The local electric utility had extra crews in place Monday in readiness for possible blackouts caused by temperatures topping 90 degrees — the highest in the metropolitan region since the 2006 heat wave, which caused 40 deaths in the city.

“There will be outages in the summertime,” a 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.”

The city opened 290 cooling centers at city-run senior centers and community centers, and Mayor Bloomberg urged residents to help prevent blackouts by conserving power and to not exert themselves in the heat.

“It is very hot,” Mr. 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. on Monday, and temperatures in the 90s were forecast through Wednesday, a meteorologist with the National Weather Service, Joe Pollina, said.

“This is the first heat wave this year,” he said.

Last year, the heat wave that struck in late July and early August caused 40 deaths directly from heat stroke and contributed to the deaths of another 60 people, city health officials said.

Monday marked the first time in 2007 that the city opened cooling centers for people without air conditioning to escape the heat — something that was done all during last year’s heat wave.

But one social worker with an agency that provides services to seniors said 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, said seniors should have buddy systems 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.

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 shuttered after Governor 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 respite 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.”