Deterministic and ensemble-based prediction of Adriatic Sea sirocco storms leading to 'acqua alta' in Venice

The accuracy of deterministic and probabilistic forecasts of storms in the Adriatic Sea that lead to the flooding of Venice is discussed. We consider ECMWF state-of-the-art high-resolution single deterministic and lower-resolution ensemble-based forecasts of meteorological and sea states (waves) for five storms that affected Venice between 1966 and 2008. Notwithstanding the complicated local orographic situation, it is shown that ECMWF single, deterministic forecasts provide accurate information up to 3-4 days in advance. This range is further extended to between 4 and 6 days if ensemble-based, probabilistic forecasts are considered. The assessment of the quality of Ensemble Prediction System (EPS) probabilistic forecasts during the winters of 2008-2009 and 2009-2010 over the Adriatic and the Mediterranean Seas, and the North Atlantic Ocean, is also discussed to provide a proper statistical evaluation of the accuracy of EPS-based probabilistic forecasts of the wind over the sea. Average results indicate that EPS probabilistic forecasts over these areas are skilful for the whole forecast range considered in this study. Copyright (C) 2011 Royal Meteorological Society