A term used to indicate that a tropical cyclone has lost its "tropical" characteristic-a warm core centre that was the storm's primary energy source. Once "going extratropical" the remains of the tropical cyclone often merges with a cold "winter type" cyclone. The resulting effect of mixing the remnants of warm tropical air with cold air creates a "combustible" type of weather system, which often supercharges the storm with very intense wind speeds and extremely large waves. Extratropical storms usually happen in the fall when late season tropical cyclones converge with early winter storm systems. The storm in the movie "Perfect Storm" was a classic example of an October extratropical storm.