A violent, whirling column of air in contact with the ground. A natural disaster. Most tornadoes have a diameter of several hundred. The largest ones exceed 1500 m in diameter. The fierce swirling winds can reach speeds of more than 400 kilometers per hour. These winds are strong enough to send cars, trees, and even entire houses flying through the air. Tornadoes usually lasts only a few minutes. More destructive ones, however, can last for several hours. When thunderstorm updrafts begin to rotate tornadoes can form. Swirling winds spiral downward from the base of the thunderstorm, creating a funnel cloud. When that funnel reaches the ground, it becomes a tornado. Although the whirling air is invisible, you can easily see the debris lifted by the tornado. Most tornadoes occur in the United States rather than anywhere else on Earth. the central USA, from Nebraska to Texas, is known as Tornado Alley because it experiences the most tornadoes. Tornadoes occur here frequently because in this area, cold air blowing Southward from Canada Routinely collides with warm, moist air moving northward from the Gulf of Mexico. Dr. Ted Fujita developed a method for classifying tornadoes based on the damage that they cause. On the modified Fujita Intensity scale, F0 tornadoes cause light damage, breaking tree branches and damaging billboards. F1 through F4 tornadoes cause moderate to devastating damage, including tearing roofs from homes, derailing trains, and throwing vehicles in the air. F5 tornadoes are the most intense and cause incredible damage such as demolishing concrete and steel buildings, and pulling the bark from trees. An intense tropical storm with winds exceeding 119 kilometers per hour. They are the most destructive storms on earth. Like tornadoes, they have a circular shape with intense, swirling winds. However, unlike tornadoes, hurricanes form in late summer over warm tropical ocean water. A typical hurricane is 480 km across, which is more than a hundred and fifty thousand times larger than a tornado. At the center of the hurricane is the eye, and area of light winds and clear skies. Damage from hurricanes occurs as a result of strong winds and flooding. Hurricanes create high waves that could flood coastal areas while still out at sea. As it crosses the coastline strong rains intensify and can flood and devastate entire areas. Once a hurricane moves over land or colder water, it loses its energy and dissipates. In other parts of the world, hurricanes are called (Asia) typhoons or (Australia) tropical cyclones.Hurricanes consist of alternating bands of heavy precipitation and sinking air. As warm, moist air rises into the atmosphere, it cools, water vapor condenses, and clouds form. As more air rises, it creates an area of low pressure over the ocean .As the air continues to rise a tropical depression forms. Tropical depressions bring thunderstorms with winds between 37 to 62 km per hour. Air continues to rise rotating clockwise. The storm builds to a tropical storm with winds in excess of 63 km per hour. It produces strong thunderstorms. When winds exceed 119 km per hour, the storm becomes a hurricane. Only 1% of tropical storms become hurricanes.