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Global Guide to Tropical Cyclone Forecasting:
CHAPTER 6: OPERATIONAL STRATEGY

6.8 PERFORMANCE VALIDATION

Another important function of a TCWC is to perform routine validation of forecast information. It is strongly recommended that each weather service should carry out a rigorous evaluation of its forecast ability. The survey conducted at IWTC-II indicated that over 60% of countries do not perform routine error analyses on their forecasts. A routine validation programme can assess any tangible improvements in forecast skill, and may even be able to suggest where resources could be most economically directed to effect forecast improvements. United States weather services (in particular the National Hurricane Center) have been routinely verifying their forecasts over a long period to assess their skill (e.g. Neumann, 1981). This long-term verification has been able to confirm a gradual decrease in forecast errors. JTWC, Guam produce comprehensive error statistics in support of their forecasting operations, which are displayed in their annual tropical cyclone reports.

Two thirds of countries surveyed at IWTC-II indicated that they already perform post-event best track analyses, so forecast verification is only a small step removed from this. The bare minimum of any weather service's validation programme should be an assessment of its forecasts of track position and intensity, at least at 12 and 24 h. Ideally, however, an office should validate all of the parameters that it uses in its warnings. Eventually parameters should include position, intensity, size, wind speed and direction (for site specific warnings and/or for islands), rainfall, storm surge, area of land under warning and time of landfall.

Performance validation can be a time consuming process, involving many hours of staff time, which some countries may struggle to afford. The advent of workstations however means that the validation process can be automated. With a database management system running in the background of normal operational tasks, forecast data can be efficiently stored, and then used by the verification program to produce the desired results very efficiently and with a minimum of human resources. It is further recommended that weather services also verify the effectiveness of any forecast guidance material that they use to produce their warnings. An analysis of such data will assist in determining the relative usefulness of individual forecast techniques and products.

Contents Chapter 6.9