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Tropical-storm watch issued for Jersey Shore and Delaware; flood watch for Philly and elsewhere

Elsa is forecast to approach the Jersey coast late Thursday. It could wring out heavy rains, but it also could have an opposite effect in Philly.

An Ocean City alley way is flooded due to Tropical Storm Fay on July 10, 2020.
An Ocean City alley way is flooded due to Tropical Storm Fay on July 10, 2020.Read moreTYGER WILLIAMS / Staff Photographer

The National Hurricane Center has issued a tropical-storm watch for the entire New Jersey and Delaware coasts with Elsa expected to track close to the beach towns early Friday.

Tropical-storm force winds — 39 mph or better — are possible at the Shore, the National Weather Service Office in Mount Holly advised, with rains of one to three inches Thursday night into Friday.

And with the atmosphere doing some serious prep work, heavy rains and flooding also are in play throughout the Philadelphia region, the National Weather Service says.

A classic July air mass has brewed what feels like a water-vapor consommé, and the weather service’s heat advisory remains in effect through 8 p.m. Wednesday for triple-figure heat indexes and highs in the mid-90s.

» READ MORE: Heavy rains cause flooding at Shore and in Philly as Tropical Storm Fay deluges the region

Thunderstorms could pop up again Wednesday, particularly just north of the city, but the main event is expected to arrive Thursday night with the approach of Tropical Storm Elsa or its remnants.

As it spends time over land, Elsa is expected to be downgraded to a “depression,” but regain its tropical-storm status when it re-emerges off the Jersey coast.

The Shore towns likely are in for a period of high winds, heavy rains, and un-swimmable surf.

Coincidentally this would occur quite close to the anniversary of the mayhem stirred up this time last year by Tropical Storm Fay.

In the meantime, the Weather Prediction Center has the entire region painted in the risk zone for “excessive rains.”

At 11 a.m. Wednesday, the National Hurricane Center reported that Elsa was making landfall on the northern Florida coast with peak winds of 65 mph and was moving north at 14 mph.

» READ MORE: Isaias leaves destruction and thousands in Philly region without power

In the region

Strong winds and heavy rains are all but a certainty at the Shore, said Dave Dombek, senior meteorologist with AccuWeather Inc. As for what happens along the I-95 corridor, he said: “That’s to be determined.”

The radius of the strongest winds might be confined to near the center of the storm, he said, and rain might be a tougher call.

Elsa could interact with an approaching front, and in that case, the heavy rains “would just get sprayed everywhere.”

» READ MORE: Feds see yet another active Atlantic hurricane season. The first tropical storm could pop Friday.

Conversely, it is possible that Philadelphia and other areas on the mainland will be situated between the front and Elsa.

In that scenario, Elsa would have a suppressing effect on inland rain totals. Rain develops when warm air rises over cooler air and condenses. But what goes up must come down, and the sinking air on either side of the rising currents would create air-drying “subsidence.”

That effect is probably most evident during snowstorms, when snow bands form over narrow corridors, while areas not that far away are snow-deprived.

In any event, this evidently is going to be an adventurous weather week as the summer heat reaches its annual climatological peak. “We pretty much have something of everything in the next several days,” Dombek said.