In addition, air quality is a concern, with high ozone levels expected today, for Southeastern Pennsylvania and all of New Jersey. Anyone with a lung condition, such as asthma, should avoid exertion or prolonged exposure outdoors. For more, go to AIRNow.gov.
Thursday is expected to be worse with a high approaching the record of 99 for June 21, which has stood since 1923.
Such conditions can be health-threatening, especially to children, the elderly, the infirm, and anyone doing strenuous activity outdoors. Use fans and air-conditioning, drink plenty of fluids, and, if you have to be outside, work in rest breaks indoors or in the shade.
Anyone with heat-related medical questions or concerns can call 215-765-9040, the Philadelphia Corporation for Aging's Heatline, today from noon till midnight, and Thursday from 8:30 a.m. to midnight. City Health Department nurses will be on-site to speak with callers.
Friday will see some relief under partly sunny skies with a chance of showers and thunderstorms and a high of 92. Conditions will feel more comfortable, with lower humidity, and with lows dipping to 68.
"It won't drop off a lot," said Hayes, who noted normal high temperatures are in the mid 80s for this time of year. "The record for Friday is 100. I don't think we'll see that. But we'll be a good 12 to 15 degrees above normal for the next few days."
Hayes explained that the cooler air, "will come in pieces," starting on Friday, then more on Saturday.
"So we'll have to wait a few days before we see a significant difference," Hayes said.
Saturday should see a high of about 87 and a low of 66. The forecast for Sunday is similar.
For the record, the summer solstice is 7:09 p.m. — that astronomical moment in time when the Sun reaches its most northern point in the sky, and marks the longest day of the year. After today, the days start getting shorter.
For more on the forecast, see Philly.com's weather page.