ABOUT HURRICANES: A hurricane is a type of tropical cyclone, a low-pressure system that usually forms in the tropics with winds that circulate counterclockwise near the earth's surface. Storms are considered hurricanes when their wind speeds surpass 74 MPH. Every hurricane arises from the combination of warm water and moist warm air. Tropical thunderstorms drift out over warm ocean waters and encounter winds from near the equator. Warm, moist air from the ocean surface rises rapidly, encounters cooler air, and condenses into water vapor to form storm clouds, releasing heat in the process. This heat causes the condensation process to continue, so that more and more warm moist air is drawn into the developing storm, creating a wind pattern that spirals around the relatively calm center, or eye, of the storm, much like water swirling down a drain. The winds keep circling and accelerating to form a classic cyclone pattern.
WHAT IS WIND SHEAR? It is the difference in wind speed and direction over a short distance. A vertical wind shear occurs when wind speeds and directions vary with altitude. It can literally tear storms apart. This has typically been associated with reduced hurricane formation and intensity. If wind shear increases in the coming decades, it may counter the effect of global warming, which has been projected to create conditions likely to increase hurricane intensity.
The American Meteorological Society and the American Geophysical Union contributed to the information contained in the TV portion of this report.