WORLD METEOROLOGICAL ORGANIZATION
___________________________________________
THE SEVENTH TROPICAL CYCLONE RSMCs/TCWCs
TECHNICAL COORDINATION MEETING
CITEKO, WEST JAVA, INDONESIA
TCM-7/Doc. 4.10.1
(8.XI.2012)
___________
ITEM 4.10.1
ENGLISH ONLY
12 TO 15 NOVEMBER 2012
COORDINATION
Review of terminology/classification of tropical cyclones
List of terminology of tropical cyclones
(Submitted by the Secretariat)
Summary and Purpose of Document
This document provides the list of tropical cyclone terminology adopted at the
previous coordination meeting and some pending issues from TCM-6.
ACTION PROPOSED
The meeting is invited to review the list of terminology and consider possible revision of as well
as addition to the list.
__________________
TCM-7/Doc. 4.10.1, p. 2
LIST OF TERMINOLOGY OF TROPICAL CYCLONES
1.
List of Standardized Terminology adopted at TCM-6
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.
CENTRE OF THE TROPICAL CYCLONE – The centre of the cloud eye or, if not discernible, 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 less than 30 nautical miles (55 kilometers)
“Position fair” – implies a radius of 30 to 60 nautical miles (55 to 110 km) and
“Position poor” – implies a radius of greater than 60 nautical miles (110 km).
DIRECTION OF MOVEMENT OF THE TROPICAL CYCLONE – The direction towards which the centre
of the tropical cyclone is moving.
EXTRA-TROPICAL CYCLONE – Low –pressure system which develops in latitudes outside the tropics.
EXTRATROPICAL TRANSITION – is an evolutionary process by which a symmetric warm-core tropical
cyclone transforms to an asymmetric cold core extratropical cyclone. This process includes a change in
the distribution of clouds, winds, and precipitation. Also, the primary energy source changes from latent
heat release in deep convective clouds of the tropical cyclone to baroclinic conversion of available
potential energy in the extratropical cyclone.
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 – maximum sustained surface wind speed of 34 to 47 knots.
HURRICANE/TYPHOON FORCE WIND – maximum sustained surface wind speed of 64 knots or more.
LOW PRESSURE AREA – Region of the atmosphere in which the pressures are lower than those of the
surrounding region at the same level.
.upon the regional practices.
RECONNAISSANCE AIRCRAFT CENTRE FIX OF THE TROPICAL CYCLONE, VORTEX FIX – The
location of the centre of a tropical cyclone obtained by reconnaissance aircraft penetration.
SPEED OF MOVEMENT OF THE TROPICAL CYCLONE – Speed of movement of the centre of the
tropical cyclone.
STORM FORCE WIND – maximum sustained surface wind speed of 48 to 63 knots
TCM-7/Doc. 4.10.1, p. 3
STORM SURGE – The difference between the actual water level under 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 TIDE – The actual sea level as influenced by a weather disturbance. The storm tide consists of
the normal astronomical tide and the storm surge.
SUB-TROPICAL CYCLONE – A low pressure system, developing over sub-tropical waters which
initially contains few tropical characteristics. With time the sub-tropical cyclone can become tropical.
TROPICAL CYCLONE – Generic term for a warm-core non-frontal synoptic scale cyclone originating
over tropical or sub-tropical waters with organized deep convection and closed cyclonic surface wind
circulation. The term is also used for a storm in the South-West Indian Ocean in which the maximum
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 sustained surface wind speed greater than 33 knots.
TROPICAL DEPRESSION WIND – maximum sustained surface wind speed less than 34 knots
TROPICAL DISTURBANCE – A non-frontal synoptic scale cyclone originating in the tropics or subtropics with enhanced convection and light surface winds.
TROPICAL STORM WIND – maximum sustained surface wind speed of 34 to 63 knots
TROPICAL WAVE – A trough or cyclonic curvature maximum in the trade wind easterlies or equatorial
westerlies. The wave may reach maximum amplitude in the lower middle troposphere, or may be the
reflection of an upper-troposphere cold low or equatorial extension of a mid-latitude trough.
ZONE OF DISTURBED WEATHER – A zone in which the pressure is low relative to the surrounding
region and there are convective cloud masses which are not organized.
WEATHER WARNING – Meteorological message issued to provide appropriate warnings of hazardous
weather conditions.
2.
Pending Issues from TCM-6
2.1
TCM-6 noted that a few words such as “EXTRA-TROPICAL CYCLONE” and
“EXTRATROPICAL TRANSITION” have slightly different definitions in respective RSMC/TCWC basins.
It recommended paying adequate attention to these differences among the basins in the international
use of the terms. Definitions of EXTRA-TROPICAL CYCLONE” and EXTRATROPICAL TRANSITION
given in the regional operational plans/manual are presented in ANNEX.
2.2
TCM-6 discussed definition of four terms - TC STRIKE, TC INPACT, TC COASTAL
CROSSING and TC LANDFALL for which IWTC-VI (Costa Rica, 2006) recommended to provide agreedupon common definitions. After TCM-6, Mr Jim Davidson, Chair of TCM-6, suggested following
definitions for consideration at TCM-7.
TC INPACT - Coastal evidence of damaging TC-generated hazard(s). (includes damaging large
swells from distant TCs).
TC COASTAL CROSSING - Eye passage across the coast.
TC LANDFALL - TC Strike (equivalence). Eye passage across the coast OR a "glancing blow"
(defined by wind gusts reaching at least 100 km/h).
______
TCM-7/Doc. 4.10.1, ANNEX
Definitions of “EXTRA-TROPICAL CYCLONE” and “EXTRATROPICAL TRANSITION”
in the regional Operational Plans/Manual
1.
Typhoon Committee:
EXTRA-TROPICAL CYCLONE: Low-pressure system which develops in latitudes outside the tropics.
EXTRATROPICAL TRANSITION: No definition.
2.
Panel on Tropical Ccyclones
EXTRA-TROPICAL CYCLONE: No definition.
EXTRATROPICAL TRANSITION: No definition.
3.
RA I TCC
EXTRA-TROPICAL CYCLONE: No definition, but
Extra-tropical disturbance : synoptic scale low pressure area outside of the tropics or former
tropical disturbance having lost its tropical characteristics.
Sub-tropical disturbance : synoptic scale low pressure area having during its life, characteristics
which could belong to both tropical and extra-tropical depressions. In the South West Indian
Ocean, the genesis of such system is regularly observed over the South of Mozambique
Channel.
EXTRATROPICAL TRANSITION: no definition, but
Post-tropical depression: A former tropical system (tropical depression, tropical storm or tropical
cyclone) in the extra-tropical transition phase, which no longer presents all the characteristics of a
tropical system but has not yet completed its transition and cannot, therefore, be considered an
extra-tropical depression and qualified as such.
4.
RA IV HC
Subtropical Cyclone : A non-frontal low-pressure system that has characteristics of both tropical
and extratropical cyclones. Like tropical cyclones, they are non-frontal, synoptic-scale cyclones
that originate over tropical or subtropical waters, and have a closed surface wind circulation
about a well-defined center. In addition, they have organized moderate to deep convection, but
lack a central dense overcast. Unlike tropical cyclones, subtropical cyclones derive a significant
proportion of their energy from baroclinic sources, and are generally cold-core in the upper
troposphere, often being associated with an upper-level low or trough. In comparison to tropical
cyclones, these systems generally have a radius of maximum winds occurring relatively far from
the center (usually greater than 60 n mi), and generally have a less symmetric wind field and
distribution of convection. It includes Subtropical Storm and Subtropical Depression.
TCM-7/Doc. 4.10.1, ANNEX, p. 2
Also in ATTACHMENT I A:
EXTRA-TROPICAL CYCLONE: A cyclone which attributes the majority of its energy from baroclinic
processes. An extra-tropical cyclone has significant vertical wind shears, and a distinctive
asymmetric temperature and moisture field. It may develop a cold core in its later stages.
EXTRATROPICAL TRANSITION: no definition.
5.
RA V TCC
EXTRA-TROPICAL CYCLONE: No Definition, but
Declassifying a Tropical Cyclone: A tropical cyclone will be declassified whenever observations
and/or Dvorak intensity analysis indicate that the system has less than gale force winds near the
centre or the system has transformed into an extra-tropical cyclone structure. Reference to the
cyclone’s name is usually dropped a short while after declassification.
EXTRATROPICAL TRANSITION: no definition.