Hundreds of thousands who remain without power in Texas and Louisiana after Hurricane Laura's wrath now are having to deal with scorching heat on Monday.

Over 350,000 customers in both states remain without power after Hurricane Laura blasted through the region last week, with major damage reported to infrastructure. So far, 18 deaths in Texas and Louisiana have been attributed to the storm; more than half of those people were killed by carbon monoxide poisoning from the unsafe operation of generators.

Extreme heat is now expected Monday across portions of the Deep South, especially in areas hardest hit by the storm.

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Heat advisories have been issued across eastern Texas and in most of Louisiana.

The forecast heat index for Monday, Aug. 31, 2020.

The forecast heat index for Monday, Aug. 31, 2020. (Fox News)

Afternoon high temperatures in these areas will range from the middle 90s into the low 100s. Heat indices will range from 108 to 114 degrees Fahrenheit.

Heat advisories stretch over parts of Texas and Louisiana still without power after Hurricane Laura.

Heat advisories stretch over parts of Texas and Louisiana still without power after Hurricane Laura. (Fox News)

Workers in Louisiana have started to patch up roofs and clean up the damage, but on Sunday most of the homes in Lake Charles that saw a direct hit from the storm were still untouched.

Rakisha Murray cries in relief as she arrives to see her mother's home largely undamaged, after she returned from evacuation with her mother and other family in Lake Charles, La., in the aftermath of Hurricane Laura, Sunday, Aug. 30, 2020.

Rakisha Murray cries in relief as she arrives to see her mother's home largely undamaged, after she returned from evacuation with her mother and other family in Lake Charles, La., in the aftermath of Hurricane Laura, Sunday, Aug. 30, 2020. (AP Photo/Gerald Herbert)

In Calcasieu Parish, where Lake Charles is located, parish spokesman Tom Hoefer said water had not been flowing from taps in many areas, and the entire area was still without power.

Linda Smoot, who evacuated from Hurricane Laura in a pickup truck with eight others, reacts as they return to see the damaged home of her niece for the first time, in Lake Charles, La., in the aftermath of the hurricane, Sunday, Aug. 30, 2020.

Linda Smoot, who evacuated from Hurricane Laura in a pickup truck with eight others, reacts as they return to see the damaged home of her niece for the first time, in Lake Charles, La., in the aftermath of the hurricane, Sunday, Aug. 30, 2020. (AP Photo/Gerald Herbert)

James Townley, who had the front of his trailer blown away by the storm, told the Associated Press he was out of medication for his heart and kidneys but was planning on remaining at his home.

James Townley, who has a heart condition, lies on his couch with no electricity in his partially destroyed mobile home in Lake Charles, La., in the aftermath of Hurricane Laura, Sunday, Aug. 30, 2020.

James Townley, who has a heart condition, lies on his couch with no electricity in his partially destroyed mobile home in Lake Charles, La., in the aftermath of Hurricane Laura, Sunday, Aug. 30, 2020. (AP Photo/Gerald Herbert)

“I’m just going to sit here and do what I can do,” he told the AP. “Maybe I’ll make it, maybe I won’t.”

Townley's only way to stay cool was a fan connected to a neighbor's generator that was circulating hot, humid air around his home.

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The Federal Emergency Management Agency (FEMA) has sent hundreds of workers to the region to help with search and rescue and other efforts.

As of Sunday, more than 52,500 people had applied for FEMA assistance, and the agency had conducted over 200 home inspections and distributed more than $650,000 in assistance, according to Tony Robinson, FEMA's administrator for the region.

But some who have requested help from the agency, such as 53-year-old Patricia Mingo Lavergne, have run into issues. Lavergne told the AP she didn't have a checking account in which to receive federal money.

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"It’s frustrating," she said. “I’ve already been going through a lot and this is a lot more on my shoulders.”

Severe storms, heavy rain possible in Plains

As the heat rises in portions of the south, strong to severe storms and heavy rain are also possible on Monday from the south-central Plains to the Mississippi River Valley.

Damaging winds, large hail and flash flooding are possible through Tuesday.

Strong to severe storms will develop from Texas and Oklahoma into Missouri and Arkansas Monday afternoon and evening, including Oklahoma City, Tulsa and Little Rock.

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Heavy downpours will continue the flood threat on Tuesday.

Fox News' Brandon Noriega and the Associated Press contributed to this report.