A puff of heated air blows off the western coast of Africa out over the warm waters of the Atlantic sometime between the months of June and November. Carried by the trade winds, this small mass of air is called a tropical wave. This wave crosses over the 80-degree ocean water, absorbing it's warmth and moisture along the way. As this warm air mass absorbs more water from the ocean, it starts to rise and releases its moisture to form thunderstorm clouds and rain.
Upon releasing it's moisture, the air mass makes a choice to either fall apart or sink back down the ocean to absorb more warm moist air from the surface. Waves that begin a cycle of absorbing warm ocean air represent the start of a tropical storm. As more warm air is absorbed, clouds continue to rise and release moisture. These clouds are pushed higher and higher, forming a tower of moist, humid air. The storm is now a tropical depression.
Certain ingredients are required for the development of a tropical storm. These storms form over deep and warm ocean water, between 5 degrees and 22 degrees of latitude. Since tropical storms gain their energy from the evaporation of warm water, ocean temperatures must be at least 80 degrees F. There must be a trigger that begins the convection, or vertical up and down movement of the air. This convection is usually created by the warm trade winds that collide to encourage warmer air to rise.
Tropical storms are like an engine. Warm air collects as the low-pressure system organizes and rises up the center of the air mass. Picture a funnel-shaped tower of clouds where air is grabbed at the bottom and forced up to release moisture. Air is then pushed outward to return to the surface to collect more moisture. On the outer edges of this system, high-pressure areas, or areas of clear weather helps contains the mass of turbulence as a unit. In the higher levels of the storm, winds are cold and unstable.
The movement of air from a high to low pressure system helps initiates the inward spinning motion of a tropical storm. In addition, the continual spinning of the earth below this supercharged mass of clouds encourages rotation of the storm. In the Northern Hemisphere, storms rotate west to east, or counterclockwise. In the Southern Hemisphere, storms turn clockwise or east to west. Once tropical storms begin to spin, centrifugal force usually results in the formation of an eye.
The eye represents the very center of the storm and often features extremely clear weather. Although there are updrafts and downdrafts in the eye, winds tend to be light. The eye is roughly circular in area, surrounded by the towering eye wall made up of thunderstorm clouds. The eye also has a lower barometric pressure reading than the surrounding storm.
Only 10 percent of tropical disturbances become actual tropical storms. In addition, tropical storms do not form in the Southeast Pacific or South Atlantic Ocean. Many tropical storms form off the coast of Africa or South America. When the winds in a tropical depression each 35-64 knots, the depression becomes a tropical storm and is given a name.