3 September 2008 MAR 110 HW8 Hurricane Damage 1Homework 8: Hurricane Damage (adapted from Pipkin et al.) Tropical cyclones have a significant impact on coastal areas of the world. In the Atlantic Ocean they are called hurricanes (from Hurican, the Carib god of evil), whereas similar storms in the Pacific Ocean are called typhoons. They are a significant part of global weather systems because they transfer large quantities of water and warm, moist air from equatorial regions to higher latitudes. In the Caribbean Sea, the Gulf of Mexico, and the southeastern United States, hurri-canes have shaped low-lying coastal areas and, at times, have caused dramatic losses of life and property. Even with the use of orbiting weather satellites, hurricane prediction and tracking remains a major challenge for meteorologists. Hurricane Generation The hurricane season extends from June 1 to October 1 in the North Atlantic Ocean. This is be-cause hurricanes get most of their energy from the equatorial oceans in the summer and early fall, when seawater temperatures are warmest, usually above 25°C (about 800F). Hurricanes begin as tropical waves, areas of organized clouds 200 - 500 kilometers in diameter (Figure 8-1), in the eastern equatorial Atlantic. As hot air rises over the warm ocean water, the atmospheric pressure drops, and cyclonic (counterclockwise) circulation begins, with strong winds rushing toward the low pressure center. At this point the wave becomes a tropical depression. It becomes a tropical storm when winds 65 -118 kilometers / hour (39 -74 miles/hour) develop. If winds exceed 118 kilometers/hour, the storm is called a hurricane (in the Atlantic and eastern Pacific oceans) or a typhoon (in the western Pacific Ocean). Figure 8-1 Atmospheric Waves West of Africa The airflow off of the western Africa in the tropics are unstable during the NH summer creating atmospheric depressions and sometimes hurricanes that propagate westward.3 September 2008 MAR 110 HW8 Hurricane Damage 2 Figure 8-2 Hurricane Structure – Satellite View Tropical storms and hurricanes have cyclonic or counterclockwise circulation in the Northern Hemisphere because the Coriolis effect deflects the inward air flow toward to the right. In the Southern Hemisphere, the Coriolis deflection is to the left so that cyclones in the southern tropics have clockwise rotation. Hurricane Naming Prior to 1953, hurricanes were named for the year or month of their occurrence, for the writer who described their passage, or for places sustaining severe damage, like the Galveston Hurricane of 1900 (Figure 8-3). During World War II, U.S. Navy and Army Air Corps meteorologists forecasting tropical cyclones in the Pacific Ocean began to informally give typhoons women's names, probably after their wives or girlfriends. Other naming schemes were women's names in alphabetical order, and by the international phonetic alphabet-Alpha, Bravo, Charlie, Delta, Echo, Foxtrot, and so on. In 1953 the U.S. Weather Bureau began to name Atlantic hurricanes with an alphabetical sequence of female names. The current hurricane-naming method is one of alternating male and female names, such as the recent names Alberto, Beryl, Chris, Debby, and so forth. Many names have been retired to the hurricane "Hall of Fame" because their storms were so devastating-Andrew, Gilbert, and Camille, for example. Figure 8-3 Galveston Damage - 1900 The 1900 hurricane that hit Galveston Texas completely destroyed the town and killed many of the inhabitants. Measuring Hurricane Strength The strength of hurricanes is measured by the Saffir-Simpson scale (Table 8-1), which uses minimum sustained wind speeds to categorize storms (Figure 8-1) from Category 1, a minimal3 September 2008 MAR 110 HW8 Hurricane Damage 3hurricane, to Category 5, the most intense hurricane. Hurricane Mitch, which devastated Central America, and Hurricane Georges, which struck the coastal United States in 1998, were Category 5 events. Figure 8-4 Hurricane Saffir Simpson Category - Damage TABLE 8-1 Since 1944, aircraft have been used to study tropical disturbances that had the potential to de-velop into hurricanes. Wind speeds and atmospheric pressure changes are measured by techni-cians in aircraft flown by Air Force personnel, who are called "The Hurricane Hunters" (Figure 8- 5). Because hurricanes have diameters of hundreds of kilometers and may have dozens of con-vective storms embedded in them, they may affect coastal areas far from the main storm center. As they approach the shoreline, NOAA's Hurricane Warning Center in Miami Beach, Florida, may is-sue a hurricane watch, a 36-hour advance notice of high winds and storm surge, or a hurricane warning, which means that hurricane winds and surge are expected within 24 hours.3 September 2008 MAR 110 HW8 Hurricane Damage 4 Figure 8-5 Weather aircraft of the "Hurricane Hunters" flying through the eye of a hurricane. [Photograph courtesy of the 53rd Weather Reconnaissance Squadron, 403rd Wing, U.S Air Force.] Hurricane damage is caused by high winds, flooding, and storm surge. Surface winds can cause an abnormal rise in sea level, reaching from 1 to 6 meters above normal sea level (Figure 8-6). Along the Gulf Coast, the estimated 330 kilometer/hour winds of Hurricane Camille in 1969 caused a maximum storm surge of 8 meters, with 3-meter-high wind-driven waves atop the surge. The end result was a l0-meter-high wall of water approaching the Mississippi coastline. Failure to evacuate caused significant loss of life. One survivor of a "hurricane party" was found floating on a sofa 8 kilometers further inland from the coastal apartment in which the party was held. Figure 8-6 Storm Surge. (top) A sea level record on Mustang Island, Texas is partitioned into the (middle) contribution of storm surge (atmospheric wind and pressure) and (bottom) astronomical (sun and moon). Note the extreme, storm surge-related high water around February 1.3 September 2008 MAR 110 HW8 Hurricane Damage 5Not all tropical storms develop into hurricanes, and not all hurricanes develop damaging storm surge. Hurricanes tend to be cyclic; with periods during which relatively weak tropical storms impact coastlines followed by periods of stronger hurricanes. This is a dangerous sequence, because coastal residents tend to remember only the most recent tropical storm events. Hurricane development and strength may be cyclical because El Nino/Southern