A case study of the extratropical transition of two Atlantic hurricanes (Felix and Iris, 1995) highlighted significant differences between the
extratropical development of the two storms. In particular, Iris developed significantly as an extratropical storm whereas Felix decreased in intensity during extratropical transition. In contrast, Felix was much more intense as a hurricane than Iris. Thus we hypothesise that the extratropical development is influenced by the structure and intensity of the hurricane as it transforms into an extratropical system. The structure and intensity of the hurricane at this time depends on both the nature of the hurricane before it moves towards the extratropics and the modification of structure and intensity which occurs as the hurricane begins to interact with extratropical weather systems.
This paper presents an idealised modelling study which investigates the above hypothesis. A three-dimensional primitive-equation model is used to study the structural changes of hurricane-like vortices as they interact with an extratropical baroclinic zone. Potential-vorticity thinking is used to interpret the development of the vortices as they transition into the extratropics. The results of the numerical experiments are discussed with reference to the case study of hurricanes Felix and Iris