How Do Hurricanes End?

Hurricane Earl passing Puerto Rico on August 31.
CREDIT: NASA/GOES Project

Hurricane Paula is growing stronger and closing in on the tip of Mexico's Yucatan Peninsula but is expected to weaken back into a tropical storm by the end of the week as the hurricane encounters unfavorable conditions.

What causes hurricanes to die down?

Several factors affect how drastically a storm deteriorates, according to Dennis Feltgen, spokesman for the National Hurricane Center (NHC).

"Like everything, a hurricane dies when it no longer has a source of energy," Feltgen told Life's Little Mysteries. "A hurricane can die in a number of ways, but the primary reasons are cold water, no water and wind shear."

Hurricanes develop out of low pressure areas that form over warm ocean waters, with evaporating water from the ocean surface fueling the storm as condensation warms the surrounding air. Therefore, a storm's winds weaken when it moves from warm to cool or cold waters.

This is the same reason why hurricanes drastically deteriorate when they travel from water to land. A sudden lack of warm water drains the storm's energy supply, Feltgen explained. Additionally, the hurricane's surface circulation can be reduced by friction when it passes over land, according to the National Oceanic and Atmospheric Administration (NOAA).

High wind shear is another culprit. Wind shear is the variation between the wind's speed (speed shear) or its direction (directional shear) over a short distance within the atmosphere. Wind shear at several thousand feet from the surface can carry away a storm's heat, killing it or at least preventing the storm from growing stronger.

"Wind shear can literally tear a storm apart in different directions," Feltgen said.

Dry air can also contribute to a hurricane's demise, since storms require warm, humid air to survive. "Dry air chokes off the hurricane," Feltgen said.

However, even a fading, weakening storm can come back to life under the right conditions. A waning hurricane or tropical cyclone can get its strength back and possibly grow even more intense than it was before if it moves into a more favorable region, such as back out to warm tropical waters.

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