An area inundated by the one percent annual chance (one in 100-year) flood. Source: Tennessee Valley Authority.
The movement (typically horizontal) of air (or water) that causes changes in the physical properties of the air (or water) such as temperature and moisture. Commonly used with temperatures. Source: NOAA-NWS SRH.
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. Source NOAA-NHC.
A particle of matter, solid or liquid, larger than a molecule but small enough to remain suspended in the atmosphere (up to 100 pico-m diameter). Natural origins include salt particles from sea spray and clay particles as a result of weathering of rocks. Aerosols can also originate as a result of the activity of man and in this case are often considered pollutants. Source: NOAA-NWS ERH.
An imaginary small body of air that is used to explain the behavior of air. A parcel is large enough to contain a very great number of molecules, but small enough so that the properties assigned to it are approximately uniform throughout. Source: NOAA-NWS ERH.
Airborne eXpendable BathyThermographs (AXBTs)
An expendable instrument that is dropped from an aircraft and used to measure the profile of temperature in the water column. The probe consists of a thermistor in a weighted, streamlined case. It falls freely at a fixed, known rate so that the elapsed time can be converted to depth. It is connected by a thin, freely unwinding wire to a small buoy with a radio transmitter through which the data are transmitted to the aircraft, which continues its flight. (c) 1999, American Meteorological Society. Used with permission.
Height expressed as the distance above a reference point, which is normally sea level or ground level.Source: NOAA-NWS ERH.
An instrument that measures wind speed. Source: NOAA-NWS ERH.
A pollutant source caused or produced by humans. Source: NOAA-NWS.
Rotation that is clockwise in the Northern Hemisphere and counter-clockwise in the Southern Hemisphere. It is the opposite of cyclonic. Source: Canadian Hurricane Centre.
The region within the Arctic Circle, or, loosely, northern regions in general, characterized by very low temperatures. Source: NOAA-NWS.
area of low pressure
A region where the atmospheric pressure is lower in relation to the surrounding area. Since air always moves from areas of high pressure to areas of low pressure, air from these adjacent areas of higher pressure will move toward the low-pressure area to equalize the pressure. This inflow of air toward the low will be affected by the rotation of the Earth (see Coriolis force) and will cause the air to spiral inward in a counterclockwise direction in the northern hemisphere (clockwise direction in the Southern Hemisphere). An area of low pressure is marked as L on a weather map and is usually accompanied by precipitation, extensive cloudiness, and moderate winds.
The s-shaped basin in which the Atlantic Ocean occupies, extending longitudinally between the Americas to the west, and Eurasia and Africa to the east. It is connected in the north to the Arctic Ocean, to the Pacific Ocean in the southwest (Panama Canal), the Indian Ocean in the southeast, and the Southern Ocean in the south. The equator subdivides the basin into the North Atlantic Ocean and South Atlantic Ocean.
Atlantic Multidecadal Oscillation (AMO)
A natural oscillation of the North Atlantic sea surface temperature (SST) between warm and cool phases. The SST difference between these warm and cool phases is about 0.5°C and the period of the oscillation is roughly 20-40 years (the period is variable, but is a few decades long).
The second-largest of the world's oceanic divisions. With a total area of about 106.4 million square kilometres (41.1 million square miles), it covers approximately one-fifth of the Earth's surface and about one-quarter of its water surface area. The first part of its name refers to the Atlas of Greek mythology, making the Atlantic the "Sea of Atlas". The oldest known mention of this name is contained in The Histories of Herodotus around 450 BCE (I 202); see also: Atlas Mountains. Another name historically used was the ancient term Ethiopic Ocean, derived from Ethiopia, whose name was sometimes used as a synonym for all of Africa and thus for the ocean. Before Europeans discovered other oceans, the term "ocean" itself was to them synonymous with the waters beyond Western Europe that we now know as the Atlantic and which the Greeks had believed to be a gigantic river encircling the world; see Oceanus. The Atlantic Ocean occupies an elongated, S-shaped basin extending longitudinally between the Americas to the west, and Eurasia and Africa to the east. A component of the all-encompassing World Ocean, it is connected in the north to the Arctic Ocean (which is sometimes considered a sea of the Atlantic), to the Pacific Ocean in the southwest, the Indian Ocean in the southeast, and the Southern Ocean in the south. (Alternatively, in lieu of it connecting to the Southern Ocean, the Atlantic may be reckoned to extend southward to Antarctica.) The equator subdivides it into the North Atlantic Ocean and South Atlantic Ocean.
The mass of air surrounding the Earth that acts as a buffer between the Earth and the sun. It is mainly composed of nitrogen and oxygen with traces of carbon dioxide, water vapor, and other gases. The atmosphere is described as a series of distinct layers: troposphere (lowest), stratosphere, mesosphere, thermosphere, and exosphere (highest).
The study of those motions of the atmosphere that are associated with weather and climate. In atmospheric dynamics, the fluid is regarded as a continuous medium, and the fundamental laws of fluid mechanics and thermodynamics are expressed in terms of partial differential equations involving the fluid velocity, density, pressure, and temperature. Source: (c) 1999, American Meteorological Society. Used with permission.
(also called air pressure or barometric pressure) Generally, the pressure asserted by the mass of the column of air directly above any specific point. Source: NOAA-NWS ERH.
The variation with depth of motions associated with variation of density with depth. The baroclinic component of the velocity is the total minus the barotropic component. In a baroclinic state, neutral surfaces are inclined to surfaces of constant pressure. The baroclinic torque vector is proportional to the vector cross product and is responsible for generating vertical shears associated with baroclinic flow. Source: (c) 1999, American Meteorological Society. Used with permission.
An instrument for measuring atmospheric pressure. Source: NOAA-NWS ERH.
The actual pressure value indicated by a pressure sensor. Source: NOAA-NWS SRH. (Also see atmospheric pressure.)
A computer model that treats the atmosphere (or any fluid) as being barotropic. In a barotropic atmosphere, temperature and pressure surfaces are coincident, i.e., temperature is uniform (no temperature gradient) on a constant pressure surface. Barotropic systems are characterized by a lack of wind shear. Source: NOAA-NWS ERH.
An elongate accumulation of sand that is separated from the mainland by open water in the form of estuaries, bays, or lagoons. These primarily sandy islands are now in great demand for both residential and recreational development. Beaches on the seaward side of barrier islands are the principal location for beach nourishment. Source: NOAA-CSC.
The water depth relative to sea level. Depth values may be either negative or positive, but should all be understood to be negative. Depths are almost always derived indirectly by measuring the time required for a signal to travel from a transmitter, to the bottom, and back to a receiver. This travel time is then converted to a depth based on a variety of estimations of the signal speed through the water column. Signal speed varies with salinity and temperature. Source: USGS.
A scale that indicates the wind speed using the effect wind has on certain familiar objects. Source: NOAA-NWS ERH.
Bermuda high (Azores high)
A semi-permanent, subtropical area of high pressure in the North Atlantic Ocean off the East Coast of North America that migrates east and west with varying central pressure. Depending on the season, it has different names. When it is displaced westward, during the Northern Hemispheric summer and fall, the center is located in the western North Atlantic, near Bermuda. In the winter and early spring, it is primarily centered near the Azores in the eastern part of the North Atlantic, during which time it may be referred to as the Azores High. Source: NOAA-NWS SRH.
A subjectively-smoothed representation of the location of a tropical cyclone and intensity over its lifetime. The best track contains the latitude, longitude, maximum sustained surface winds, and minimum sea-level pressure of the cyclone at 6-hour 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. Source NOAA-NHC.
The drift of a tropical cyclone through the large-scale background wind in which it is embedded. The drift is caused by the advection of the background potential vorticity field by the storm circulation. Beta drift generally causes tropical cyclones to move poleward and westward relative to the motion they would have if the background potential vorticity field were unperturbed by the storms. This drift speed is generally around 1–2 m/s. Source: (c) 1999, American Meteorological Society. Used with permission.
The mass of living biological organisms in a given area or ecosystem at a given time. Biomass can refer to species biomass, which is the mass of one or more species, or to community biomass, which is the mass of all species in the community.
Pertaining to waters with a salt concentration between that of pure ocean water and freshwater (ie, bay water). Source: NOAA.
Standards and guidelines for construction of buildings to ensure a minimum level of safety for the occupants. Source: Canadian Hurricane Centre.
Canadian Hurricane Centre
The Canadian Hurricane Centre (CHC) provides Canadians with meteorological information on hurricanes, tropical storms, and post-tropical storms to help them make informed decisions to protect their safety and secure their property. Source: CHC.
Cape Verde-type hurricane
An Atlantic basin tropical cyclone that develops into a tropical storm fairly close to (<1000 km [600 mi] or so) the Cape Verde Islands and then becomes a hurricane before reaching the Caribbean. Typically, they may occur in August and September, but in rare years (like 1995), there may be some in late July and/or early October. The quantities range from none up to around five per year - with an average of around two. Source: NOAA-HRD.
A sea of the Atlantic Ocean situated in the tropics. It is bordered by the coasts of (clockwise from the south) the South American countries of Venezuela and Colombia on the south; the Central American countries of Panama on the southwest, and Costa Rica, Nicaragua, Honduras, Guatemala, Belize, and Mexico on the west; the Greater Antilles (Cuba, Jamaica, Hispaniola, and Puerto Rico) on the north, and the Lesser Antilles on the east. The entire area of the Caribbean Sea, the numerous islands of the West Indies, and adjacent coasts, are collectively known as the Caribbean.
center of a tropical cyclone
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. Source NOAA-NHC.
central north Pacific basin
The region north of the Equator between 140W and the International Dateline. The Central Pacific Hurricane Center (CPHC) in Honolulu, Hawaii is responsible for tracking tropical cyclones in this region. Source NOAA-NHC.
At any given instant, the atmospheric pressure at the center of a tropical storm (or the center of any high pressure or low pressure system).
The apparent force in a rotating system, deflecting masses radially outward from the axis of rotation.
The prevalent long term weather conditions in a particular area. Climatic elements include precipitation, temperature, humidity, sunshine, wind velocity, and phenomena such as fog, frost, and hail storms. Climate cannot be considered a satisfactory indicator of actual conditions since it is based upon a vast number of elements taken as an average. Source: NOAA-NWS ERH.
Refers to all forms of climatic inconsistency. but is often used in a more restricted sense to imply a significant change. Within the media, climate change has been used synonymously with global warming. Scientists, however, use the term in a wider sense to include past climate changes also. Source: NOAA-NWS ERH.
The long-term average of one or more weather elements or ocean properties, such as temperature.
A thermodynamic system in which no heat or mass is transported across its boundaries. Source: (c) 1999, American Meteorological Society. Used with permission.
A visible cluster of tiny water droplets and/or ice crystals in the atmosphere. Source: NOAA-NWS ERH.
Small particles of liquid water, approximately 4-100 micrometers in diameter, formed by the condensation of atmospheric water vapor. These small particles remain suspended in the air.
cold core low
At a given level in the atmosphere, any low that is generally characterized by colder air near its center than around its periphery; the opposite of a warm core low. The cyclonic intensity of a cold core low increases with height.
An intense tropical cyclone will often have two eyewalls nearly concentric about the center of the storm, with the outer eyewall surrounding the inner one. A local wind maximum is generally present in each eyewall. Sometimes, more than two eyewalls occur. Source: (c) 1999, American Meteorological Society. Used with permission.
The process by which water vapor becomes a liquid; the opposite of evaporation, which is the conversion of liquid to vapor. Source: NOAA-NWS ERH.
The zone bordering a continent and extending to a depth, usually around 100 fathoms (183 m, 600 ft), from which there is a steep descent toward greater depth. Source: NOAA-NWS SRH.
The vertical transport of heat and moisture, especially by updrafts and downdrafts in an unstable atmosphere. Source: NOAA-NWS ERH.
An atmospheric condition that exists when the winds cause a horizontal net inflow of air into a specified region. Divergence is the opposite, where winds cause a horizontal net outflow of air from a specified region. Source: NOAA-NWS ERH.
Apparent effect of the earth’s rotation to deflect the direction of any object - including the wind - to the right in the northern hemisphere and to the left in the southern hemisphere. The Coriolis Force is responsible for giving a cyclone its spin, and without it, tropical cyclones would not form. Source: Canadian Hurricane Centre.
Crypsis is the ability of an organism to avoid observation or detection by other organisms.
A general term for a vertically-developed cloud (such as cumulus, cumulus congestus, and cumulonimbus). The most well-developed of the cumuliform clouds is the cumulonimbus, which is often capped by an anvil shaped cloud. Also called a thunderstorm cloud, cumulonimbus clouds are frequently accompanied by heavy showers, lightning, thunder, and sometimes hail, gusty winds, and/or tornadoes. Source: NOAA-NWS ERH.
An atmospheric closed circulation rotating counter-clockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. Source NOAA-NHC.
Rotation that is counter-clockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. It is the opposite of anticyclonic. Source: Canadian Hurricane Centre.
The combining of diverse data, possibly sampled at different times and intervals and different locations, into a unified and consistent description of a physical system, such as the state of the atmosphere. One or more data assimilation techniques are often used during the initialization of an atmosphere or ocean forecast model. Source: (c) 1999, American Meteorological Society. Used with permission.
A clause in an insurance policy that relieves the insurer of responsibility to pay the initial loss up to a stated amount.
The removal of leaves off a tree.
Digital Flood Insurance Rate Maps (DFIRM)
The Digital Flood Insurance Rate Map (DFIRM) is comprised of all digital data required to create the hardcopy FIRM. This includes base map information, graphics, text, shading, and other geographic and graphic data required to create the final hardcopy FIRM product to FEMA standards and specifications. These data serve the purpose of map design and provides the database from which the Digital Line Graph thematic product of the flood risks can be extracted to create the DFIRM-DLG. These products are generally produced in a countywide format. DFIRMs are subjected to community review and approval and are, therefore, the official basis for implementing the regulations and requirements of the NFIP within the community. Source: ABAG.ca.gov
A close approach of a tropical cyclone to a particular location. For locations on the left-hand side of a track of a tropical cyclone (looking in the direction of motion), a direct hit occurs when the cyclone passes to within a distance equal to the radius of maximum wind of a cyclone. 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. Compare indirect hit, strike. Source NOAA-NHC.
A type of weather radar that determines whether atmospheric motion is toward or away from the radar. Doppler radar determines the intensity of rainfall and uses the Doppler effect to measure the velocity of droplets in the atmosphere. Source: NOAA-NWS ERH.
The change in observed frequency of wave energy due to the relative motion of the observer and wave source. For example, as a train approaches your location, you hear a higher pitch sound. After the train has passed your location, you will hear a lower pitch sound. The Doppler radar uses this change in frequency to determine the velocity and direction of the wind. Source: NOAA-NWS SRH.
A column of generally cool air that rapidly sinks to the ground, usually accompanied by precipitation as in a shower or thunderstorm. Source: NOAA-NWS ERH.
(Also called parachute radiosonde.) A radiosonde with a parachute dropped from an airplane carrying receiving equipment for the purpose of obtaining an upper-air sounding during descent. Source: (c) 1999, American Meteorological Society. Used with permission.
dynamical model of the atmosphere
Also known as a numerical weather prediction model, it is a computer program that uses a supercomputer to solve the mathematical equations governing the physics and motion of the atmosphere.
A migratory wavelike disturbance in the tropical region (over the North Atlantic and Caribbean/ general easterly trade wind circulation) that develops off the sub-Saharan, East African coast at rate of one every three days. It is a wave within the broad easterly current and moves from east to west, causing areas of cloudiness and thunderstorms. Although best described in terms of its wavelike characteristics in the wind field, it also consists of a weak trough of low pressure. The presence of a disturbance like this indicates atmospheric instability and is often associated with tropical cyclone development.
eastern north Pacific basin
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. Source NOAA-NHC.
eddies in the ocean
A closed warm or cold core circulation system in the ocean, produced as an offshoot from an ocean current.
A warming of the ocean current along the coasts of Peru and Ecuador that is generally associated with dramatic changes in the weather patterns of the region; a major El Niño event generally occurs every 3 to 7 years and is associated with changes in the weather patterns worldwide. Source: NOAA NWS.
El Nino-Southern Oscillation (ENSO)
ENSO is the term used to define the oceanic El Nino/ La Nina cycle and the associated atmospheric Southern Oscillation.
A species whose continued existence is in jeopardy and is provided special protection by law. Source: USGS
The average of a predicted variable or field over an ensemble of forecasts. Source: (c) 1999, American Meteorological Society. Used with permission.
A plant, fungus, or microbe sustained entirely by nutrients and water received nonparasitically from within the canopy in which it resides.
Geographically, on the surface of the earth, the imaginary great circle of latitude 0 degrees, which is equidistant from the poles, and which separates the Northern Hemisphere from the Southern Hemisphere.
The process in which a material is worn away by a stream of liquid (water) or air, often due to the presence of abrasive particles in the stream. Source: USGS.
The area where the salty ocean meets a freshwater stream/river. Source: US NPS.
Any area required to evacuate during a storm event.
The process of a liquid changing into a vapor or gas. Source: NOAA-NWS ERH.
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 six hours. Source NOAA-NHC.
The influence on the Earth system (or one of its components) by an external agent such as solar radiation, volcanic eruptions, or the impact of extraterrestrial bodies such as meteorites.
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. Extratropical cyclones have cold air at their core, and derive their energy from the release of potential energy when cold and warm air masses interact. It is important to note that systems can become extratropical and still retain winds of hurricane or tropical storm force. Extratropical cyclones are also referred to as mid-latitude cyclones or wave cyclones. Source NOAA-NHC.
Extratropical Transition (ET)
The transformation of a tropical cyclone into an extratropical cyclone. More than 40% of Atlantic tropical cyclones undergo such a transformation at the end of their tropical existence. The metamorphosis typically starts as the system begins to be driven by atmospheric temperature differences rather than latent heat release. The cyclone begins losing its tropical characteristics and often develops front-like qualities. During the transformation, the rain area usually shifts to the left of the storm track while the strongest winds diminish but become elongated to the right of the storm track. Some extratropical transition events can result in a more powerful storm than the originating tropical cyclone. Source: Canadian Hurricane Centre.
The relatively calm center in a hurricane that is at least halfway surrounded by clouds comprising the eyewall. The winds are light, the skies are partly cloudy or even clear (the skies are usually free of rain), and radar depicts it as an echo-free area within the eyewall. The hurricane eye typically forms when the maximum sustained tangential wind speeds exceeds about 125 km/h (78 mph) The eye diameter, as depicted by radar, ranges typically from as small as 8 to 16 km (5 to 10 mi) upwards to about 160 km (100 mi). The average hurricane eye diameter is a little over 32 km (20 mi). When the eye is shrinking in size, the hurricane is generally intensifying. Source: NOAA Jetstream.
An organized ring or band of cumulonimbus clouds that surround the eye of a tropical cyclone. This roughly circular ring of deep convection is the area of heaviest rain, strongest surface winds, and generally the most severe turbulence in the tropical cyclone. Source NOAA-NHC.
All the animal life in a particular region.
Federal Alliance for Safe Homes (FLASH)
Is a non-profit organization dedicated to promoting disaster safety and property loss mitigation. Source: FLASH.org
Federal Emergency Management Agency: An agency of the federal government having responsibilities in hazard mitigation; FEMA also administers the National Flood Insurance Program. Source: NOAA-NWS SRH
the distance the wind has blown over the sea.
Refers to large numbers of fish being killed, usually because there is not enough oxygen in the water or because of a chemical spill. Source: US EPA
A flood which follows within a few hours (usually less than 6 hours) of heavy or excessive rainfall, dam or levee failure, or the sudden release of water impounded by an ice jam. This is a dangerous situation that threatens lives and property. Source: NOAA-NWS SRH
Flood Insurance Rate Maps (FIRMs)
The official map of a community on which FEMA has delineated both the special hazard areas and the risk premium zones applicable to the community. Source: FEMA
Florida Coastal Monitoring Program (FCMP)
A joint venture focusing on full-scale experimental methods to quantify near-surface hurricane wind behavior and the resultant loads on residential structures. Source: FCMP
Organic substances, such as oil, coal, and natural gas, found underground in deposits formed from the fossilized remains of dead plants and animals. These irreplaceable fuels are used as an energy source and their burning generates carbon dioxide.
The mechanical resistive force of one object on the relative movement of another object when in contact with the first object. In meteorology, friction affects the motion of air (wind) at and near the surface of the Earth. Source: NOAA-NWS
In meteorology, the interface or transition zone between two air masses of different density. Since air density is determined largely by air temperature, a front can also be defined as the interface or transition zone between two air masses of different temperature.
The tendency of two nearby tropical cyclones to rotate cyclonically about each other. Source NOAA-NHC.
A rotating, cone-shaped column of air extending downward from the base of a thunderstorm but not touching the ground. When it reaches the ground it is called a tornado. Source: NOAA-NWS ERH
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, either predicted or occurring and not directly associated with tropical cyclones. Source NOAA-NHC.
The early development of a tropical cyclone.
National Weather Service (NWS) Geophysical Fluid Dynamics Laboratory model Source: NOAA-NWS
Another global model used by NCEP is the Global Ocean Model. The ocean model forecasts seasonal changes in oceanic variables, such as sea surface temperature and ocean currents. The ocean model is coupled with an atmospheric model to help determine how forecasted changes in oceanic variables, such as sea surface temperature, will affect the atmosphere. This model tandem is not used to give detailed daily forecasts for the ocean or the atmosphere like some of the other models. Instead it is mainly used to help forecast seasonal or yearly variations of the ocean and the atmosphere. The ocean model coupled with the atmospheric model is used to forecast events such as an El Niño warming event in the Pacific Ocean and in long range seasonal outlooks. Source: NOAA-NWS SRH
Global Positioning System (GPS)
A navigation system based on a constellation of 24 low earth-orbiting satellites having highly accurate clocks and the computational capacity to triangulate positions near the surface of the earth. Developed by the U.S. Department of Defense, the system has the capability of determining position to an accuracy of 30–100 m. If systems at two locations are used with long integration times, positions may be determined within millimeters of a known reference position. Source: (c) 1999, American Meteorological Society. Used with permission.
Geostationary Operational Environmental Satellite: Applies to both the satellites themselves and to the overall system of geostationary observations used by the United States. The current operational series of GOES satellites were preceded by the ATS and SMS satellites, with GOES-1 being launched on 16 October 1975. The early GOES (1 through 7) were spin- stabilized spacecraft, while the latest GOES are three-axis stabilized. Two GOES satellites are normally in operation, one at 75° W longitude and the other at 135° W longitude. Before launch, GOES satellites are given a letter designation (e.g., GOES-J) that is changed to a number designation (e.g., GOES-9) when the satellite becomes operational. The current generation of GOES satellites supports separate imager and sounder systems, SEM and DCS. The imager is a five-channel scanning radiometer with a 1-km resolution visible channel, along with slightly lower resolution images in the midinfrared, water vapor, and thermal IR bands. The sounder has 18 thermal infrared bands and a low-resolution visible band. Source: (c) 1999, American Meteorological Society. Used with permission.
The force of attraction between all masses in the universe including the attraction of the mass of the earth for bodies near its surface
The heating effect exerted by the atmosphere upon the earth because certain trace gases in the atmosphere (water vapor, carbon dioxide, etc.) absorb and reemit infrared radiation. Most of the sunlight incident on the earth is transmitted through the atmosphere and absorbed at the surface of the Earth. The annual mean surface temperature of Earth is 15°C, which is .33°C higher as a result of the greenhouse effect than the mean temperature resulting from radiative equilibrium of a blackbody at the mean distance of the earth from the sun. The term greenhouse effect is something of a misnomer. It is an analogy to the trapping of heat by the glass panes of a greenhouse, which let sunlight in. In the atmosphere, however, heat is trapped radiatively, while in an actual greenhouse, heat is mechanically prevented from escaping (via convection) by the glass enclosure. Source: Glossary of Meteorology. (c)American Meteorological Society. Reprinted with permission.
A set of points arranged in an orderly fashion on which specified variables are analyzed or predicted. Various forms of horizontal and vertical grids, each with particular characteristics, have been devised for use in numerical weather prediction. Source: (c) 1999, American Meteorological Society. Used with permission.
Any measurement of an observed quantity that can be used to validate or verify a new (often remote sensing) measurement or technique. Source: (c) 1999, American Meteorological Society. Used with permission.
Warm water current extending from the Gulf of Mexico and Florida up the U.S. east coast then east/northeast to Iceland and Norway.
A brief sudden increase in wind speed. Generally the duration is less than 20 seconds and the fluctuation greater than 10 mph. Source: NOAA-NWS ERH
Oceanic current systems of planetary scale driven by the global wind system. Source: NOAA-NWS
A layer of water in which the salinity increases rapidly with depth. The principal haloclines in the ocean are either seasonal, due to freshwater inputs, or permanent.
A dense stand of broad-leafed trees that grow on a natural rise of only a few inches in elevation.
Periods of abnormally and uncomfortably hot and usually humid weather. To be a heat wave such a period should last at least one day, but conventionally it lasts from several days to several weeks. In 1900, A. T. Burrows more rigidly defined a “hot wave” as a spell of three or more days on each of which the maximum shade temperature reaches or exceeds 90°F. More realistically, the comfort criteria for any one region are dependent upon the normal conditions of that region. In the eastern United States, heat waves generally build up with southerly winds on the western flank of an anticyclone centered over the southeastern states, the air being warmed by passage over a land surface heated by the sun. Source: (c) 1999, American Meteorological Society. Used with permission.
Half of the Earth, usually conceived as resulting from the division of the globe into two equal parts, north and south or east and west.
Having the texture, color or appearance of a leaf, with little or no woody tissue. Source: State of Florida
high wind warning
A high wind warning is defined as 1-minute average surface winds of 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 regardless of duration that are either expected or observed over land. Source NOAA-NHC.
An elongated area of relatively high atmospheric pressure, generally associated with light winds and dry weather, and almost always correlated with and most clearly identified as an area of anticyclonic wind flow.
horizontal boundary condition
A set of mathematical conditions to be satisfied, in the solution of a differential equation, at the edges or physical boundaries (including fluid boundaries) of the region in which the solution is sought. The nature of these conditions is usually determined by the physical nature of the problem, and is a necessary part of the complete formulation of the problem. Common boundary conditions for the atmosphere are that the velocity component normal to the surface of the earth vanish, and that the individual derivative of pressure vanish at the upper surface. The term is also used in the context of the time evolution of an open dynamical system that interacts with other external systems. The state of the external systems must be specified as a boundary condition to infer the evolution of the dynamical system under consideration. For example, the evolution of the atmospheric state of the earth requires the specification of sea surface temperature as a boundary condition. Source: (c) 1999, American Meteorological Society. Used with permission.
The amount of water vapor in the atmosphere. Source: NOAA-NWS ERH
A tropical cyclone with maximum sustained winds of 119 km/h (74 mph) or greater. 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 equator, west of the International Dateline. Hurricanes are further designated by categories on the Saffir-Simpson Scale. Hurricanes in categories 3, 4, 5 are known as “major” or “intense” hurricanes.
Buoys deployed to measure wind, wave, barometric pressure and temperature data to help the NOAA Tropical Prediction Center more accurately determine formation or dissipation, extent of wind circulation, maximum intensity and center location of the tropical cyclones. In addition, direction, height and distribution of ocean waves generated by hurricane activity are be measured. Beyond their measurements of tropical cyclones, the buoys also provide year-round data for analysis and forecasts of other marine disturbances. Data from the buoys, some as large as 12-meters wide, is used to validate the quality of measurements and estimates obtained from remote-sensing reconnaissance aircraft and satellites, and National Weather Service forecasts. Source: NOAA Public Affairs
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. Source NOAA-NHC.
An announcement that hurricane conditions (sustained winds of 118 km/h [74 mph] or higher) are expected somewhere within the specified coastal area. Because hurricane preparedness activities become difficult once winds reach tropical storm force, the hurricane warning is issued 36 hours in advance of the anticipated onset of tropical-storm-force winds. Source NOAA-NHC.
An announcement that hurricane conditions (sustained winds of 118 km/h [74 mph] or higher) are possible within the specified coastal area. 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. Source NOAA-NHC.
hurricane’s primary circulation
The prevailing fundamental atmospheric circulation on a planetary scale that must exist in response to 1) radiation differences with latitude, 2) the rotation of the earth, and 3) the particular distribution of land and oceans; and that is required from the viewpoint of conservation of energy. Primary circulation and general circulation are sometimes taken synonymously. They may be distinguished, however, on the basis of approach; that is, primary circulation is the basic system of winds, of which the secondary and tertiary circulation are perturbations, while general circulation encompasses at least the secondary circulations. Source: (c) 1999, American Meteorological Society. Used with permission.
hurricane’s secondary circulation
1. Atmospheric circulation features of cyclonic scale. Use of the term is usually reserved for distinguishing between the various dimensions of atmospheric circulation, that is, primary circulation, tertiary circulation. See also general circulation.2. A circulation induced by the presence of a stronger circulation as a result of dynamical constraints. A frictional secondary flow is an example. 3. Organized flow superimposed on a larger-scale mean circulation. For example, roll vortices are a secondary circulation in the atmospheric boundary layer. They “fill” the boundary layer vertically, but have a width of only two to three times the boundary layer depth, while the mean wind profile extends over a much broader region. Source: Glossary of Meteorology. (c)American Meteorological Society. Reprinted with permission.
The attractive force between a hydrogen attached to an electronegative (attracts electrons) atom of one molecule and an electronegative atom of a different molecule. Usually the electronegative atom is oxygen, nitrogen, or fluorine. Hydrogen bonds that form between water molecules account for some of the essential properties of water (e.g. that it can be found in all three physical states, solid, liquid, and gas).
The study of the waters of the earth with relation to the effects of precipitation and evaporation upon the water in streams, rivers, lakes, and its effect on land surfaces. Source: NOAA-NWS ERH
A condition where there is not enough oxygen in the water. This forces fish to either swim away or die and can suffocate plants living in the water. Hypoxia occurs when there are too many nutrients in the water. Source: US EPA
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 1.2 meters (4 feet) above normal. Source NOAA-NHC.
A process where the measurement of some entity is not obtained by the direct reading of a measuring tool, or by counting of units superimposed alongside or on that entity. For example if the length and width of a rectangle are multiplied to find the area of that rectangle, then the area is an indirect measurement.
The strengthening of a hurricane causing it to become more extreme.
The strength of a hurricane, usually described by the wind speed. Intensity is often given as a number from the Saffir-Simpson Hurricane Wind Scale.
Intertropical Convergence Zone (ITCZ)
The region where the northeasterly and southeasterly trade winds converge, forming an often continuous band of clouds or thunderstorms near the equator. Source: NOAA-NWS ERH
The process of covering normally dry areas with flood waters.Source: NOAA-NWS
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. Source NOAA-NHC.
During the period of inundation, currents and waves carry large volumes of sand from the seaward to the landward side of the island. When water levels subside, currents may reverse direction carrying sediment from sounds and bays back to the open ocean. These strong currents may carve a channel in the island, causing the island to be bisected in a process known as island breaching. Source: USGS
Strong winds concentrated within a narrow band in the upper atmosphere. It normally refers to horizontal, high-altitude winds. The jet stream often steers surface features such as front and low pressure systems. Source: NOAA-NWS ERH
La Nina, a phase of ENSO, is a periodic cooling of surface ocean waters in the eastern tropical Pacific along with a shift in convection in the western Pacific further west than the climatological average. These conditions affect weather patterns around the world. The preliminary CPC definition of La Nina is a phenomenon in the equatorial Pacific Ocean characterized by a negative sea surface temperature departure from normal. Source: NOAA-NWS
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 the strongest winds in a cyclone 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. Compare direct hit, indirect hit, and strike. Source NOAA-NHC.
A wide range of ground movement, such as rock falls, deep failure of slopes, and shallow debris flows. Although gravity acting on an over-steepened slope is the primary reason for a landslide, there are other contributing factors including: erosion by rivers, glaciers, or ocean waves create oversteepened slopes; rock and soil slopes are weakened through saturation by snowmelt or heavy rains; earthquakes create stresses that make weak slopes fail; earthquakes of magnitude 4.0 and greater have been known to trigger landslides; volcanic eruptions produce loose ash deposits, heavy rain, and debris flows; excess weight from accumulation of rain or snow, stockpiling of rock or ore, from waste piles, or from man-made structures may stress weak slopes to failure and other structures. Source: USGS
The angular distance north or south from the equator. Source: NASA
The length of time between the issuance of a forecast and the occurrence of the phenomena that were predicted. Source: (c) 1999, American Meteorological Society. Used with permission.
long wave radiation
A term used loosely to describe heat radiation emitted by the earth and atmosphere at wavelengths greater than about 4?m (greater than that of visible light). Source: (c) 1999, American Meteorological Society. Used with permission.
The passage of warm water through the Gulf of Mexico from the Yucatan Strait to the Straits of Florida and the connection between the Caribbean and Florida Currents. The Loop Current is part of the western boundary current system of the North Atlantic subtropical gyre and as such, is swift flowing, extending to great depth, and prone to instabilities. Its path includes a large northward excursion into the Gulf beyond 27°N but retreats to 25°N when shedding an eddy. Eddies drift slowly westward into the central and western Gulf of Mexico. Source: (c) 1999, American Meteorological Society. Used with permission.
An area of a relative pressure minimum that has converging winds and rotates in the same direction as the earth. This is counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. Also known as an cyclone, it is the opposite of an area of high pressure, or a anticyclone. Source: NOAA-NWS
A hurricane that reaches Category 3 (sustained winds greater than 110 mph) on the Saffir-Simpson Hurricane Wind Scale. Source NOAA-NHC.
A situation where authorities put maximum emphasis on encouraging evacuation and limiting ingress to potentially impacted areas. These events also occur when evacuation transportation plans go into effect. Source: US DOT
Mangroves are trees and shrubs that grow in tropical and subtropical tidelands throughout the world. Mangroves grow in areas that are frequently inundated with salt water due to tidal activity of gulfs, seas and oceans. Mangroves are able to thrive salt water inundation because of specialized rooting structures (such as prop roots and pneumatophores), specialized reproduction (vivipary or live birth) and the ability to exclude or excrete salt. Source: Lee County Government
Maximum of Maximum (MOM) maps
A MOM is a composite map showing the maximum inundation at every grid cell of the SLOSH model resulting from 2,000 to 4,000 model runs forced by a family of hurricanes with different intensity, size, direction, forward speed, and landfall point.
maximum surface wind speed
The maximum 10-minute averaged (1-minute averaged in the U.S. only) wind speed found anywhere in the tropical cyclone at 10 meters (33 ft) height.
maximum sustained winds
Steady winds within a tropical cyclone. Unlike gusts, maximum sustained winds must last over twenty seconds continuously.
Mesoscale Convective Complex (MCC)
A large mesoscale convective system, generally round or oval-shaped, which normally reaches peak intensity at night. The formal definition includes specific minimum criteria for size, duration, and eccentricity (i.e., roundness), based on the cloud shield as seen on infrared satellite photographs. Source: NOAA-NWS ERH
Mesoscale Convective System (MCS)
A complex of thunderstorms which becomes organized on a scale larger than the individual thunderstorms, and normally persists for several hours or more. MCSs may be round or linear in shape, and include systems such as tropical cyclones, squall lines, and MCCs (among others). MCS often is used to describe a cluster of thunderstorms that does not satisfy the size, shape, or duration criteria of an MCC. Source: NOAA-NWS ERH
Mesoscale Convective Vortex (MCV)
A low-pressure center within an mesoscale convective system (MCS) that pulls winds into a circling pattern, or vortex.
A person who studies meteorology. Some examples include research meteorologist, climatologist, operational meteorologist, TV meteorologist. Source: NOAA-NWS ERH
Electromagnetic radiation generally in the frequency range between 300 MHz and 300 GHz (free-space wavelengths between 1 and 1000 mm). Within these frequencies lie the UHF, SHF, and EHF radio frequency bands. Radars operate at microwave frequencies. Source: (c) 1999, American Meteorological Society. Used with permission.
The areas on earth between the tropics and the polar regions, roughly between 35°N and 65°S degrees.
Actions that reduce the long-term risks to life and property from hurricanes.
[of the ocean]: Any process or series of processes by which parcels of ocean water with different properties are brought into contact, so that molecular diffusion (spreading out) erases the differences between them. Source: (c) 1999, American Meteorological Society. Used with permission.
The simplest structural unit of substance which can exist and still maintain the characteristics of that substance.
The line in a weather map showing the locations of relatively minimum sea level pressure in a monsoon region (area of seasonal winds, strongest on the southern and eastern sides of Asia, but also occurring on the coasts of tropical regions such as Spain, northern Australia, Africa except the Mediterranean, Texas, and the western coasts of the United States and Chile). Most of the active transient disturbances producing the monsoon rain develop and move along the monsoon trough region.
Referring to a time span that involves multiple decades
multiple-nest grid configuration
A set of grids in a regional dynamical hurricane model where a high-resolution grid (with small spacing between grid points) is embedded in a larger, coarse-resolution grid (with more space between grid points). There can be any number of high-resolution grids embedded in any number of coarser resolution grids. In some models, the smaller high-resolution grid(s) follow the hurricane's forecast track while the larger, lower-resolution grid(s) remain stationary throughout the model forecast.
National Data Buoy Center (NDBC)
NDBC designs, develops, operates, and maintains a network of data collecting buoys and coastal stations. Source: NOAA-NDBC
National Hurricane Center (NHC)
The NHC maintains a continuous watch on tropical cyclones over the Atlantic, Caribbean, Gulf of Mexico, and the Eastern Pacific from 15 May through November 30. The Center prepares and distributes hurricane watches and warnings for the general public, and also prepares and distributes marine and military advisories for other users. During the off-season NHC provides training for U.S. emergency managers and representatives from many other countries that are affected by tropical cyclones. NHC also conducts applied research to evaluate and improve hurricane forecasting techniques, and is involved in public awareness programs. Source: NOAA-NWS SRH
National Oceanic and Atmospheric Administration (NOAA)
A branch of the U.S. Department of Commerce, NOAA is the parent organization of the National Weather Service. Source: NOAA-NWS ERH
National Water level Observation Network (NWLON)
The NWLON is a network of 175 long-term, continuously operating water-level stations throughout the USA, including its island possessions and territories and the Great Lakes. Source: NOAA-NWLON
National Weather Service (NWS)
The federal agency in the National Oceanic and Atmospheric Administration that is responsible for weather forecast and preparation of weather maps
A unit of distance used in marine navigation and marine forecasts. It is equal to 1.15 statue miles (1.85 kilometers). It is also the approximate length of 1 minute of latitude. Source: NOAA-NWS SRH
Next-Generation Radar (NEXRAD)
NEXt Generation RADar. A National Weather Service network of about 140 Doppler radars operating nationwide. Source: NOAA-NWS ERH
North Atlantic Oscillation (NAO)
A large-scale fluctuation in atmospheric pressure between the subtropical high pressure system located near the Azores in the Atlantic Ocean and the sub-polar low pressure system near Iceland and is quantified in the NAO Index. The surface pressure drives surface winds and wintertime storms from west to east across the North Atlantic affecting the climate from New England to western Europe as far eastward as central Siberia and the eastern Mediterranean, and southward to West Africa.
Numerical Weather Prediction (NWP)
Forecasting the weather through digital computations carried out by supercomputers. Source: NOAA-NWS SRH
The nutrient load refers to the total amount of nitrogen or phosphorus entering the water during a given time, such as tons of nitrogen per year. Nutrients may enter the water from runoff, groundwater, or the air. Source: State of Maryland
The path of a celestial body or an artificial satellite as it revolves around another body.
Carbon based, living materials that are capable of decay
A shift in position of various high and low pressure systems that in climate terms is usually defined as an index (i.e., a single numerically-derived number, that represents the distribution of temperature and pressure over a wide ocean area, such as the El Niño-Southern Oscillation, North Atlantic Oscillation, and Pacific Decadal Oscillation).
If wave runup exceeds the elevation of the dune, or in the absence of a dune, the beach berm, the system will be overtopped, transporting sand landward. Source: USGS
Pacific Decadal Oscillation (PDO)
A basin-scale pattern of climate variation similar to ENSO though on a timescale of decades (20-to-30 years) and not seasons. It primarily affects weather patterns and sea surface temperatures in the Pacific Northwest, Alaska, and northern Pacific Islands. Causes for the PDO have not yet been explained.
defining the variables for a model.
The time between two successive crests or troughs of a wave. Source: Canadian Hurricane Centre
A former tropical cyclone. This generic term describes a cyclone that no longer possesses sufficient tropical characteristics to be considered a tropical cyclone. Post-tropical cyclones can continue carrying heavy rains and high winds. Note that former tropical cyclones that have become fully extratropical...as well as remnant lows...are two classes of post-tropical cyclones. Source: NOAA-NHC.
The process where water vapor condenses in the atmosphere to form water droplets that fall to the Earth as rain, sleet, snow, hail, etc.
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. Source: NOAA-NHC.
(symbol: p or sometimes P) The force per unit area applied to an object in a direction perpendicular to the surface. Atmospheric pressure is sometimes defined as the force per unit area exerted against a surface by the weight of air above that surface at any given point in the atmosphere of the Earth. In most circumstances atmospheric pressure is closely approximated by hydrostatic pressure (the pressure at any given point of a non-moving [static] fluid) caused by the weight of air above the measurement point. Low-pressure areas have less atmospheric mass above their location, whereas high-pressure areas have more atmospheric mass above their location. The standard atmosphere (symbol: atm) is a unit of pressure and is defined as being equal to 101.325 kPa. These other units are equivalent: 760 mmHg (torr), 29.92 inHg, 14.696 PSI, 1013.25 millibars.
pressure gradient force
Force acting on air that causes it to move from areas of higher pressure to areas of lower pressure. Source: NOAA-NWS ERH
The movement of an atmospheric phenomenon. This term is frequently applied to the motion of thunderstorms (or in this case hurricanes) into regions favorable for their continued development.
A vertical density gradient (as determined by the vertical temperature and salinity gradients and equation of state) in some layer of a body of water, which is appreciably greater than the gradients above and below it; also a layer in which such a gradient occurs. The principal pycnoclines in the ocean are either seasonal, due to heating of the surface water in summer or freshwater inputs, or permanent. Source: (c) 1999, American Meteorological Society. Used with permission.
Coined word for radio detection and ranging. An electronic instrument, consisting of a transmitter, receiver, antenna, display, and associated equipment for control and signal processing, which is used for the detection and ranging of distant objects (such as tropical cyclones) that scatter or reflect radio energy. The colors in a radar output correspond to the different values of energy that are reflected back toward the radar. Called echoes, the reflected intensities are measured in dBZ (decibels of z). As the strength of the signal returned to the radar increases (i.e. there is more precipitation to cause a reflection in energy) the dBZ values increases. Source: Glossary of Meteorology. (c)American Meteorological Society. Reprinted with permission.
radial wind velocity
Speed component of the wind at a point in a direction along a radius vector from the center of a circulating wind system. Source: (c) 1999, American Meteorological Society. Used with permission.
Energy that comes from a source and is transmitted in the form of rays, waves, or particles. Light and heat are types of radiation.
An instrument attached to a weather balloon that transmits pressure, humidity, temperature and winds as it ascends to the upper atmosphere. Source: NOAA-NWS ERH
radius of maximum winds
The distance from the center of a tropical cyclone to the location of the maximum winds of a cyclone. In well-developed hurricanes, the radius of maximum winds is generally found at the inner edge of the eyewall. Source NOAA-NHC.
A decrease in the minimum sea-level pressure of a tropical cyclone of 1.75 mb/hr or 42 mb for 24 hours. Source NOAA-NHC.
A balloon that is tracked by radar to measure wind speeds and wind directions in the atmosphere. Source: NOAA-NWS ERH
A change in direction of a wave, such as a light or sound wave, away from a boundary the wave encounters.
Radar term referring to the ability of a radar target to return energy; used to estimate precipitation intensity and rainfall rates. Source: NOAA-NWS ERH
A dimensionless ratio, expressed in percent, of the amount of atmospheric moisture present relative to the amount that would be present if the air were saturated. Since the latter amount is dependent on temperature, relative humidity is a function of both moisture content and temperature. As such, relative humidity by itself does not directly indicate the actual amount of atmospheric moisture present. See dew point. Source: NOAA-NWS SRH
A post-tropical cyclone that no longer possesses the convective organization required of a tropical cyclone and has maximum sustained winds of less than 62 km/h (39 mph). The term is most commonly applied to the nearly deep-convection-free swirls of stratocumulus in the eastern North Pacific. Source NOAA-NHC.
The scale in space or time of a model. High resolution means the spatial scale between model points is smaller.
Really Simple Syndication or Rich Site Summary feed: provides summaries of web content in a simple format. It is available through an RSS feed reader, or through some browsers.
Saffir-Simpson Hurricane Wind Scale
The Saffir-Simpson Hurricane Wind Scale is a 1 to 5 categorization based on the intensity of the hurricane 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. A detailed description of the Saffir-Simpson Hurricane Wind Scale, which was revised in early 2010, is available at http://www.nhc.noaa.gov/sshws.shtml. Source: NOAA-NHC.
The amount of chemical salts (compounds that include Na, K, Mg, Ca) contained in a solution. Source: US NPS
When the roots of the plant come in contact with more salt in the soil then they can cope with.
Spray of salt or salt water that forms when ocean waves crash.
The region (actually in the horse latitudes) of the North Atlantic Ocean to the east and south of the Gulf Stream system. This is a region of convergence of the surface waters, and is characterized by clear, warm water, a deep blue color, and large quantities of floating sargassum or “gulf weed.” Source: (c) 1999, American Meteorological Society. Used with permission.
A man-made device orbiting around the earth, moon, or another planet. Satellites are used for research, communications, weather information, and navigation.
In meteorological terms, a condition in which air at a specific temperature contains all the water vapor it can hold. At this point, the air cannot absorb any more water vapor, and additional amounts of the vapor will appear as precipitation.
The spreading of waves, such as light, over a range of directions as a result of encountering a rough boundary (water) or collisions with particles.
The average height of the ocean.
sea level pressure
The atmospheric pressure at sea level at a given location. Once calculated, horizontal variations of sea level pressure may be compared for location of high and low pressure areas and fronts.
Sea Surface Temperature (SST)
The term refers to the mean temperature of the ocean in the upper few meters. Source: NOAA-NWS
Statistical Hurricane Intensity Forecast, a type of statistical model. Source: HSS
Statistical Hurricane Intensity Prediction Scheme, a type of statistical-dynamical model. Source: HSSM
Sea, Lake, and Overland Surges by Hurricanes, a computer model used by the National Hurricane Center to estimate storm surge heights and winds resulting from historical, hypothetical, or predicted hurricanes by taking into account pressure, size, forward speed, track, and winds. Source: NOAA (See www.nhc.noaa.gov/HAW2/english/surge/slosh.shtml, Jelesnianski et al., 1992)
Southern Oscillation (SO)
A "see-saw" in surface pressure in the tropical Pacific characterized by simultaneously opposite sea level pressure anomalies at Tahiti, in the eastern tropical Pacific and Darwin, on the northwest coast of Australia. The SO was discovered by Sir Gilbert Walker in the early 1920s. Walker was among the first meteorologists to use the statistical techniques to analyze and predict meteorological phenomena. Later, the three-dimensional east-west circulation related to the SO was discovered and named the "Walker Circulation". The SO oscillates with a period of 2-5 years. During one phase, when the sea level pressure is low at Tahiti and High at Darwin, the El Niño occurs. The cold phase of the SO, called La Niña, is characterized by high pressure in the eastern equatorial Pacific, low in the west, and by anomalously cold sea surface temperature (SST) in the central and eastern Pacific. This is called El Niño Southern Oscillation or ENSO. Source: NOAA Jetstream
Southern Oscillation Index (SOI)
A numerical index measuring the state of the Southern Oscillation. The SOI is based on the (atmospheric) pressure difference between Tahiti and Darwin, Australia. It is highly correlated with tropical sea surface temperature anomaly indices recorded in El Nino/La Nina.
spiral rain bands
Bands of thunderstorms and intense rain that wrap around a hurricane. Source: Canadian Hurricane Centre
Are based on historical relationships between hurricane-specific information, such as the location and time of year, and the behavior of historical hurricanes. These models are much simpler than dynamical models, and they can produce a computer-generated forecast much more quickly, often within seconds. Source: HSS
Statistical-dynamical models blend both dynamical and statistical techniques by making a forecast based on established historical relationships between storm behavior and atmospheric variables provided by dynamical models. Source: HSS
A stable condition where a system has numerous properties that are unchanging in time, or in which a change in one direction is continuously balanced by a change in another direction.
(Or steering current) A prevailing synoptic scale flow which governs the movement of smaller features embedded within it. Source: NOAA-NWS
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. Source NOAA-NHC.
storm surge warning system
A warning that significant wind-forced flooding is to be expected along low-lying coastal areas if weather patterns develop as forecast.
The actual sea level resulting from astronomical tide combined with the storm surge. This term is used interchangeably with hurricane tide. Source: NOAA-NWS SRH
A warning of 1-minute sustained surface winds of 88 km/h (55 mph) or greater, either predicted or occurring, not directly associated with tropical cyclones. Source NOAA-NHC.
The second major layer of the atmosphere of the Earth, just above the troposphere, and below the mesosphere. It is stratified in temperature, with warmer layers higher up and cooler layers farther down.
For any particular location, a hurricane strike occurs if that location passes within the strike circle of the hurricane, a circle of 230 km (144 mi) diameter, centered 23 km (14 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 139 km (86 mi) to the right of the center and 93 km (57 mi) to the left. Source NOAA-NHC.
A subtropical cyclone in which the maximum sustained surface wind speed (using the U.S. 1-minute average) is 33 kt (38 mph or 62 km/hr) or less. Source NOAA-NHC.
One of the two bands of high atmospheric pressure that are centered near 30°N and 30°S latitudes.
A non-frontal low pressure system that has characteristics of both tropical and extratropical cyclones. This system is typically an upper-level cold low with circulation extending to the surface layer and maximum sustained winds generally occurring at a radius of about 100 miles or more from the center. In comparison to tropical cyclones, such systems have a relatively broad zone of maximum winds that is located farther from the center, and typically have a less symmetric wind field and distribution of convection. Source: NOAA-NHC.
A subtropical cyclone in which the maximum sustained surface wind speed (using the U.S. 1-minute average) is 63 km/h (39 mph) or more. Source NOAA-NHC.
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. Source NOAA-NHC.
The part of the surface of the Earth between the Tropic of Cancer (23.4° N latitude) and the Tropic of Capricorn (23.4° S latitude), characterized by a hot climate.
Stresses in plants that develop as temperatures rise more than 1°C (1.8°F) above the average expected in the hottest months of the year. Source: NOAA
Electrical resistance devices used in the measurement of temperature. Source: NOAA-NWS NHC
The boundary layer separating the near-surface warm waters from the colder, deeper layers of a body of water. Water temperature changes rapidly with depth within this layer. In the ocean, the thermocline also separates the fresher waters near the surface from the saltier waters below.
A local storm produced by cumulonimbus clouds. It is always accompanied by lightning and thunder. It is estimated that nearly 2,000 thunderstorms occur simultaneously around the Earth at any given instant. There are 3 types of thunderstorms: Single Cell, Multicell, and Severe Supercell. Source: NOAA Jetstream
Refers to the surface landscape of a geographic area, especially changes in elevation. Source: US NPS
A violent rotating column of air, in contact with the ground, pendant from a cumulonimbus cloud. A tornado does not require the visible presence of a funnel cloud. It has a typical width of tens to hundreds of meters and a lifespan of minutes to hours. Source: NOAA-NWS ERH
(Of a hurricane): The path a hurricane follows over a given period of time.
The belts of winds on either side of the equator, blowing from the northeast in the Northern Hemisphere and from the southeast in the Southern Hemisphere. In both hemispheres the winds become more easterly closer to the equator. Source: Canadian Hurricane Centre
A warm-core non-frontal synoptic-scale cyclone, originating over tropical or subtropical waters, with organized deep convection and a closed surface wind circulation about a well-defined center. Once formed, a tropical cyclone is maintained by the extraction of heat energy from the ocean at high temperature and heat export at the low temperatures of the upper troposphere. In this they differ from extratropical cyclones, which derive their energy from horizontal temperature contrasts in the atmosphere (baroclinic effects). Source: NOAA-NHC.
A tropical cyclone in which the maximum sustained surface wind speed (using the U.S. 1-minute average) is 62 km/h (38 mph) or less. Source: NOAA-NHC.
A discrete tropical weather system of apparently organized convection -- generally 184 to 552 km (145 to 345 mi) in diameter -- 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. Source: NOAA-NHC.
(also known as The Tropics, Tropical Zone or Torrid Zone) The part of the surface of the Earth between the Tropic of Cancer (23°26 [23.4°] N latitude) and the Tropic of Capricorn (23°26 [23.4°] S latitude), characterized by a hot climate.
A tropical cyclone in which the maximum sustained surface wind speed (using the U.S. 1-minute average) ranges from 63 km/h (39 mph) to 118 km/h (73 mph). Source: NOAA-NHC.
tropical storm warning
An announcement that tropical storm conditions (sustained winds of 39 to 73 mph) are expected somewhere within the specified coastal area within 36 hours. Source: NOAA-NHC.
tropical storm watch
An announcement that tropical storm conditions (sustained winds of 39 to 73 mph) are possible within the specified coastal area within 48 hours. Source NOAA-NHC.
The usually slow development of an extratropically cold core vortex into a tropical cyclone. Although tropical cyclones generally weaken as they move poleward due to increased wind shear, lower sea surface temperatures and lower tropospheric humidities / landfall, some may develop explosively into extratropical depressions.
A trough or cyclonic curvature maximum in the trade-wind easterlies. The wave may reach maximum amplitude in the lower middle troposphere. Source NOAA-NHC.
The boundary between troposphere and the stratosphere. It is usually characterized by an abrupt change in temperature with height from positive (decreasing temperature with height) to neutral or negative (temperature constant or increasing with height). Source: NOAA- NWS ERH
The layer of the atmosphere from the surface of the earth up to the tropopause, characterized by decreasing temperature with height. It is the layer of the atmosphere where most of the weather occurs. Source: NOAA- NWS ERH
An elongated area of relatively low atmospheric pressure surface or aloft. Usually not associated with a closed circulation, and thus used to distinguish from a closed low. The opposite of ridge. Source: NOAA- NWS ERH
(in the ocean): Irregular motions of ocean waters. Turbulence increases ocean mixing, such as that at the edge of currents, which causes eddies to form.
A tropical cyclone with maximum sustained winds of 119 km/h (74 mph) or greater. The term “typhoon” is used for Pacific tropical cyclones north of the equator, west of the International Dateline. The term “hurricane” is used for Northern Hemisphere tropical cyclones east of the International Dateline to the Greenwich Meridian. Source NOAA-NHC.
The process by which cold waters from the depths of a lake or ocean rise to the surface. Source: NOAA-NWS SRH
Coordinated Universal Time (UTC) is a time standard that is roughly the same as Greenwhich Mean Time (GMT). UTC is much more precise than GMT. UTC is based on International Atomic Time and modified with leap seconds to account for minor variations in the rotation of the Earth.
A volume of space that is essentially empty of matter, such that its gaseous pressure is much lower than atmospheric pressure.
vertical wind shear
The condition produced by a change in wind velocity (speed and/or direction) with height. Vertical wind shear can weaken or destroy a tropical cyclone by interfering with the symmetric nature and organization of the deep convection around the cyclone centre. Source: Canadian Hurricane Centre
The greatest distance an observer can see and identify prominent objects. Source: NOAA-NWS SRH
This type of evacuation is targeted toward people most vulnerable to the threat, including offshore workers, persons on coastal islands and other flood prone areas, and other special populations having particularly long lead-time evacuation requirements. This also includes people in harm’s way from other events. No special traffic control or transportation measures are usually taken during voluntary evacuations, and people may remain if they so choose. Source: US DOT
An atmospheric feature that tends to rotate. It has vorticity and usually has closed streamlines. Source: NOAA-NWS ERH
The location of the center of a tropical or subtropical cyclone obtained by reconnaissance aircraft penetration, satellite, radar, or synoptic data. Source NOAA-NHC.
A measure of the local rotation in a fluid flow. In weather analysis and forecasting, it usually refers to the vertical component of rotation (i.e., rotation about a vertical axis) and is used most often in reference to synoptic scale or mesoscale weather systems. By convention, positive values indicate cyclonic rotation. Source: NOAA-NWS ERH
A low-pressure area which is warmer at its center than at its periphery.
Water Runoff is water originating as rain or snow that runs off the land in to streams, eventually reaching oceans, inland seas or aquifers unless it evaporates first.
The gas phase of water. Under normal atmospheric conditions, water vapor is continuously generated by evaporation and removed by condensation.
The highest point in a wave.
The transmission of waves through water.
Weather Forecast Offices (WFOs)
This National Weather Service office is responsible for issuing advisories, warnings, statements, and short-term forecasts for its county warning area. Source: NOAA-NWS SRH
The prevailing winds that blow from the west in the mid-latitudes.