As summer heat bakes New England, the operator of the region’s power grid is asking residents to cut back on electricity use. Mainers, meanwhile, are flocking to stores in search of air conditioners and extra fans.

ISO New England said Tuesday that the combination of heat and high humidity that’s expected all week could drive power use in the region to near-record levels.

Electricity supplies are adequate now, the system’s operator said, but they likely will get tight as the heat persists. Voluntary conservation will help keep supply and demand in balance and maintain reliable service, it said.

The high temperature in Portland on Tuesday was 90 degrees, 11 degrees above normal for the date, said Mike Kistner, a meteorologist with the National Weather Service in Gray. It also was nearly 10 degrees warmer than Tuesday afternoon’s temperatures in Orlando and Miami.

Kistner said Portland’s record high for July 16 is 96 degrees, set in 1968.

On Monday, Portland had its warmest low temperature ever for July 15. The low of 70 was a degree warmer than the previous record of 69 degrees, set in 1998.

A spokesman for Central Maine Power Co. said the utility is not taking any special action and is following ISO New England’s directions.

The grid operator is targeting its request for noon to 8 p.m., when demand for power is greatest. It suggests these measures, when they don’t interfere with health or safety:

• Raise air conditioning temperatures to 74 to 78 degrees.

• Turn off air conditioners when leaving home for an extended period.

• Turn off unneeded lights, appliances and office equipment.

• Wait until early morning or late evening to do laundry or other chores that use a lot of electricity.

In a note to businesses that are heavy power users, ISO New England said it’s not asking for formal conservation measures such as switching off machines or motors. But it said the forecasted electricity load from Tuesday through Thursday showed potential for exceeding capacity.

ISO New England projects that demand will grow through the week, peaking at 27,800 megawatts on Thursday. Demand on Tuesday exceeded 26,200 megawatts around 3 p.m. The forecast for Wednesday is 27,700.

New England’s record for electricity use was set on Aug. 2, 2006, with a peak of 28,130 megawatts.

One megawatt of electricity can power about 1,000 homes in New England.

The demand comes from all of New England, so even if Maine cools down, demand will stay up if other states stay hot.

Residents who want new air conditioning units in Greater Portland may have to make a little extra effort. Many stores in the area have run out because of brisk weekend sales.

“It takes good hot weather like this to push people over the edge,” said Tim Currier, manager of Maine Hardware in Portland. “This is the time when everyone starts calling because they’re panicking and can’t find (air conditioners) anywhere.”

Employees at the store on St. John Street were busy Tuesday afternoon taking phone calls from people who wanted air conditioners and helping walk-in customers choose units.

One employee, Gary Smith, said most customers have similar stories: After trying to sleep in the heat night after night, they are fed up.

“A couple of hundred bucks is worth a good night’s sleep,” Smith said as he restocked a shelf with air conditioners. “Our storeroom was full a month ago, but we’re getting down there now.”

As she bought an air conditioner at Maine Hardware, the only thought on Katie Capron’s mind was relief. The Portland resident said she was “finally breaking down after years and years and years” of using only fans to stay cool.

“It’s already been so hot this year and I don’t see that trend changing, so I’m biting the bullet,” she said.

Mark Flowers of Scarborough spent three hours searching for a new air conditioner after his unit at home died. He said he went to “every conceivable” store looking for one before calling his wife to tell her they would have to go the night without air conditioning. She told him to keep looking and sent him to Maine Hardware, where he bought the last 6,000-BTU window unit for about $230.

Flowers, who works outdoors, said dealing with the heat during the day is “no big deal,” but he runs his air conditioner at home around the clock to make sure it’s comfortable for sleeping.

For Robert Odlin of Scarborough, finding an air conditioner was essential to make working on the fishing boat Maria and Dorothy more tolerable. He spent about $500 for a large portable unit for the cabin, where it was 85 degrees, he said. He bought an extra fan to keep on deck.

“At least the cabin will be cool for sleeping,” he said.

Joe Dehart, assistant manager of the Lowe’s store in Portland, said the store still has a few larger air conditioners but is out of the smaller window units that more customers are seeking. The store expects a shipment of air conditioners, he said.

Ann Wedge, assistant manager of Aubuchon Hardware in Buxton, said the store is out of air conditioners but customers are also looking for other ways to stay cool.

“We’re going through pool (chemicals) like crazy,” she said. “We’re also selling quite a few pool floats because people are going down to the river to float around.”

The Portland Fire Department is asking the public to take precautions because of the heat, and to look out for the elderly and others who may be vulnerable to heat-related illnesses.

Precautions include drinking liquids that don’t include alcohol, caffeine or sugar and staying in air-conditioned buildings.

Most vulnerable to the heat are the elderly, young children, the obese, people with medical conditions such as cardiac or pulmonary problems, and people who take medications such as anti-depressants and anti-anxiety drugs, which may increase the effects of sun and heat exposure.

Kistner, from the National Weather Service, said Mainers can expect some relief — but not until Saturday. The rest of the workweek is expected to be humid, with temperatures around 90, but a front will move in Saturday with cooler air.

He said Sunday is expected to be “gorgeous,” with less humidity and highs in the 70s.

Tux Turkel can be contacted at 791-6462 or at:

tturkel@pressherald.com

Gillian Graham can be contacted at 791-6315 or at:

ggraham@pressherald.com

Twitter: grahamgillian