Isaac's probable track will take it close to New Orleans. The storm's intensity is harder to predict, but it's a large system — meaning that the storm surge will likely be stronger and more damaging than the wind speed would suggest.
It's a mild year for hurricanes, so far. But as emergency managers like to point out, it only takes one hurricane to ruin your day. And for residents of the Mississippi and Louisiana coasts, that one hurricane could be headed their way, bearing the name Isaac. If the most likely forecast track holds true, Hurricane Isaac is set to follow the path of Katrina, and to make landfall as a Category One hurricane near New Orleans — seven years to the day after Katrina's deadly arrival on shore.
But Isaac is unlikely to pack Katrina's punch. Hurricane expert Jeff Masters pointed out days ago that the Gulf waters, which will fuel Isaac with heat energy, are much cooler this year than was the case in 2005, when Katrina strengthened rapidly after passing over Florida as a Category 1 storm.
On Monday, Masters was continuing to follow the storm as it tracked across the Gulf from the Florida Keys toward the Mississippi Delta. "Isaac is currently crossing over a relatively cool eddy of water, which will keep intensification slow today," he noted. "A storm this large will have trouble undergoing rapid intensification, and Isaac's most likely intensity at landfall will be as a Category 1 hurricane, which is what most of the intensity models are forecasting."
But wind intensity is one thing; storm surge, a major threat to the low-lying coast, is another. Writes Masters: "Isaac is a huge storm, with tropical storm-force winds that extend out 205 miles from the center. Isaac's large size will enable it to set a large area of the ocean into motion, which will generate a large storm surge once the storm approaches land on the Gulf Coast. I expect that Isaac's storm surge will be about 30% higher than the typical surge one would expect based on the maximum wind speeds."
Depending on its track and strength, Isaac's storm surge could pose the first serious test of New Orleans' newly reconstructed levees, notes Masters. "I expect New Orleans' new flood defenses will be able to hold back Isaac's surge," he writes, "but areas outside the levees are at risk of heavy storm surge damage."