By the time the concert began shortly before sunset, conditions had improved enough for officials to allow the event to proceed.
"The heat broke a little bit," said Michael DelBene, CEO of Welcome America.
The delayed concert featured performer Idina Menzel and drew thousands of attendees to Independence Mall. While many concertgoers were eager to see Menzel perform, the dangerous heat dominated much of the day and led to the cancellation of earlier events.
"This afternoon it was really, really dangerous," DelBene said. "If we can't do it safely, we just simply won't do it."
All week amid a heatwave, Fourth of July celebrations and events tied to America's semiquincentennial have required organizers to balance public safety concerns with efforts to provide public festivities.
Those attending Friday night's concert continue to take precautions.
"I usually have my electric handheld fan and my water bottle," said Jedah Poleon of Brooklyn, New York.
Health officials warned that triple-digit temperatures and high humidity can increase the risk of heat-related illness.
"Nausea, vomiting, diarrhea, abdominal cramping and a lot of people don't equate those G.I.-type symptoms with heat illness, but that is part of the picture," said Dr. Craig Turner of Virtua Health.
Turner also advised people spending extended periods outdoors to avoid alcohol and caffeine and, in addition to drinking water, consider sports drinks containing electrolytes.
He added people experiencing symptoms should take immediate steps to cool down.
"Get out of the direct sunlight, get somewhere where you can cool off, step inside air conditioning for several minutes," he said.
Despite the heat, many attendees said they were willing to adjust their plans and continue celebrating.
"We're working around it, and we're just sucking it up and we're going for it. We're sweat warriors, we're good," said Michelle Wolfson of Gilbert, Arizona.