Isaac is expected to develop into a Category 2 hurricane by the time it reaches land, with Tuesday seen as a likely landfall date. A Category 2 hurricane has sustained winds between 154-177 kilometers per hour (96 and 110 miles per hour).
"As we prepare for Isaac to hit, I want to encourage all residents of the Gulf Coast to listen to your local officials and follow their directions, including if they tell you to evacuate," Obama said. "Now is not the time to tempt fate, now is not the time to dismiss official warnings," he added. "You need to take this seriously."
The storm is threatening some of the same areas hit by hurricane Katrina, which struck New Orleans and other parts of Louisiana almost exactly seven years ago. However, the entire Gulf Coast region is on alert and heavy rain - and flooding - is expected soon.
The storm was originally predicted to make landfall in the coastal town of Destin, Florida. DW correspondent Simon Bone is in Destin, where he reports authorities there have ordered people to stay indoors. Local residents have been stocking up on fuel and groceries.
"The weather will start going downhill overnight [Monday] on the northern Gulf Coast," Rick Knabb, director of the US National Hurricane Center, told reporters. "Wherever it is people are going to be during the storm, they need to get there tonight."
The bad weather that has moved into the area forced a postponement of the national Republican Convention, which briefly got underway on Monday in Tampa, Florida. Republican National Committee chairman Reince Priebus declared the session in recess immediately after opening it.
Republicans at the convention are scheduled to officially nominate their candidate for November's presidential nomination. The actual voting among the delegates is a formality, as Mitt Romney has been the party's front runner for months.
Some oil and natural gas installations have also been shut down in the Gulf of Mexico due to fears that personnel on board could be in harm's way as Isaac rolls on toward the coast.
mz/jm/sgb (AFP, Reuters, dpa)