Record heat brewed in soup-thick humidity is making this one of the most-uncomfortable days in Philadelphia history.

At 5 p.m., the mercury hovered at 104, breaking a record for the date that had held since 1957. The heat index was a steamy 114.

In fact, Philadelphia evidently set a record even before the sun came up. The lowest reading overnight, unofficially, was 82 at the airport, symptomatic of the mass amounts of water vapor in the air; humidity inhibits cooling.

If you haven't been outside lately, be prepared to walk into adjective-breaking, breath-sucking heat and humidity. In short, you're going to break a sweat just by existing.

The National Weather Service has issued an excessive heat warning through 8 p.m. tomorrow, and the warning zone extends all the way from the Poconos to the Shore.

Intense heat could return late next week, said Greg Heavener, meteorologist at the National Weather Service office in Mount Holly.

But first heat, first.

Given the lack of cooling overnight - that 82 would become the second-warmest "low" - this has a chance to be one of the warmest 24-hour periods in the era of Philadelphia recordkeeping, dating to 1874. No. 1 was the 84 of July 24, 2010.

This also could become the seventh-hottest 24-hour period. The all-time champ, Aug. 7, 1918, with an average temperature of 94 from midnight to midnight, appears safe in the steamy clubhouse.

"We're already starting off five or six degrees higher than yesterday," Kines said. Yesterday, it reached 98 at 3:53 p.m.

"Anytime you get near record highs three days in a row, it's pretty significant," he said. "It's certainly bad that we're getting near 100, but the humidity is the real killer."

Kines said the Philadelphia region is reaching humidity levels akin to the Gulf Coast of Florida.

"To get such high dew points up here is rather unusual," he noted.

The NWS is warning that the combination of extreme high temperatures and high humidity pose a body-threatening situation.

Worse, night will bring no relief. It's not expected to drop below the low 80s again tonight, and the high humidity will remain, causing a sweltering, sticky sleep for those without air-conditioning.

Saturday won't be much better. It will remain hot and humid with a heat index of about 110.

Relief - if you can call it that - could come Sunday with possible thunderstorms and highs in the low 90s.

Monday looks better with highs in the upper 80s.

But it will be back into the 90s by the end of the week, and perhaps the upper 90s, said Heavener.

The Philadelphia Corporation for Aging in the meantime has activated its Heatline - 215-765-9040 - for anyone seeking information on coping with the heat. The information line will operate from 8:30 a.m. until midnight Friday, and 8:30 a.m. until 8 p.m. Saturday.