New Scientist: Typhoon or hurricane? A tropical cyclone starts life as a tropical depression – an organised, spinning storm system with wind speeds of less than 63 kilometres per hour. When the winds grow faster, the system is given a name and classified as a tropical storm. When the winds reach 119 km/h, a ring of intense thunderstorms called the “eyewall” forms around the storm’s centre. Within the eyewall is the “eye” of the storm, a clear, calm region of sinking air. Once the sustained …