A hurricane consists of bands of thunderstorms that move in a spiral motion towards the center, or eye, of the storm. The eye is a calm area at the center of the storm that is usually between 20 and 40 miles across. Here, the sky is clear and there is little or no wind. Encircling the eye is the eyewall, a wall of thunderstorms with the strongest winds in the storm. Both the eye and the eyewall can change structure, which can cause the wind speed to change. The eye can expand or become smaller, and two eyewalls can develop. The outer edges of the storm are called the spiral rainbands. These are bands of thunderstorms that slowly spiral counterclockwise, and can stretch a few hundred miles from the storm’s center. They can be as small as a few miles or as large as 300 miles long.
Hurricanes generally move forward between 15 and 20 miles per hour, although they can stall, producing devastating rainstorms. Others have far exceeded the typical speed, reaching more than 60 miles per hour. Their paths can vary as well, from a relatively straight course, to one that is erratic and difficult to predict. Hurricanes also produce massive waves that reach in all directions, in addition to accumulating large amounts of water. This accumulation of water is called a storm surge, and can cause sea level to raise more than 20 feet when the hurricane hits land.