NEW ORLEANS — Tropical Storm Isaac’s once fierce winds slowed to 40 miles per hour on Thursday as it finally moved out of southern Louisiana and headed north while continuing to bring heavy rains and flooding along its path.


The storm continued at its now familiar exceedingly slow pace — 9 m.p.h. — as it moved into central Louisiana and on toward Arkansas, which it may not reach until some time Friday, forecasters said.


At 10 a.m., the vastly weakened system was 50 miles south of Monroe, La. — and more than 165 miles northwest of a New Orleans glad to see it gone.


The storm however, continued to create major problems in a wide area of the Gulf Coast on Thursday.


Louisiana officials ordered an evacuation for some 60,000 people living in communities along the rain-swollen Tangipahoa River after warning that the Tangipahoa Dam in Mississippi was in danger of failing.


While the Tangipahoa Parish Web site warned of “imminent failure” of the earthen dam upriver, Mississippi officials were circumspect.


In Pike County, Miss., for instance, officials called only for a “precautionary evacuation” of the area of the county south of 700-acre Lake Tangipahoa.


In a statement, Pike County said “the dam has been badly damaged by heavy rains,” but it had not been breached.


The Mississippi Emergency Management Agency also said that the dam was in no immediate danger.


“There’s no water coming through it. There hasn’t been a breach,” said Greg Flynn, a spokesman for the agency. Mr. Flynn said that even if the dam did fail, however, very few people would be in danger — only about 12 homes would be threatened by floodwaters.


“It’s a very sparsely populated area,” he said.


Reasons for the widely disparate views about the danger posed by the dam were not immediately clear, but at a news conference, Gov. Bobby Jindal of Louisiana said an evacuation had been ordered for one mile on either side of the Tangipahoa River in Louisiana.


He said if the dam failed that it would take 90 minutes for floodwaters to reach the town of Kentwood — hometown of Britney Spears — downstream.


“They are planning a planned breach of the dam to prevent the dam from breaking,” he said, adding that an unplanned breach could cause the kind of river flooding that occurred in 1983 and 1990.


The 1990 flood, Mr. Jindal said, “was actually bad enough to take out some bridges.”


“You would see that kind of impact again,” he said, adding, “there are many more people living in those areas” now.


But if a planned breach takes place, Mr. Jindal said, there would be no impact expected in Louisiana.


The governor said there are six nursing homes in the area, but only two would have to be evacuated and that the local hospitals and a prison would not have to be cleared.


It is, he said, “obviously, a fluid situation.”


The storm — which had been a Category 1 hurricane — pummeled much of the Gulf Coast, pinning portions of Louisiana, Mississippi and Alabama under a saturating rainfall and creating 12-foot storm surges.


In Slidell, a city of about 30,000 people on the northeast shore of Lake Pontchartrain, floodwaters from creeks flowing into the area’s bayous have begun to inundate Olde Towne, a residential area and tourist destination, and Mayor Freddy Drennan encouraged residents in several neighborhoods to evacuate.


“Water is currently backing up into the city through Bayou Pattasat,” Mayor Drennan said on the city’s Facebook page Thursday morning. “The water levels in Bayou Bonfouca got so high that it has gone around the pump stations into Bayou Bonfouca and back up into Slidell through that natural drain. The pumps are currently unable to pump the water out as fast as it’s coming in.”