5. Meaning of terms used for international exchange
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TERM |
MEANING |
Average wind speed
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Speed of the wind averaged over the previous 10 minutes
(mean surface wind) as read from the anemogram or the 3 minutes
mean determined with the non-recording anemometer
or estimated wind at sea by the mariners using the Beaufort scale. |
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Bulletin
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Cyclone warning bulletin
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Central pressure of a tropical cyclone
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Surface 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 estimated location of the centre of a tropical cyclone.
(obtained by means other than the aircraft probing of the cyclone ie fixation
of the centre with the help of lan-based and other radars, satellite and
conventional observations like surface and upper-air observations,
ships' reports, commercial aircraft observations, etc.)
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Centre of the tropical cyclone |
The centre of the cloud eye, or if not discernible,
of the wind/pressure 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 30 nautical miles (55 kilometres) or less.
- 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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Cyclone
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Tropical cyclone
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Cyclone Alert*
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A priority message for the
Government officials containing tropical cyclone information and advisories issued
generally 48 hours before the commencement of adverse weather.**
A priority message for the Government officials containing information on the
formation of a tropical disturbance as soon as it is detected.+
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Cyclonic disturbance
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A nonfrontal synoptic
scale low pressure area originating over tropical waters with organized
convection and definite cyclonic wind circulation.
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Cyclone warning*
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A priority message
containing tropical cyclone warning and advisories issued generally 24 hours
in advance of the commencement of adverse weather.
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Cyclone warning bulletin
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A priority
message for exchange of tropical cyclone information and advisories.
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Cyclonic storm
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A cyclonic disturbance
in which the maximum average surface wind speed is in the range of 34 to
47 knots (62 to 88 km/h).
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Depression*
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A cyclonic disturbance
in which the maximum sustained surface wind speed is between 17 and 33 knots
(31 and 61 km/h).
If the maximum sustained wind speed lies in the range 28 knots
(52 km/h) to 33 knots (61 km/h) the system may be called a
"deep depression".
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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 calm area inside the circular wall
of convective clouds, the geometric centre of which is
the centre of the tropical cyclone.
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Gale force wind
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Average surface wind speed of 34 to 47 knots (62 to 88 km/h).
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Global Maritime Distress and Safety SystemGlobal Maritime Distress and Safety System
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GMDSS
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Global Maritime Distress and Safety System.
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Gust
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Instantaneous peak value of surface wind speed,
recorded or expected.
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Hurricane force wind
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Average surface wind speed 64 knots or more.
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Low or Low pressure area
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An area enclosed by a closed isobar with minimum pressure
inside when mean surface wind is less than 17 knots (31 km/h).
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Maximum sustained wind |
Maximum
value of the average wind speed at the surface. |
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Mean wind speed |
Average wind speed. |
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Name of the Tropical Cyclone |
Once wind speed in a cyclonic disturbance attains a 34 kt
threshold value it will be given an identification name by RSMC -
tropical cyclones New Delhi from the consolidated name list.
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Panel members or member countries or countries |
Countries constituting the WMO/ESCAP Panel on
Tropical Cyclones viz: Bangladesh, India, Maldives, Myanmar,
Oman (Sultanate of), Pakistan, Sri Lanka and Thailand.
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Post-Landfall Outlook |
This bulletin is issued 12 hours before cyclone landfall and
contains more specific forecasts about place and time of landfall.
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Pre Cyclone Watch |
This bulletin contains early warning about likely development of
a cyclonic storm and an indication of the coastal belt likely
to experience adverse weather.
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Severe cyclonic storm |
A cyclonic disturbance in which the maximum average surface wind speed
is in the range of 48 to 63 knots (89 to 118 km/h).
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Severe cyclonic storm with a core of hurricane winds+
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A cyclonic disturbance in which the maximum average surface
wind speed is 64 knots (119 km/h) or more.
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Speed of movement of the tropical cyclone |
Speed of movement of the centre of the tropical cyclone.
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Squally wind |
When sudden increases of wind speed occur
in squalls with the increased speed reaching a minimum
of 22 knots (40 km/h) and persist for at least one minute.
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Storm force wind |
Average surface wind speed of 48 to 63 knots. |
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Storm season |
The periods April to May and October to December during which most of
the cyclonic storms occur in the Bay of Bengal and Arabian Sea.
The periods April to May and October to mid-December during which
most of the cyclonic storms occur in
the Bay of Bengal.
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Storm surge |
The
difference between the actual water level
under the influence of a meteorological disturbance
(storm tide) and the level which would have
been attained in the absence of the meteorological
disturbance (i.e. astronomical tide).
(Storm surge results mainly from the shoreward
movement of water under the action of wind
stress. A minor contribution is also made
by the hydrostatic rise of water resulting
from the lowered barometric pressure).
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Storm tide |
The
actual water level as influenced by a weather
disturbance. The storm tide consists of the
normal astronomical tide and the storm surge.
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Super cyclone |
A cyclonic disturbance in which maximum wind speed is
120 knots and above (222 km/h and above).
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Tropical cyclone |
Generic term for a non frontal synoptic scale cyclone originating
over tropical or subtropical waters with organized convection and
definite cyclonic surface wind circulation. The term is also used
for a storm in the South-West Indian Ocean in which the maximum of
sustained wind speed#
is estimated to be in the range of 64 to 90 knots and in the
South Pacific and South-East Indian Ocean with
the maximum of the sustained wind speed over 33 knots.
(Note: #Maximum sustained wind speed: Average period of one, three,
or ten minutes depending upon the regional practices.)
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Tropical cyclone advisory |
A priority
message for exchanging information, internationally,
on tropical cyclones in the Bay of Bengal and the Arabian Sea.
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Tropical depression |
Depression |
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Tropical storm |
Tropical cyclone |
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Tropical Weather Outlook |
A priority message for exchange between the Panel countries of
synoptic and satellite inferences for the Bay of Bengal and the Arabian Sea region.
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Very severe cyclonic storm |
A cyclonic disturbance in which maximum wind average is 64 knots
to 119 knots (119 to 221 km/h).
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Visual storm signals |
Visual
signals displayed at coastal points to warn
ships of squally winds, gales and tropical cyclones.
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Weather warning |
Meteorological message issued to provide appropriate warnings
of hazardous weather conditions.
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Zone of disturbed weather |
A zone
in which the pressure is low relative to the
surrounding region and there is convective
cloud masses which are not organized.
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