Yesterday afternoon the temperature made it to 90 for the first time since Sept. 24, and it appears that an early-season heat wave is on the horizon.
The forecast is calling for 90-plus temperatures for Monday, Tuesday, and Wednesday, and that techinically would constitute a heat wave if the forecast held up.
Of more significance than the temperatures, the air is going to be full of water vapor, and it's going to feel quite uncomfortable.
The dewpoints -- which measure the absolute moisture content of the air -- are going to be a mid-summer discomfort levels, and the temperatures are going to fight to get below 70 at night in the city.
Don't be surprised if Philadelphia hoists a heat advisory by Sunday.