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5. Meaning of terms used for regional exchange
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B |
C |
D |
E |
F |
G |
H |
I |
J | K | L |
M |
N |
O |
P |
Q | R |
S |
T |
U |
V |
W |
X | Y |
Z
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| TERM |
MEANING |
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Advice
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See Tropical cyclone advice |
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Alert
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See Tropical cyclone alert. |
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Average wind speed
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Speed of the wind averaged over the previous 1**** or 10 minutes. |
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Central pressure
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Pressure at the centre of the
tropical cyclone as measured or estimated.
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Centre fix of the tropical cyclone
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The position of the centre of the tropical cyclone.
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Centre of the tropical cyclone |
The estimated position of the surface centre. |
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Confidence in the centre position |
Degree of confidence in the centre position of a
tropical cyclone expressed as the radius of
the smallest circle within which the centre
may be located by the analysis.
- Position good implies a radius
of less than 30 nautical miles (55 kilometres).
- Position fair, a radius of
30 to 60 nautical miles (55 to 110 km) and
- Position poor, a radius of
greater than 60 nautical miles (110 km).
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| Convergence zone
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A zone where air
streams of different directions or speeds merge.
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| Cyclone
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See Tropical cyclone
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Depression
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A synoptic low pressure area with
extra-tropical characteristics where the average wind speed
may exceed 33 knots (63 km per hour) or Beaufort Force 7.
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Direction of movement
of the tropical cyclone
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The direction towards which the centre of the tropical
cyclone is moving.
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Eye of the tropical cyclone
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The relatively clear and clam area inside the circular,
convective wall clouds.
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Gale force wind
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Average surface wind speed of 34 to 47 knots (63 to 87 km per
hour or wind force of 8 or 9 in the Beaufort Scale).
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Gale warning
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Meteorological message intended to warn those concerned of
the occurrence or expected occurrence of gale force winds.
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Gust
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Sudden, brief increase of the wind speed over its average value.
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Hurricane or severe tropical cyclone
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A tropical cyclone with hurricane force winds.
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Hurricane force wind
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Average surface wind speed 64 knots (118 km per hour,
Beaufort Force 12) or more.
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Hurricane warning
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Meteorological message intended to warn those concerned
of the impact of a tropical cyclone with hurricane force winds.
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Intertropical Convergence Zone (ITCZ)
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A relatively narrow zone where the trade winds from both the
Northern Hemisphere and the Southern Hemisphere merge.
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Mean wind speed |
Average wind speed. |
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| Monsoon trough |
A shear zone with westerly monsoon winds on the equatorial
side and easterly trade winds on the polarward side. |
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Naming a Tropical Cyclone
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A non-frontal low pressure system of synoptic scale
developing over warm waters will be named whenever
observations and/or Dvorak intensity analysis indicate the
presence of gale force or stronger winds near the centre
which are likely to continue.
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South Pacific Convergence Zone (SPCZ) |
A semi-permanent convergence zone found in the tropical
South Pacific marked by the boundary between the usually
cooler and stronger southeast trade wind flow and warmer
and lighter east or northeast winds, or northwesterly winds
when the SPCZ is active.
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Special Advisory |
A message to a National Meteorological Centre giving
information on a tropical disturbance or a tropical cyclone.
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Special Weather Bulletin |
Bulletins issued, whenever the need arises, to put the
community on the alert, to give progress reports on development
or to give specific warnings of tropical cyclones or other
disturbances.
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Speed of movement
of the cyclone |
Speed of movement of the centre of the tropical cyclone.
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| Storm force wind |
Average surface wind speed of 48 to 63 knots (88 to 117
kilometres per hour or Beaufort Fource 10 or 11). |
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Storm surge |
The
difference between the actual sea level
under the influence of a meteorological disturbance
(storm tide) and the normal astronomical tide.
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Storm tide |
The actual sea level as influenced by a weather disturbance.
The storm tide consists of the normal astronomical tide
and the storm surge.
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Storm warning* |
Meteorological message intended to warn those concerned of
the impact of storm force winds.
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Sustained wind speed
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See Average wind speed. |
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Tropical cyclone |
A non-frontal low pressure system of synoptic scale developing
over warm waters and having a definite organized wind circulation
with a maximum 10-minute average wind speed of 34 knots
(63 km per hour, ie. gale force) or greater near the centre.
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Tropical cyclone advice |
A tropical cyclone watch and/or a tropical cyclone warning.
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Tropical cyclone alert
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A special weather bulletin providing information on the progress of a cyclone
still some distance away and with a significant probability of giving gales
or stronger winds to a community in the next 24 to 48 hours.
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| Tropical cyclone season
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The period of the year with a relatively high incidence of
tropical cyclones. In the South Pacific and South-East Indian
Ocean, it is the period from 1 November to 30 April.
(Note: cyclones occasionally occur outside of this period.)
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Tropical cyclone warning
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A warning of gales or stronger winds associated with a tropical cyclone
occurring within 24 hours.
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Tropical cyclone watch
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A forecast messge of gales or stronger winds associated with a
tropical cyclone occurring after 24 hours and before 48 hours.
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| Tropical cyclone year
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1 July to 30 June.
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Tropical depression
= tropical low |
A tropical disturbance with a clearly defined cyclonic wind
circulation in which the central position can be estimated,
and a maximum 10-minute average wind speed of less than 34 knots
(63 km per hour ie. gale force) near the centre. There may be gale
force or stronger winds in one or more quadrants but not near the centre.
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Tropical disturbance |
A non-frontal system of synoptic scale originating over the
tropics with persistent enhanced convection and/or some
indications of cyclonic wind circulation.
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Tropical Disturbance Advisory / Bulletin / Summary |
A message for exchanging information, internationally,
on a range of disturbances including tropical depressions
and tropical cyclones.
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Tropical low |
See Tropical depression
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Tropical storm |
A tropical cyclone with gale or storm force winds. |
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Trough or trough of low pressure |
An elongated zone of low pressure, V-shaped in the easteries
in the Southern Hemisphere and an inverted V-shape in the westerlies.
The axis of a trough is known as the trough line.
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Watch |
Tropical Cyclone Watch
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Weather Bulletin |
A bulletin issued at regular times to give weather information and
forecasts to the general public or marine interests.
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* Storm warning: Papua New Guinea uses the term
for all events with storm force or stronger winds
**** Used by Micronesia and USA (American Samoa)
