(CNN) The levees held. The power grid did not.
Millions of Gulf Coast residents who survived Ida's devastating winds and deluge of rain face a new danger -- widespread power outages that are expected to last for weeks, coupled with a period of excessive heat.
Ida, which made landfall Sunday as a Category 4 hurricane, has already contributed to five deaths, including a drowning in Lafitte, Louisiana. Hundreds of people have been rescued, but search-and-rescue crews haven't been able to access some of the hardest-hit areas, so it's not yet clear how many residents might be still be trapped by flooding or debris.
Officials say electricity might not be restored to some areas for a month, which could prove life-threatening as intense heat moves into the region.
New Orleans Mayor LaToya Cantrell said Tuesday evening that "some level of (power) transmission" could begin soon.
"The first step is transmission, and there's been significant progress as it relates to that," the mayor said. "The next step will be focusing on distribution lines. So we're getting closer, and it could mean we do see some level of electricity or light in the city come tomorrow night."
The National Weather Service issued a heat advisory for southeast Louisiana and southern Mississippi until 5 p.m. Wednesday.
Hurricane Ida devastates Gulf Coast
Philip Adams walks through what remains of his living room and kitchen at his destroyed home in Lockport, Louisiana, on Monday, September 6.
Damage is seen on the roof of a New Orleans apartment complex on Sunday, September 5. Elderly residents were still living at the building with water-soaked carpets and no power, a week after Hurricane Ida made landfall in Louisiana.
Shoppers buy supplies at a grocery store in New Orleans despite the power still being out on Thursday, September 2.
Cows are herded into a pen in Belle Chasse, Louisiana, on Thursday. "All of our neighbors' cows are mixed up in this bunch, so we're here rescuing them, getting them off the road and out of the water," Chris Shivers said when asked why his group was herding the cows. "They've been standing in the water now for several days without anything to eat or drink, so they're under a lot of stress and have seen a lot. The hurricane is a disaster, and these cows will probably never be the same."
National Guard members unload ice at a distribution center in Montegut, Louisiana, on Thursday.
Unattended horses are seen during a storm in Belle Chasse on Thursday.
Tiffany Miller embraces her daughter Desilynn, left, and godchild Charleigh after the family returned to their destroyed home in Golden Meadow, Louisiana, on Wednesday, September 1.
This aerial photo shows the hurricane aftermath in Grand Isle, Louisiana, on August 31. Grand Isle, Louisiana's last remaining inhabited barrier island at the southern tip of the state,
bore the brunt of the Category 4 hurricane.
The Maldonado family stands outside their damaged home in Barataria, Louisiana, on August 31. "I've lost everything in my trailer because of the hurricane," said Fusto Maldonado when asked about the storm's impact. "I've lost everything, my family has lost everything, and we're now trying to find help. We all live in this area and now it's all gone."
A dead fish lies on a road in Leeville, Louisiana, on August 31.
A shrimper works to salvage his partially submerged boat in Golden Meadow on August 31.
A palm tree is bent in half in Galliano, Louisiana, on August 31.
People wait for a gas truck to arrive at a gas station in New Orleans on August 31.
Destroyed homes are surrounded by floodwaters near Point-aux-Chenes, Louisiana, on August 31.
Workers remove a tree that fell on a home in Houma, Louisiana.
What's left of a home stands in Grand Isle on August 31.
Michael Wilson stands in the doorway of his flood-damaged home in Norco, Louisiana, on August 30.
Homes near Norco are surrounded by floodwaters on August 30.
A rain shower soaks evacuees in LaPlace, Louisiana, on August 30.
A damaged McDonald's sign is seen in Raceland, Louisiana, on August 30.
A man rides a bicycle in front of a damaged building in Houma on August 30.
An oil slick is seen on top of floodwaters in Kraemer, Louisiana, on August 30.
Residents wave at a US Coast Guard helicopter while waiting to be rescued from their flooded home in LaPlace on August 30.
Theophilus Charles sits inside his damaged home in Houma on August 30.
A highway is flooded near LaPlace on August 30.
Residents are rescued from floodwaters in LaPlace on August 30.
A damaged historic building lies in ruins in New Orleans' Central Business District on August 30.
A barge damages a bridge connecting Lafitte and Jean Lafitte, Louisiana, on August 30.
Marquita Jenkins stands in the ruins of her hair salon in LaPlace on August 30.
A destroyed car is seen after an apartment building burned overnight in Kenner, Louisiana.
A resident walks through floodwaters in LaPlace on August 30.
Siblings watch men assess damage outside a hotel in Houma on August 30.
A woman pushes a stroller past a boarded-up building in the French Quarter of New Orleans on August 30.
A downed tree lies on a house in New Orleans on August 30.
Members of the Louisiana National Guard help with recovery efforts in New Orleans on August 30.
A man looks up next to a section of roof that was ripped off a building in the French Quarter of New Orleans on August 30.
Lights from a TV broadcast illuminate an otherwise dark Bourbon Street in New Orleans on August 30.
Montegut Fire Chief Toby Henry walks back to his fire truck in the rain as firefighters cut through trees on the road in Bourg, Louisiana, on August 29.
Firefighters cut through downed trees on a road in Bourg on August 29.
Barges are seen docked on the Mississippi River as Hurricane Ida hit Destrehan, Louisiana, on August 29.
People walk through the French Quarter in New Orleans on August 29.
European Space Agency astronaut Thomas Pesquet took this photo of Hurricane Ida from the International Space Station on August 29.
The Royal Dutch Shell refinery in Norco is seen as Hurricane Ida made landfall on August 29. More than 95% of the Gulf of Mexico's oil production facilities were shut down, regulators said, indicating the storm's
significant impact on energy supply.
People work inside the Federal Emergency Management Agency's headquarters in Washington, DC, on August 29.
A cyclist wears a face mask while riding through the rain and high winds in New Orleans on August 29.
Firefighters look out the window of a shelter in Bourg on August 29.
Storm clouds pass over a cemetery in New Orleans on August 29.
LaKeisha Verdin holds her 3-month-old son, Kevin, as she walks onto the front porch where her family was watching weather updates on the local news in Houma.
A news crew reports from the edge of Lake Pontchartrain in New Orleans on August 29.
Wind blows Monroe Best's hair and face mask in New Orleans.
New Orleans' Bourbon Street is nearly empty on August 29.
A vehicle is abandoned in a flooded ditch next to a highway in Bay Saint Louis, Mississippi.
A man carrying his belongings walks past a sign outside the Ernest N. Morial Convention Center in New Orleans on August 29.
A wall of rain moves over downtown New Orleans on August 29.
The Boudreaux family sits on their front porch as they await the arrival of Hurricane Ida.
A man walks along the Mississippi River near the French Quarter in New Orleans early on August 29.
People stand in line at the Louis Armstrong New Orleans International Airport on August 28. Many residents were evacuating the area ahead of Hurricane Ida.
Crews reopen a flood gate to help trapped motorists who missed a closure deadline on August 28.
Keith Clark brings a rope to a friend to help tie down a houseboat before he evacuated Jean Lafitte on August 28.
Nikeia Washington holds her granddaughter, Halia Zenon, at a hotel in downtown Shreveport, Louisiana, where they evacuated ahead of the storm.
People walk down Bourbon Street in New Orleans on August 28.
Evacuation was voluntary for parts of the city inside its flood protection system. Other areas were under a mandatory evacuation order.
Larry Ackman, bottom, helps neighbor Mike Jackson, left, and his son Cody board up windows in Morgan City, Louisiana.
Traffic moves slowly August 28 along Interstate 10 West in Vinton, Louisiana.
A man drives a tractor through a flooded street in Guanimar, Cuba, on August 28. Before entering the Gulf, Ida made landfall twice over Cuba as a Category 1 hurricane.
US President Joe Biden speaks during a FEMA briefing on August 28. "This weekend is the anniversary of Hurricane Katrina," Biden said, "and it's a stark reminder that we have to do everything we can to prepare the people in the region to make sure we're ready to respond."
Dawn breaks over a Hurricane Katrina memorial at Shell Beach in St. Bernard, Louisiana, on August 28.
Katrina made landfall on August 29, 2005.
Clare and Joe Cermak work on putting storm shutters up on their home in Louisiana's St. Charles Parish on August 28.
Highway traffic moves slowly near Kenner as many residents fled the Louisiana city.
Gregory Moore, left, helps fill sand bags as residents in Gulfport, Mississippi, prepared for the storm on August 28.
John Guenther unloads about 400 crab traps that he had to pull out of the water near his home in the eastern St. Bernard Parish on August 27.
Jennifer Tate fuels up a gas can August 27 in Pass Christian, Mississippi.
Workers stack bags of ice into a gas station freezer in Jefferson, Louisiana, on August 27.
A resident hammers the shutters of a 100-year-old house in New Orleans on August 27.
That means some residents who stayed and rode out the storm will face heat indices of 105 to 107 degrees -- without air conditioning. Heat is the No. 1 weather-related cause of fatalities in the US, the weather service said.
Many local officials have urged those who evacuated not to come home yet, citing downed power lines, impassable roads and potential hindrances to rescue workers.
"Many of the life-supporting infrastructure elements are not present, are not operating right now," Gov. John Bel Edwards said Tuesday. "Please don't come home before they tell you that it's time."
Yolanda Teague lives with her eight children, her mother and others in a house in the New Orleans neighborhood of Algiers. The roof and ceiling were damaged by Ida.
One of her sons has a heart condition. She is worried his health will deteriorate.
"It's going to get rough. You know what I'm saying? No electricity," she told CNN outside her storm-damaged house. "People don't know what's their next move. So it's probably going to get rough."
She said her other concern was running out of food and drinks.
At a center that was handing out groceries in the neighborhood, the line went on for several blocks.
Plaquemines Parish told evacuated residents that items like water, groceries, fuel and medical supplies are depleted.
"Therefore, please obtain the necessary supplies prior to returning to Plaquemines Parish," officials warned.
Still, the damage left in Ida's wake is a far cry from that left by Hurricane Katrina, the 2005 storm that caused New Orleans' flood protection system to fail, flooding 80% of the city and killing more than 1,800 people along the Gulf Coast. The government has spent billions of dollars in the 16 years since rebuilding and strengthening that levee system, and the infrastructure upgrades appear to have worked as designed.
"There were a few smaller levees that were overtopped, to some degree, and for some duration of time, and that did result in some people's homes are being flooded," Edwards said Monday. "But they did not fail."
Ida remains a threat for other states across the eastern US. Now a tropical depression, the storm is bringing heavy rain and the threat of flash floods to Tennessee, the scene of deadly flooding just last week.
There is a high risk (level 4 out of 4) of flooding for portions of the Northeast from Wednesday into Thursday morning, according to the National Oceanic and Atmospheric Administration's Weather Prediction Center.
The high risk stretches from extreme northern West Virginia, across Pennsylvania, northern New Jersey, southern New York and Connecticut. A moderate and slight risk surrounds this area, stretching from southern Virginia to southern Vermont and New Hampshire.
Weeks without electricity
The downtown skyline is shown after Hurricane Ida passed through on August 30 in New Orleans, Louisiana.
The short-term challenge for Louisiana is the failure of its power grid and its impact on gas supplies, communication networks, clean water and hospitals.
More than 1 million homes and businesses in Louisiana, 42,000 in Mississippi, and 8,800 in Georgia are without power, according to PowerOutage.US.
The Louisiana outages are concentrated in the southeastern part of the state in and around New Orleans. Power is out for more than 90% of customers in Orleans, Jefferson and St. Tammany parishes, three of the four most populated parishes in the state.
The vast majority of these outages are among customers of Entergy, which said Monday the storm damaged eight high-voltage lines serving New Orleans and other parishes. Restoring power could take more than three weeks based on historical restoration times, Entergy said. The utility said 85,000 customers had their power restored by Tuesday morning.
St. John the Baptist Parish President Jaclyn Hotard said all of her parish is without power and infrastructure is extensively damaged, meaning recovery will take even longer.
In parts of Jefferson Parish, power is expected to be out for at least three or four weeks, Councilman Ricky Templet said. Another councilman, Byron Lee, said supplies are limited, grocery stores are closed and there is a two-hour line for gas. And officials in St. Charles Parish said it's "highly likely" the area won't have power for a month, according to a Facebook post.
To beat the heat, New Orleans plans to open cooling centers and mobile resources, including water, food, air conditioning and charging devices, the mayor said.
The electricity problems have also led to gas shortages and issues at local hospitals.
Lines of cars waited for hours Monday at the one or two gas stations still open in St. Bernard Parish, Louisiana, Council Member Richard Lewis said. Many stocked up on fuel for their generators.
In addition, four hospitals in Louisiana were evacuated Monday, the governor said. In the aftermath of the hurricane, many Gulf Coast hospitals are grappling with how to keep caring for patients amid the damage.
"We really need our hospitals, more than anything else, to come back up, so that people who are in ICU rooms and on ventilators and so forth can continue to receive the life-saving care that they need," Edwards said.
"That's important all the time. It's certainly important, even more so, because of the Covid situation."
Five people dead, hundreds rescued
Workers remove a tree that fell on a home during Hurricane Ida on August 31 in Houma, Louisiana.
Five people have died due to Ida so far, and hundreds have been rescued.
In Mississippi, heavy rain washed away part of Highway 26, killing two people and injuring 10 others. Seven vehicles went into a hole created by the washout, which was about 50 feet long and 20 feet deep, Mississippi Highway Patrol Trooper Cal Robertson said.
Louisiana has confirmed three deaths. The first came when a tree fell on a home in Prairieville, the Ascension Parish Sheriff's Office said Sunday. In New Orleans, a man drowned after trying to drive through floodwater near I-10 and West End Boulevard, the Louisiana Department of Health said Monday. And a 65-year-old identified as Emily Boffone drowned in Lafitte, according to Jefferson Parish Coroner Dr. Gerry Cvitanovich.
The Louisiana National Guard has rescued 359 people and 55 pets in southeastern Louisiana, the agency tweeted Tuesday afternoon.
Travel, too, has been sharply limited by unpassable roads and limited gasoline supply.
Louisiana's interstate highways, including I-10 and I-55, were clear of debris and open for travel Tuesday, but many other state roadways remain limited because of the storm, the Louisiana Department of Transportation and Development said Tuesday.
For those who able to return home, they may come back to an unrecognizable landscape.
Lafourche Parish residents, who were subject to mandatory evacuations, were allowed to return home Tuesday at noon. However, power is out and will not be restored for some time, a nightly curfew is in place, there is no access to clean water and alcohol sales are suspended, the parish said.
"Nearly all communication is down, including cell phone service parish-wide. Your home may be severely damaged and uninhabitable," the parish said.
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Correction: An earlier version of this story gave an incorrect high temperature forecast for Louisiana. The forecasted temperature will be in the upper 80s with a heat index in the 100s.
CNN's Taylor Ward, Brian Todd, Steve Almasy, Keith Allen, Monica Garrett, Kay Jones, Gregory Lemos, Paul P. Murphy, Rebekah Riess, Jenn Selva and Amanda Watts contributed to this report.