GLOSSARY
OF TROPICAL TERMS
Back
to hurricane background and preparedness information
[
A |
B | C |
D |
E |
F | G |
H |
I |
J | K |
L |
M |
N | O |
P |
R |
S | T |
U |
V |
W | Z ]
A
ADVANCED
WEATHER INTERACTIVE PROCESSING SYSTEM (AWIPS): It
is the computerized system that processes NEXRAD
and ASOS data received at National Weather Service
Forecast Offices.
ADVISORY:
A message from the National Hurricane Center
in Miami giving warning information with details
on tropical cyclone location, intensity, movement
and precautions that should be taken. The advisory
will contain a resume of all warnings in effect
AERIAL
RECONNAISSANCE WEATHER OFFICER (ARWO): The flight
meteorologist for weather reconnaissance flights
into a tropical cyclone.
ANEMOMETER:
An instrument that measures the speed or force
of the wind.
ATMOSPHERIC
PRESSURE: The pressure exerted by the atmosphere
at a given point. Its measurement can be expressed
in several ways. One is in millibars. Another is
in inches or millimeters of mercury (Hg). Also known
as barometric pressure.
AUTOMATED
SURFACE OBSERVING SYSTEMS (ASOS): This system
is a collection of automated weather instruments
that collect data. It performs surface based observations
from places that do not have a human observer, or
that do not have an observer 24 hours a day.
AUTOMATION
OF FIELD OPERATIONS AND SERVICES (AFOS): It
is the computer system that links National Weather
Service offices together for weather data transmission.
B
Back
to top
BAROMETER:
An instrument for determining the pressure of
the atmosphere
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.
C
Back
to top
CAPE
VERDE ISLANDS: A group of volcanic islands in
the eastern Atlantic Ocean off the coast of West
Africa. A Cape Verde hurricane originates near here.
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 140W and the International Dateline.
The Central Pacific Hurricane Center (CPHC) in Honolulu,
HI is responsible for tracking tropical cyclones
in this region.
CHIEF,
AERIAL RECONNAISSANCE COORDINATION, ALL HURRICANES
(CARCAH): The 53rd Weather Reconnaissance Squadron's
Air Force Reserve civilians who bridge the gap between
the Hurricane Specialists at NHC and the flying
squadron. Each day, they publish the Tropical Cyclone
Plan of the Day.
CLOSEST
POINT OF APPROACH: Point where hurricane eye
makes closest contact to shore without actually
making landfall.
COASTAL
FLOOD WARNING: A warning that significant wind-forced
flooding is to be expected along low-lying coastal
areas if weather patterns develop as forecast.
COASTAL
FLOOD WATCH: An announcement that significant
wind-forced flooding is to be expected along low-lying
coastal areas if weather patterns develop as forecast.
COLD
FRONT: The leading edge of an advancing cold
air mass that is underrunning and displacing the
warmer air in its path. Generally, with the passage
of a cold front, the temperature and humidity decrease,
the pressure rises, and the wind shifts (usually
from the southwest to the northwest in the Northern
Hemisphere). Precipitation is generally at and/or
behind the front, and with a fast-moving system,
a squall line may develop ahead of the front. See
occluded front and warm front.
CONVECTION:
Atmospheric motions in the vertical direction
resulting from surface heating and the subsequent
rising of warm air. This lifting mechanism is capable
of generating the rising motions necessary for clouds
and precipitation to form.
CONVERGENCE:
Wind movement that results in a horizontal net
inflow of air into a particular region. Convergent
winds at lower levels are associated with upward
motion. Contrast with divergence.
CYCLONE:
An atmospheric m. circulation (low-pressure system)
with rotating and converging winds, in which the
center has a relative pressure minimum. It usually
has a diameter of 2000 to 3000 kilometers. When
developing, a cyclone typically consists of a warm
front pushing northward and a cold front pushing
southward with the center of low pressure (cyclone
center) located at the junction of the two fronts.
Cyclones in the Northern Hemisphere rotate counter-clockwise
while Southern Hemisphere cyclones rotate clockwise.
D
Back
to top
DATA
BUOYS: Buoys placed throughout the Gulf of Mexico
and along the Atlantic and Pacific coasts of the
United States that relay information on air and
water temperature, wind speed, air pressure, and
wave conditions via radio signals.
DEPRESSION:
In meteorology, it is another name for an area of
low pressure, a low, or trough. It also applies
to a stage of tropical cyclone development and is
known as a tropical depression to distinguish it
from other synoptic features.
DEEPENING:
Used in describing the history of a low-pressure
system or an area of cyclonic circulation, it means
a decrease in the central pressure of the system.
Although it usually describes the action of a pressure
system on a constant pressure chart, it also means
a surface low is increasing in cyclonic circulation
and acquiring more energy. It is the opposite of
filling.
DISTURBANCE:
This has several applications. It can apply to a
low or cyclone that is small in size and influence.
It can also apply to an area that is exhibiting
signs of cyclonic development. It may also apply
to a stage of tropical cyclone development and is
known as a tropical disturbance to distinguish it
from other synoptic features
DOPPLER
RADAR: Weather radar that measures direction
and speed of a moving object, such as drops of precipitation,
by determining whether atmospheric motion is horizontally
toward or away from the radar. Using the Doppler
effect, it measures the velocity of particles.
E
Back
to top
EASTERLY
WAVE: An inverted, migratory wave-like disturbance
or trough in the tropical region that moves from
east to west, generally creating only a shift in
winds and rain. The low-level convergence and associated
convective weather occur on the eastern side of
the wave axis. Normally, it moves slower than the
atmospheric current in which it is embedded and
is considered a weak trough of low pressure. It
is often associated with possible tropical cyclone
development and is also known as a tropical wave.
EASTERN
NORTH PACIFIC BASIN: The region north of the
Equator east of 140W. The National Hurricane Center
in Miami, FL is responsible for tracking tropical
cyclones in this region.
EL
NIÑO: A warming of the Pacific Ocean currents
along the coasts of Peru and Ecuador near the Equator
that is generally associated with dramatic changes
or a shift 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 including hurricane.
EMERGENCY
ALERT SYSTEM (EAS): A system designed to permit
government officials to issue up-to-date and continuous
emergency information and instructions to the public
in case of a threatened or actual emergency. It
is replacing the Emergency Broadcast System.
EMERGENCY
PUBLIC INFORMATION: Information disseminated
primarily, but not unconditionally, at the time
of an emergency frequently includes actions, instructions
and direct orders.
EMERGENCY
PUBLIC SHELTER: Generally a public school or
other such structure designated by county or city
officials as a place of refuge. A volunteer group
such as the American Red Cross or Salvation Army
usually manages a shelter.
EMERGENCY
OPERATIONS CENTER (EOC): A State, county, or
city emergency facility that serves as a central
location for the coordination and control of all
emergency preparedness and response disaster activities.
EQUATOR:
The geographic circle at 0 degrees latitude
on the earth's surface. It is equal distance from
the North and South Poles and divides the Northern
Hemisphere from the Southern.
EVACUATION
TIME: The lead-time that a populated coastal
area must have to safely relocates all residents
of vulnerable areas from an approaching hurricane.
This time can also be perceived as the necessary
amount of time between the local official evacuation
order and the arrival of sustained gale force winds
(40 mph) and/or flooding.
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 six hours.
EXTENT
OF EVACUATION: The identification of vulnerable
people who must evacuate based on estimated damage
and/or homes susceptible to hurricane force winds.
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.
EXTRATROPICAL
CYCLONE: A cyclone in the middle and high latitudes
often being 2000 kilometers in diameter and usually
containing a cold front that extends toward the
equator for hundreds of kilometers. These cyclones
forms outside the tropics, the center of storm is
colder than the surrounding air, have fronts and
the strongest winds in the upper atmosphere.
EYE:
The center of a tropical storm or hurricane characterized
by a roughly circular area of light winds and rain-free
skies and the lowest pressure. An eye will usually
develop when the maximum sustained wind speeds exceed
78 mph. It can range in size from as small as 5
miles to up to 60 miles (20-50 km) but the average
size is 20 miles. In general, when the eye begins
to shrink in size, the storm is intensifying.
EYE
WALL: An organized band of convection surrounding
the eye, or center, of a tropical cyclone. It contains
cumulonimbus clouds, severest thunderstorms, heaviest
precipitation and strongest winds.
F
Back
to top
FEEDER
BANDS: In tropical parlance, the lines or bands
of thunderstorms that spiral into and around the
center of a tropical system. Also known as outer
convective bands, a typical hurricane may have three
or more of these bands. They occur in advance of
the main rain shield and are usually 40 to 80 miles
apart. In thunderstorm development, they are the
lines or bands of low-level clouds that move or
feed into the updraft region of a thunderstorm.
FILLING:
Used in describing the history of a low-pressure
system or an area of cyclonic circulation, it means
an increase in the central pressure of the system.
Although it usually describes the action of a pressure
system on a constant pressure chart, it also means
a surface low is decreasing in cyclonic circulation
and losing its characteristics. The opposite of
deepening.
FLOODING:
A general and temporary condition of 1) partial
or complete inundation of normally dry land areas
from the overflow of inland or tidal water or rapid
accumulation or runoff of surface waters from any
source.
FLOOD
PLAIN: Any land area susceptible to being inundated
by water from any source. Normally the regulatory
flood plain is characterized by the 100-year meaning
there is a 1% chance of flooding per year. The flood
plain is often referred to as flood prone areas.
FLOOD
STAGE: The level of a river or stream where
overflow onto surrounding areas can occur.
FLOOD
WARNING: The expected severity of flooding (minor,
moderate or major) as well as where and when the
flooding will begin.
FORECAST:
A statement of expected future occurrences. Weather
forecasting includes the use of objective models
based on certain atmospheric parameters, along with
the skill and experience of a meteorologist. Also
called a prediction.
FORWARD
SPEED: The rate of movement (propagation) of
the hurricane eye in miles per hour or knots
FRONT:
The boundary between two dissimilar air masses.
FUJIWHARA
EFFECT: A binary interaction where tropical
cyclones within a certain distance (300-750 nautical
miles depending on the sizes of the cyclones) of
each other begin to rotate about a common midpoint.
G
Back
to top
GALE
WARNING: A warning of 1-minute sustained surface
winds in the range 39 to 54 mph (34 to 47 knots)
inclusive, either predicted or occurring not directly
associated with tropical cyclones.
GEOSTATIONARY
OPERATIONAL ENVIRONMENTAL SATELLITES (GOES): Family
of NWS weather satellites, which orbit 22,300 miles
above the earth and maintain a velocity that allows
it to remain over a fixed place above the equator.
Images are available to forecasters every 30 minutes.
GREENWICH
MEAN TIME (GMT): The name of the twenty-four
hour time scale that is used throughout the scientific
and military communities. Standard Time begins at
Greenwich, England, which is the Prime Meridian
of Longitude. The globe is divided into twenty-four
(24) time zones of 15 degrees of arc, or one hour
in time apart. To the east of this meridian, time
zones are numbered 1 to 12 and prefixed with a minus
(-), while to the west, the time zones are also
numbered 1 through 12 but prefixed with a plus (+).
Other names for this time measurement are Universal
Time Coordinate (UTC) and Zulu (Z).
H
Back
to top
HIGH-PRESSURE
SYSTEM: An area of relative pressure maximum
that has diverging winds and a rotation opposite
to the earth's rotation. This is clockwise the in
Northern Hemisphere and counterclockwise in the
Southern Hemisphere. Also known as an anticyclone,
it is the opposite of an area of low pressure or
a cyclone.
HIGH
WIND ADVISORY: Announcement issued by the National
Weather Service for substained winds exceeding 25
mph (19 knots).
HIGH
WIND WATCH/WARNING: A high inland wind watch/warning
issued by the National Weather Service when either
of the following occurs or are expected to occur
in the near term: 1) Sustained surface winds (1-minute
average) of 40 mph (35 knots) or greater lasting
for 1 hour or longer; or 2) Sustained winds or gusts
of 58 mph (50 knots) or greater for any duration.
HUMIDITY:
The amount of water vapor in the air.
HURRICANE:
A tropical cyclone in the Northern Hemisphere with
substained winds of at least 74 mph (64 knots) or
greater in the North Atlantic Ocean, Caribbean Sea
or Gulf of Mexico. These winds blow in a large spiral
around a relatively calm center of extremely low
pressure known as the eye. Around the rim of the
eye, winds may gust to more than 200 miles per hour.
The entire storm, which can be up to 340 (550) in
diameter, dominates the ocean surface and lower
atmosphere over tens of thousands of square miles.
Hurricanes draw their energy from the warm surface
water of the tropics (usually above 27 Celsius)
and latent heat of condensation, which explains
why hurricanes dissipate rapidly once they move
over cold water or large land masses.
HURRICANE
ADVISORY: Notice, issued by the National Hurricane
Center, numbered consecutively for each storm, describing
the present and forecasted position and intensity.
Advisories are issued at six-hour intervals at midnight,
6 a.m., noon, and 6 p.m., Eastern Daylight Time.
Bulletins provide additional information. Each message
gives the name, eye position, intensity and forecast
movement of the storm.
HURRICANE
CLIPS: A structural bracing device used on the
installation of roofs which reinforce the joints
of a house and give a stronger connection of wood
to wood roofing trusses than just nails. In many
coastal communities, hurricane clips are enforced
as a code restriction for new homes.
HURRICANE
EYE: The relatively calm area near the center
of the storm. In this area, winds are light and
the sky is often partly covered by clouds.
HURRICANE
EYE LANDFALL: When the eye, or physical center
of the hurricane, reaches the coastline from the
hurricane's approach over water.
HURRICANE
HUNTERS: The 53rd Weather Reconnaissance Squadron
of the U.S. Air Force Reserve, based out of Keesler
Air Force Base in Biloxi, Mississippi. As a part
of the 403rd Air Wing, the crew flies Lockheed WC-130
aircraft into tropical storms and hurricanes to
gather meteorological data for the National Hurricane
Center.
HURRICANE
LIAISON TEAM: A team of FEMA, NWS, State and
local emergency management officials which respond
to the National Hurricane Center prior to the landfall
of a hurricane in the Atlantic Ocean, Caribbean
Sea or Gulf of Mexico. The primary purpose of the
Team is to assist in coordinating the latest advisories
from the NHC to the Federal, State and local emergency
management agencies.
HURRICANE
LOCAL STATEMENT: A public release prepared by
local National Weather Service Field 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
PATH OR TRACK: Line of movement (propagation)
of the eye through an area.
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/TROPICAL
STORM PROBABILITIES: The National Weather Service
issues hurricane/tropical storm probabilities in
public advisories to realistically assess the threat
of a hurricane or tropical storm hitting your community.
The probabilities are defined as the chance in percent
that the center of the storm will pass within approximately
65 miles of 44 selected locations from Brownsville,
Texas, to Eastport, Maine.
HURRICANE
WARNING: A warning
added to a hurricane advisory that sustained winds
of 74 mph (64 knots) or higher associated with a
hurricane are expected in a specified coastal area
within 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. A warning is used to inform
the public and marine interests of the storm's location,
intensity, and movement. The NHC chooses a distance
of approximately 300 miles.
HURRICANE
WATCH: An announcement added to a hurricane
advisory that hurricane conditions pose a possible
threat to a specified coastal area within 36 hours.
A watch is used to inform the public and marine
interests of the storm's location, intensity, and
movement.
I
Back
to top
INCHES
OF MERCURY (Hg): The name comes from the use
of mercurial barometers that equate the height of
a column of mercury with air pressure. One inch
of mercury is equivalent to 33.86 millibars or 25.40
millimeters.
INLAND
HIGH WIND WARNING FOR HURRICANE FORCE WINDS: Announcement
issued for force winds 74 mph (64 knots) or greater
within 12 hours.
INLAND
HIGH WIND WATCH FOR HURRICANE FORCE WINDS: Announcement
issued for hurricane force winds 74 mph (64 knots)
or greater within 24 hours.
INSTABILITY:
Occurs when a rising air parcel becomes less dense
than the surrounding air. Since its temperature
will not cool as rapidly as the surrounding environment,
it will continue to rise on its own. Contrasts with
stable air.
INTERTROPICAL
CONVERGENCE ZONE (ITCZ): The axis dividing the
southeast trades from the northeast trades, toward
which the surface winds tend to converge The easterly
trade winds of both hemispheres converge at an area
near the equator called the "Intertropical
Convergence Zone (ICTZ)", producing a narrow
band of clouds and thunderstorms that encircle portions
of the globe.
ISOBAR:
The line drawn on a weather map connecting points
of equal barometric pressure.
J
Back
to top
JET
STREAM: Relatively strong winds concentrated
within a narrow current in the atmosphere.
K
Back
to top
KNOT:
A unit for the measurement of speed in the nautical
system. It is the nautical miles per hour.
L
Back
to top
LANDFALL:
The term used to describe where the hurricane eye
actually passes over land, usually used to describe
the continental States rather than islands in the
Caribbean.
LATITUDE:
The location north or south in reference to the
equator, which is designated at zero (0) degrees.
Parallel lines that circle the globe both north
and south of the equator. The poles are at 90 degrees
North and South latitude.
LEEWARD:
The side of an object or obstacle, such as a
ship's sail, a mountain, or a hill, furthest away
from the wind, and therefore, protected from the
direct force of the wind. The opposite of windward.
LOCAL
ACTION STATEMENT: A release prepared by a National
Weather Service Forecast Office in or near a threatened
area giving specific details for its area of responsibility.
LONGITUDE:
The location east or west in reference to the
Prime Meridian, which is designated as zero (0)
degrees longitude. The distance between lines of
longitude are greater at the equator and smaller
at the higher latitudes, intersecting at the earth's
North and South Poles. Time zones are correlated
to longitude.
LOW:
A region of low pressure.
LOW-LEVEL
INVEST: An investigative mission for tropical
disturbances to: 1) determine the existence or non-existence
of a "closed circulation" (winds blowing
in a complete circle); 2) supply weather observations
in required areas, and; 3) determine the vortex
center, if any. These missions are flown at 500
to 1500 feet.
LOW-PRESSURE
SYSTEM: 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. See closed low, cold low, and cut-off
low for further examples.
M
Back
to top
MAXIMUM
ENVELOPE OF WATER (MEOW): Describes the predicted
areas inundated and amount of storm surge for a
particular area during the landfall of a hurricane.
Used in the SLOSH Model.
MAXIMUM
ENVELOPE OF WIND (MEOW): Describes the predicted
areas inundated and amount of wind for a particular
area during the landfall of a hurricane. Used in
the Inland Wind Model.
MEAN
SEA LEVEL: The heights of the sea surface midway
between its average high and low water positions.
MILLIBAR
(MB): A metric measurement of atmospheric pressure
used by the National Weather Service.. Standard
surface pressure is 1,013.2 millibars.
N
Back
to top
NATIONAL
CENTERS FOR ENVIRONMENTAL PREDICTION (NCEP): As
part of the National Weather Service, the centers
provide timely, accurate, and continually improving
worldwide forecast guidance products. Some of the
centers include the Aviation Weather Center, the
Climate Prediction Center, the Storm Prediction
Center, and the Tropical Prediction Center. Formerly
known as NMC.
NATIONAL
HURRICANE CENTER (NHC): A Branch of the Tropical
Prediction Center under the National Weather Service,
it is responsible for tracking and forecasting tropical
cyclones over the North Atlantic, Caribbean, Gulf
of Mexico, and the Eastern Pacific.
NATIONAL
OCEANIC AND ATMOSPHERIC ADMINISTRATION (NOAA): An
Administration of the U.S. Department of Commerce,
it is the parent organization of the National Weather
Service. It promotes global environmental stewardship,
emphasizing atmospheric and marine resources.
NATIONAL
WEATHER SERVICE (NWS): A primary office of the
National Oceanic and Atmospheric Administration,
it is responsible for all aspects of observing and
forecasting atmospheric conditions and their consequences,
including severe weather and flood warnings.
NAUTICAL
MILE: A unit of length used in marine navigation
that is equal to a minute of arc of a great circle
on a sphere. One international nautical mile is
equivalent to 1,852 meters or 1.151 statue miles.
Refer to a sea mile.
NEXRAD
(NEXT GENERATION WEATHER RADAR): A network of
advanced Doppler radars implemented in the United
States between 1992 and 1996, it detects the location
and intensity of precipitation out to a range of
143 miles from the radar site. NEXRAD Doppler radar
is highly sensitive and can detect precipitation
from very light rain and snow up to the strongest
thunderstorms with accuracy and detail. Sometimes,
however, the radar's extreme sensitivity will cause
ground clutter and other non-precipitation echoes
to be displayed in the vicinity of the radar site
NOAA
WEATHER RADIO: A 24-hour continuous broadcast
of existing and forecasted weather conditions operated
and broadcast by the local field offices of the
National Weather Service.
NORTH
ATLANTIC BASIN (SOMETIMES CALLED THE ATLANTIC BASIN):
The Atlantic Ocean north of the equator, the
Caribbean Sea, and the Gulf of Mexico.
O
Back
to top
OCCLUDED
FRONT: The front formed by a cold front overtaking
a warm or stationary front and lifting the warm
air above the earth's surface
P
Back
to top
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.
POLAR-ORBITING
SATELLITE: A satellite whose orbit passes over
both of the earth's between poles. Compare with
a geostationary satellite.
PRE-EYE
LANDFALL TIME: The time before actual hurricane
eye landfall within which evacuation cannot be carried
out because of earlier effects, such as the inundation
of evacuation routes from the storm surge or rainfall
and the arrival of sustained gale force winds. It
is composed of the time of arrival of sustained
gale-force winds or the time roadway inundation
from storm surge/rainfall begins, whichever comes
first.
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.
PRESSURE:
The force per unit area exerted by the weight of
the atmosphere above a point on or above the earth's
surface. Also known as atmospheric pressure or barometric
pressure.
PROBABILITY
OF TROPICAL CYCLONE CONDITIONS: The probability,
in percent, that the cyclone center will pass within
50 miles to the right or 75 miles 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.
PUBLIC
INFORMATION OFFICER: A person appointed by a
County Emergency Operations Center to be responsible
for the formulating and coordinating of the dissemination
of emergency public information with both the electronic
and written media, ensuring that accurate information
is being released to the general public.
R
Back
to top
RADAR
(RADIO DETECTION AND RANGING): An electronic
instrument using ultra high-frequency radio waves
to detect distant objects and measure their range
by how they scatter or reflect radio energy. Precipitation
and clouds are detected by measuring the strength
of the electromagnetic signal reflected back. Doppler
radar and NEXRAD are examples
RAIN:
Precipitation in the form of liquid water droplets
greater than 0.5 mm. If widely scattered, the drop
size may be smaller. It is reported as "R"
in an observation and on the METAR. The intensity
of rain is based on rate of fall. "Very light"
(R--) means that the scattered drops do not completely
wet a surface. "Light" (R-) means it is
greater than a trace and up to 0.10 inch an hour.
"Moderate" (R) means the rate of fall
is between 0.11 to 0.30 inch per hour. "Heavy"
(R+) means over 0.30 inch per hour.
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.
RECONNAISSANCE
(RECCO) CODE: An aircraft weather reconnaissance
code that has come to refer primarily to in-flight
tropical weather observations, but actually signifies
any detailed weather observation or investigation
from an aircraft in flight.
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.
S
Back
to top
SAFFIR-SIMPSON
DAMAGE-POTENTIAL SCALE: A scale, developed in
the early 1970's by Herbert Saffir, a consulting
engineer, and Robert Simpson, then Director of the
National Hurricane Center, to measure the intensity
of a hurricane from 1 to 5. The scale categorizes
potential damage based on barometric pressure, wind
speeds, and storm surge. Scale numbers are available
to public safety officials when a hurricane is within
72 hours of landfall. Scale assessments are revised
regularly as new observations are made. Public safety
organizations are kept informed of new estimates
of the hurricane's disaster potential. In practice,
sustained surface wind speed (1-minute average)
is the parameter that determines the category since
storm surge is strongly dependent on the slope of
the continental shelf.
SATELLITE:
Used in reference to the manufactured objects that
orbit the earth, either in a geostationary or a
polar manner. Some of the information that is gathered
by weather satellites, such as GOES9, includes upper
air temperatures and humidity, recording the temperatures
of cloud tops, land, and ocean, monitoring the movement
of clouds to determine upper level wind speeds,
tracing the movement of water vapor, monitoring
the sun and solar activity, and relaying data from
weather instruments around the world.
SATELLITE
PICTURES: Pictures taken by a weather satellite,
such as GOES-9, that reveal information, such as
the flow of water vapor, the movement of frontal
systems, and the development of a tropical system.
Looping individual pictures aids meteorologists
in forecasting. One way a picture can be taken is
as a visible shot, which is best during times of
visible light (daylight). Another way is as an IR
(infrared) shot, which reveals cloud temperatures
and can be used day or night.
SEVERE
THUNDERSTORM WARNING: Indicates that severe
thunderstorms have been sighted or indicated on
radar.
SEVERE
THUNDERSTORM WATCH: Indicates that conditions
are favorable for lightning, damaging winds greater
than 58 miles an hour and hail and/or heavy rainfall.
SHELTER
PERIOD: The period in which people are forced
to evacuate their homes. This time may vary from
several hours to a couple of days depending upon
the severity of the hurricane.
SHUTTERS:
A physical wind barrier that is affixed over the
outside of windows and/or doors to protect these
vulnerable areas during a tropical storm. These
products are classified by the styles of panel,
accordion, or rolling and are manufactured from
steel, aluminum, plastic or plywood.
SLOSH
(SEA, LAKE AND OVERLAND SURGES FROM HURRICANES):
A computerized model that is able to estimate
the overland tidal surge heights and winds that
result from hypothetical hurricanes with selected
characteristics in pressure, size, forward speed,
track and winds. The resultant tidal surge is then
applied to a specific locale's shoreline, incorporating
the unique bay and river configurations, water depths,
bridges, roads and other physical features. The
model estimates open coastline heights as well as
surge heights over land, thus predicting the degree
of propagation or run-up of the surge into inland
areas.
SMALL
CRAFT ADVISORY: An advisory issued for marine
interests, especially for operators of small boats
or other vessels. Conditions include wind speeds
between 20 knots (23 mph) and 34 knots (39 mph).
Issued up to 12 hours ahead of conditions.
SPECIAL
MARINE WARNING: A warning for hazardous weather
conditions, usually short and not adequately covered
by existing marine warnings. Such conditions include
sustained winds or gusts of 35 knots or more for
2 hours or less.
SPIRAL
RAINBANDS: Bands of thunderstorms that spiral
inward towards the center, where they wrap themselves
around the eye.
SQUALL:
A sudden increase of wind speed by at least
18 miles per hour (16 knots) and rising to 25 miles
per hour (22 knots) or more and lasting for at least
one minute.
STANDARD
SURFACE PRESSURE: The measurement of one atmosphere
of pressure under standard conditions. It is equivalent
to 1,013.25 millibars, 29.92 inches of mercury,
760 millimeters of mercury, 14.7 pounds per square
inch, or 1.033 grams per square centimeter.
STATE
OF EMERGENCY: A declaration made by the Chief
Elected Official of a State, County or City government
which entails a heightened level of activation and
mobilization of staff to protect property and lives.
STATIONARY
FRONT: The boundary between two air masses,
neither of which is replacing the other.
STATUTE
MILE: Commonly known as a ground mile.
STORM:
An individual low-pressure disturbance, complete
with winds, clouds, and precipitation. Examples
include thunderstorms, tornadoes, or even tropical
cyclones. The name is associated with destructive
or unpleasant weather
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. Note: waves
on top of the storm surge will create an even greater
high-water mark.
STORM
TIDE: The actual level of seawater resulting
from the astronomic tide combined with the storm
surge. If the storm comes ashore during astronomical
low tide, the surge will be decreased by the amount
of the low tide. If the storm makes landfall during
astronomical high tide, the surge will be that much
higher.
STORM
TRACKS: The path or tracks generally followed
by a cyclonic disturbance.
SUBTROPICAL:
The region between the tropical and temperate regions,
an area between 35 and 40 degrees North and South
latitude. This is generally an area of semi-permanent
high pressure that exists and is where the Azores
and North Pacific Highs may be found.
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
DEPRESSION: A subtropical cyclone in which the
maximum sustained surface wind speed (using the
U.S. 1-minute average) is 38 mph (33 knots) or less.
SUBTROPICAL
HIGH: A semi-permanent high-pressure region
near 30 degrees latitude.
SUBTROPICAL
STORM: A subtropical cyclone in which the maximum
sustained surface wind speed (using the U.S. 1-minute
average) is 39 mph (34 knots) or more.
SWATH:
The width of the path of the hurricane. Usually
this path area is about 125 miles wide with 75 miles
to the right of the eye and 50 miles to the left
of the eye.
SYNOPTIC
SCALE: The size of migratory high and low pressure
systems in the lower troposphere that cover a horizontal
area of several hundred miles or more such as hurricanes.
Contrasts with macroscale, mesoscale, and storms.
SYNOPTIC
SURVEILLANCE 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.
T
Back
to top
THUNDER:
The sound that follows a flash of lightning and
is caused by sudden expansion of the air in the
path of the electrical discharge.
THUNDERSTORM:
A local storm produced by a cumulonimbus cloud,
always with lightning and thunder, and usually accompanied
by strong gusts of wind, heavy rain, and sometimes
hail.
TORNADO:
A violently rotating column of air in contact with
and extending between a convective cloud and the
surface of the earth. It is the most destructive
of all storm-scale atmospheric phenomena. They can
occur anywhere in the world given the right conditions,
especially after the landfall of hurricanes.
TRADE
WINDS: The wind system, occupying most of the
tropics, which are northeasterly in the Northern
Hemisphere and southeasterly in the Southern Hemisphere.
TROPICS/TROPICAL:
The region of the earth located between the
Tropic of Cancer, at 23.5 degrees North latitude,
and the Tropic of Capricorn, at 23.5 degrees South
latitude. It encompasses the equatorial region,
an area of high temperatures and considerable precipitation
during part of the year.
TROPICAL
CYCLONE: A general term for all cyclone circulations
originating over tropical waters. Its characteristics
include a warm-core, non-frontal pressure system
of synoptic scale that originates over the tropical
or subtropical waters and has a definite organized
surface. Used to define wind circulations rotating
around an atmosphere which include tropical depressions,
tropical storms, and hurricanes. The strongest winds
of this cyclone are near the Earth's center.
TROPICAL
CYCLONE PLAN OF THE DAY: A coordinated mission
plan that tasks operational weather reconnaissance
requirements during the next 1100 to 1100 UTC or
Zulu day or as required, describes reconnaissance
flights committed to satisfy both operational and
research requirements, and identifies possible reconnaissance
requirements for the succeeding 24-hour period.
TROPICAL
DEPRESSION (TD): A tropical cyclone in which
the maximum sustained surface winds (1 minute average)
are 38 miles per hour (33 knots) or less. Characteristically
having one or more closed isobars, it may form slowly
from a tropical disturbance or an easterly wave,
which has continued to organize. At this point,
it gets a cyclone number, starting with "TD01"
at the beginning of each storm season.
TROPICAL
DISTURBANCE: A discrete system of clouds, showers,
and thunderstorms (organized convection) that originate
in the tropics. Generally 100 to 300 miles in diameter
and originating in the tropics or subtropics, disturbances
have a nonfrontal migratory character, and maintain
their identity for 24 hours or more. It may or may
not be associated with a detectable perturbation
of the wind field. An upper level of low pressure
causes this to occur. Approximately 100 of these
types of events occur annually during hurricane
season.
TROPICAL
PREDICTION CENTER: A Division of the National
Centers for Environmental Prediction, the Center
issues watches, warnings, forecasts, and analyses
of hazardous weather conditions in the tropics for
both domestic and international communities which
include the Atlantic, Caribbean, Gulf of Mexico
and Eastern Pacific. The National Hurricane Center
is one of its Branches.
TROPICAL
STORM (TS): A tropical cyclone in which the
maximum sustained surface wind speed (1 minute average)
is within the range of 39 to 73 mph (34 to 63 knots).
At this point, the system is given a name to identify
and track it. In the Atlantic/Caribbean/Gulf of
Mexico basin, the names start with "A"
each season.
TROPICAL
STORM WATCH: An announcement issued by the National
Hurricane Center for specific areas that a tropical
storm or a forecast of tropical storm conditions
poses a possible threat to coastal areas generally
within 36 hours. A tropical storm watch normally
should not be issued if the system is forecast to
attain hurricane strength.
TROPICAL
STORM WARNING: A warning issued by the National
Hurricane Center for tropical storm conditions including
possible sustained winds within the range 39 to
73 mph (34 to 63 knots) which are expected in a
specified coastal area within 24 hours or less.
TROPICAL
WAVE: Another name for an easterly wave, it
is an area of relatively low pressure (trough) moving
westward through the trade wind easterlies. Generally,
it is associated with extensive cloudiness and showers,
and may be associated with possible tropical cyclone
development.
TYPHOON:
A hurricane that occurs in the Pacific Region of
the Philippines or the China Sea.
U
Back
to top
UPWELLING:
The process by which water rises from a lower to
a higher depth, usually as a result of divergence
and offshore currents. It influences climate by
bringing colder, more nutrient-rich water to the
surface. This is a vital factor of the El Niño event.
UNIVERSAL
TIME COORDINATE (UTC): One of several names
for the twenty-four hour time that is used throughout
the scientific and military communities. Other names
for this time measurement are Greenwich Mean Time
(GMT) or Zulu Time (Z). See Greenwich Mean Time
for more information.
V
Back
to top
VORTEX:
Any circular or rotary flow in the atmosphere that
possesses vorticity.
VORTEX
FIX: The location of the surface and/or flight
level center of a tropical or subtropical cyclone
obtained by reconnaissance aircraft penetration.
VORTICITY:
The measurement of the rotation of a small air parcel.
It has vorticity when the parcel spins as it moves
along its path. Although the axis of the rotation
can extend in any direction, meteorologists are
primarily concerned with the rotational motion about
an axis that is perpendicular to the earth's surface.
If it does not spin, it is said to have zero vorticity.
In the Northern Hemisphere, the vorticity is positive
when the parcel has a counterclockwise, or cyclonic,
rotation. It is negative when the parcel has clockwise,
or anticyclonic, rotation.
W
Back
to top
WARM
FRONT: The leading edge of an advancing warm
air mass that is replacing a retreating relatively
colder air mass. Generally, with the passage of
a warm front, the temperature and humidity increase,
the pressure rises, and although the wind shifts
(usually from the southwest to the northwest in
the Northern Hemisphere), it is not as pronounced
as with a cold frontal passage. Precipitation, in
the form of rain, snow, or drizzle, is generally
found ahead of the surface front, as well as convective
showers and thunderstorms. Fog is common in the
cold air ahead of the front. Although clearing usually
occurs after passage, some conditions may produced
fog in the warm air. See occluded front and cold
front.
WARNING:
An announcement that is issued when severe weather:
1) has developed; 2) is already occurring and reported;
or 3) is detected on radar. Warnings state a particular
hazard or imminent danger, such as tornadoes, severe
thunderstorms, flash and river floods, hurricanes,
etc
WEATHER
SURVEILLANCE RADAR (WSR-88D): The newest generation
of Doppler radars. These radar units, with help
from a set of computers, show very detailed images
of precipitation and other phenomena, including
air motions within a storm.
WINDWARD:
The direction from which the wind is blowing. Also
known as the upwind side of an object. It is the
opposite of the downwind or leeward side.
Z
Back
to top
ZULU
TIME (Z): One of several names for the twenty-four
hour time that is used throughout the scientific
and military communities. Other names for this time
measurement are Universal Time Coordinate (UTC)
or Greenwich Mean Time (GMT). See Greenwich
Mean Time for more information.
