New York City opened nearly 300 cooling centers as temperatures across much of the U.S. Northeast surpassed 90 degrees Fahrenheit (32 degrees Celsius) - the hottest in the metropolitan area since a heat wave last year that was blamed for 40 deaths.
Extra utility crews were on hand in case of power outages, and 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 F (32 degrees C) at 1 p.m. High temperatures were forecast in the 90s F (above 32 C) 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.
On Monday, the 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.
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 F (above 32 C) prompted state officials to issue a hazardous weather alert. Richmond city officials opened three cooling shelters.
In Washington, D.C., where the high temperature at Reagan National Airport was 97 degrees F (36 degrees C), the city set up several air-conditioned cooling where people could take a break from the heat and have a cup of cold water.
Unhealthy air quality also led some local transit systems to offer free bus rides in hopes of keeping cars off the roads.
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.
But late Monday, Pennsylvania legislators and the governor brokered a deal to end the budget impasse, allowing state workers to return to their jobs the next day.
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