Section 6. FORMATION FORECASTING PROCEDURES

All major TC forecast centers follow certain procedures when producing their daily forecasts. An understanding of these procedures is necessary if the forecaster is to provide the best meteorological recommendation possible when operating in TC regions.

6.1 Formation Forecasting Procedures at JTWC

At both National Hurricane Center (NHC) and Joint Typhoon Warning Center (JTWC) the primary method of TC formation forecasting and detection is through use of geostationary satellite imagery. Hourly satellite imagery is monitored for increased convective activity associated with areas of disturbed weather in the tropics. JTWC monitors surface and gradient level data for areas with persistent low-level circulations and relatively low sea-level pressures. Areas where the pressures continue to fall and winds increase are watched. Mid-level analyses are performed to identify closed circulations or troughs. Upper-level analyses are used to identify weak vertical wind shear, TUTT interactions and anticyclone development.

Each feature described above can be an indicator of TC development and is discussed in the tropical weather advisories applicable for the basin. Table 3.2 is an example of an experimental TC Formation Alert (TCFA) Checklist for the Western Pacific and North Indian Ocean used at JTWC to assess the current situation.

JTWC issues a daily narrative message, describing areas of significant tropical activity and evaluating potential for development 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 TCFA. JTWC issues the Significant Tropical Weather Advisory for the Western Pacific (ABPW10) message at 0600 UTC for the western North Pacific and Southern Hemisphere east of 135E, and the Significant Tropical Weather Advisory for the Indian Ocean (ABIO10) message at 1800 UTC for the North Indian Ocean and Southern Hemisphere west of 135E.

When a tropical disturbance is listed as a suspect area on one of these advisories, JTWC must maintain continuity as to the disposition of the disturbance. In addition, this message will be re-issued if one of the suspect areas is upgraded. For example, if a suspect area goes from a poor to a fair the ABPW10 and ABIO10 will be re-issued. If a suspect area goes from a fair to a good, the ABPW10 and ABIO10 will be referenced in the TCFA that is issued to cover the area. This TCFA is considered the re-issued advisory.

Section 5.3 Section 6.2

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