In case of power outages, staffers at New York City's main power company, Con Edison, which services nine million residents, were working 12-hour shifts, reports CBS News correspondent Kelly Wallace.
Mayor Michael Bloomberg urged residents to help prevent blackouts by conserving power. He urged New Yorkers not to exert themselves in the sweltering conditions.
"It is very hot," Bloomberg said. "I don't care how good a runner you are, I don't care how strong you are, you should take some precautions to prevent strokes."
The temperature in Central Park hit 90 degrees at 1 p.m. High temperatures were forecast in the 90s through Wednesday.
"This is the first heat wave this year," said Joe Pollina, a meteorologist with the National Weather Service.
Last year, a heat wave in late July and early August caused 40 deaths from heat stroke and contributed to the deaths of another 60 people.
The blistering heat, slamming the West since last week, has been rolling across the country, adds Wallace. It was 93 degrees in Chicago and 96 degrees in Philadelphia and Washington D.C. — near record highs.
Baltimore declared a code red heat alert for today and tomorrow, with officials especially concerned about air quality, reports Wallace.
On Monday, the New York City opened its network of 290 cooling shelters for the first time in 2007, offering people without air conditioning a break from the heat at senior centers and community buildings.
But one social worker with a senior-service agency cautioned that the cooling centers may not be enough.
"We've seen that the city has done a good job of publicizing the cooling centers, but it's often hard for seniors to get there," said Karen Fuller, director of health and nutrition services for Dorot, an agency that delivers meals and other services to homebound seniors.
The commissioner of the city's Department for the Aging, Edwin Mendez-Santiago, urged seniors to make sure someone checks on them.
"Make sure you're planning in advance, that you have water, that you use your air conditioner. And if you don't have an air conditioner, seek respite at a cooling site or any other location where you can cool off," he said.
Extra utility workers were in place to guard against blackouts like the ones that plagued the borough of Queens and suburban Westchester County in July 2006, when 174,000 people lost service or experienced low voltage.
"There will be outages in the summertime," Consolidated Edison utility spokesman Alfonso Quiroz said. "And we're just hoping that when they come they are short in duration and few in number."
Monday's heat spread as far south as Virginia, where temperatures in the 90s prompted state officials to issue a hazardous weather alert. Richmond city officials opened three cooling shelters.
State parks in Pennsylvania were closed after Gov. Ed Rendell furloughed more than 24,000 state employees because of a partisan deadlock that is holding up a state budget, a move that put state-run swimming areas off limits to those seeking relief from the heat.
Seven-year-old McClane Dyerson looked dejected after his family had to cut short its weeklong camping trip at Black Moshannon State Park in Philipsburg.
"I like going to the beach," he said. "That's what most people like to do here most."