The winds of Tropical Storm Isaac weakened Thursday but its rain still posed a flooding threat as it continued on a northern path over the U.S. Gulf Coast state of Louisiana.

Officials in Louisiana and the neighboring state of Mississippi urged residents to evacuate homes near their border after finding that a dam had sustained heavy damage in the storm and could burst.

The National Hurricane Center said Isaac is carrying maximum sustained winds of 65 kilometers an hour, but is expected to diminish to a tropical depression later in the day. The storm could still dump as much as 63 centimeters of rain in isolated parts of Louisiana, Mississippi, Alabama and Arkansas through Friday. Later, it is expected to move into the drought-stricken midwestern United States, where rain is badly needed.

Isaac struck Louisiana and the neighboring Gulf Coast states of Mississippi and Alabama as a minimal, Category One hurricane, causing strong winds, heavy rain, and massive flooding. Hundreds of residents in Louisiana's Plaquemines Parish, a small coastal area located south of New Orleans, were trapped after floodwaters spilled over levees.

The parish's president, Billy Nungesser, said the flooding in his community was unprecedented, surpassing the damage from deadly Hurricane Katrina in 2005.

''We've never seen anything like this, not even Katrina.''

Authorities and residents scrambled to rescue neighbors who had ignored evacuation orders ahead of Isaac's arrival.

The storm hit the U.S. coastline seven years to the day that Katrina devastated New Orleans and killed 1,800 people in the region. Isaac caused more than 20 deaths on Caribbean islands, but only one possible storm-related death was reported in the United States.

Federal officials say the extensive system of levees, canals and pumps built after Katrina helped spare New Orleans from extensive damage this time.

Seven-hundred-thousand people were without power at the peak of the storm. Authorities say they will assess storm damage and look for victims once the wind and rain let up.

U.S. President Barack Obama declared emergencies in Louisiana and Mississippi, making both states eligible for federal funding and other aid. Emergency assistance teams were dispatched to the region in advance of the storm.