Observational analysis of two waterspouts in northwestern Italy using an OPERA Doppler radar

Data from a C-band dual-polarization Doppler radar are used to analyze the evolution of two waterspouts in the Mediterranean Sea, observed in front of the coastal city of Sanremo, northwestern Italy, on December 1, 2017. The integration of reflectivity and wind data allows to identify a mesocyclone aloft, and a Doppler velocity couplet, corresponding to a change in wind speed and/or direction in two adjacent individual pixels on radar display, at two different elevations. The latter signal is classified as a Tornado Vortex Signature, suggesting the presence of two vortices moving northward through the coast near Sanremo. The reconstructed paths agree well with the damage and eyewitness evidence. Radar data also suggest that the two waterspouts developed in the region of convergence separating the incoming cold air from the warm and moist inflow.