Supertyphoon Abby—An Example of Present Track Forecast Inadequacies

Abstract

Supertyphoon Abby (1983), although not one of the most destructive on record, received a great deal of attention from the typhoon forecasters in Guam. For a large part of Abby's lifetime, nearly all objectively predicted tracks were almost 90° to the left of the actual track of the cyclone. This study is an attempt to understand the reasons for the failure of the forecast models. The intensity and size (horizontal extent) of the supertyphoon are hypothesized to be the main factors contributing to such a forecast failure. After intensifying to a maximum wind speed of 75 m s?1 (145 kt), Abby continued to grow, with the radius of 15 m s?1 (30 kt) winds extending beyond 600 km. Abby's circulation, which can be readily identified on synoptic charts, apparently affected the performance of the dynamical models. The ?steering flow? vector as estimated from the operational analyses is found to be almost normal to the motion vector of Abby, which might provide a partial explanation of the forecasts by the objective methods. These results suggest the need to analyze the performance of forecast models under different synoptic as well as storm-related factors. They also suggest the importance of studying the interaction between the tropical cyclone circulation and its environment.