GULFPORT, Miss. -- Although the National Weather Service downgraded Isaac late Wednesday afternoon, the slow-moving tropical storm continued to menace the Louisiana, Mississippi and Alabama coasts with high winds, heavy rains and flooding as it drifted slowly northwest.
Isaac had made landfall earlier in the day as a Category 1 hurricane, exactly seven years after Hurricane Katrina struck the region, and even after its downgrade it was expected to pound the coastline well into Thursday with 70-mph winds, storm surges of as much as 12 feet and localized rainfall of as much as 25 inches.
"Now is not the time to let your guard down," New Orleans Mayor Mitch Landrieu said in a news conference.
Stronger levees in New Orleans, built after Katrina, appeared to be holding.
"Right now, we're in good shape," said Ricky Boyett, a spokesman for the Army Corps of Engineers New Orleans District, which manages the levee system. "The system is doing exactly as it is designed to do right now."
As of 5 a.m. EDT, Issac, with winds of 45 mph, remained a tropical storm. It was located about 55 miles southeast of Alexandria, La., or 110 miles northwest of New Orleans. It was moving to the northwest at 8 mph, according to the National Hurricane Center.
The Mississippi coast appeared to have escaped much of the storm's wrath, with minimal damage and no reported injuries. But officials said a full damage assessment wouldn't be possible until more of the storm clears.
In a haunting reminder of Katrina's aftermath, Louisiana National Guard troops rescued dozens of people from their flooded homes in Plaquemines Parish, a swampy area that sticks out like a finger in the Gulf of Mexico southeast of New Orleans.
More than 1,800 people along the Gulf Coast died during and after Katrina, and the disaster displaced tens of thousands more residents, many of whom never returned.
"For those of us who live here, this brings back very painful memories," Landrieu said.
Louisiana Gov. Bobby Jindal said in a news conference Wednesday in Baton Rouge that the storm surge had topped a levee in the parish, and that officials were considering whether to breach the levee intentionally to relieve the pressure.
Coast Guard spokeswoman Elizabeth Bordelon said late Wednesday afternoon that two rescue helicopters were on their way to Plaquemines Parish and other hard-hit areas, something weather conditions hadn't allowed earlier.
"They know what they can safely execute, mission-wise," she said of the helicopter pilots. "Hopefully, we'll have someone on the ground."
The Federal Emergency Management Agency dispatched four Black Hawk helicopters from Fort Campbell, Ky., and two Seahawk helicopters from Norfolk, Va., to assist with the rescue effort.
More than 600,000 Entergy customers in the region were without power Wednesday afternoon, most of them in Louisiana, and flooding and downed trees complicated efforts to restore service. The storm closed major roads and bridges, halted trains and barges, and shut down ports.
Jindal, who canceled his appearance this week at the Republican National Convention in Tampa, Fla., advised Louisiana residents to hunker down, with the storm expected to linger. Isaac was moving northwest at 6 mph late Wednesday and was forecast to move farther into Louisiana and southern Arkansas on Thursday and Friday.
"There is much more coming, not just in Baton Rouge but other parts of our state as well," Jindal said.
He said he had asked President Barack Obama for federal disaster assistance in all 64 of Louisiana's parishes, the equivalent of counties. Obama on Sunday approved a disaster declaration for a limited number of Louisiana parishes and Mississippi counties. Jindal, Mississippi Gov. Phil Bryant and Alabama Gov. Robert Bentley had declared states of emergency earlier in the week and ordered mandatory evacuations of the most vulnerable areas.
The president received a briefing Wednesday morning on the storm's impact, and he later spoke by phone with Gulf Coast governors, mayors and emergency responders, the White House said.
Gulfport Mayor George Schloegel said there was some damage, "but everybody seems to be OK."
"That's the most important thing," he said. "Everything else can be fixed."
Mark Kirsch and his family have lived on the Gulf Coast only a couple of years, but he's a hurricane veteran. Kirsch, who worked as a meteorologist in the Coast Guard, has ridden out other hurricanes along the East Coast.
He noticed that Gulf Coast residents gathered supplies and did what they needed to do to get ready for Isaac.
"When you live through storms," Kirsch said, "it brings your level of preparedness up. ... We know what they can do."
There were some dramatic rescues, however.
First responders in Biloxi rescued an elderly couple and their son who were trapped on a 44-foot yacht.
"We don't know if they were headed somewhere to anchor down or what. Who knows?" Biloxi Police Chief John Miller said. "We had to tie a rope around an officer to get them off the boat."
The trio survived without any injuries.