Packing winds of 75 kilometres per hour, the Miami-based National Hurricane Center said the storm would take "a slow northeastward motion … followed by a turn to the east northeast tonight (Sunday)."
Officials have warned that the slow-moving storm could bring the same kind of flooding that residents in the northeast are still grappling with after Hurricane Irene tore up the US East Coast last weekend, leaving nearly 50 people dead and millions of households without power.
Some areas are forecast to receive up to 50 centimetres of rain over the Labor Day holiday weekend and residents of coastal states as well as landlocked Kentucky and Tennessee have been told to prepare for extensive flooding.
Lee is battering the Gulf Coast six years after the region was devastated y Hurricane Katrina.
The levee system around New Orleans failed after Katrina, putting much of the city underwater. More than 1,500 people died.
The intense rain that Lee is already dumping on the city is expected to provide the most severe test of the levee and canal systems at Lake Pontchartrain and elsewhere since Hurricane Gustav came close to overwhelming the levees three years ago.