Advisory:
Official information
issued by tropical cyclone warning centers describing all
tropical cyclone watches and warnings in effect along with
details concerning tropical cyclone locations, intensity and
movement, and precautions that should be taken. Advisories are
also issued to describe: (a) tropical cyclones prior to issuance
of watches and warnings and (b) subtropical cyclones.
Cyclone:
An atmospheric closed
circulation rotating counter-clockwise in the Northern Hemisphere
and clockwise in the Southern Hemisphere.
Eye:
The relatively calm
center of the tropical cyclone that is more than one half
surrounded by wall cloud.
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.
Gale Warning:
A warning of 1-minute
sustained surface winds in the range 34 kt (39 mph or 63 kph) to
47 kt
(54 mph or 87 kph)
inclusive, either predicted or occurring not directly associated
with tropical cyclones.
Hurricane/Typhoon:
A warm-core tropical
cyclone in which the maximum sustained surface wind (using the
U.S. 1-minute average) is 64 kt (74 mph or 119 kph) or more. The
term hurricane is used for Northern Hemisphere cyclones east of
the International Dateline to the Greenwich Meridian. The term
typhoon is used for Pacific cyclones north of the Equator west of
the International Dateline.
Hurricane
Local Statement:
A public release
prepared by local National Weather Service offices in or near a
threatened area giving specific details for its county/parish
warning area on (1)weather conditions, (2) evacuation decisions
made by local officials, and (3) other precautions necessary to
protect life and property.
Hurricane
Warning:
A warning that
sustained winds 64 kt (74 mph or 119 kph) or higher associated
with a hurricane are expected in a specified coastal area in 24
hours or less. A hurricane warning can remain in effect when
dangerously high water or a combination of dangerously high water
and exceptionally high waves continue, even though winds may be
less than hurricane force.
Hurricane
Watch:
An announcement of
specific coastal areas that a hurricane or an incipient hurricane
condition poses a possible threat, generally within 36 hours.
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.
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.
Tropical
Depression:
A tropical cyclone in
which the maximum sustained surface wind speed (using the U.S.
1-minute average) is 33 kt (38 mph or 62 kph) or less.
Tropical
Disturbance:
A discrete tropical
weather system of apparently organized convection--generally 100
to 300 nmi in diameter---originating in the tropics or
subtropics, having a nonfrontal migratory character, and
maintaining its identity for 24 hours or more. It may or may not
be associated with a detectable perturbation of the wind field.
Tropical
Storm:
A tropical cyclone in
which the maximum sustained surface wind speed (using the U.S.
1-minute average) ranges from 34 kt (39 mph or 63 kph) to 63 kt
(73 mph or 118 kph).
Tropical
Storm Warning:
A warning for tropical
storm conditions including sustained winds within the range of 34
to 63 kt (39 to 73 mph or 63 to 118 kph) that are expected in a
specified coastal area within 24 hours or less.
Tropical
Storm Watch:
An announcement that a
tropical storm poses or tropical storm conditions pose a threat
to coastal areas generally within 36 hours. A tropical storm
watch should normally not be issued if the system is forecast to
attain hurricane strength.
Tropical
Wave:
A trough or cyclonic
curvature maximum in the trade-wind easterlies. The wave may
reach maximum amplitude in the lower middle troposphere.
Terms
from the National Hurricane Center