Severe hurricanes are a fact of life from June 1 through November 30. August and September are the most active months.
Any tropical disturbance can be upgraded to hurricane status when it picks up enough strength and its wind speed exceed 120 km/hr (75 mph).
Hurricanes begin as minor disturbances in the atmosphere over the warm tropical waters of the Atlantic, just north of the equator.
They pull their energy from the extremely humid air near the ocean's surface. In late summer or early fall, surface temperatures of the ocean are highest. The temperature must be a least 27ºC. (80ºF.). Evaporation is the main source of energy. Hurricanes typically develop within 20 degrees of the equator. Driven by the heat of the tropical sun, enormous quantities of seawater evaporate into the air, forming a deep layer of warm, moist air.
During the condensation of the water vapor, latent heat is released which warms the air producing buoyancy to lift the air.
The updraft of air currents causes more and more warm moist air to rise into the center of the updraft and adds energy to the storm.
In the center, the air pressure is very low. In the Northern Hemisphere, the air is drawn inwards toward the low pressure creating a counter-clockwise whirling spiral of air.
Around the calm core-or center of the storm-these fierce revolving wind system blow. This is the eye of the storm. The eye averaging more than 12½ miles in diameter, is and awesome sight. It is a zone without clouds surrounded by large circular patterns of heavy cloud.
Near the top of the storm (often as much as 40,000 feet above the ocean surface) the air flow is outward, carrying the rising air away from the eye to make room for the inward rush of air at the surface.
A well-developed hurricane feeds on large quantities of warm, moist air and a continuous supply is need to remain self-perpetuating. A hurricane has the potential to grow to enormous size and strength.
Still, there are many tropical disturbances and storms in the warm sector of the Atlantic each year, but few of them become strong enough to become hurricanes.