Nights could be especially dangerous as heat wave gains steam in Philly

With a “dangerously hot” Thursday looming and a heat advisory in effect through Sunday, what almost certainly is going to be Philadelphia’s longest heat wave of the year to date is about to gain steam.

And while the heat won’t be in a league with what’s going on in Europe, and it is unlikely that any records are going to fall around here after the sun comes up, health officials are concerned about what might happen after the sun goes down.

Philadelphia could flirt with a record this week for a highest minimum temperature in a sequence of potentially hazardous warm nights that could persist well into next week. “There’s not going to be much of a break at night at all,” said Matt Brudy, a meteorologist at the National Weather Service Office in Mount Holly.

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“The high overnight temperatures … are very concerning,” said James Garrow, spokesperson for the Philadelphia Public Health Department.

Hot nights are especially dangerous for the elderly who live alone without air-conditioning, health experts say, and the city doesn’t offer overnight cooling resources. Those warm nights impede the body’s ability to cool off and can trap heat in rowhouses, which then warm up faster in daytime.

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With global temperatures rising, the planet has more heat to distribute, and this is the logical period for Philadelphia to get its share.

We are in the heart of the “Dog Days,” so named for the period before and after the rising of Sirius, the dog star, in conjunction with the sun. Some of our ancient ancestors believed Sirius contributed to our sun’s heat. Siriusly, it was not the brightest idea in human history.

On average, Philadelphia is in its hottest period of the year, with a “normal” daily high of 88 degrees through July 29.

Temperatures made it to 93 Tuesday and are due to reach the mid-90s the rest of the workweek and upper 90s on the weekend.

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As often happens this time of year, we are caught in the atmospheric doldrums when upper-air steering currents go on summer break and relief can be fleeting.

With all the water around here, the air also tends to be steamy, and water vapor inhibits daytime warmth from escaping at night, making the overnights uncomfortable.

Paul Walker, senior meteorologist at AccuWeather Inc., added that the recent dry spell — rainfall for the last 30 days has been about a third of normal in Philadelphia — has dried out surfaces and allowed the sun to spend more of its energy on heating.

High humidity is oppressive, but it can cap daytime high temperatures. For example, only once has Miami recorded a 100-degree reading, and that was on July 21, 1942.

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Overall, this has been quite a benign summer in Philadelphia. While temperatures approaching 110 degrees have been reported in France, and extreme heat has parched areas elsewhere, the National Weather Service has yet to issue a single “excessive heat warning” for Philadelphia.

Garrow said not one heat-related death has been reported in the city. In the last 10 years, Philadelphia has reported only 33 heat-related deaths total. In the 10-year period ending in 2002, it recorded nearly 400, according to health department figures.

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Temperatures have averaged about 1.4 degrees above normal since June 1 but haven’t reached 95 since May, and no heat wave has lasted more than four days.

That is about to change. As this one enters its third day Wednesday, Philadelphia already has experienced eight consecutive days in which the low temperature failed to get below 70.

Heat index values of 100 to 105 are expected Wednesday.They might even be a shad higher Thursday.Thursday morning temperature readings aren’t expected to drop below the upper 70s, challenging the record-high minimum for the date, 81.

Both the National Oceanic and Atmospheric Administration and the Centers for Disease Control and Prevention have praised Philadelphia’s heat-response plan when heat emergencies are declared. It includes setting up cooling centers and activating a hotline run by the Philadelphia Corporation for Aging.

It is uncertain whether the plan will be in effect on Thursday, but PCA will be operating its Heatline starting at 8:30 a.m. Thursday, said Heatline director Nolan Lawrence.

The city is advising people to drink plenty of water, keep the air conditioners running at night, or use fans with the windows open. A cool bath or shower can’t hurt, nor can spending time in air-conditioning during the day.

The heat evidently isn’t going anywhere for a while. As to what finally will end the hot spell, said AccuWeather’s Walker: “I’m not seeing anything.”