If you live along the coast, especially the Gulf or southeastern Atlantic, you’re probably keenly aware of the weather during hurricane season. These devastating storms can cause an enormous amount of damage from storm surges and raging winds. But, just what is a hurricane?
How Hurricanes Form
Hurricanes form over water. Those that hit the Gulf and Atlantic coasts of the United States are born in the waters of the Atlantic Ocean off the coast of West Africa. They begin when hot air is drawn up into the atmosphere and begin to spiral in the upper atmosphere, creating storm clouds. Cool air descends into the center of the spiral, creating an eye, or small center of calm weather. The winds around the wall of the eye are the fiercest.
In the lower part of the hurricane, air flows in towards the center and upward in a counterclockwise direction. The winds gain in speed as they approach the eye. When the winds first start, it is called a tropical disturbance, which is often accompanied by heavy clouds and precipitation. If sustained winds reach speeds of 20 to 34 knots, the phenomenon is called a tropical depression. Once speeds reach 35 knots, but less than 64 knots, a tropical depression is upgraded to a tropical storm, which closely resembles a hurricane, but lack its intensity and potential to cause damage. When sustained wind speed exceeds 64 knots, a tropical storm is upgraded to hurricane, with heaviest rain and strongest winds at the eye wall.
The Source of Strength for Hurricanes
As a hurricane moves across the water, it draws its strength from the solar energy stored in the warm moist air over the water. Waters of the Gulf of Mexico, being shallower and warmer than the Atlantic, cause the strength of hurricanes to increase. There are a number of things that will dissipate the power of a hurricane.
If a storm stays in one area of the ocean for too long, the sea surface temperature may drop. Since the storm needs warm surface water for energy, it will eventually subside when that source of energy is no longer available.
What Happens to a Hurricane after Landfall
While the damage from hurricanes is mostly on land, paradoxically, making landfall is often the downfall of these storms. The irregularities of the land surface and areas of low pressure over land disorganize the storm, breaking it up and causing it to lose strength. This is especially true over hilly or mountainous areas where the friction causes a drop in wind speed. The surface energy from which a hurricane gathers its energy is not present over land to the same degree as over water; mainly the lack of moisture; and gradually as a hurricane moves over the land surface it dissipates. Note that if a hurricane that has made landfall passes over a large body of warm water, such as a large lake, it can reconstitute itself.