Tropical storm formation in a baroclinic environment

Abstract

An analysis is presented of the large-scale conditions associated with the initial development of Tropical Storm Diana (September 1984) in a baroclinic environment. Ordinary extratropical wave cyclogenesis began along an old frontal boundary east of Florida after 0000 UTC 7 September and culminated in tropical cyclogenesis 48 h later. Water-vapor satellite imagery showed that the initial cyclogenesis and incipient tropical storm formation was nearly indistinguishable from a classical midlatitude development. Cyclogenesis occurred in three stages. A large-scale cold trough and associated frontal system crossed the Atlantic coast, while a small potential vorticity maximum aloft fractured off the main trough and stalled over central Florida in the first stage. Cyclogenesis intensified during the second stage in response to positive potential vorticity advection aloft ahead of the slow moving cutoff cyclone over Florida. The third stage of cyclogenesis was marked by the collapse of the mid- and upper tropospheric cold dome and associated potential vorticity maximum and the simultaneous initiation of a warm thickness ridge. The interaction of the upper- and lower-level potential vorticity anomalies appeared to be important in the initial strengthening of the tropical cyclone. -from Authors