As predicted, Isaac is now a Category 1 hurricane, with maximum sustained winds of 80 mph. The storm is less than 30 miles from the mouth of the Mississippi river, and the nearby coastline began feeling its wet and windy front edge early today. It is expected to make landfall overnight.
President Barack Obama pleaded with the Gulf Coast to take the storm seriously and ordered federal aid for Mississippi and surrounding areas, many of which are under mandatory evacuation orders.
"Now is not the time to tempt fate. Now is not the time to dismiss official warnings. You need to take this seriously," Obama said.
"If it's a Category 1 when it hits land, you'll have at least 50 percent more damage than a [faster-moving] Category 1. The damage will be a full category higher," says Jeff Masters, co-founder and director of meteorology at Weatherunderground. "It's going to last at least 24 hours, in some places 36 hours. People are going to have to hunker down. It's going to be nasty."
The Gulf Coast has begun to see rain and some wind, says John Schroeder, a professor of atmospheric science at Texas Tech University who is measuring the storm from Louisiana.
"There's certainly a possibility it could come to the coast and stall for a while, which would cause all sorts of flooding issues--the ground is already saturated," Schroeder says.
The storm is expected to inundate areas well outside where it hits directly. Storm surges, some 6 feet high across hundreds of miles of coastline, will likely stretch from central Florida to Texas. Then there's the rain--one of Isaac's spiral bands is dumping water on Florida and much of the Southeast as far north as North Carolina.
"To have a storm spreading 10 inches of rain more than 200 miles from its center is remarkable," says Masters. "That doesn't usually happen except for maybe 50 miles from the center for most hurricanes."
There's a strong possibility the storm could become a Category 2 hurricane Wednesday, according to Masters. As forecast by Schroeder, Isaac has slowed its speed somewhat – it is now moving northwest at just 8 mph – and storm surges and associated flash floods have begun to occur along the coasts of Louisiana and Mississippi.
Seth Cline is a reporter with U.S. News and World Report. Contact him at email@example.com or follow him on Twitter.
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Updated at 5:50 p.m. ET on 8/28/12