By 3 this afternoon, the temperature at Philadelphia International Airport had hit 92, and although the dewpoints still were in the 50s, it's safe to say the heat wave is under way.
The National Weather Service has posted an "excessive heat warning" for noon tomorrow through 8 p.m. Sunday.
It's turned up the official forecast slightly, now calling for a high of 99 tomorrow in the city, with heat index values up to 103. The record high for the date is 102, set in the Dust Bowl era of 1934.
Then a subtle - and we mean very subtle - cool-down will begin. Saturday's projected high is 97, and 96 for Sunday.
The heat should back off early next week, but temperatures still could top out in the low 90s.
The nights won't be pleasant, and it may be at least a week before overnight temperatures get as low as 70 again.
Despite the rocketing temperatures, the weather service is holding out the possibility that late-day dewpoints could back off enough to lower heat indices.
Also, isolated showers are possible Friday,Saturday and Sunday to offer some temporary cooling.
Right now, the Fourth is looking hot, but not blazing, with temperatures around 90, and dry.
We also mention a 100 percent chance of a 99-percent full moon on the Fourth, rising at 9:10 p.m.