The basic grid is essentially the same as that used in the 500-hPa method except that gradients were computed at intervals of 2.5 latitude instead of 5. The previous 12-hour motion was also incorporated into the forecast. This method was tested on 23 forecasts during the 1958 hurricane season. The average error was 95 nautical miles for the 24-hour forecast and ranged from 15 nautical miles to 170 nautical miles.

A further explanation of this method and its procedure for application may be found in the Bulletin of the American Meteorological Society, Vol. 41, No. 2, February 1960.

Tropical cyclone warnings are issued to protect not only Department of Defense assets but also those of allied nations.

Tropical cyclone warnings are issued to operating forces of the Atlantic Ocean, the Gulf of Mexico, and the Caribbean region by NAVLANTMETOCCEN Norfolk, Va. Warnings for the southern hemisphere are provided as required. NAVLANTMETOCCEN primarily uses the National Hurricane Centers interagency and public advisories as guidance. Hurricane, tropical storm, and tropical depression warnings are issued four times daily at 0300 UTC, 0900 UTC, 1500 UTC, and 2100 UTC. They are listed under the MAANOP heading WHNT__ KNGU. The blank space is for the numerical sequence of the warning. Special advisories and warnings are issued in the event of significant changes in intensity or movement. Daily tropical weather summaries are issued at 1800 UTC from 01 June through 30 November for the subtropical Atlantic (south of 30N), the Caribbean, and the Gulf of Mexico. Daily tropical weather summaries are listed under the MANOP heading ABCA KNGU. Tropical cyclone warning messages are transmitted via AUTODIN and the Fleet Multichannel Broadcast every 6 hours for storms in the Northern Hemisphere.

Tropical cyclone warnings are issued to operating forces of the Pacific Ocean (west of 180 longitude), Philippine Sea, South China Sea, Bay of Bengal, and Indian Ocean in both the Northern and Southern Hemispheres by the Joint Typhoon Warning Center (JTWC), Guam.

Tropical cyclone warnings are issued to operating forces of the Pacific Ocean east of 180 longitude by NAVPACMETOCCEN Pearl Harbor, Hawaii. Warnings for the Southern Hemisphere are provided as required. NAVPACMETOCCEN primarily uses the National Hurricane Centers interagency and public advisories as guidance.

Typhoon, tropical storm, tropical depression, and tropical cyclone warnings are issued four times daily at 0300 UTC, 0900 UTC, 1500 UTC, and 2100 UTC. The warnings from the JTWC are listed under the MANOP heading WTPN PGTW and the warnings from NAVPACMETOCCEN Pearl Harbor are listed under the MANOP heading WTPZ PHNL. The blank space is for the numerical sequence of the warning. Special advisories and warnings are issued in the event of significant changes in intensity or movement. Tropical cyclone warning messages are transmitted via AUTODIN and the Fleet Multichannel Broadcast every 6 hours for storms in the Northern Hemisphere. NAVMETOCCOM centers monitor Southern Hemisphere tropical cyclones in their individual AORs. Because of the limited data and weather satellite coverage of the Southern Hemisphere, warnings are issued by AUTODIN and Fleet Multichannel Broadcast only at 12- and 24-hour intervals and may contain less specific information than Northern Hemisphere warnings.

In this chapter we have discussed various topics related to tropical forecasting. Our discussion first dealt with local area forecasts in general. Following local area forecasting we then discussed tropical cyclone forecasting. First discussed was the problem involved with forecasting tropical cyclones, followed by the dynamics associated with these systems. Tropical covered intensity changes and factors affecting those changes, along with a discussion of various objective forecasting techniques for tropical cyclones. Finally, we looked at tropical cyclone warnings, forecast issuing authorities, and forecast issue times.

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