The Atlantic hurricane season ends today. Emily Johnston of Westminster writes: "What is the difference between a hurricane, typhoon, cyclone and tornado? Is [it] ... semantic, or is there a meteorological basis for the ... terms?" Hurricane and typhoon are regional names for "tropical cyclones" -storms that form over warm oceans. They're hurricanes in the Atlantic and the eastern Pacific, typhoons in the northwest Pacific. Tornadoes, pipsqueaks by comparison, are spawned by rotating air in thunderstorms.