Analysis of a mesoscale cyclone in the Adriatic Sea

In the evening of November 12, 2019, an exceptional high tide - the second most intense since sea level data are recorded - hit the city of Venice and the entire lagoon, flooding and damaging a large part of the historical center. The causes of this event are due to a small mesoscale cyclonic structure characterized by a warm core, grown in the central Adriatic, which, moving towards the Northwest, strengthened and passed over the Venice lagoon. The passage of the cyclone was anticipated by intense Bora, which turned into Sirocco first and Libeccio afterward, causing the sudden rise of the sea level in the lagoon. This work investigates the factors that determined the development of the cyclone, as well as the characteristics of its particular structure. For this purpose, simulations were carried out with the WRF-ARW model, with initial and boundary conditions supplied by the global GFS model. Three simulations with different starting times were performed, each initialized with a different analysis of the GFS model. The results were compared on the basis of the prediction of the minimum sea level pressure value and of the trajectory of the cyclone. The simulation whose results are closest to the data observed by the meteorological stations is identified, and the factors that have contributed the most to the development of the cyclone are searched for. The interaction between a strong potential vorticity anomaly at 300 hPa and the advection of warm, humid air in the lower layers was the main factor responsible for the cyclone development. The pre-existence of positive cyclonic vorticity, resulting from the convergence of the Sirocco and Bora winds in the northern Adriatic, also made the environment favorable to the cyclone development. Therefore it appears as the cyclone developed by a baroclinic instability process typical of extra-tropical cyclones, but with much smaller dimensions and characteristics.