Tropical Storm Isaac is expected to soak the U.S. Gulf Coast state of Louisiana for another day Thursday with forecasters warning that the weakening storm is still a threat to life and property.

Isaac was downgraded from a Category One hurricane after slamming into Louisiana, Mississippi, and Alabama with heavy rain, strong winds, and isolated tornadoes.

Authorities in the city of New Orleans have imposed an overnight curfew and say they will not be able to fully assess the damage and look for storm victims until the wind and rain let up.

More than 100 people in a fishing community south of New Orleans, who refused orders to evacuate, needed to be rescued when floodwaters breached a levee. Engineers are considering punching a hole in the levee to relieve the pressure.

But experts say the extensive system of levees, canals and pumps, built after Hurricane Katrina caused widespread death and destruction seven years ago, helped spare New Orleans from extensive damage this time.

Forecasters say Tropical Storm Isaac will move into the neighboring state of Arkansas Friday and into the drought-stricken midwestern United States, where rain is badly needed.

U.S. President Barack Obama declared states of emergency for 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.