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 on end, coupled with a period of excessive heat.

Ida, which made landfall Sunday as a Category 4 hurricane, has already contributed to four deaths. 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.

The National Weather Service issued a heat advisory for southern Louisiana and Mississippi from 10 a.m. to 5 p.m. Tuesday. More than 2 million people in the area are under the advisory, CNN meteorologist Michael Guy said.

That means some residents who stayed and rode out the storm will face heat indices of up to 105 degrees — without air conditioning. Heat is the No. 1 weather-related cause of fatalities in the US, the NWS 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.”

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’ levee system to fail, flooding 80% of the city and killing over 1,800 people. 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. Ida is then set to move toward the mid-Atlantic and Northeast. Nearly 80 million people are under a flash flood threat from the storm, stretching from Alabama to Massachusetts.

The center of Ida was 60 miles west-northwest of Huntsville, Alabama, or 100 miles southwest of Nashville, Tennessee, as of the 11 a.m. ET Weather Prediction Center update. Rainfall around Ida stretches over 600 miles from Kentucky southward to the Gulf Coast. The heaviest rain is located across Kentucky and along the lines of thunderstorms stretching through Alabama and Georgia.

Weeks without electricity

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 power customers in Louisiana, 60,000 in Mississippi, and 16,000 in Alabama are without power, according to PowerOutage.US. An electricity customer can represent an entire household or business, so the number of people who lost power is likely much higher.

The vast majority of Louisiana’s 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.

In parts of Jefferson Parish, power is expected to be out for at least three or four weeks, Councilman at Large Ricky Templet said. Another councilman, Bryon Lee, said supplies are limited, grocery stores are closed and there is a two-hour line for gas.

And officials in St. Charles Parish it’s “highly likely” the area won’t have power for a month, according to a Facebook post.

More than 25,000 workers from at least 32 states and the District of Columbia have been mobilized to help restore power in Louisiana, the Edison Electric Institute said in a statement Monday.

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.”

Part of a highway washed away

Heavy rain in Mississippi washed away part of Highway 26, a main artery between Mississippi and Louisiana, killing two people and injuring 10 others.

Seven vehicles went into a hole created by the washout, which was about about 50 feet long and 20 feet deep, Mississippi Highway Patrol Trooper Cal Robertson said.

At least two deaths in Louisiana have been linked to Ida. The first happened when a tree fell on a home in Prairieville, the Ascension Parish Sheriff’s Office said Sunday. And 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.

In Louisiana, state police gave a blunt message to some residents Monday: “It may be difficult to get help to you for quite some time.” With many roads impassable or blocked by debris, “the full extent of damage is yet to be seen,” police said.

Some people closer to those in need volunteered to help. Paul Middendorf spent hours Monday rescuing people with his canoe in LaPlace, Louisiana, volunteering with the group Crowdsource Rescue.

“Most of (the rescues) were in the attic,” he said. “The water in the back of that neighborhood was about 10 feet deep or higher.”

Middendorf said the water slowly started to recede. Although it was only knee deep in some parts, it was still chest deep with a strong current in many areas that were still flooded in LaPlace, he said.

Those who did evacuate may not be able to return anytime soon due to unpassable roads. For those who can return, they may come back to an unrecognizable landscape.

Lafourche Parish residents, who were subject to mandatory evacuations, will be 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.

Catera Whitson (C) and Kyler Melancon (R) ride in the back of a high water truck as they volunteer to help evacuate people from homes after neighborhoods flooded in LaPlace, Louisiana on August 30, 2021 in the aftermath of Hurricane Ida. – Rescuers on Monday combed through the "catastrophic" damage Hurricane Ida did to Louisiana, a day after the fierce storm killed at least two people, stranded others in rising floodwaters and sheared the roofs off homes. (Photo by PATRICK T. FALLON/AFP via Getty Images)