Record-breaking heat and humidity seared the city yesterday, filling subway stations with steam, drenching pedestrians, and driving electricity usage to all-time highs.

Con Edison reported its peak electricity usage at 5 p.m., of 13,059 megawatts, which shattered the old record of 12,551 megawatts set July 19.

The National Weather Service said parts of the city reached record temperatures yesterday afternoon before welcome thunderstorms doused the area.

LaGuardia Airport’s temperature hit 100 degrees at 4 p.m., breaking its previous high for the date of 96 degrees, set in 1999. Central Park temperatures reached a peak of 97 degrees, falling one short of the 98-degree record, set in 1966. The Weather Service predicted a frontal system would move in last night, dropping temperatures across the region and lowering today’s expected high into the mid-80s.

Yesterday afternoon, citing problems with electrical feeder cables supplying power to Harlem, Con Ed asked about 85,000 customers in the area to stop using nonessential electrical appliances, such as air-conditioners, washers, and dryers. As a precautionary measure, the utility also reduced voltage to the area by 8%, which it said should not affect area customers.

Con Ed made a similar request to 81,000 residents of four Brooklyn neighborhoods – Greenpoint, Williamsburg, Castle Hill, and Fort Greene – Tuesday evening through yesterday morning. On Tuesday, Mayor Bloomberg announced the opening of cooling centers across the five boroughs, including air-conditioned public spaces.

Some New Yorkers have complained recently to city leaders about excessive beach closures in Coney Island, the city’s most popular beach, with about 9.5 million visitors a year.

The complaints led the president of Brooklyn, Marty Markowitz, to deliver a letter yesterday to the parks commissioner, Adrian Benepe, asking to keep a higher percentage of Coney Island’s swimming bays open and to stop the practice of cordoning off beaches where lifeguards are not present.

Mr. Markowitz acknowledged a chronic citywide shortage of lifeguards and offered the use of his office’s resources to increase recruitment. “Coney Island’s beach is a citywide and regional priority,” he wrote.

The letter comes on the heels of a similar demand by the City Council speaker, Gifford Miller, who recently sent a letter to Messrs. Benepe and Bloomberg arguing that the number of Coney Island beaches closed during the week was “simply unacceptable.”

A spokesman for the Department of Parks & Recreation, Warner Johnston, said in a statement that Brooklyn beaches have 10% more lifeguards than last year. He also said the 2005 beach season is the busiest in recent history.

At 2 p.m. yesterday, the corporation in charge of overseeing the state’s power grid, the New York Independent Service Operator, for the first time in at least two years activated its emergency demand-response program and asked hundreds of large commercial and industrial customers downstate to immediately lower their use of electricity. That reduction, along with thunderstorms in the Albany area, lowered statewide consumption considerably in the afternoon.

In heat-wave conditions, the city’s Office of Emergency Management coordinates citywide response. It held two conference calls yesterday with Con Ed, the health and fire departments, and Emergency Medical Services, and reported no spikes in the number of heat-related 911 calls or hospitalizations.