Description

Over 40% of all Atlantic tropical cyclones  move into the the midlatitudes,   undergo structural changes and transform into extratropical storms, i.e. undergo extratropical transition (ET). Through their synoptic-scale influence on the midlatitude flow such systems present a threat not only to the countries where they make landfall, but are associated also with the development of severe weather on the eastern side of the ocean basin in which they form. Thus a hurricane in the western North Atlantic can play a crucial role in the development of a European wind storm or severe flooding event. Through idealised modelling, analysis of operational numerical weather prediction model output and experiments with the ECMWF Ensemble Prediction System we aim to quantify the reduction in predictability associated with ET and highlight areas in which models must be improved.