An Observational Analysis of Tropical Cyclone Recurvature

Abstract

Abstract Data for 21 years (1957–77) of North Pacific rawinsondes were examined to investigate the interaction between the synoptic-scale circulation and tropical cyclones 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. For tropical cyclones that recurve, significant changes in the upper-tropospheric zonal wind fields were observed 1–2 days prior to beginning recurvature in the environmental sector northwest of the storm. Cyclones actually began to recurve when positive zonal winds (westerlies) penetrated the middle and upper troposphere to within 6° of the cyclone's center. Tropical cyclones that did not recurve consistently showed negative zonal winds at this radius. From the results of this study, a recurvature forecasting scheme was developed that uses environmental wind field data for the region nor...