Observational analysis of tropical cyclone recurvature

May 1991.Also issued as author's thesis (M.S.) -- Colorado State University, 1991.Includes bibliographical references.Twenty-one years (1957-77) of North Pacific rawinsonde data are used to show how the large scale synoptic pattern interacts with the tropical cyclones' environment just prior to, and during the recurvature process. This study is believed to be the first to quantitatively examine how the environmental wind fields at all levels of the troposphere are related to tropical cyclone motion prior to, and during, recurvature. Significant changes in the upper tropospheric zonal wind fields were found to the north and northwest of tropical cyclones one to two days prior to beginning recurvature. These cyclones actually began to recurve when positive zonal winds penetrated into the mid and upper troposphere, 6° from the cyclones' center. Tropical cyclones which did not recurve showed negative zonal winds at this radius. Based on the results of this study, a recurvature forecasting scheme was developed using the environmental windfields measured in the northwest region of the cyclone. This recurvature scheme was then tested on 55 tropical cyclones which developed in the northwest Pacific in 1984-86. It was found that tropical cyclone direction related fairly well to the mid and upper tropospheric windfields to the north, northwest and west of the cyclone. This recurvature scheme was then used in real-time during the Tropical Cyclone Motion (TCM-90) experiment which was conducted during the summer of 1990 in the Northwest Pacific. This scheme was found to be generally successful.On cover page: ONR N00014-87-K-0203 P05