'Extreme' Weather In Eastern PA This Week, Heat Index Could Hit 110

A dangerous heat wave which weather officials are describing as "extreme" will descend over much of the greater Philadelphia this week, with temperatures soaring up to 100 degrees or more and the heat index rising to 110 in some areas.

"We simply cannot stress this enough: it will be dangerously hot the next three days," the National Weather Service's Mt. Holly, New Jersey branch shared in a statement.

The agency has issued an extreme heat warning through 8 p.m. Wednesday, citing a significant increase in the threat of heat-related illnesses like heat exhaustion and heat stroke.

The hottest times will be in the afternoon on Monday and Tuesday, when the high temperature in much of the greater Philadelphia area is expected to be around 100 or 101 degrees, forecasters said. It will still be extremely hot on Wednesday, as well, with afternoon highs rising to around 98 or 99.

Extreme heat like this coupled with high humidity is "rare," the National Weather Service said, and it could impact the health of all individuals, not just groups sensitive to heat like children and the elderly.

The extreme heat warning covers all of southeastern Pennsylvania and much of the surrounding region in southern New Jersey.

"Low temperatures near 75 to 80 degrees and high humidity will not offer much relief from the heat at night," the National Weather Service added. Accuweather added that Philadelphia has never had consecutive days in June in which the low temperature was not below 80.

Additionally, this week appears likely to "mark the first time for some in many decades since triple-digit heat has been experienced in June," Accuweather added.

Philadelphia's all-time records of 97 and 99 for Monday and Tuesday, respectively, are in jeopardy, the Weather Service added.

Slight relief will be gained from the heat, with forecasted thunderstorms and rain on Thursday and Friday, according to forecasters. However, the high will still be an uncomfortable 91 on Thursday, and oppressive humidity will continue as the storms roll through the area.

Many local counties and municipalities have declared heat emergencies, which allows them to open emergency cooling centers in public spaces. Find resources in your county below:

• Heat Health Emergency Issued In Philadelphia
• Extreme Heat Warning Renewed In Montgomery County
• Excessive Heat Warning Issued In Bucks County
• Code Red Heat Alert Issued In Delaware County

Here's the full forecast for the coming days, according to the National Weather Service:

Monday
Sunny and hot, with a high near 100. Heat index values as high as 107. Northwest wind around 5 mph.

Monday Night
Mostly clear, with a low around 80. West wind around 5 mph becoming calm.

Tuesday
Sunny and hot, with a high near 101. Heat index values as high as 105. Calm wind becoming northwest around 5 mph in the afternoon.

Tuesday Night
Mostly clear, with a low around 81. Northwest wind around 5 mph becoming calm in the evening.

Wednesday
A slight chance of showers and thunderstorms after 2 p.m. Sunny and hot, with a high near 98. Calm wind becoming northwest around 5 mph in the afternoon. Chance of precipitation is 20 percent

Wednesday Night
A chance of showers and thunderstorms between 8 p.m. and 2 a.m., then a slight chance of showers. Partly cloudy, with a low around 76. Chance of precipitation is 30 percent. New rainfall amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

Thursday
A chance of showers and thunderstorms after 2 p.m. Partly sunny, with a high near 91. Chance of precipitation is 50 percent.

Thursday Night
A chance of showers and thunderstorms. Mostly cloudy, with a low around 69. Chance of precipitation is 50 percent.