This paper will describe the algorithm used in the NCEP tropical cyclone tracker and will include a discussion of the system's quadrant wind radii detection scheme as well as verification results and selected case studies from the past four years.

In 1998, a new tropical cyclone tracking algorithm became operational at NCEP. This algorithm is part of a system that provides forecast track and intensity guidance to various NCEP centers, including TPC, HPC and EMC. The core of the algorithm is a multiple-pass barnes analysis that analyzes input data on successively smaller grids to obtain position estimates of five primary parameters (MSLP; 850 and 700 mb relative vorticity; 850 and 700 mb geopotential height) and two secondary parameters (850 and 700 mb minimum wind speed). The center fixes obtained from these parameters are averaged together to produce a forecast position estimate at each forecast hour. Included in the output are estimates of the forecasted minimum sea-level pressure and the maximum surface or near-surface winds obtained from the data. Also included are estimates of the forecasted radii of 34-, 50- and 64-knot winds in each quadrant of the storm at each forecast hour. The system currently running at NCEP produces output track and intensity files for the following models: NCEP AVN, NCEP AVN Ensemble, NCEP Eta, NCEP NGM, GFDL Hurricane Model, UKMET, FNMOC/NOGAPS.