Section 2The tropical cyclone (TC) warning support or service is a regional and international effort to provide recipients with tropical cyclone watches, forecasts, warnings and assessments. Tropical cyclone is a generic term for a surface cyclone that is located in the equatorial, tropical, or subtropical region. A tropical cyclone that moves into the mid-latitude region and is not completely transformed into a mid-latitude cyclone is still considered a tropical cyclone. Neumann (1993) provides a global overview of tropical cyclones including the World Meteorological Organization (WMO) global TC forecasting concept, areas of forecast responsibility, and forecast procedures. The forecast procedures differ between oceanic basins and forecast agencies.
The US Department of Defense (DOD) global TC warning structure is subdivided into three regions: the Western Pacific, Eastern Pacific, and Atlantic. The Western Pacific region includes the Indian Ocean. The National Oceanic and Atmospheric Administration (NOAA) of the Department of Commerce (DOC) is responsible for providing the similar services for the North Atlantic Ocean (including the Gulf of Mexico and Caribbean Sea) and the Eastern (east of 140 deg. West) and Central (140 - 180 deg. West) North Pacific Ocean. In the DOC's area of responsibility, DOC provides support to DOD in terms of day-to-day requirements for cyclone assessments, dissemination of weather data, basic meteorological information, warning, forecasts and prognostic reasoning (NHOP, 1994).
1.1 Western Pacific Region
The Naval Oceanography Command Center/Joint Typhoon Warning Center (JTWC), established on 1 May 1959 by the United States Commander in Chief, Pacific Command (USCINCPAC), is a joint USAF and USN organization under the command of Commanding Officer, U. S. Naval Oceanography Command Center, Guam (Fuller, 1990). United States Commander in Chief, Pacific Command Instruction (USCINCPACINST, 3140.1V, 1993) tasks JTWC to provide TC warning support to DON and other United States government agencies and operational military units within the assigned area of responsibility (AOR). The AOR of JTWC ( Fig. 1.1) encompasses four broad oceanic areas of TC activity stretching westward from the International Date Line to the east coast of Africa, in both hemispheres. This instruction is the western Pacific and Indian Ocean equivalent of the National Hurricane Operations Plan (NHOP, 1993) for the Atlantic and Eastern and Central Pacific Ocean. JTWC also provides warnings to the Governments of the Territory of Guam, the Commonwealth of the Northern Mariana Islands, the Republic of Belau, the Federated States of Micronesia, and the Republic of the Marshall Islands (Guard et al., 1992). JTWC warnings and reconnaissance information are made available to all nations in or near its AOR. JTWC assigns formal names to all TCs in the western North Pacific Ocean and in the South China Sea, after the cyclone reaches tropical storm intensity criteria, i. e. the maximum sustained one minute mean surface wind speed is greater than or equals to 34 kts.
1.1.1 JTWC Warning Support Charter
JTWC is a well-known TC warning center, preparing and issuing alerts and warnings on an average of 60 TCs each year. This area of 180 million square kilometers encompasses ten time zones, four broad ocean basins, and seven TC areas. Seventy-one percent of the world's TCs develop in JTWC's AOR (Fig. 1.2).
1.1.2 Western North Pacific and North Indian Ocean Warnings and Bulletin Headers
Tropical Cyclone Warnings for Western North Pacific/North Indian Ocean (Bulletin Headers: WTPN31-36 PGTW/WT1031-35 PGTW): JTWC issues warnings on TCs in the western North Pacific and North Indian Ocean areas every six hours, valid at standard synoptic times of 00, 06, 12, and 18 Z (or UTC). The warnings are released to the communications network no earlier than synoptic time and no later than synoptic time plus two and one half hours. Recipients can reasonably expect to have all warnings "in hand" by synoptic time plus three hours (i.e. 03, 09, 15, 21 Z). Warnings normally contain position and wind forecasts out to 72 hours unless dissipation or extratropical transition are expected to occur earlier.
1.1.3 Western South Pacific and South Indian Ocean Warnings and Bulletin Headers
Tropical Cyclone Warnings for the Western South Pacific/South Indian Ocean (Bulletin Headers: WTXS31-39 PGTW): JTWC issues warnings on TCs in the western South Pacific and South Indian Ocean areas of responsibility. Warnings are generated every twelve hours valid at standard synoptic times of 00 and 12 Z, or 06 and 18 Z. JTWC determines which set of valid times to use. Once established, times do not change for the duration of a particular tropical cyclone. However, when DOD assets are seriously threatened by a tropical cyclone, JTWC will send warnings every six hours. All Southern Hemisphere warnings are released no earlier than synoptic time and no later than synoptic time plus two and one half-hours. Recipients can reasonably expect to have the warnings in hand prior to synoptic time plus three hours. Warnings normally contain position and wind forecasts out to 48 hours unless dissipation or extratropical transition is predicted to occur earlier.
1.1.4 Other JTWC Products
a. Western Pacific/Indian Ocean Significant Tropical Weather Advisory (Bulletin Headers: ABPWIO PGTW/ABI010): JTWC issues a daily narrative message, describing areas of significant tropical weather activity. These messages evaluate the potential for suspect areas to develop into significant TCs. The words "poor", "fair" and "good" describe potential for development. "Poor" describes a tropical disturbance in which meteorological conditions are currently unfavorable for development. "Fair" describes a tropical disturbance in which meteorological conditions are currently favorable for development but significant development has not commenced. "Good" describes the potential for development of a disturbance covered by a Tropical Cyclone Formation Alert (TCFA). JTWC issues the Significant Tropical Weather Advisories at 06Z daily for the western North Pacific and Southern Hemisphere east of 135E and at 18Z for the North Indian Ocean and Southern Hemisphere west of 135E.
b. Tropical Cyclone Formation Alerts for the western North Pacific and North Indian Ocean (Bulletin Headers: WTPN21-25/WT1021-25 PGTW): JTWC issues formation alerts when interpretation of synoptic and other meteorological data suggest likely formation of a significant TC. The alerts are not serially numbered. An alert has a specified valid period (not to exceed 24 hours) and must be canceled or reissued by the end of the valid period. Cancellations are accomplished by separate message or inclusion of a remark at the end of the initial warning on a cyclone developing in the alert area.
c. Tropical Cyclone Formation Alerts for the Western South Pacific and South Indian Ocean (Bulletin Headers: WTXS21-29 PGTW): JTWC issues formation alerts in the Southern Hemisphere AOR using the same requirements specified in the other basins.
d. Prognostic Reasoning Message for the Western North Pacific (Bulletin Headers: VMPA31-36 PGTW): Following the issuance of tropical cyclone warnings in the western North Pacific, JTWC sends meteorologists a prognostic forecast reasoning message for each TC in warning status. The message is issued as soon as possible after warnings. The message includes: (a) a synoptic discussion, (b) forecast track reasoning, (c) forecast intensity reasoning, (d) alternate scenarios under discussion, and (e) a qualitative assessment of probable occurrences.
1.2 Eastern Pacific Region
The Depart of Commerce (DOC) is charged with the overall responsibility to implement a responsive, effective national tropical cyclone warning service in the Eastern Pacific Region ( Fig. 1.3). Joint participation by the DOD and the Department of Transportation (DOT) with the DOC brings to bear the limited and expensive resources considered essential for storm detection and forecasting. This cooperative effort has proven to be a cost effective, highly responsive solution to meet national requirements for tropical cyclone warning information.
1.2.1 North Eastern Pacific Warnings
North of the equator and east of 14OW, advisories are the responsibility of the National Hurricane Center (NHC) at Miami, Florida. NHC issues advisories at 03, 09, 15, and 21 Z (UTC). The Naval Western Oceanography Center (NAVWESTOCEANCEN) then issues military tropical cyclone warnings (Bulletin Header: WHPN(xx) PHNC) containing the same information as soon after receipt of the advisories as practicable.
1.2.2 North Central Pacific Warnings
North of the equator between 14OW and 180E/W - advisories are the responsibility of the Director, Central Pacific Hurricane Center (CPHC) Honolulu, HI. The CPHC will consult with NAVWESTOCEANCEN prior to issuing any advisory that indicates a significant change in forecasted intensity or track from the previous advisory. Exchange of information is encouraged on subsequent warnings when significant changes are made or otherwise required. CPHC issues forecasts/advisories at 03, 09, 15, and 21 Z or UTC. NAVWESTOCEANCEN then issues military tropical cyclone warnings (WHPN(xx) PHNC) containing the same information as soon after receipt of the advisories as practicable.
1.2.3 South Eastern Pacific Warnings (WHPS(xx) PHNC)
NAVWESTOCEANCEN issues warnings on tropical cyclones in the Eastern South Pacific area of responsibility every twelve hours no later than 03 and 15Z, or 09 and 21Z, to be valid at 00Z and 12Z or 06Z and 18Z, respectively. NAVWESTOCEANCEN determines which set of valid times to use. Once established, times do not change for the duration of a particular tropical cyclone. These warnings normally carry position and wind forecasts out to 48 hours unless dissipation or extratropical transition are predicted to occur earlier.
1.2.4 Civilian Advisories on Hurricanes. Tropical Storms, and Depressions for the Eastern Pacific
All advisories on hurricanes, tropical storms, and depressions are under WT (Warning Tropical), AB (Advisory Bulletin), WO (Warning Observation/statement), or WW (Weather Warning) abbreviated headings as follows: Bulletins issued for the eastern Pacific come from Miami (KMIA). Bulletins for the central Pacific come from Honolulu (PHNL). Table 1.1 lists civilian advisory bulletins for the Eastern Pacific.
1.3 Atlantic Region
The DOC is charged with the overall responsibility to implement a responsive, effective national tropical cyclone warning service in the Atlantic Region ( Fig. 1.3). Joint participation by the DOD and the DOT with the DOC brings to bear the limited and expensive resources considered essential for storm detection and forecasting.
1.3.1 Atlantic Warnings (WHNT(xx) KNGU)
North of the equator including the Caribbean Sea and Gulf of Mexico tropical cyclone advisories are the responsibility of the NHC, Miami, FL. NHC issues advisories at 03, 09, 15, and 21 Z (UTC). Naval Eastern Oceanography Center (NAVEASTOCEANCEN) then issues military tropical cyclone warnings containing the same information as soon after receipt of the advisories as practicable.
1.3.2 Civilian Advisories on Hurricanes, Tropical Storms, and, Depressions for the Atlantic
All advisories on hurricanes, tropical storms, and depressions are under WT abbreviated headings as follows: Bulletins issued for the Atlantic come from Miami (KMIA). Table 1.2 lists civilian advisory bulletins for the Atlantic.
1.4 Other Regions and Tropical Cyclone Forecast Agencies
Table 1.3a and Table 1.3b are a comprehensive list of all other warning agencies within the JTWC AOR. This includes the forecast product bulletin heading (Bulletin), the station identifier (Stn ID), station name (Station), frequency of issuance (Issuance), duration of forecast (Forecast), and the coverage of the respective agency's AOR modified from Guard et al. (1992).
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Chapter 1
