The influences of post-tropical reintensification and dissipation on North Atlantic shipping routes

Many North Atlantic tropical cyclones undergo a process of extratropical transition in which their tropical characteristics are entirely replaced by extratropical characteristics as the storm moves northward. After extratropical transition, the post-tropical cyclone can reintensify into a deep extratropical storm with hurricane force winds and high seas. This can be especially dangerous to mariners along North Atlantic shipping routes as northerly routes are favoured during hurricane season to remain clear of the normal domain of North Atlantic tropical cyclones. Due to the lack of understanding of extratropical transition, post-tropical forecasts are generally inaccurate. This study compares extratropical transitioned storms during the extratropical transition process. Two groups of storms were compared and contrasted: one group of storms that reintensified and the other that dissipated shortly after extratropical transition. In this study, we focused on baroclinic effects of shear and synoptic circulation interaction. A relationship between storm shear and pressure during post-tropical transition has been developed in this study. This results showed that lower sea level pressures (i.e., 978 hPa) combined with wind shear differences between upper and lower levels of the atmosphere (i.e., 9 m s−1) during extratropical transition was present in nearly all events in which post-tropical reintensification occurred. The methods developed in this study can be easily implemented into the operations for the marine routing and shipping industry.