An isolated thunderstorm is possible this evening north and west of Philly, but elsewhere will just be hot and humid. Overnight, it will remain warm and muggy and any thunderstorm activity will fade away. Lows will only drop into the low 70s in the city.
Thursday won't reach 90 (we've gotten to 92 so far today), but upper 80s is the most likely scenario with hazy skies and continued oppressive humidity. Scattered thunderstorms will begin to develop toward the midday hours, and any of these storms could produce very heavy downpours. There may be a storm or two that turns severe north and west of the city, but instability parameters are marginal.
Behind Thursday's cold front is much cooler air for the next week. The weather will be downright awesome right through at least next Wednesday with plenty of sunshine, low humidity, and high temperatures in the 70s.
7 AM 73 degrees, Humid
Noon 84 degrees, Hazy
5 PM high 89 degrees, Scattered Storms
Sunrise 6:39 AM
Sunset 7:14 PM