Southern Hemisphere Application of the Systematic Approach to Tropical Cyclone Track Forecasting. Part IV : sources of large track errors by dynamical models

Abstract

Sources of 72-h track errors > 300 n mi by four dynamical model tropical cyclone predictions in the Southern Hemisphere during the 1997-98 and 1998-99 seasons are studied using conceptual models Carr and Elsberry have previously developed for the western North Pacific. Each of these conceptual models describes how the dynamical model incorrectly predicts a known physical cause of tropical cyclone motion. Midlatitude circulation-related error sources occur more frequently in the Southern Hemisphere, which is as expected since deeply penetrating midlatitude trough-ridge circulations have more of an effect on tropical cyclone motion. In addition to erroneous predictions of midlatitude cyclogenesis and anticyclogenesis, the dynamical models error in their response to midlatitude vertical wind shear and baroclinic cyclone interactions with the tropical cyclones. One frequently occurring tropical-related large track-error mechanism is Excessive-Direct Cyclone Interaction, which occurs for similar reasons in the Southern Hemisphere as in the western North Pacific study of Carr and Elsberry. Although this is a retrospective study of known large track errors, the ultimate goal is to help the forecaster detect likely erroneous tracks in real-time.