The 2005 Atlantic hurricane season broke several records, including the most named tropical storms in a single year, totaling 27 (the average is 10), and the most hurricanes, 15 (the average is 5); and 7 of these were rated intense, or greater than Category 3 (the average is 2—i.e., sustained winds above 111 mi./hr. [miles per hour], or 179 km/hr. [kilometers per hour]). The 2005 season was the only time two Category 5 storms were in the Gulf of Mexico (Katrina and Rita) and the first time three Category 3 or more hurricanes made U.S. landfall in subsequent years (2004 and 2005). Hurricane Katrina was the costliest storm in U.S. history, at an estimated $105 billion. The 2005 season experienced the greatest damage total in 1 yr. (year), estimated at $150 billion (2008 dollars).
Katrina began as a slow-moving easterly wave of low pressure in the trade wind belt near the west coast of Africa. The mass of rain clouds traveled across the Atlantic Ocean, becoming Tropical Depression 12 on August 23, 2005. The system intensified overnight to Tropical Storm Katrina (39 mi./hr., or 63 km/hr.) east of the Bahamas. Rapid strengthening followed as the system passed over 82 °F (28 °C) water. These storms feed on the latent heat of condensation, and warmer water provides more energy for the storm.
Hurricane warnings were posted along the Southern Florida coast. On August 25, Katrina reached 74 mi./hr. (119 km/hr.) and Category 1 status on the Saffir-Simpson Hurricane Damage Potential Scale. At 5 p.m., Katrina made landfall near North Miami Beach with sustained winds of 80 mi./hr. (128 km/hr.), causing flooding and damage and taking 14 human lives. By morning, Katrina had reached the Gulf of Mexico and moved westward over the warm water of the Loop Current. Sea surface temperatures reached 92 °F (33 °C), feeding rapid intensification.
By August 27, the system shifted course to the northwest and then north, provoking warnings for the Gulf Coast from Western Florida to Louisiana. Category 5 status was achieved on August 28, when winds crossed the 155-mi./hr. (250 km/hr.) mark, only to increase to 175 mi./hr. (280 km/hr.), with a central pressure of 902 mb (millibars) (26.61 in./hg [inches per hectogram]) later that day; normal sea-level pressure is 1,013.2 mb.
The governor of Louisiana declared a state of emergency for her state on August 26, followed by President George W. Bush's major disaster declaration on the afternoon of August 28. Evacuation efforts were underway by the morning of August 28. Estimates place the number of people who were evacuated at nearly 1 million, with 374,000 of these listed at shelters in other states. The critical problem was that 120,000 residents of the New Orleans area did not have personal automobiles and had to rely on public transportation.
A buoy 50 mi. southeast from the mouth of the Mississippi River measured a wave height of 55 feet (16.8 meters) on the morning of August 29—a record for the National Data Buoy Center. Landfall occurred at 6:10 a.m. CDT (central daylight time) in Plaquemines Parish between the Mississippi River mouth and Grand Isle. Katrina slowed to a Category 3 with sustained winds up to 130 mi./hr. (210 km/hr.). By 8:00 a.m., Katrina was 40 mi. southeast of New Orleans, shifting slightly to the east; then, by 10:00 a.m., it made a second landfall along the Louisiana-Mississippi border. The lethal front-right quadrant of the storm was hitting the Mississippi Gulf Coast, while easterly winds north of the eye wall were pushing the waters of Lake Pontchartrain into New Orleans. The storm surge and winds obliterated many towns, with the damage extending east into coastal Alabama. Sixty oil spills, totaling 4 million gallons, occurred as facilities along the coast broke and more than 100 oil-drilling platforms were destroyed.
As happens with these latent heat engines, Katrina started to weaken as it moved inland, though it was still a powerful rainfall event. By 7 p.m., on the day of landfall, it was about 30 mi. north of Meridian, Mississippi, with winds below 74 mi./hr. (119 km/hr.)—it was now Tropical Storm Katrina. By the time it reached Tennessee on August 30, Katrina dropped to a tropical depression. On August 31, it became an extratropical depression as it crossed the Great Lakes into Canada.
In the days following landfall, the nation watched the grim story unfold on television. Twenty-five thousand people were stranded at the Louisiana Superdome and another 20,000 at the convention center in New Orleans with little food, water, or any sanitation facilities—24 people died at the center. Tragically, four hospitals with intensive care patients were likewise stranded without electricity or supplies for days after landfall. Many days passed as the federal government and its Federal Emergency Management Administration (FEMA) delayed their response for as yet unexplained reasons. The head of FEMA was removed from office on September 9, but the slow response continued. Eventually, 1.2 million people underwent some form of evacuation.
Katrina nearly obliterated the sandy barrier islands that lay offshore. Under normal circumstances, these islands serve to protect the Mississippi River delta from wave action. The Chandeleur Islands, 19 to 25 mi. (30-40 km) from the LouisianaMississippi Gulf Coast, lost half their sand inventory due to Hurricane Georges (1988). More sand losses followed from Hurricanes Lili (2002), Ivan (2004), and Dennis (2005). However, Katrina basically wiped out the islands, leaving about 10% of the former sand volume.
The city of New Orleans is almost entirely below the elevation of the Mississippi River, with sections of the city below sea level. Severe flooding is a certainty for existing and planned settlements. The events of 2005, following the passage of Hurricane Katrina, will remain for many years as one of the greatest engineering failures by the government and the U.S. Army Corps of Engineers. Fully 80% of New Orleans was under water. Four levee breaks and at least 50 levee breaches (topping) led to the inundation of a major city.
More than 4 yrs. after the disaster, much of the debris of lost neighborhoods still remains. Six investigations by civil engineers, scientists, and political bodies agreed that the design, construction, and maintenance of the “protection” system were flawed. Many structures failed before they reached the design failure limits. After all, Hurricane Katrina was a Category 3 as it moved onshore. Several of the levee floodwalls were weak because they were not anchored to the correct depth, such as along the 17th Street Canal. In 2007, civil engineers inspecting the levee and floodwall repair discovered that the composition of fill materials was too low in clays and too high in sand. At the end of 2009, repair work in New Orleans was still not completed.
Research has established a “total dissipation index” to rate the potential destructiveness of tropical cyclones over their lifetime. The MIT (Massachusetts Institute of Technology) scientist Kerry Emanuel defined an “index of potential destructiveness” and found that the intensity of tropical storms and hurricanes had increased markedly since the 1970s. Storms have been lasting longer, with increased intensity. Emanuel determined strong correlations between tropical sea surface temperatures and the doubling of power of storms.
Another research team, headed by Carlos Hoyos, Georgia Institute of Technology, completed work in 2006 and found that the increasing numbers of Categories 4 and 5 hurricanes since 1970 were directly linked to increasing sea surface temperatures. These increases in temperature were the only statistically significant variables explaining the intensification of global hurricane strength. Given the climate change now underway, the forecast is for further intensification.
Researchers suggest that global climate change, when considered alongside increased coastal population settlement and rising sea levels of more than 0.4 in. (1 centimeter) per year along the Gulf Coast, will produce substantial future hurricane-related losses. Warmer seas provide more energy, and warmer air absorbs more water vapor, with all this energy converted into tropical cyclone winds. Researchers identified the key role of higher ocean and air temperatures. The forecast for vulnerable coastal regions is not positive.
Coastal Hazards, Hurricanes, Physical Geography of, Hurricanes, Risk and Hazard, Natural Hazards and Risk Analysis, Weather and Climate Controls
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