Hurricane Katrina caused an estimated $125 billion in damages, making it the most expensive natural disaster in U.S history, and killed more than 1,800 people when it hit New Orleans on Aug. 29, 2005.
Exactly seven years after Hurricane Katrina, Hurricane Isaac has slammed into the Gulf coast, bringing flooding and high winds with it.
Tropical cyclones — the scientific name for hurricanes and tropical storms — form when warm air above the ocean rises. More air from the surrounding areas of higher pressure push in under this rising air, pushing it up and cooling it. The entire system just keeps growing and starts to swirl.
After several severe hurricanes, and two of the most productive hurricane seasons on record, we started to wonder — What makes hurricanes strong and destructive? Are hurricanes getting worse or is it just us? Why and what can we do about it? What if we don’t?
A combination of factors made Hurricane Katrina so devastating. From a scientific standpoint, Katrina was a Category 3 hurricane with maximum sustained winds of 125 mph when it hit New Orleans on Aug. 29. 2005. This is a strong hurricane, but not atypical.
Katrina wasn't as fast as, say, Hurricane Camille in 1969. But it was huge and it's approach over shallow water resulted in a stronger storm surge.
There were also engineering problems. Katrina was especially damaging because the levees designed to protect the below-sea-level city burst under the hurricane's 25-foot high storm surge. So what's different now?
Since 2005, the U.S. Army Corps of Engineers has spent $14.5 billion to improve New Orleans' system of levees, floodwalls, pump stations and surge barriers. As Hurricane Isaac was approaching the Gulf, President Obama declared a state of emergency in Louisiana and Mississippi on Aug. 28, mobilizing disaster response teams before the storm made landfall.
So far, all of the levees are holding strong inside of New Orleans, according to New Orleans Mayor Mitchell Landrieu. However, the storm surge has overtaken an 8-foot levee outside of the city, in Plaquemines Parish.
Unlike Hurricane Katrina, which formed with rapid speed, Isaac is a slow moving storm, and when it made landfall was a Category 1 storm, unlike Katrina's Category 3 status.
Even though its going slow, Isaac is just as huge as Katrina was. On Aug. 27, it measured more than 400 miles wide, which means more rainfall — up to 20 inches in some places.
Isaac's path and the timing of the storm are very similar to Katrina's path when it hit the Gulf Coast. Eerie, but not that unusual.
In an average decade the mainland U.S. gets hit with about seven Category 1 hurricanes, four to five hurricanes that rank as Category 2 and about the same number that hit as Category 3 hurricanes, but just one Category 4 hurricane.
Hurricanes that make landfall as Category 5 storms are so rare that they only hit once every few decades.
Many factors go into the creation of one of these terrible storms, some which weaken it and others that strengthen it. Wind shear can stifle hurricane formation, and travelling over land weakens a storm. Storms can also interact with other storms, weakening both. Some researchers think that stronger storms develop because these weakening factors aren't in play.
Hurricane Isaac, which is currently barreling down on the Gulf Coast, is a Category 1 hurricane. More hurricanes like Isaac will probably hit this season, which ends on November 30. So far in 2012 we've seen 11 tropical cyclones, 4 of which have turned into hurricanes.
Recent hurricane seasons have been relatively strong: 2011 and 2010 are tied with 1995 as the third most active storm season on record. Interestingly, 1933 is the second most active season on record.
2005 was one of the most active Atlantic hurricane season to date — yielding 28 tropical cyclones, 15 of which became hurricanes.
The hunch that hurricanes are getting worse seems to hold up to scientific scrutiny. Researchers have noted a steady upward trend in the maximum wind speeds of the strongest hurricanes in recent years.
Researchers led by James Elsner, of Florida State University, studied hurricane data from across the world between 1981 and 2006. They found a 31 per cent increase in strong storms (those in the top fifth in a ranking of storms by their intensities), from 13 to 17 strong cyclones for a 1.8 F rise in ocean temperature.
Researchers like Elsner think that these increases in strength and numbers of storms could be due in part to global warming. The theory goes that as the oceans heat up, and hurricanes get stronger because they feed off this heat.
If hurricanes get bigger, stronger and more frequent, one nightmare scenario may just become a reality: Thousands of lives could be lost and billions of dollars of damage done if a large, strong hurricane made landfall in New York City, the way Hurricane Irene did in 2011.
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