Ethan Siegel in Forbes:
The most destructive storms to occur on Earth — although they’re not limited to Earth — are hurricanes, typhoons and cyclones. Strong, sustained winds coupled with torrential, downpouring rain often brings with it severe flooding, incredible property damage capable of cresting 100 billion dollars and, quite frequently, death tolls that rise into the thousands. These storms all the same phenomenon, just given different names dependent on where they form on our world; generically, they’re known as tropical cyclones. While the big, sweeping, cloudy arms surrounding a quiet “eye” are familiar sights to even casual storm-watchers looking at a radar image or photo from space, the scientific ingredients are so few and so simple you might not believe it:
1. Warm ocean water.
That’s it. Those are the only two ingredients you need, and that’s what gives you, at least on Earth, a tropical cyclone. Here’s how.