June 25, 2019
The mercury has only reached 90 degrees in Philadelphia once so far this year, but that is about to change with a real chance for a heat wave this week.
The humidity will climb as well this week, according to forecasters.
The temperature hit a high of 90 on May 29, and has yet to climb as high. But with high temperatures forecast at or near 90 degrees through Sunday, the region has a good chance for its first heat wave of the year, less than a week after the start of astronomical summer.
Mostly sunny skies are in the forecast from Wednesday through Friday, which looks to be the hottest day of the stretch, with temperatures expected to climb near 93 degrees and the heat index likely to approach 100 degrees in the city, forecasters said. (Temperatures look to be about 5-10 degrees lower at the Jersey Shore and Poconos.)
The National Weather Service defines a heat wave as three or more consecutive days with the temperature reaching or exceeding 90 degrees.
The Philadelphia region had four heat waves in 2018, including a 7-day spell. That stretch kicked off June 29 and featured six days with temperatures of 94 degrees or higher, including the Fourth of July, and two days of 97 degrees or higher.
Three more heatwaves – all four days in duration – came in early and late August, and early September. On three days during those stretches the temperature peaked at 95 degrees.
According to forecasters, this week's heat and humidity will come from the south and hang around through the Sunday-Monday arrival of a cold front that will lower temperatures and dew points a bit.
Here is a 7-day forecast from the weather service for Philadelphia:
Tuesday: A slight chance of showers before 1 p.m. Partly sunny, with a high near 88. West wind 7 to 9 mph. Chance of precipitation is 20 percent.
Tuesday night: Partly cloudy, with a low around 70. Northwest wind 6 to 9 mph.
Wednesday: Sunny, with a high near 90. West wind around 6 mph.
Wednesday night: Partly cloudy, with a low around 71. West wind 3 to 5 mph.
Thursday: Sunny, with a high near 90. West wind 3 to 7 mph.
Thursday night: Mostly clear, with a low around 71.
Friday: Mostly sunny, with a high near 93.
Friday night: Partly cloudy, with a low around 72.
Saturday: A chance of showers and thunderstorms. Partly sunny, with a high near 92. Chance of precipitation is 30 percent.
Saturday night: Partly cloudy, with a low around 72.
Sunday: Mostly sunny, with a high near 89.
Sunday night: Partly cloudy, with a low around 66.
Monday: Sunny, with a high near 85.