Heat: As bad as yesterday

No records will be set today or for the next several days, but even though the temperature is going to be 10 degrees lower than yesterday's, this afternoon will match yesterday afternoon for discomfort.

A high of 93 won't get nearly the attention of 103, but for the heat-vulnerable today actually may be more dangerous.

The invisible enemy, water vapor, is building into the atmosphere over the region, and later today the heat indexes are forecast to approach 100, almost exactly where they were at the peak of yesterday's heat.

When the air is engorged with water vapor, it makes a mockery of sweat. Sweat cools the body as it vanishes; it doesn't help if it doesn't vanish.

Water vapor also inhibits the temperature drop at night, and the succession of very warm nights is a major source of concern. The "low" Tuesday morning at Philadelphia International Airport was 83.

That would have been a record-high minimum for any calendar day if the temperature hadn't dropped to 80 just before midnight. As it was, 80 was a record for a July 7. This morning, it got down to 77.

Overnight heat allows brick rowhomes to turn into brick ovens quickly when the sun comes up. That can be deadly for the elderly live-alone residents who are most vulnerable to the heat.

Health experts agree that the dry heat of the last few days probably held down the death toll. The wind was coming from the west and drying out as it descended the mountains.

As Laurence Kalkstein, the retired University of Delaware climatologist who is an expert in heat mortality pointed out, that explains why it got up to 95 all the way to Burlington, Vt., which is due east of the Adirondacks.

But the water vapor is coming back with a vengeance, and Kalkstein says that today could be even more dangerous than the last two days.

Dr. Donald Schwarz says the cumulative effects of this heat wave, now in its fifth day, may be taking its toll.