Skip to Content

Extratropical Transitions: Dynamics, Impacts, and Forecasting Issues

In August 2011, Hurricane Irene lashed the east coast of the United States, causing damaging winds, heavy rains, high surf, and coastal erosion. Arguably the largest impacts from Irene were felt inland throughout Vermont and New York State, primarily due to flash flooding. Inland flooding is a large concern when a tropical cyclone moves poleward and undergoes extratropical transition (ET) into a large and powerful mid-latitude cyclone, with much of the precipitation often oriented to the left side of the storm. However, the impacts of ET are not necessarily confined to the event itself. Often, significant ET’s are responsible for the excitation of Rossby wave trains which can have significant downstream impacts. In fact, in some exceptional cases (i.e. Dale 1996 and Noel 2007), ET can result in a collapse of the Hemispheric Available Potential Energy (APE). Finally, because many of the processes in ET are associated with diabatic heating from latent heat release in deep convection and because their interactions with mid-latitude features are highly sensitive to the precise intensity and location of the storm, ET events can have a significant negative impact on predictability in both short and medium range forecasts. This talk is designed to give an overview of the dynamics and impacts of ET in terms of the sensible weather as well as the implications for both short term and medium range forecasting.