Wrung out from a profoundly soggy air mass and the remnants of Fred, that was a month’s-plus worth of rain that deluged parts of the region into the early-morning hours of Thursday, overwhelming sewers and creek banks and prompting multiple water rescues. And yet again, a tornadoes were confirmed.
“It’s just another day,” said Jason Franklin, chief meteorologist at the National Weather Service Office in Mount Holly, which was flooded with storm reports bearing outsize rain totals.
The Wissahickon, Pennypack, and Frankford Creeks in Philly all sloshed over their banks Thursday morning, and a flood warning was in effect along Ridley Creek in Media, Delaware County, into the afternoon.
The weather service confirmed that about 12:30 a.m. an EF-1 tornado — winds ranging from 86 to 110 mph — touched down in Franconia Township, near its border with Souderton, in Montgomery County, and migrated to Perkasie, Bucks County. From 18 to 20 homes were damaged, but no one was injured, said Steve Coll, fire marshal for both Franconia and Perkasie, who was on the survey team. Investigators also confirmed a tornado in Berks County and were looking at damage in North Jersey.
What was so unusual about this latest assault was the timing: These type of events are more appropriate to late afternoon and early evening, when storms can better exploit the sun’s energy — more apt to occur around happy hour than closer to last call.
In this case, however, the wild card was Fred, whose juicy leftovers acted like a performance-enhancement substance, conspiring with the moisture-laden air in place.
“In a tropical environment, because it’s so warm and humid, the atmosphere actually doesn’t need the daytime heating that can boost the instability that can cause severe weather,” said Bill Bunting, chief of the Forecast Operations Operations Branch at the government’s Storm Prediction Center.
The storms also had an element of caprice: Not much happened in adjacent South Jersey. In fact, while creeks sloshed over in parts of the city, nothing was reported at the official measuring station at Philadelphia International Airport.
“Normal doesn’t apply when it comes to tropical systems,” Franklin said.
Nothing was normal about the drama in the skies. For several hours, lightning flickered like so many faulty fluorescent bulbs. The bass-drum thunder was incessant.
A tropical system can affect the atmosphere in such a way so as to trap sound waves, Bunting said: “You’re not only hearing the thunder from the storms near you.”
If the thunder didn’t keep people awake — “It was nonstop,” Franklin said — the smartphone alerts were worthy supplements.
“I think there’s a lot of tired people this morning,” he said.
The rains that set off the alarms were prodigious. In Wayne along the Main Line, 3.71 inches was measured — about 3.5 is the monthly average for Philly — and 3.3 inches of that fell in just one hour. Storm totals approaching 4 inches were measured elsewhere in parts of Philly and the adjacent Pennsylvania counties.
Any molecular analysis notwithstanding, it would be impossible to determine whether much of the rain was Fred-related, but Bunting said the interaction of Fred with a frontal system “enlarged” the area of precipitation.
The heaviest rains had been forecast to fall well to the west of the city, said Paul Walker, senior meteorologist with AccuWeather Inc., but the deluges oozed to more-populated and developed areas 50 to 100 miles farther east than expected, and did so ponderously.
The core of the heavy rain was falling in the Harrisburg area around nightfall, and “it took all evening to go a couple of counties,” he said. Then it took several hours for it go away.
The downpours were over by daybreak, but the muggy air mass remains and is likely to stick around until early next week.
Another tropical system, Henri, which was about 500 miles southeast of Cape Hatteras, N.C., on Thursday afternoon, is forecast to grow into a hurricane Friday night and take a track almost due north. It is expected to parallel the New Jersey coast during the weekend but stay well offshore, although the forecast has been trending subtly westward, Walker said.
It likely will stir up dangerous rip currents and might cause some minor flooding at the Shore, Franklin said.
“If that’s all we have to deal with, we’ll be in good shape,” he said.
At least, relatively speaking.