After record-setting heat in July in some areas, August is starting out hotter as temperatures force heat advisories in 18 states from Texas to New York.
Meteorologist Tom Moore of The Weather Channel said the South will get a short reprieve this weekend but predicts that 100-degree temperatures will return by Monday.
Government officials in Memphis and elsewhere are urging police officers, firefighters and even utility-meter readers to check on vulnerable residents.
The heat has resulted in the deaths of at least 16 people in Mississippi and Tennessee alone, according to the Associated Press.
"It's been awful, that's for sure," said Marian O'Briant of the Blount County, Tenn., Sheriff's Office, which lost a police dog, Hansen, to heat exhaustion Wednesday after he helped track two burglary suspects. O'Briant said another police dog in Fayette County, Ga., died from heat exhaustion this week.
Among National Weather Service reports:
In Little Rock, the number of 100-degree days in a year averages less than one. This year, which included a record high of 105 degrees Thursday, there have been 13.
After tying the record for its hottest month ever in July, Washington, D.C., continued to swelter Thursday with its 46th day of 90-degree heat or more this year, compared with 22 in 2009.
Through Thursday, Birmingham, Ala., had endured 32 consecutive days of 90 degrees or higher, approaching the record of 37 days set in 2007.
Memphis recorded a heat index — when relative humidity is factored in with the temperature — of 123 degrees Tuesday. The city sweltered through its 63rd 90-degree-or-above day Thursday.
The Virginia Department of Transportation has crews on alert to respond to roadway damage caused by heat, which expands pavement and causes it to crack or buckle. Department spokeswoman Joan Morris said crews also check on road construction workers around the state.
"They're advised to drink lots of water, take as many breaks as needed and take it a little slower," she said.