Heat: Shockingly comfortable

The late-afternoon temperature at Philadelphia International Airport was hovering around 96, which was expected.

But the heat index was hovering 92, an unexpected shot of relative comfort. That's right, the heat index value was lower than the actual air temperature.

"That doesn't happen very often around here," said Jim Hayes, a meteorologist at the National Weather Service office in Mount Holly.

During the afternoon, dry air from aloft mixed down into the lower atmosphere, and by 3 p.m. the relative humidity was down to 18 percent.

That also happened to be the humidity reading in Phoenix, Ariz., at mid-afternoon.

At the Shore, it was several degrees cooler with a light onshore wind. Tomorrow, however, nature will turn up the jets at the beach and everywhere else.

The excessive heat warning covers the entire region, including the Shore, which will be getting face-fulls of land breezes tomorrow.

The official forecast high for Philly is for a near-record 102. It won't get quite that warm along the beach, but heat index values could reach 103, the weather service says.

Sunday, a cool-down begins, and the weather service has upped the thunderstorm chances to 50 percent. Still, expect an 11th straight day of temperatures in the 90s.

A reminder: The Philadelphia Corporation for the Aging heatline will be operating from 8:30 a.m. until midnight Saturday. The number is 215-765-9040.

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