Hurricane Sandy spared Philadelphia from the worst of its devastating fury.
But in the aftermath of the epic storm that inflicted some $20 billion in damage along the Eastern seaboard, the region’s leading government meteorologist warns that the Delaware Valley is far from immune to the type of destruction seen in coastal cities and towns.
“The strongest winds and strongest push of waters onto the shore were from the Jersey shore to New York. But if the track of the storm had been farther south, all of those impacts would’ve shifted south with it,” said Gary Szatkowski, the meteorologist-in-charge for the National Weather Service’s Mount Holly, N.J., office. “Everything you’re seeing in New York City, you would’ve seen [here]. It would’ve been disastrous for Philadelphia.”
Not even a 60-mile buffer zone between Philly and the Atlantic Ocean might’ve shielded the city from mass flooding to go along with hurricane-strength winds and even more-widespread power outages than experienced throughout the region.
Officially, Sandy made landfall at about 8 p.m. on Oct. 29 about five miles southwest of Atlantic City. That would place the eye of the storm at Margate. By that time, however, it was no longer a hurricane.
One hour earlier, with the storm still at sea, the NWS reclassified it as a post-tropical cyclone, a Nor’easter. The transition did not diminish its wallop.
“This was a major storm and it transitioned from being a hurricane to a very major Nor’easter,” Szatkowski said. “That happens [to other storms], but it doesn’t typically happen just as it’s coming to shore. In terms of intensity, it was one for the record books.”
Both varieties have similar anatomy. They feature a central eye, which is a calm, clear low pressure area usually about 20 to 40 miles in diameter; an eye wall composed of dense clouds with the highest wind speeds in the storm; and outer, spiraling bands that can fan hundreds of miles from the center.
While hurricanes and other tropical cyclones are “warm-core” systems, thriving on warm air, Nor’easters are “cold-core” thriving on cold air.
In Sandy’s case, the transition occurred as it circled and ultimately merged with a low-pressure cold air mass that had moved over the Eastern U.S. in concert with a trough in the jet stream.
“Technically, [Sandy] was a Nor’easter when it arrived,” Szatkowski said. “Nor’easters normally parallel the coast and go out to sea.”
However, in Sandy’s case, the swirling interaction between low-pressure systems — known as the Fujiwhara Effect — influenced the storm to make a sharp turn toward the northwest just before making landfall.
“That’s what steered the storm,” Szatkowski said. “That’s what led to the rather unusual track.”
The storm’s track or path, along with its winds, were the key factors in its disastrous outcome.
“The main impact you’ve been seeing on the news was from the storm surge, the higher-than-normal water level that Sandy brought to shore,” Szatkowski said. “That has to do with the strength of winds, the direction of winds and the track of the storm.”
In the Northern Hemisphere, Nor’easters circulate counter-clockwise, so the strongest winds and tidal surges are felt in the northwest quadrant of the storm. The winds blow from the northeast.
So, Szatkowski explained, had the eye of the storm made landfall along the Delaware coast instead of South Jersey, the storm surge that struck New York Harbor instead would’ve traveled into the Delaware Bay and ultimately up the Delaware River, which is tidal as far as Trenton, N.J.
Tributary waterways such as the Schuylkill River, Cobbs Creek, Frankford Creek, Pennypack Creek and Poquessing Creek would’ve overflowed their banks.
Instead, the Delaware encountered what is considered minor flooding along Columbus Boulevard, as did Cobbs Creek in Southwest Philadelphia, according to Joanne Dahme, a spokeswoman for the Philadelphia Water Department.
The Pennypack crested at 6.5 feet near Rhawn Street, about 6 inches below minor flood stage. The Frankford crested at 5.5 feet, about 18 inches short of minor flood stage. The Poquessing crested at 6.5 feet near Grant Avenue and did not flood.
Dahme, the PWD’s general manager for public affairs, attributed the lack of flooding to the relatively low volume of rain during the storm — it was measured at about 3 inches at Philadelphia International Airport — as well as the rain’s lack of intensity.
Also, the water department “proactively cleaned [storm water] inlets days before the storm in preparation,” Dahme said.
PWD crews and citizen volunteers visited 2,954 storm inlets, cleared 2,616 inlets and removed 155 tons of debris from them.
In the absence of flooding, power outages and the resulting traffic snarls were the most widespread local problem. Sixty-five thousand PECO customers lost power in Philadelphia. More than a day after the storm, some 37,000 Philadelphia homes and businesses remained without power. As of Tuesday, the utility company reported only “scattered” outages in the city.
Even within that context, however, Northeast Philly and the city made out well. In the five-county Philadelphia region 850,000 lost power in the storm. About 2,000 remained powerless on Tuesday, a week after the storm, including about 1,000 in Bucks County and another 500 in Montgomery County. ••
Reporter William Kenny can be reached at 215-354-3031 or firstname.lastname@example.org