Philly set a temperature record Monday, and it may hit 100 Tuesday

The official temperature in Philly hit 99 degrees late Monday afternoon, setting a record for the date. At one point it felt like it was 110. And it may top 100 for the first time in 13 years on Tuesday.

By 7 a.m., the official temperature in Philly Tuesday was 87, one degree above the normal afternoon high for the date.

But health experts say the Philly region may have caught a significant break from an unforeseen storm system on Sunday. It generated all of a thimbleful of rain, but it pushed back the start of the season’s first serious hot spell.

While the National Weather Service has posted a warning for potentially dangerous “extreme heat” through Wednesday, with highs at or near 100 again Tuesday and upper 90s on Wednesday, some letup is expected Thursday.

And “Friday looks much cooler,” said Zack Cooper, meteorologist with the weather service in Mount Holly.

Some computer guidance last week had suggested the heat wave might be long-enduring, starting Sunday and perhaps persisting through the week.

In the meantime, a “code orange” air quality alert was in effect through Tuesday for Southeastern Pennsylvania, and people with respiratory or heart conditions were advised to limit time outside.

Said Tom Kines, senior meteorologist with AccuWeather Inc., “There’s still a lot to complain about.”

Some Peco customers who were among the more than 10,000 who remained without power Monday following Thursday’s storm, one of the utility’s worst outage events on record, likely would agree with Kines. Despite the lingering outages from damaged and downed trees, Peco didn’t anticipate major issues associated with the heat, nor with meeting power demands.

» READ MORE: Philadelphia summer heat: How to stay cool, avoid heat exhaustion, and find public pools and cooling centers

In addition to besting the standing record for a June 23, 98 degrees, set in last year’s June heat wave, the air is so infused with water vapor that it is capable of sabotaging the body’s cooling system.

While heat indexes are forecast to be subtly gentler Tuesday, topping out around 105, Philadelphia has an excellent chance of reaching 100 for the first time since 2012, said Alex Staarmann, a weather service meteorologist in Mount Holly.

The air will be ever so slightly drier, which would be more favorable for temperatures to rise. Philadelphia’s 100-less streak is the longest since the one that ended in 1917. The record high for a June 24, 99 degrees, was set in 1923.

In any event, by any measure the body’s cooling system is in for a serious challenge Tuesday. Sweat cools the skin when it evaporates, but when the air is so stocked with water vapor, the sweat oozing from the body’s millions of sweat glands just won’t disappear.

Also, the moisture in the air impedes cooling at night. Temperatures may struggle to drop below 80 degrees Tuesday, Wednesday, and Thursday morning.

That’s especially dangerous and physically stressful for people without air-conditioning, said Samuel Eldrich, medical director of the Temple Health-Chestnut Hill Hospital Emergency Department.

For one thing, cooling centers aren’t 24-hour operations. Plus, “When you’re sleeping, you don’t realize how hot you’re actually getting,” he said. Even a window fan offers a modicum of cooling.

Without benefit of overnight cooling, buildings are going to heat up in a hurry when the sun comes up.

» READ MORE: Peco says power to all Philly-area customers will be restored today amid heat wave

We learned anew Sunday that the atmosphere can outwit some of the best minds and machines of meteorological science.

Unforeseen by computer models, “ring of fire” storms developed on the northern periphery of the dome of high-pressure that is baking much of the East, said Kines.

The storm complex formed well north of the region and it didn’t rain much around here, but “it kept some cloud debris in the area and that kept temperatures down,” said the weather service’s Nick Guzzo. The sky was about 70% cloud covered, the weather service reported.

The official high at Philadelphia International Airport was just 88 degrees: The forecasts had called for highs in the mid-and upper 90s.

The delay may end up being important for saving lives.

Heat-related mortality is very much dependent on duration, said Laurence Kalstein, a climatologist who is a heat-health expert and has worked with Philadelphia and other cities to develop heat-response systems.

“We always note that the first day or two of excessive heat does not lead to disastrous rises in mortality,“ he said. In short, the shorter the better.

The cumulative effects of heat and persistent sweating can be life-threatening, said Temple Health-Chestnut Hill Hospital’s Eldrich.

“It’s that volume loss and water loss that starts to cause problems,” he said, “especially for the elderly population so prone to dehydration.”

Philadelphia’s heat-response plan, developed in the 1990s, includes opening more than 40 cooling centers throughout the city and nudging people to look in on older neighbors.

The Philadelphia Corporation for Aging’s Heatline, 215-765-9040, will again be operating from 8:30 a.m. to 8:30 p.m. Tuesday and Wednesday.

It is unclear just how much of a factor that system has been in lowering heat deaths. Philadelphia has not experienced a run a 90-degree plus days that match those of the 1990s.

However, overall summer temperatures have been rising, and heat-related deaths have fallen off dramatically.

In the 10-year period that ended in 2002, Philadelphia averaged about 40 heat-related deaths a year. Since the summer of 2013, the average has been about four, according to the Health Department.

Staff writer Rob Tornoe contributed to this article.