Thermal structure and dynamical precursor of a Mediterranean tropical-like cyclone

A detailed analysis of a Mediterranean tropical-like cyclone (MTLC) that occurred in January 2014 has been conducted. After having identified the cyclone path and its general features, the GLOBO, BOLAM and MOLOCH numerical weather prediction (NWP) models, developed at the National Research Council - Institute of Atmospheric Sciences and Climate (CNR-ISAC) in Bologna, were used to simulate the phenomenon. Particular attention was paid to the Mediterranean phase of the system life cycle as well as to the Atlantic phase, since the cyclone showed a well-defined precursor up to 3 days before the formation of the mean sea-level pressure (MSLP) minimum over the Alboran Sea. The Mediterranean phase was studied using different combinations of the aforementioned models, so as to evaluate the sensitivity to boundary and initial conditions. The analysis of the cyclone thermal phase showed the presence of a deep warm-core quasi-symmetric structure, thus confirming the tropical-like nature of the system. In the Atlantic phase, the precursor, in the form of a low-pressure system, was traced from North America to the Mediterranean. The thermal phase analysis showed evidence of a deep cold-core asymmetric structure during the whole Atlantic phase, while the first contact with the Mediterranean Sea caused a sudden transition to a shallow warm-core structure. The examination of potential vorticity (PV) three-dimensional structure revealed the presence of a PV streamer that formed individually over the Labrador Sea and subsequently interacted with the low-pressure system near the northwestern coast of the Iberian peninsula, favouring the first phase of the cyclone intensification.