@George-Willfer Why do tropical cyclones (or TRS if you prefer) follow generally a curved track, first westerly then northerly and finally easterly in the Northern Hemisphere, and symmetrically in the Southern Hemisphere ? Here is an explanation in simple words : http://www.applet-magic.com/hurricanerecurve.htm More simply, tropical systems move globally to the west with a small component towards the poles. A weakness may appear in the subtropical belt of high pressures in connection with the formation of a trough; at this point the tropical system can bend its trajectory towards the pole and then towards the east with the westerly flow of polar depressions.