Isaac hit the Gulf Coast along a track moving from southeast to northwest. Since hurricanes and tropical storms spin counterclockwise (in the Northern Hemisphere, at least), Louisiana lay in the path of the winds as they swung northward and westward, allowing the storm to push even more ocean water toward land. In that situation, a tropical cyclone "will pile up more water," Henson said.
What's in a name?
Yesterday afternoon, Isaac was downgraded to a tropical storm — its winds dropped to 70 mph (110 kph), falling 4 mph short of the dividing line between a Category 1 hurricane and a tropical storm.
"Whew #Isaac down to a Tropical Storm," wrote Sam Champion, the weather anchor for ABC's "Good Morning America," just after the National Hurricane Center (NHC) announced the storm was no longer a hurricane.
Yet the message from the NHC wasn't one to inspire relief: "Isaac weakens to a tropical storm. Life-threatening hazards from storm surge and inland flooding are still occurring," forecasters wrote. [Video: Isaac Makes Landfall]
The downgrade had done little to change immediate conditions on the ground.
Quite a few tropical storms and Category 1 hurricanes have proved incredibly destructive in the past, yet their power still seems to surprise. Just last year, Irene made landfall in New York as a strong tropical storm, and caused some $19 billion in damage, Henson said — much of it because of horrific flooding.
In the face of continued shock at the power of relatively low-ranked storms, some say that the labels themselves can promote a false sense of security.
"The public has really latched onto the Saffir-Simpson category number," said Mark Powell, an atmospheric scientist with the National Oceanic and Atmospheric Administration's (NOAA) hurricane research division.
"They know what category they're going to move for, and if they hear something is just a tropical storm or just a Category 1, they may think it's not worth considering evacuation or even putting shutters on," Powell said, emphasizing that these are his views as a scientist, and not necessarily those of NOAA.
Powell has partnered with an engineer to come up with a different way to quantify hurricanes. The system takes more factors than wind speed into consideration when labeling a storm. Called Integrated Kinetic Energy, the methodology tries to paint a more nuanced portrait of a storm's power by accounting for its overall wind energy, and looking at its sheer size, both of which affect its destructive potential.
"We've tried pretty hard to push for changing the way we're doing things right now so these large storms are given more consideration," Powell said. "Unfortunately, this is an area that is in desperate need of change, but has not changed yet."
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