Do hurricanes form in unsettled or calm weather?

Dateline article| David Murphy|

by David Murphy

Hurricanes form in calm weather. This may not make sense, at first. After all, doesn't it figure that the largest, most violent storms on earth would be the result of a stormy, turbulent weather pattern?

Here's the explanation: While regular storm systems require a clash of different types of air masses to get started (usually brought about by an approaching cold front), a hurricane is its own storm engine, without need of any fronts or external sources of turbulence to form or survive. In fact, the presence of a cold front would cut the hurricane down before it ever had a chance to get started.

This is because a hurricane develops its own internal weather system.

Evaporating ocean water places great amounts of moisture into the atmosphere, some of which condenses into rain clouds and thunderstorms. Next, the developing hurricane is influenced by forces in the atmosphere like gravity and pressure, which cause it to rotate. The humid air around the storm's center begins rising faster and faster and evaporating more and more water. Eventually, all that rising air has no place to go and must dive through the center of the storm to replace all the additional air that's being drawn up from below.

Perhaps you can now begin to imagine the self-propelling circulation that makes a hurricane possible. Warm air from the surface is rising through the perimeter of the hurricane and then sinking through the center to begin the cycle anew. The storm has become an independent, self-sustaining weather machine that keeps going until either its fuel runs out, or invading mid-level winds slice into the storm, cutting off its internal circulation.

What's more, the hurricane has accomplished this feat without the aid of any external weather system. All it needed was an enormous volume of warm, evaporating water and otherwise stormless skies.

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