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Hurricane Katrina

An aerial shot taken on Sept. 11, 2005, of houses in the Chalmette neighborhood in St. Bernard Parish, near New Orleans.

Jerry Grayson/Helifilms Australia PTY Ltd/Getty Images

Although the death toll from this furious storm wasn't a record-breaker, Hurricane Katrina's financial impact was incomparable, and the storm forever changed New Orleans and the Gulf Coast region.

Trouble began brewing in the Atlantic in August 2005, when the storm formed in the vicinity of the Bahamas and swept across southern Florida. Upon returning to open waters, Katrina strengthened into a Category 5 hurricane -- the highest Saffir-Simpson rating possible. In the 18 hours before landfall, it mellowed somewhat into a Category 3 storm.

A Category 5 hurricane produces sustained winds greater than 155 mph (249 kph), whereas a Category 3 pumps out winds at 111-130 mph (178-209 kph). Both are horrifying.

Katrina's size and reach were remarkable. Tropical-storm-force winds could be felt 161 nautical miles from the eye of the hurricane [source: Knabb].

For all of its remarkable winds, the aspect of a hurricane that frequently poses the greatest threat to life and property is its storm surge -- the upwelling of water caused by shoreward-blowing hurricane winds. Katrina's storm surge towered almost 30 feet (9 meters) in some places, and its effects registered throughout the Gulf Coast region. The combination of extreme storm surges and time-weakened levees caused severe flooding in New Orleans and the surrounding communities. At one point, roughly 80 percent of New Orleans lay underwater -- up to 20 feet (6 meters) deep in some places -- and it would be 43 days before the last of the deluge would recede, its progress slowed by the arrival of Hurricane Rita a month later [source: Knabb].

In all, Katrina spawned 62 tornadoes across the Southeast and killed more than 1,800 people in numerous states [sources: Johnson; Louisiana Department of Health]. Louisiana suffered the greatest number of fatalities. There and in Mississippi, the storm surge annihilated entire coastal communities.

Due to the complex interplay of lost jobs, missed revenue opportunities and destroyed businesses, the final financial toll of Katrina is nearly incalculable, but estimates place the total financial impact at $200 billion [source: Galvin].

Read on to see what happens when a very different kind of precipitation gets out of control.

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