HS3 Extratropical Transition

An important interaction between hurricanes and their environment occurs during the process of extratropical transition (ET) when the tropical vortex moves into the middle latitudes. There, the vortex comes under increasing influence of colder sea-surface temperatures (SSTs), increasing Coriolis effect, dry continental air masses, faster steering flow and baroclinic influences such as frontal boundaries and disturbances in the polar jet stream (i.e. shortwave troughs, jet streaks). ET is associated with large changes in the wind and precipitation structure of storms and, in some cases, substantial increases in storm intensity (Evans and Hart 2003). In situ observations of storms undergoing this transformation are sparse, and there is no “one size fits all” paradigm that completely describes the interaction of tropical vortices with weather systems of the higher latitudes. Much can be learned by sampling tropical cyclones continuously (using one or more GHs) along the trajectory of storm evolution from low to high latitudes.

Evans, J.L., and R.E. Hart, 2003: Objective Indicators of the Life Cycle Evolution of Extratropical Transition for Atlantic Tropical Cyclones. Mon. Wea. Rev., 131, 909–925.