Synoptic analysis of Cyclone Ianos via surface, satellite and reanalysis data

Mediterranean Tropical-like Cyclones, or commonly named as medicanes are a special type of cyclone over the Mediterranean Sea. These cyclones are quite similar to tropical cyclones, although smaller. Their development process is the same as that of subtropical or tropical cyclones forming over the higher latitude subtropical areas of the Atlantic Ocean: they mainly originate from extratropical lows that cut off from the main westerly flow and gradually acquire subtropical and then tropical characteristics if they remain long enough over relatively warm waters. This type of cyclones is officially classified in the Atlantic region by the National Hurricane Center (USA), and nowadays some meteorological services, for example the UK Met Office already admit the medicanes as subtropical or tropical cyclones, too.

In September 2020, a unique cyclone developed over the central Mediterranean Sea, named 'Ianos' after the Greek Meteorological Service. The genesis occurred over warm water of 26-27 °C from a larger cluster of thunderstorms and it did not have extratropical precursor. Later, the cyclone gradually strengthened and built up a well-defined tropical-like structure with sustained deep convection and occasionally with an eye. In our work, we investigated this cyclone based on available surface and satellite-based measurements and the ECMWF ERA-5 reanalysis data with 0.75° resolution to determine whether it is really a tropical cyclone. We analysed the low-level, vertical and high-level structure of the cyclone and compared reanalysis parameters that typically differ between tropical and extratropical cyclones. The results show that Ianos had more tropical than subtropical characteristics and did not show any extratropical sign, so it could be classified as a tropical cyclone. Furthermore, surface measurements confirmed that the cyclone reached at least the middle part of the Category 1 intensity interval on the Saffir-Simpson hurricane wind scale before it made landfall in Greece, and it is also possible that it had been a Category 1 hurricane for a short period the previous day, too.