Tropical cyclones which transform into extratropical weather systems can still be characterised by strong winds, heavy rains and , like tropical cyclones, can cause loss of life and damage to property. Extratropical transition is not always well forecast in NWP models and deserves attention. This work is concerned with the extatropical transitions that occur over the Atlantic. It focusses is on two events which took place in 1995. The strongest extratropical development occurred in the case of Iris which transformed over the ocean, deepened by 38hPa and affected Europe. We contrast this with the case of Felix which also transformed over the ocean and reached Europe but did not develop. The study examines and compares the two cases using UKMO unified model analysis data. Significant differences are seen in terms of structure, interactions with the ocean and large-scale shear. Ideas linked to the vertical shear are further developed in an idealised modelling study.