"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.
The White House is aiming to balance leadership on the storm with the president's campaign plans. Obama made brief remarks about the storm just before departing on a two-day campaign trip to Iowa, Colorado and Virginia.
Republicans canceled the first day of their convention in Tampa when the storm appeared to be headed for landfall in Florida. But the party is resuming convention activities Tuesday.
The tropical storm is on the verge of becoming a hurricane as it veers toward New Orleans. Obama said the storm could cause significant flooding and other damage.
The president declared a state of emergency in Louisiana late Monday, more than 24 hours before the storm was expected to hit the Gulf Coast. The declaration makes federal support available to save lives, protect public health and safety and preserve property in coastal areas.
Louisiana Gov. Bobby Jindal, a Republican, said the declaration fell short of the help he was requesting. Jindal wants the federal government to pay for all emergency protective measures.
Obama has asked the Federal Emergency Management Agency to coordinate disaster relief efforts with state and local officials along the Gulf Coast. FEMA has placed incident-response teams at emergency operations centers in Gulf states and has moved two support teams near areas where the storm could hit. More teams also are ready to be deployed if necessary, the White House said.
FEMA has distribution centers in Atlanta and Dallas-Fort Worth area, and in coordination with the Defense Department, has pre-positioned supplies in Jacksonville, Fla. and Montgomery, Ala., closer to areas where the storm could hit.
Forecasters predict Isaac will intensify into a Category 2 hurricane with winds of about 100 mph by early Wednesday, with a projected path directly toward New Orleans. Isaac could become the first hurricane to hit the Gulf Coast since 2008.