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With 4 to 6 inches expected north and west of the city and 2 to 4 to the south and east — no, this is not a February snow forecast — heavy rains from Ida’s remnants expected Wednesday into Thursday are all but certain to set off widespread flooding, forecasters say.
In addition, the National Weather Service has issued a tornado watch for the entire region, all of Delaware, and most of New Jersey, in effect until 10 p.m. Wednesday.
The most-significant flooding in 10 years is possible along the Delaware River, which is forecast to crest near the moderate stage Friday morning.
“This could be a long couple of days,” said Nicholas Carr, a lead forecaster at the National Weather Service Office in Mount Holly. “I don’t see a way we escape.”
Heavy rain started moving through the area early Wednesday, dropping between 1 and 2 inches by 7 a.m. and placing Philadelphia, Delaware County, and Chester Counties under flash flood warning for a period.
All of eastern Pennsylvania, New Jersey, and Delaware are under a flash-flood watch until 11 a.m. Thursday. Areas in extreme South Jersey, near the Shore, and Delaware might be spared the heaviest rains, but that could come at a price, Carr said.
The government’s Storm Prediction Center has placed South Jersey, Delaware, and Philadelphia all in the “enhanced risk” area for severe weather Wednesday.
Tropical storm leftovers are notorious for spinning up tornadoes, as was the case in August 2020 with Isaias.
“We’ve been using Isaias as an analog,” Carr said. In fact, the Isaias-related rain totals were quite similar to what is forecast to unfold Wednesday and Thursday.
The likeliest period for the heaviest rains would be between about 5 p.m. Wednesday and 7 a.m. Thursday, said Dave Dombek, senior meteorologist with AccuWeather Inc. “It’s getting out of here quickly,” he said.
The Schuylkill, however, is not forecast to crest at Norristown until very late Thursday night, and the Delaware at Trenton not until sometime Friday.
The remnants will be importing copious amounts of tropical moisture. “You got a lot of juice involved,” said Dombek, and to help wring it out, the remnants will be interacting with a stalled front and powerful upper-level winds.
The rains are likely to overwhelm some waterways, and several streams were forecast to reach at least the pre-flood action phase.
Moderate flooding was expected along the Schuylkill in Montgomery County, with the Norristown gauge projected to reach 17.4 feet; flood stage is 13.
Local officials in Pennsylvania and New Jersey said they were making their preparations.
“This isn’t our first rodeo,” said Jason Bobst, manager and emergency-management director in historically flood-prone West Norriton Township, on the banks of the Schuylkill. The local fire company was getting its three boats and marine-rescue craft ready.
The residents of the township’s large apartment complexes were a concern, said Bobst, since many of them might not have experienced a serious flood.
In Yardley, Bucks County, along the Delaware River, which hasn’t experienced widespread significant flooding in 10 years, “it’s safe to say we’ll be closing River Road for a period of time,” said borough emergency director Wes Foraker.
However, that would involve only two sections of road, and he said he wasn’t expecting major issues from the river, just from the three streams that run through town.
“We’re going to have trouble with the streams, but we know that,” he said, “and that doesn’t cause permanent damage.”
» READ MORE: What to do after a flood in the Philly area
While the rainfall outlook for the Jersey Shore isn’t particularly scary, Marty Pagliughi, director of
Cape May County’s Office of Emergency Management, said that county officials are paying attention and that the rains would be worrisome if they came during the high tides at 4:30 p.m. Wednesday and 5 a.m. Thursday. That could lead to road closings.
”If we get heavy rain during a high tide, there’s no place for the water to go,” Pagliughi said.
Ocean City Mayor Jay Gillian cautioned people to stay off flooded streets, adding that “far too many people were on the road” during last weekend’s flooding. Aside from personal risks, “the wakes created by vehicles plowing that quickly through flood waters can swamp other vehicles and nearby properties and cause substantial damage,” Gillian said in a statement.
Forecasters advised that the core of the heavy rains could shift north or south in the next 24 hours, and Dombek said the very heaviest rain will be occurring in a fairly narrow corridor.
Forecasters added that a major concern is the amount of saturated ground north of Philadelphia in areas soaked by the remnants of Henri. Downpours up that way could have downstream effects on the Delaware.
The one thing that appeared certain Tuesday was that the calls of 4 to 6 inches north and west of the city and 2 to 4 south were unlikely to change much.
“Some people wish it was a snow forecast from February,” said Carr. For the record, 6 inches of rain would translate to about 5 feet of snow.