Tropical Storm Isaac swirled into the Gulf of Mexico early Monday, after lashing the Florida Keys and Miami area with wind and rain.
The National Hurricane Center says Isaac is expected to strengthen into a hurricane Tuesday, before hitting the Gulf Coast somewhere between Florida and Louisiana.
Four states -- Alabama, Florida, Louisiana and Mississippi -- have declared states of emergency as they brace for Isaac's deluge.
New Orleans Mayor Mitch Landrieu has declared a state of emergency for his city, telling residents to be prepared to live without regular water or power supplies for several days. He also urged them to leave if an evacuation order is issued.
Many did not leave seven years ago when Hurricane Katrina struck New Orleans. Wednesday marks Katrina's seventh anniversary. Katrina ravaged New Orleans and much of the Gulf Coast, killing more than 1,800 people and leaving thousands more homeless.