(CNN) -- As more residents in southern Louisiana return home after Hurricane Isaac, many must now contend with a new obstacle: rebuilding their lives amid blistering temperatures and no air conditioning.

"Heat index values will continue to range in the 100- to 105-degree range, possibly higher in some locations, and (will) continue to have a greater impact on people who still do not have power," the National Weather Service said.



While many residents are focused on recovery, "we need everyone to take their risk of heat stroke seriously," said Bruce D. Greenstein, Louisiana Department of Health and Hospitals secretary. "This is a serious condition that can kill you."

More than 100,000 utility customers on the Gulf Coast remained without power almost a week after Isaac's landfall, while about 2,800 were still in shelters in Louisiana and Mississippi because of flooding.

Scattered thunderstorms Tuesday through Saturday could produce "frequent lightning and heavy downpours" in parts of southeastern Louisiana and southern Mississippi, forecasters said

Authorities are still dealing with threats posed by rain-swollen rivers and lakes, particularly in St. Tammany Parish, northeast of New Orleans.

The Pearl River, along the Mississippi state line, was projected to crest at more than 5 feet above flood stage on Tuesday as authorities monitored a weakened lock on an adjoining canal. Parish officials warned people to stay away from the area, but authorities lifted a mandatory evacuation order over the weekend after they released water from the lock to relieve pressure.

More flood warnings were in effect Tuesday for parts of the Mississippi coast, where rivers north of Pascagoula and Gulfport were running high.

In St. Tammany Parish, the Louisiana National Guard had 253 members prepared to assist with security and evacuations near the Pearl River with 22 high-water vehicles, 23 Humvees and 21 boat teams, according to a statement Monday from Gov. Bobby Jindal's office.

On Monday, President Barack Obama praised rescuers and volunteers helping clean up after Hurricane Isaac and offered federal help to beef up flood protection in the stricken area.

Obama viewed storm damage in St. John the Baptist Parish, west of New Orleans, which suffered extensive flooding after Isaac struck the northern Gulf Coast. Thousands of residents were driven from their homes when the storm forced water over the banks of Lake Pontchartrain, but there were no fatalities in the parish.

"I want to commend everybody who's here for the excellent work they've done in making sure that lives were saved, that although there was tremendous property damage, that people were in a position to get out quickly," Obama told reporters after viewing the damage.

He praised authorities who carried out rescues despite their own losses and the "resilient" people of Louisiana and Mississippi, many of whom still face the threat of flooding.

"We are going to make sure at the federal level, we are getting on the case very quickly about figuring out what exactly happened here, what can we do to make sure that it doesn't happen again and expediting some of the decisions that may need to be made to make sure we've got the infrastructure to protect people's properly and protect people's lives," Obama said.

Authorities have blamed eight U.S. deaths on Isaac, six of them in Louisiana. The latest came Monday, when a 90-year-old man was found dead in his home in suburban New Orleans, Jefferson Parish Coroner Gerry Cvitanovich said.

The home was equipped with air conditioning, but the system didn't work with the electricity out, Cvitanovich said. Temperatures in the area were in the low 90s on Monday.

"It's the very young and very old and chronically ill people that are affected," he said. "The folks in my office are urging everyone to please check on family and get them in air conditioning or get them to a shelter."

Greenstein, the Louisiana health and hospitals secretary, offered the following tips for dealing with the heat: "Drink plenty of fluids, wear light, loose-fitting clothing and sunscreen and take breaks in the shade or a cool area frequently." Officials say a heat stroke victim's body temperature can rise to 105 degrees withing 10 to 15 minutes.

Isaac struck the Gulf Coast south of New Orleans as a Category 1 hurricane early Wednesday, the seventh anniversary of the devastating Hurricane Katrina. It had already killed 19 people in the Caribbean nation of Haiti, where it struck before moving into the Gulf of Mexico.

The storm posed the first real test to New Orleans since a $14.5 billion federal effort to reconstruct the city's flood control system after it failed during Katrina in 2005. Katrina killed almost 1,800 people, most when the storm overwhelmed the levee system and flooded the city.

Most of the areas hit hard by Isaac were outside the rebuilt levee system.

CNN's Matt Smith, Rick Martin and George Howell contributed to this report.