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Tropical Cyclone
Advisories & Warnings
 Bay of Bengal and the
 Arabian Sea
This web site is operated
on behalf of WMO by

Hong Kong Observatory
of Hong Kong, China.
Terminologies used in the region of the Bay of Bengal and the Arabian Sea
 
  1. General
  2. Classification of tropical cyclones
  3. Tropical cyclone characteristics
  4. Terms related to the warning and warning system
  5. Meaning of terms used for international exchange
  6. Names of Tropical Cyclone at the Bay of Bengal and the Arabian Sea
    Tropical cyclones are identified by a location code, that is BOB for those in the Bay of Bengal and for those in the Arabian Sea it will be ARB, followed by a four-digit number. The number will comprise the last two digits of the year followed by a two-digit sequential number, starting with 01 each year.
    Example: The second tropical cyclone of 2004 in the Bay of Bengal will be identified as BOB 0402.
 
  1. General
* Term used nationally in Bangladesh, India and Pakistan;
 
  2. Classification of cyclonic disturbances and tropical cyclones
+ Term used nationally in Bangladesh.
* Term used nationally in Bangladesh, India and Pakistan;
 
  3. Tropical cyclone characteristics
 
  4. Terms related to the warning and warning system
** Term used nationally in India
* Term used nationally in Bangladesh, India and Pakistan;
 
  5. Meaning of terms used for international exchange
  A  |  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 
TERM MEANING
Average wind speed 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.
   
Bulletin Cyclone warning bulletin
   
Central pressure of a tropical cyclone Surface pressure at the centre of the tropical cyclone as measured or estimated.
 
Centre fix of the tropical cyclone 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.)
 
Centre of the tropical cyclone The centre of the cloud eye, or if not discernible, of the wind/pressure centre.
 
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).
 
Cyclone Tropical cyclone
 
Cyclone Alert* 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.+
   
Cyclonic disturbance A nonfrontal synoptic scale low pressure area originating over tropical waters with organized convection and definite cyclonic wind circulation.
   
Cyclone warning* A priority message containing tropical cyclone warning and advisories issued generally 24 hours in advance of the commencement of adverse weather.
   
Cyclone warning bulletin A priority message for exchange of tropical cyclone information and advisories.
   
Cyclonic storm 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).
   
Depression* 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".
   
Direction of movement
of the tropical cyclone
The direction towards which the centre of the tropical cyclone is moving.
   
Eye of the tropical cyclone 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.
   
Gale force wind Average surface wind speed of 34 to 47 knots (62 to 88 km/h).
   
Global Maritime Distress and Safety SystemGlobal Maritime Distress and Safety System
   
GMDSS Global Maritime Distress and Safety System.
   
Gust Instantaneous peak value of surface wind speed, recorded or expected.
   
Hurricane force wind Average surface wind speed 64 knots or more.
   
Low or Low pressure area An area enclosed by a closed isobar with minimum pressure inside when mean surface wind is less than 17 knots (31 km/h).
   
Maximum sustained wind Maximum value of the average wind speed at the surface.
 
Mean wind speed Average wind speed.
   
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.
   
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.
   
Post-Landfall Outlook This bulletin is issued 12 hours before cyclone landfall and contains more specific forecasts about place and time of landfall.
 
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.
 
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).
 
Severe cyclonic storm with a core of hurricane winds+ A cyclonic disturbance in which the maximum average surface wind speed is 64 knots (119 km/h) or more.
 
Speed of movement of the tropical cyclone Speed of movement of the centre of the tropical cyclone.
 
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.
 
Storm force wind Average surface wind speed of 48 to 63 knots.
 
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.
 
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).
 
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.
 
Super cyclone A cyclonic disturbance in which maximum wind speed is 120 knots and above (222 km/h and above).
 
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.)
 
Tropical cyclone advisory A priority message for exchanging information, internationally, on tropical cyclones in the Bay of Bengal and the Arabian Sea.
 
Tropical depression Depression
 
Tropical storm Tropical cyclone
 
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.
 
Very severe cyclonic storm A cyclonic disturbance in which maximum wind average is 64 knots to 119 knots (119 to 221 km/h).
 
Visual storm signals Visual signals displayed at coastal points to warn ships of squally winds, gales and tropical cyclones.
   
Weather warning Meteorological message issued to provide appropriate warnings of hazardous weather conditions.
   
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.
   
+ Term used nationally in Bangladesh.
* Term used nationally in Bangladesh, India and Pakistan;

The above information is extracted from World Meteorological Organization Technical Document, Tropical Cyclone Programme, Report No. TCP-21, Typhoon Cyclone Operational Plan for the Bay of Bengal and the Arabian Sea 2010 Edition
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