Thursday, September 1, 2011

Hurricane Katrina

Hurricane Katrina : A Problem-Based Learning Module

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Katrina was one of the most powerful hurricanes ever, and will go down as the costliest natural disaster in recorded memory. At one point, wind speeds topped 170 mph, and surface pressures tanked to below 905 mb—extraordinary for an Atlantic hurricane. She resembled to epitome of all Atlantic hurricanes, and revealed the staggering amount of suffering a storm of her magnitude (Category 3 at landfall) can cause to those unprepared.

Storm History

Katrina had her origins in the Bahamas as a rather disorganized area of cloudiness and thunderstorms. During her early stages of development, the would-be Katrina looked like a sloppy concoction of disorganized cloudiness, and it seemed improbable that this area of low pressure could develop into anything consequential. During the afternoon hours of 23 August, a Hurricane Reconnaissance Aircraft, along with buoy data and ship reports indicated that the area of disturbed weather in the southeastern Bahamas had become organized enough to be classified as a Tropical Depression (TD12)1. A short 24 hours later, the shoddy mass of convection had organized into a concentrated area of showers and thunderstorms just east of Nassau, and was named Tropical Storm Katrina2.

Katrina continued on a lazy westward track towards eastern Florida through the next 24 hours, and became a hurricane during the afternoon of 25 August, just 30 miles south-southeast of Boca-Raton, FL3. At this point, Katrina looked like a healthy, developing hurricane with cloud top temperatures as low as –80C. It was expected that Katrina would weaken shortly after making landfall in southern Florida, but she veered slightly off course and passed over the very moist Everglades south of lake Okeechobee, and was able to maintain hurricane intensity into the extreme eastern Gulf of Mexico.

On 26 August, Katrina entered the Gulf of Mexico, where shear was low and Sea Surface Temperatures (SSTs) were high, ranging from 30-32C—a perfect environment for intensification. During the overnight hours of 27 August, Katrina’s central pressure dropped from 950 mb, to nearly 930 mb—all in less than 12 hours. Early on 28 August, the National Hurricane Center revised the intensity of Katrina upwards to a Category 5 with surface winds near 160 mph. Less than three hours later, Hurricane Hunters measured a 166 kt flight level winds, and a 907 mb central pressure, which corresponded to surface wind speeds close to 175 mph—absolutely astonishing for an Atlantic Hurricane4.

In a report issued by the Hurricane Center on December 20, 2005, Katrina made landfall as a strong Category 3 storm, instead of the Category 4 as originally thought.5 Still, the incredibly high storm surge coupled with the strong winds proved too much for the New Orleans area to bear, and the consequences were unfathomable. As the Hurricane Center’s Tropical Cyclone Report so eloquently states:

“The scope of human suffering inflicted by Hurricane Katrina in the United States has been greater than that of any hurricane to strike this country in several generations.”

New Orleans, LA