MIAMI (AP) -- Forecasters say Isaac has strengthened into a Category 1 hurricane with 75 mph winds as it makes its way toward Louisiana.
The U.S. National Hurricane Center said Tuesday that Isaac gained strength as it moved over the warm, open waters of the Gulf of Mexico.
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Isaac is expected to make landfall over southeastern Louisiana, possibly the New Orleans area, either late Tuesday or early Wednesday.
President Barack Obama called on Gulf Coast residents to prepare. "Now's not the time to tempt fate," he said. "Now's not the time to dismiss official warnings. You need to take this seriously."
The National Weather service cautioned residents of the region not to focus on the exact forecast track and to prepare: "Now is the time to rush to completion preparations for the protection of life and property. Evacuate if directed to do so by local officials or if your home is vulnerable to high winds or flooding."
In Biloxi, Mississippi, popular casinos began to close down Tuesday.
Isaac's center was about 185 miles (300 kilometers) southeast of New Orleans, and about 185 miles south of Gulfport, Mississippi. It was moving northwest at 7 miles per hour.
Maximum sustained winds were at 70 mph. A storm reaches hurricane status when those winds are at 74 mph.
The hurricane center called on people at ports, docks and marinas to "urgently complete" emergency preparations. For people who live on boats, it was time to "make final preparations for securing your craft before leaving it."
"We have a plan in place to secure the city, and we have a plan to respond quickly in the event of emergencies," New Orleans Mayor Mitch Landrieu said. "We're confident that the work we've done in the last few years makes us fully capable of handling this type of storm."
By Tuesday morning, it was too late to evacuate New Orleans, Landrieu said.
Several New Orleans residents told CNN they planned to wait out the storm and were not concerned that the nightmare of Hurricane Katrina in 2005 would be repeated. Isaac is not predicted to bring such dire conditions, and law and order have improved vastly, they said.
If Isaac slows and landfall comes after midnight, it will hit on Katrina's seventh anniversary.
Jackie Grosch had to rebuild her home in Louisiana after Hurricane Katrina, but the St. Bernard Parish resident said she was going to wait Isaac out.
"Well, it gets old after a while -- packing up, taking the journey to wherever we're going to go. We thought about it and decided to stay," she said.
Nonetheless, her family is prepared with a generator, weather radio and life jackets -- "just in case."
A levee system fortified after Katrina will keep her home safe, she said.
"I don't know if it's going to be a true test, because they're saying it's not going to be that bad. But you never know what bad is. We didn't think Katrina was going to be bad, either."
Katrina made landfall as a Category 3 hurricane with 125-mph winds
Most of Katrina's nearly 1,800 deaths occurred when the protective levees around New Orleans failed, flooding the city. But Landrieu said the levees have had $10 billion in improvements since 2005, and the city's pump stations have backup generators ready in case of electrical outages.
One of those stations is the biggest in the world, and some can move as much as 150,000 gallons per second.
"This is the best system that the greater New Orleans area has ever seen," said Col. Ed Fleming of the Army Corps of Engineers.
A hurricane warning was in effect east of Morgan City, Louisiana, to the Alabama-Florida border, including metropolitan New Orleans. A hurricane watch was in effect from Intracoastal City to Morgan City, Louisiana.
Tropical storm warnings and watches extended to the east and west.
As the storm heads north, its rain is expected to benefit some drought-ravaged states like Arkansas, Illinois, Indiana and Missouri.
Some people in low-lying Louisiana parishes and coastal counties and barrier islands of Mississippi, Alabama and northwest Florida were told to clear out ahead of the storm. In Alabama, state Emergency Management Agency Director Art Faulkner warned that strong winds and high water may affect the Mobile area even if the storm hits as far west as Louisiana.
"It is a very large storm," Faulkner said. "And oftentimes we confuse and focus on a specific dot that may be identified as the center of the storm when very dangerous conditions may exist as far as 200 miles from that specific dot."
The storm lashed Cuba and the Florida Keys over the weekend after slamming into Haiti, where at least 19 people