MODELS OF TROPICAL CYCLONE WIND DISTRIBUTION AND BETA-EFFECT PROPAGATION FOR APPLICATION TO TROPICAL CYCLONE TRACK FORECASTING

A model of the tangential wind speed in the outer regions of tropical cyclones is proposed based on approximate conservation of angular mome ntum. The purpose is to derive an operationally useful model of the be ta-effect propagation (BEP), which barotropic numerical models have sh own to be primarily related to the outer wind structure. The functiona l dependence of the predicted BEP speeds over a range of latitudes and the radii R-o at which the cyclonic winds are reduced to zero is dete rmined from dimensional analysis. Given the empirical nature of the pr ofile and imprecise estimates of R-o, only four tropical cyclone sizes or outer wind structures are defined based on the magnitude of the BE P speeds and their relative contributions to the total motion. A secon d aspect of BEP from the barotropic model integrations is the developm ent of a trailing anticyclone to the southeast of the tropical cyclone as a result of Rossby wave dispersion. The four tropical cyclone size categories or outer wind structures are also characterized in terms o f the potential for the trailing anticyclone to be part of a change in the tropical cyclone environment structure. Whereas small tropical cy clones have a small BEP speed and do not change their environment, lar ge tropical cyclones have BEP speeds exceeding 2 m s(-1) and have a la rge amplitude peripheral anticyclone that may introduce significant ch anges in the environment structure, which can indirectly contribute to a track change.