More Debby-related downpours, wind gusts to 60 mph and tornadoes are possible Friday, forecasters warn

The core of Debby’s remnants are due to pass well to the west of Philly on Friday, and that could put the region in an especially dicey position, forecasters are warning, with the potential for tornadoes.

Thursday night — when Debby, downgraded to a depression, was still in the Deep South — was quite a prequel.

» READ MORE: Live updates on Tropical Depression Debby in Philly

A tornado was confirmed in New Castle County, where over a half-foot of rain had fallen Thursday as random Debby-related rain bands pulsed northward. Flash flood warnings were in effect for portions of Chester County where up to 5 inches of rain was reported.

Streets were closed and vehicles were stranded in the West Marlborough Township area, the weather service said, and several water rescues were executed in Coatesville.

Debby’s remains were forecast to enter central Pennsylvania sometime Friday before arcing toward New England. While the heaviest rains on Friday are likely to fall well to the north and west, Philadelphia should expect at least 1 to 2 inches of rain, more in areas that end up under downpours.

In addition to the flood warnings Thursday night, the National Weather Service issued a flood watch in effect until 1 a.m. Saturday for northern Delaware, Chester County and northern portions of Bucks and Montgomery Counties.

It has issued advisories for wind gusts potentially up to 60 mph across the region, said Alex Staarmann, meteorologist in the weather service’s Mount Holly office. And with the soil softened by those heavy antecedent rains and two days that would merit the term drizz-mal, the trees would be vulnerable. Thus, power outages would be in play.

Friday could be yet another rough day at Philadelphia International Airport, where FlightAware.com reported 334 arrival and departure delays Thursday. In addition, inbound flights being held at their points of origin an average of 28 minutes, said airport spokesperson Heather Redfern.

Late Thursday afternoon, Debby’s center still was hundreds of miles away, inland of South Carolina, the National Hurricane Center reported, and preparing to make a radical move northward. Its sprinkler system-like rain bands already were spreading across the region.

As Debby’s leftovers approach central Pennsylvania, meteorologists warned that Philadelphia will be on the volatile and dangerous east side of the storm’s core, where the air is especially volatile.

Emergency management officials are well aware of the hazards, said MaryAnn Tierney, FEMA’s Philadelphia regional administrator, who advised people to keep up with weather alerts and check out the preparation advice on ready.gov.

“The east part is always the worst part of the storm because you get not only the effects of the wind but the effects of the forward motion of the storm itself, so it can exacerbate the wind,” she said.

Winds circulate counterclockwise around storm centers, and as the core of Debby’s leftovers speed through central Pennsylvania and arc toward New England, Philadelphia will experience breezes from the south and southeast.

The weather service warned that the atmosphere is primed for a spell of riot. It said that aircraft observations are “verifying that we are solidly in a tropical environment.”

“There’s certainly growing concern for tornadoes tomorrow,” Mike Lee, a meteorologist with the National Weather Service in Mount Holly, said Thursday. “We could see a couple of isolated tornadoes.”

» READ MORE: Tornadoes have been known to happen here with tropical remnants. See Ida

Short-lived Debby-related rain bands have been spiraling toward the region, at one point triggering a flood warning for northern Delaware and parts of Chester County.

But Lee said the early-morning hours of Friday “is when we could see the first round of moderate to heavy rainfall coming through.”

» READ MORE: The Philly region received quite a soaking Tuesday into Wednesday. Here are some rain totals

Those south to southeast winds will be picking up during the afternoon, and Staarmann said that frequent gusts or 35 to 45 mph are expected, and on occasion may reach 60.

The weather service says it expects “favorable conditions” for tornadoes during the day, and again with the approach of a squall line in the late afternoon or early evening.

“You’re working with a lot of juice in the atmosphere,” said Dave Dombek, a senior meteorologist with AccuWeather Inc.

Disruptive weather can spiral around all sides of a tropical storm; however, the areas east of the center are especially prone to unwanted atmospheric drama, said Dombek.

In addition to the forward speed of the north-moving storm adding to the winds from the south, on the east “you get a lot of spin in the atmosphere.”

The air is considerably more unstable — thus more prone to severe thunderstorms that can spawn twisters — than it is to the north and west of the center, where steadier rains are more likely. In fact, the highest amounts are likely to fall in central Pennsylvania and the front range of the Appalachians, said Paul Dorian, a meteorologist with Arcfield Weather, who is based in Valley Forge.

By contrast, said AccuWeather’s Dombek, while rain amounts may be less on the east side, “You’ve got a lot of spin in the atmosphere.”

» READ MORE: Debby-related rains even had some impacts on the presidential campaigns this week

Coming soon is a weekend that would be almost too good to be August, computer models and meteorologists agree.

Along with the changes in the track forecast, Debby’s remnants are due to speed toward Canada faster than previous forecasts suggested, which means they will be vacating the region sooner than expected.

The forecasts call for the sun to rule Saturday and Sunday with comfortable temperatures in the 80s, the air drying out, and the winds backing off. Those conditions are due to persist for the next several days with nothing to fear but the next tropical storm threat itself, whenever that might arise.

And if you’re up for it, the Perseids meteor showers peak in the early-morning hours of Monday.