Courtesy of National
The process by which a disturbance forms and subsequently strengthens into a hurricane
depends on at least three conditions. Warm waters and moisture are mentioned above. The
third condition is a wind pattern near the ocean surface that spirals air inward. Bands of
thunderstorms form, allowing the air to warm further and rise higher into the atmosphere.
If the winds at these higher levels are relatively light,this structure can remain intact
and allow for additional strengthening.
The center, or eye, of a hurricane is relatively calm. The most violent activity takes
place in the area immediately around the eye, called the eyewall. At the top of the
eyewall (about 50,000 feet), most of the air is propelled outward, increasing the air's
upward motion. Some of the air, however, moves inward and sinks into the eye, creating a
In the eastern Pacific, hurricanes begin forming by mid-May, while in the Atlantic,
Caribbean, and Gulf of Mexico, hurricane development starts in June. For the United
States, the peak hurricane threat exists from mid-August to late October although the
official hurricane season extends through November. Over other parts of the world, such as
the western Pacific, hurricanes can occur year-round.
Developing hurricanes gather heat and energy through contact with warm ocean waters. The
addition of moisture by evaporation from the sea surface powers them like giant heat
Storm Surge. Storm surge is a large dome of water often 50 to 100 miles wide that sweeps
across the coastline near where a hurricane makes landfall. The surge of high water topped
by waves is devastating. The stronger the hurricane and the shallower the offshore water,
the higher the surge will be. Along the immediate coast, storm surge is the greatest
threat to life and property.
If the storm surge arrives at the same time as the high tide, the water height will be
even greater. The storm tide is the combination of the storm surge and the normal
Widespread torrential rains often in excess of 6 inches can produce deadly and destructive
floods. This is the major threat to areas well inland.
Hurricane-force winds, 74 mph or more, can destroy poorly constructed buildings and mobile
homes. Debris, such as signs, roofing material, siding, and small items left outside,
become flying missiles in hurricanes. Winds often stay above hurricane strength well
Hurricanes also produce tornadoes, which add to the hurricane's destructive power. These
tornadoes most often occur in thunderstorms embedded in rain bands well away from the
center of the hurricane. However, they can also occur near the eyewall.