What Makes a Hurricane?

Think of a hurricane as a giant heat pump--pumping the energy stored in tropical ocean water warmed by the blazing sun to at least 80 degrees Fahrenheit (27 degrees Celsius).

Such water can make for one heck of a beach vacation. But it also makes for warm humid air that can cause big trouble, when ocean winds coming from different directions converge and help push the humid air upward. As the humid air rises, it cools and condenses into powerful storm clouds and releases the latent heat energy of the tropical ocean water.

Three Ifs

Of course, garden-variety thunderclouds are a far cry from a neighborhood-destroying hurricane. As the humid air rises, it leaves behind a low-pressure area that literally sucks in more warm humid air--more fuel for the growing storm.

• If the rising and condensing air encounters even more humid air as it rises--even more fuel--and
• If the winds higher up in the atmosphere don't shear the growing storm apart, and
• If there's a high-pressure area above it, the steamy, sea-stirring storm may become a hurricane.

The high-pressure area above the storm is the hurricane's "exhaust pipe," halting the rising air and pushing it out and away, so that more air can get sucked into the space below. In fact, a hurricane's gargantuan winds come from air rushing in to replace the air that's rising up in the center of the storm and, eventually, being pushed out and away high in the sky.

Ocean Creature

If this whole heat-pumping system--sucking in tropical ocean air, condensing its moisture into powerful storm clouds, and pushing the air away so that more can rush in to take its place--becomes large enough, the daily rotation of the Earth can take the disturbed area and spin it around. This helps organize the massive storm even more, forming the "eye" and pushing its cloud bands into a pinwheel shape.

Once created, a hurricane can draw life from the warm ocean for days. If, however, it makes landfall or moves into colder climes--abandoning the sun-touched ocean waters that fuel it--the organized storm will quickly fall apart. Without heat to pump, even a catastrophic category 5 hurricane can weaken into a tropical storm in hours.