The Tropical Cyclone On Land
All of the cyclone development described thus far takes place at sea, but the entire cyclone also is blown along with the prevailing winds. Often this movement brings the storm toward land. As tropical cyclones approach land they begin affecting the coastal areas with sea swells, large waves caused by the storm's high winds. Swells often reach 33 ft (10 m) in height and can travel thousands of kilometers from the storm. Coastal areas are at risk of severe damage from these swells that destroy piers, beach houses, and harbor structures every hurricane season. Particularly high swells may cause flooding farther inland.
Perhaps more dangerous than the gradually rising swells are the sudden rises in sea level known as storm surges. Storm surges occur when the low barometric pressure near the center of a cyclone causes the water surface below to rise. Then strong winds blowing toward the coast push this "bulge" of water out ahead of the storm. The water piles up against the coast, quickly raising sea level as much as 16 ft (5 m) or more. The highest storm surge generally occurs to the right of the storm's path. When storm-tossed waves 23-33 ft (7-10 m) high are added to this wall of water land areas may be inundated. In 1900 the city of Galveston, Texas, was hit with a storm surge during a hurricane. One eyewitness reported that the sea rose 4 ft (1.3m) in a matter of seconds. Over 5,000 people lost their lives in the Galveston Hurricane and resulting flooding, making it the deadliest storm ever recorded in the United States.
Tropical cyclones that travel onto the land immediately begin to weaken since humid air, their source of energy, is cut off. The winds at the base of the cyclone encounter greater friction as they drag across uneven terrain that slows them. Nevertheless tropical cyclones at this stage are still capable of producing heavy rains, thunderstorms, and even tornadoes. Occasionally, the remnants of a tropical cyclone that has begun to weaken over land will unite with an extratropical low pressure system, forming a very potent rain-making storm front that may bring flooding to areas far from the coast.
Until relatively recently, people in the path of a tropical cyclone had little warning of approaching storms. Usually their only warning signs were the appearance of high clouds and a gradual increase in winds. Hurricane watch services were established beginning in the early years of the twentieth century. By the 1930s hurricanes were detected with weather balloons and ship reports while the 1940s saw the introduction of airplanes as hurricane spotters. Radar became available after World War II and has remained a powerful tool for storm detection in the years since. Today a global network of weather satellites allows meteorologists to identify and track tropical cyclones from their earliest appearance as disturbances over the remote ocean. This improved ability to watch storms develop anywhere in the world has meant that warnings and evacuation orders can be issued well in advance of a tropical cyclone reaching land. Even though coastal areas have more people living near them today than ever before and tropical cyclones remain just as powerful as they have always been far fewer storm related deaths are reported each year than 60 years ago thanks to advances in storm detection and forecasting.
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