It was “only” 97 degrees in Washington on Sunday, not enough to set a record. But by some measures, Washington was one of the hottest cities in the nation Sunday.

After setting a record for the date — 102 degrees — on Saturday, the heat did not relax its grip on the city. Warm temperatures persisted into Sunday morning; shortly before sunrise, when temperatures should be near their lowest for the day, the thermometer at Reagan National Airport showed 84 degrees.

In few if any cities across the nation did the mercury remain so stubbornly high in the morning Sunday.

On the East Coast, where the heat wave continued, the mercury reached 98 degrees in Philadelphia, setting a record there. But in the morning, it was as low as 82. In Wilmington, Del., the day’s 98-degree high also set a record. But it got as cool as 79 degrees at 4:26 a.m.

As of 5 p.m., the average temperature for the day in Washington was listed as 91 degrees. That was higher than the average in such hot spots as Atlanta, which was 83; Houston, 88; Memphis, 87; and San Antonio, 89.

It has been a time of extreme heat in the District and in much of the nation. In Washington, the average high temperature for the four days that ended Sunday was 100 degrees.

Unusual conditions have prompted unusual responses.

In recognition of the heat, the Metro transit system made an exception to the rules against drinking in its trains, buses and stations. On Friday, Metro suspended the rules to allow passengers to carry and consume bottled water. That suspension was to remain in force until the transit system closed Sunday night, Metro said.

Metro also said that it had deployed more than three dozen technicians to respond to reports of hot rail cars.

In addition, the agency said it had authorized overtime for its technicians so they could keep elevators and escalators going.