Heavy rainfall from Isaac is threatening a dam in southern Mississippi, leading local officials to order an evacuation.
But even as the rains continued to pour upon flood-ravaged Gulf Coast states, flagging winds got Isaac downgraded to a tropical depression and caused a tropical storm warning from Morgan City, La., to the Mississippi-Alabama border to be discontinued.
The storm's center was approximately 35 miles west-northwest of Monroe, La., and 40 miles south-southeast of El Dorado, Ark., according to the National Hurricane Center's 4 p.m. CT advisory. It was moving north-northwest at 12 mph and its center was expected to cross into Arkansas Friday.
"Even though Isaac is no longer a tropical storm, life threatening hazards from storm surge, inland flooding and tornadoes are still occurring," the National Hurricane Center said.
Louisiana Gov. Bobby Jindal told reporters at a 3 p.m. ET that officials were optimistic their efforts to prevent a breach in a Mississippi dam and additional flooding downstream in Louisiana would work.
"Initial reports are they do believe the integrity is still sound," Jindal said. "But, again, there's as many caveats around that as we can [put]. We don't know that for a fact."
Officials will not be sure of the dam's status until they are able to "get down there" and inspect it closely, Jindal added. He repeatedly urged residents to listen to their local officials and follow their instructions.
"Evacuate out of an abundance of caution. Hopefully, it'll turn out the dam doesn't breach," Jindal said. "If there's a breach several hours from now, we wouldn't want people to be moved in the middle of the night.
Jindal said the evacuation could affect 40,000 to 60,000 people, but called the figures "very rough estimates."
Mississippi emergency management officials earlier notified the Tangipahoa Parish, La., government and Louisiana's Governor's Office of Homeland Security and Emergency Preparedness (GOSHEP) of an "imminent failure" of the dam at Lake Tangipahoa in Mississippi's Percy Quin State Park. The park and dam are near the Louisiana border.
Such a failure could cause additional flooding along the already swollen Tangipahoa River, though Mississippi officials didn't think the volume of water in the 700-acre lake would add enough flow to the river to cause catastrophic flooding.
The Department of Environmental Quality, looking to relieve the pressure of the dam, was continuing to sandbag the area, pumping water over the dam into the surrounding agricultural areas and attempting a controlled breach of levees to relieve water pressure.