 Although the geographical dimensions of tropical oceans and the Mediterranean Sea are clearly different, the precursor mechanisms of these perturbations, based on the air-sea thermodynamic imbalance, are similar.Their origins are typically non-tropical, and develop over open waters under strong, initially cold-core cyclones, similar to subtropical cyclones or anomalous tropical cyclones in the Atlantic Basin, like Karl (1980), Vince (2005), Grace (2009), Chris (2012), or Ophelia (2017).Sea surface temperatures in late-August and early-September are quite high over the basin (24/28 °C or 75/82 °F), though research indicates water temperatures of 20 °C (68 °F) are normally required for development.