Use of ensemble forecasts to investigate synoptic influences on the structural evolution and predictability of Hurricane Alex (2016) in the midlatitudes

AbstractHurricane Alex was an extremely rare hurricane event, the first North Atlantic hurricane to form in January since 1938. Alex developed from an extratropical low pressure system that formed over the western North Atlantic basin, and then underwent tropical transition after moving to the eastern basin. It subsequently underwent anomalous extratropical transition (ET) just north of the Azores Islands. We examine the factors affecting Alex’s structural evolution and the predictability of that evolution. Potential scenarios of structural development are identified from a 51-member forecast ensemble from the European Centre for Medium-Range Weather Forecasts Ensemble Prediction System (ECMWF-EPS), initialized at 0000 UTC 10 January 2016. The EPS forecasts are clustered using a regression mixture model based on the storm’s path through the cyclone phase space. Composite maps constructed from these clusters are used to investigate the role of synoptic-scale features on the evolving structure of Hurricane ...