(CBS/AP) CHAUVIN, La. - Isaac officially ballooned into a hurricane Tuesday that could flood the coasts of four states with storm surge and heavy rains on its way to New Orleans, where residents hunkered down behind levies fortified after Katrina struck seven years ago this week.
Shelters were open for those who chose to stay or missed the chance to get away before the outer bands of the large storm blow ashore ahead of a forecast landfall in southeast Louisiana on Tuesday night or early Wednesday.
Forecasters warned that Isaac was a large storm whose effects could reach out 200 miles from its center. Water may be worse than wind because the storm could push walls of water while dumping rain to flood the low-lying coast in Louisiana, Mississippi, Alabama and the Florida Panhandle.
The U.S. National Hurricane Center in Miami upgraded Isaac to a Category 1 hurricane midday Tuesday, with surface wind speeds of 75 mph and flight level winds even stronger, at 110 mph.
CBS News hurricane consultant David Bernard reports from CBS station WFOR-TV in Miami that some areas hit by Isaac could see as many as 20 inches of rain.
In Washington, President Obama urged Gulf Coast residents to listen to local authorities, saying in brief remarks at the White House that "now is not the time to tempt fate."
The storm system was centered about 75 miles south-southeast of the mouth of the Mississippi River at 12:20 a.m. ET and was moving northwest at 10 mph, according to the National Hurricane Center in Miami. It was 160 miles southeast of New Orleans.
Isaac's track is forecast to bring it to New Orleans seven years after Katrina hit as a much stronger storm on Aug. 29, 2005.
This time, federal officials say the updated levees around the city are equipped to handle storms stronger than Isaac. The Army Corps of Engineers was given about $14 billion to improve flood defenses, and most of the work has been completed.
In New Orleans, Mayor Mitch Landrieu insists the city is ready, CBS News correspondent Byron Pitts reports. When asked about the comfortable and confident stance people have about the storm - and if that's a good place to be - Landrieu said, "I think what they're comfortable and confident in is that, given the level of this storm, that the levees can hold and we're not gonna have a Katrina event."
Landrieu did not activate a mandatory evacuation Monday. Instead, officials urged residents to hunker down and make do with the supplies they had.
In Cocodrie, La., the biggest concern is the expected storm surge, CBS News correspondent Manuel Bojorquez reports. Two major flood gates meant to protect this coastal community are still under construction. One of them, the Houma Navigation Canal, won't be complete until next hurricane season. Everyone in the area is under a mandatory evacuation notice.