The mercury rose above 100 degrees in Washington for the second consecutive day Saturday, setting a record for the date and taxing the coping skills of residents and visitors.

Reports of a decline in the heat index, a joint measure of heat and humidity, seemed to offer little comfort. The index was lower than Friday’s, but it was still high enough to prompt the National Weather Service to issue an excessive- heat warning.

In Northwest Washington, a man was found dead Saturday morning, and his cousin said she suspected it might have been linked to the heat.

Annette Williams, of Huntingtown, said her cousin, Lawrence Graves, 89, was found on his lawn.

She said Graves had diabetes and heart problems but probably went out into Friday evening’s simmer to water his garden. He “shouldn’t have been outside to begin with,” she said of the retired high school principal.

No official ruling on the cause of Graves’s death could be obtained Saturday.

Conditions in Washington and its surroundings were far from salubrious. In the eight hours starting at 7 a.m. Saturday, the DC Fire and EMS department responded to about 75 or 80 calls that were directly related to the heat, said department spokesman Pete Piringer.

It was fiercely hot Friday throughout the area, and when the sun went down Friday night, the heat scarcely subsided. In the hours before sunrise Saturday morning, in what is usually the coolest part of the day, the temperature at Reagan National Airport fell no lower than 84 degrees.

Even at the height of summer, that is not a common reading at that time of day, and, according to the Washington Post’s Capital Weather Gang, if things did not go suddenly cooler Saturday night, it would match the city’s highest-ever low temperature.

It was 13 degrees above the normal low for July 23, and it helped bring the average temperature for the day to 93 degrees. That is higher than the average high temperature of 89 degrees in Washington for that date.

Even in the forbidding conditions, some people visited the Mall. And some of those who did were overwhelmed.

“This would be a really bad day in Florida,” said Tina Cripps of Orlando, who visited the District for the weekend with her husband and four children.

In Manassas, many people who had gathered for a reenactment of the first major battle of the Civil War found themselves in a battle with the swelter.

A Prince William County fire department official, Joseph Robertson, said that rescue workers checked out almost 150 people in air-conditioned medical tents at the site where the Battle of Bull Run was being reenacted. Eleven were taken to hospitals.

In Washington, the 102-degree reading at National set the city’s record for July 23. It was 1 degree higher than the 101-degree mark set 20 years ago.

It was hot all over the East Coast. In New York, the 100 degrees at Central Park set a record. Philadelphia set a record of 101. Norfolk set a record with 103 degrees. It was 101 in Richmond and 103 at the Raleigh-Durham airport.

National’s 102 was the same as Friday’s, but at Dulles the high fell from 105 Friday to 99.

A thunderstorm crossed the Potomac River Saturday evening, apparently knocking out power to hundreds of homes and businesses in the Fort Washington area.

Several hundred District residents were also without electricity Saturday evening.

Even amid the searing rigors of a record-setting day, some, it must be said, appeared to hearken to a different drummer.

They included Daniel Saraceno of Fairfax County, who lay on a towel in the middle of the Mall. His shirt was off. He said he had planned to head into a museum but thought he would take the opportunity to catch some rays.

“I love the heat,” he said.

Dan Stillman of the Capital Weather Gang contributed to this report.