During hurricane season, thunderstorms form over Africa and travel west across the Atlantic, The Atlantic hurricanes usually start as weak tropical disturbances off the West African coast and intensify into rotating storms with weak winds, called tropical depressions. Once the winds exceed 35 miles per hour, the system, now called a "tropical storm," gets an alphabetical name. where some develop into tropical cyclones. Bertha developed from a tropical wave that emerged off the coast of Africa on July 1. Bertha continued to gain strength from warm ocean water, high humidity and favorable atmospheric and upward spiraling wind patterns off the ocean surface. and became the first hurricane of the season on July 7.
The storm now has the circular structure of a hurricane, Bertha strengthened into a Category 3 hurricane that feeds on herself to gain strength. In their energy flow, hurricanes resemble large thunderstorms. But while thunderstorms can start over land or water, hurricanes only start over water. Hurricanes also last much longer, carry far greater energy, and cause much greater destruction. Due to the Coriolis effect, the lower levels of a tropical cyclone start rotating counter-clockwise in the Northern Hemisphere, but clockwise in the Southern. Eyeball the eye wall Hurricane winds whirl around the bizarrely calm "eye," a circular region with little wind, no rain and often a blue sky. The placid eye is surrounded by a circular "eye wall" of furious, thunderstorm-type clouds and the fiercest winds.
The force of the release is tremendous—the amount of heat energy released by an average hurricane is equivalent to the amount of electric energy produced by the U.S. in an entire year. A small portion of the energy released actually warms what has become the inner core of the storm. As the temperature of the air in the inner core rises, its pressure drops, increasing the speed and intensity of the winds swirling around it. These stronger winds bring more warm, moist air to the clouds surrounding the inner core of the storm further fueling its energy. When the swirling winds reach a speed of 74 miles per hour or more, the tropical storm becomes a hurricane. Once a storm officially becomes a hurricane, it receives an intensity rating based on its wind speed and potential to cause damage. As a hurricane develops, its intensity rating often changes.
I Category Once hurricanes have wind speeds between 74 and 95 miles per hour and are expected to cause minimal damage to buildings and homes. Trees, shrubbery and mobile homes tend to bear the brunt of the damage caused by Category One hurricanes.
With wind speeds reaching 100 miles per hour, this is typical of a Category Two storm.
Category Three and Four hurricanes are characterized by even stronger winds and much more damage to homes, buildings and trees.
The most intense classification of a storm is the Category Five hurricane. A Category Five storm will have sustained winds of 155 miles per hour or more and is capable of extensive damage. The inner core of the hurricane is known as the eye of the storm—a calm, often clear-skied patch where winds are lightest and pressure is lowest.
Surrounding the paradoxically calm region of the hurricane is a ring of clouds called the eye wall. The eye wall clouds are thunderstorm clouds, and it is in this region of the hurricane where the heaviest rains and winds originate. The outermost ring of the hurricane is made up of bands of heavy rains that swirl inward toward the storm's center, called spiral rain bands. While the clouds and rain bands are forming in the sky above, the weather on the land below the hurricane turns nasty. The spiraling winds that accompany hurricanes can extend even further beyond the eye of the storm. Typically, hurricanes are about 300 miles wide, so they can affect fairly large areas at one time. Unfortunately for those in its path, a hurricane's speed of travel is hard to predict and varies greatly from storm to storm. Weather experts have calculated that hurricanes move forward at an average speed of 15-20 miles per hour, but a big storm also has the potential to linger over one area for a while, causing torrential rains, or move so quickly that there is no time to prepare for its arrival. Eventually, a hurricane's energy begins to dissipate and the storm weakens. Weather experts have identified several factors that contribute to a hurricane's demise, including the storm's movement over cooler water or drier areas. Even when a hurricane appears to have blown over, however, it can potentially re intensify if it hits weather conditions that are favorable for its development. Every year between June 1 and November 30 (commonly called hurricane season), hurricanes threaten the eastern and gulf coasts of the United States, Mexico, Central America and the Caribbean. In other parts of the world, the same types of storms are called typhoons or cyclones. Hurricanes wreak havoc when they make landfall, and they can kill thousands of people and cause billions of dollars of property damage when they hit heavily populated areas.
