With a forecast of temperatures flirting with 100 and heat index values up to 110, the fourth day of the heat wave dawned ominously on Monday, with Philadelphia tying a record for highest minimum temperature — 81 — for the date.
“When we came in and saw that,” said Jonathan O’Brien, a Monday day shift meteorologist at the National Weather Service office in Mount Holly, forecasters concluded that “it looks like it’s going to be as expected.”
But in this case, the atmosphere had a mildly pleasant surprise in store. After climbing to 92 degrees by 11 a.m., the temperature surprisingly backed off to 90 at Philadelphia International Airport an hour later, and west winds gusted to 21 mph. More significantly, the noon heat index was 93; the forecast for noon had been 105.
It warmed up to 96, and the heat index made it to 102 at 6 p.m., unmistakably hot, but three degrees below the heat-warning criterion, and well past the peak of the sun.
“The heat isn’t quite as extreme,” said Paul Walker, senior meteorologist at AccuWeather Inc. And looking ahead to the rest of the week, he said, the heat wave isn’t looking as ferocious as it had been.
But heat indexes could top 100 again on Wednesday, the weather service said, and might meet the “heat advisory” level.
The City of Philadelphia will continue its heat emergency through 11:59 p.m. Tuesday, and the Philadelphia Corporation for Aging will operate its heat “helpline” (215-765-9040) again Tuesday. It’s possible that the emergency will extend into Wednesday.
However, O’Brien said the week might pass without another weather service heat warning.
Early in the day, it appeared that hitting the warning criterion on Monday was all but a certainty. But around lunchtime, forecasters said, in response to an approaching frontal feature, some drier air mixed down from the upper atmosphere. That plus some mid-level cloudiness held the temperatures and the heat index to more bearable levels.
For those seeking asylum at the Shore, with a land breeze, the air was quite steamy, and the heat index made it to 104 at Atlantic City International Airport. Then again, folks in the beach towns did have access to the Atlantic Ocean.
Behind the front, Tuesday will be hot, with highs in the mid-90s, but heat index values are forecast to stay below 100. Wednesday, the discomfort level is due to increase, but showers are possible, and they might be more likely on Thursday, said Walker.
Temperatures might not make it to 90 on Friday and Saturday — not that the upper 80s would be polar vortex territory — and readings aren’t forecast to drop below 70 overnight for the rest of the week.
The lack of nighttime cooling allows dwellings without air-conditioning to heat up dangerously when the sun comes up, a particular hazard for the elderly who live alone.
In Philadelphia, Health Commissioner Thomas Farley advised relatives and neighbors to check on seniors by telephone or video, or to knock on doors — but while practicing the coronavirus protocols of wearing masks and keeping social distance.
In the meantime, O’Brien said he and colleagues like what they have seen so far and are rooting against their own forecasts.
“Hopefully, these trends continue,” he said. “It wouldn’t be the best for our forecasts, but it’s better for the public.”
The coronavirus has presented unique challenges for operating cooling centers, but Philadelphia will have several operating.
Those using them are asked to wear masks and maintain social distancing.
In addition, all the city’s “spraygrounds” will be open.
Here is a complete map of the city’s cooling options.
Staff writer Valerie Russ contributed to this article.