Progress toward a generalized description of the environment structure contribution to tropical cyclone track types

Abstract

A critical meteorological knowledge base for the application of the Systematic Approach to Tropical Cyclone Track Forecasting of Carr and Elsberry is the environment structure, which is a small set of synoptic patterns and synoptic regions that characterize the tracks. As the original Systematic Approach for the western North Pacific has been applied to the eastern and central North Pacific by Boothe and to the Southern Hemisphere by Bannister et al., the conceptual models of the synoptic patterns have been generalized. Whereas only slight modifications of three of the original four synoptic patterns are required in the two new basin applications, the monsoon gyre pattern of the western North Pacific must be replaced with an upper-low pattern in the eastern and central North Pacific and by a high-amplitude midlatitude trough/ridge in the Southern Hemisphere. An important conclusion is that the environment structure of all tropical cyclones in these three basins could be classified into these small sets. Furthermore, each synoptic pattern/region has a set of characteristic tracks, and a change in environment structure has an associated track change. Comparisons and contrasts of these environmental structures demonstrates that the relative importance of the monsoon trough, subtropical ridge, and midlatitude circulations can account for first-order variations in TC tracks within these three tropical cyclone basins. Summaries of the occurrence of synoptic pattern/region transitions are given for the three basins. Although each TC basin has special characteristics, the general application of the Systematic Approach suggests a unified treatment is possible. Further development along this line is expected to improve the accuracy and consistency of forecasts and warnings.