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Global Guide to Tropical Cyclone Forecasting:
CHAPTER 1: GLOBAL OVERVIEW

1.2 THE GLOBAL TROPICAL CYCLONE FORECASTING NETWORK

The global functions of the WMO are divided into six continental regions (WMO, 1973). Respectively, these regions (Region I through VI) encompass the landmasses of Africa, Asia, South America, North and Central America, southwest Pacific and Europe, together with their surrounding islands and oceanic areas.

The WMO Tropical Cyclone Programme (WMO/TCP) seeks to promote and coordinate the planning and implementation of measures to mitigate tropical cyclone disasters on a worldwide basis. Since not all regions are effected by tropical cyclones, and the regional structure does not always coincide with tropical cyclone basins, the TCP has established tropical cyclone committees that extend across the regional bodies (Table 1.1). These committees also extend across the ocean basins defined in Table 1.2. The WMO Technical Manuals referred to in Table 1.1 contain practical information, such as: station duties, addresses, telephone and other communication numbers, communication procedures, terminology, definitions, procedures, tropical cyclone naming conventions, unit conversions, coordination, analysis requirements, radar and satellite observations and dissemination, aircraft reconnaissance (where applicable), and wording of warnings. Through the efforts of the WMO/TCP there has been considerable procedural standardisation among the regional bodies. However, some differences still remain, as discussed in this section.

1.2.1 Tropical Cyclone Warnings

There are two general types of tropical cyclone warnings: those for land areas and coastal waters and those for the high seas (sometimes referred to as marine warnings). Each Member of a regional body is normally responsible for its land and coastal waters warnings. There are some exceptions, however, for example, the United States National Hurricane Center in Miami, Florida (NHC), issues warnings for Haiti, Aruba and the Netherlands Antilles, St. Barthelemy, St. Martin and their coastal waters. The relevant details are discussed in the appropriate WMO Manuals cited in Table 1.1.

The areas of high seas warning responsibility are defined in the manuals specified in Table 1.1 and are indicated in Figs. 1.1, 1.2, 1.4, 1.5 and 1.6. The area of responsibility for JTWC extends over several ocean basins, as shown in Fig. 1.3.

1.2.2 Naming of Tropical Cyclones

The assignment of a name or number to a tropical cyclone facilitates identification of a given cyclone in both operations and archives. The three non-ESCAP (Economic and Social Commission for Asia and the Pacific) regional bodies and the JTWC use cyclone names, but the two ESCAP bodies (and JTWC for certain basins) use a numbering system. Names or numbers are assigned whenever the intensity of a cyclone reaches a threshold intensity of 63 km h^-1 (34 kt). The Cyclone Operational Plan for the Bay of Bengal, uses a threshold intensity of 52 km h^-1 (28 kt). However, Mandal (personal communication, 1993) indicates that the operational practice is to use the global standard of 63 km h^-1 (34 kt), and that action is being taken to change the operational plan. This standard value is used here.

Tropical cyclone names are obtained from predesignated lists maintained and periodically updated by the various regional bodies. If a tropical cyclone attains special notoriety because of strength, deaths, damage or other special reasons, its name may be withdrawn from the list.

For Regional Association I (RA I), moderate tropical cyclones (63 km h^-1 or 34 kt, see Fig. 1.7) developing between 55^oE and 90^oE are assigned one of a predesignated series of names by the national Meteorological Service of Mauritius. Tropical cyclones developing to the west of 55^oE are named by the National Meteorological Service of Madagascar.

Three sets of cyclone names are used within RA IV: two by NHC for North Atlantic and for eastern North Pacific cyclones; and a third by the Central Pacific Hurricane Center (CPHC) in Hawaii for tropical cyclones forming in the area of responsibility shown in Fig. 1.2. This latter set of names is specified by OFCM (1990) but is not included in the RA IV WMO Reference manual (WMO, 1988).

The naming of a tropical cyclone in RA V is accomplished by the Tropical Cyclone Warning Centre (Fig. 1.4) that is responsible for the area in which the required intensity of 63 km h^-1 (34 kt) is first analysed. Separate lists of names are used by each of three Australian Tropical Cyclone Warning Centres (Perth, Darwin and Brisbane), by the Fiji Meteorological Service and by the Papua New Guinea National Weather Service.

Figure 1.1: Regional Association I (WMO, 1983a). High seas tropical cyclone warning responsibility areas for the southwest Indian Ocean: a) Madagascar (Antananarivo) and Mauritius (Vacoas); b) Réunion (Sainte Clotilde); c) Mozambique (Maputo) and Kenya (Nairobi).

Figure 1.2: Regional Association IV (WMO, 1988). High seas tropical cyclone warning responsibility areas for the NHC (Miami) and for the CPHC (Honolulu).

Figure 1.3: JTWC (Guam) area of high seas warning responsibility (USCINPAC Instruction 3140.IT, 8 February, 1989)

Figure 1.4: Regional Association V (WMO, 1989). High seas tropical cyclone warning responsibility areas for the South Pacific and southeast Indian Oceans; a) Australia (Perth, Darwin and Brisbane), Papua New Guinea (Port Moresby) and Indonesia (Jakarta); b) Fiji (Nadi) and New Zealand (Wellington).

Figure 1.5: ESCAP/WMO Panel on Tropical Cyclones (WMO, 1986). High seas tropical cyclone warning responsibility areas for the Bay of Bengal, the Arabian Sea and vicinity; a) India (Calcutta for the Bay of Bengal, with rebroadcast bulletins from Madras; Bombay for the Arabian Sea) and Thailand (Bangkok, the eastern portion of which is in the ESCAP/WMO Typhoon Committee Region); b) Pakistan (Karachi), Bangladesh (Dhaka), Burma (Rangoon) and Sri Lanka (Columbo).

Figure 1.6: ESCAP/WMO Typhoon Committee (WMO, 1987). High seas tropical cyclone warning responsibility areas for the western North Pacific: a) Peoples Republic of China (Dalian, Shanghai and Guangzhou), together with eastern edge of Thailand area (stippled, see Fig. 1.5a); b) Republic of Korea (Seoul), Vietnam (Hanoi) and Japan (Tokyo, which includes entire western North Pacific basin); c) Philippines (Manila) and Hong Kong.

The tropical cyclone identification system in the two ESCAP regional bodies differs from other regional associations. RSMC (Regional Specialized Meteorological Center) New Delhi provides an identification number for all tropical cyclones in the region (Fig. 1.5). These codes consist of the letters BOB or ARB, to identify cyclones in the Bay of Bengal and the Arabian Sea, respectively, followed by the year and a two digit sequential number. For example, the second tropical cyclone of the year 1992 over the Arabian Sea is designated ARB 9202. No letters are used in the Typhoon Committee Region; thus, the first tropical cyclone of 1992 is identified as 9201 by the appropriate RSMC.

Several countries use local names for tropical cyclones directly affecting their nation. JTWC assigns names for all western North Pacific cyclones and most of the advisories issued by Typhoon Committee members include this name, together with their number designator. In the north Indian Ocean, JTWC uses a sequential numbering system with the suffixes A and B for the Arabian Sea and the Bay of Bengal, respectively. Additional information on JTWC naming conventions can be found in a recent issue of the Annual Tropical Cyclone Report.

1.2.3 Terminology

A considerable variation occurs in terminology used for the different stages of tropical cyclones (Fig.s 1.7, 1.8). Also, significant differences exist among the north Indian basin nations (Fig. 1.8). Differences in wind averaging times further compound the confusion, since 1-min, 3-min and 10-min averages are used in different countries. Thus, a tropical system may acquire a name or number in one country, but not in another with the same wind criteria but different averaging times (Section 1.3.3).

Contents Chapter 1.3