated- A term used in an advisory to indicate that a vector drawn from the preceding advisory position to the latest known position is not necessarily a reasonable representation of the cyclone’s movement.
Saffir-Simpson Hurricane 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.
Shear- Variation in wind speed and/or direction over a short distance. Shear usually refers to vertical wind shear, i.e., the change in wind with height, but the term also is used in Doppler radar to describe changes in radial velocity over short horizontal distances.
Spaghetti Model- Diagram designed to show what direction storm systems MAY go depending on certain relevant factors (pressure, wind, etc). When clustered together confidence grows on location to be hit.
Squall Line- A solid or nearly solid line or band of active thunderstorms.
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 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, or potential tropical cyclones, a subtropical cyclone or a post-tropical cyclone. The watch may be issued earlier when other conditions, such as the onset of tropical-storm-force winds are expected to limit the time available to take protective actions for surge (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 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 or potential tropical cyclones, a subtropical cyclone or a post-tropical cyclone. The warning may be issued earlier when other conditions, such as the onset of tropical-storm-force winds are expected to limit the time available to take protective actions for surge (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 Tide- The actual level of sea water resulting from the astronomic tide combined with the storm surge.
Strike- For any particular location, a hurricane strike occurs if that location passes within the hurricane’s strike circle, a circle of 125 n mi diameter, centered 12.5 n mi to the right of the hurricane center (looking in the direction of motion). This circle is meant to depict the typical extent of hurricane force winds, which are approximately 75 n mi to the 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 to tropical 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- A subtropical cyclone in which the maximum sustained surface wind speed (using the U.S. 1-minute average) is 33 knots (38 mph or 62 km/hr) or less.
Subtropical Storm- A subtropical cyclone in which the maximum sustained surface wind speed (using the U.S. 1-minute average) is 33 knots (38 mph or 62 km/hr) or less.
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.
Trajectory- The path followed by a projectile flying or an object moving under the action of given forces. (aka path of storm).
Tropical Depression- A tropical cyclone in which the maximum sustained surface wind speed (using the U.S. 1-minute average) is 33 knots (38 mph or 62 km/hr) or less.
Tropical Disturbance- A discrete tropical weather system of apparently organized convection — generally 100 to 300 nmi in diameter — originating in the tropics or subtropics, having a non-frontal 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 Wave- A trough or cyclonic curvature maximum in the trade-wind easterlies. The wave may reach maximum amplitude in the lower middle troposphere.
Warning- A product issued by NWS local offices indicating that a particular weather hazard is either imminent or has been reported. A warning indicates the need to take action to protect life and property. The type of hazard is reflected in the type of warning (e.g., tornado warning, blizzard warning).
Watch- An NWS product indicating that a particular hazard is possible, i.e., that conditions are more favorable than usual for its occurrence. A watch is a recommendation for planning, preparation, and increased awareness
Waterspout- In general, a tornado occurring over water. Specifically, it normally refers to a small, relatively weak rotating column of air over water beneath a CB or towering cumulus cloud. Waterspouts are most common over tropical or subtropical waters
Sources: NHC, NOAA, & NWS