Posttropical

Posttropical is a term used in meteorology to describe a weather system that was once a tropical cyclone but has lost its tropical characteristics. These systems typically occur as a tropical cyclone moves over cooler waters or interacts with mid-latitude weather systems. The transition involves a shift in the storm's energy source from warm ocean waters to atmospheric temperature differences. As a result, the storm's structure changes from a symmetrical, warm-core system to a more asymmetrical, cold-core system. The defining feature of a posttropical cyclone is the absence of a well-defined eye and the presence of a broad area of low pressure with associated frontal systems. While they may still produce significant rainfall, strong winds, and coastal flooding, they are no longer classified as tropical. The term is often used by national meteorological agencies, such as Environment Canada, to communicate the ongoing threat posed by these transitioning systems to the public. The intensity of a posttropical cyclone is usually described using wind speed categories, similar to tropical cyclones, but without the tropical designation. These storms can persist for a considerable time and impact areas far from their original tropical origin.