BETHLEHEM, Pa. — The Lehigh Valley will begin to see impacts from Tropical Cyclone Debby on Tuesday, forecasters warn, calling expected rainfall a '"predecessor" event as the storm begins to crawl up the coast.
As of 3:12 p.m. EST, The National Weather Service issued a flood watch for Lehigh and Northampton counties. It will expire Wednesday morning.
The Weather Prediction Center has raised a slight (2 out of 4) to moderate risk (3 out of 4) for excessive rainfall from around the Lehigh Valley area through parts of southeast Pennsylvania, central and southern New Jersey and extreme northeast Maryland.
The setup
According to the latest outlooks, a cold front and trough draped over the region will become the focus for scattered showers and thunderstorms Tuesday afternoon.
The Storm Prediction Center has most of the region in a slight risk for severe weather, where the main threat will be strong downbursts and damaging wind gusts.
Going into Tuesday night, forecasters say the trough will interact with tropical moisture associated with Debby over the Southeast, and heavy downpours are likely.
They will be “slow moving heavy rain producers, and you’re going to have training of storms,” EPAWA meteorologist Bobby Martrich said in his latest video.
“That means you’re going to have one area get hit and it might be dry for an hour or so, then you’ll have another one come in and another one," Martrich said.
"You just keep going over the same areas."
That’s going to lead to flash-flooding concerns, with total rainfall amounts of 1 to 2 inches across the region, with locally higher amounts possible.
“While there is some spread in the guidance in where the front will stall, the training storms will be capable of dumping 2 to 4 inches, locally 5+ inches, which would quickly surpass local flash flood guidance and lead to scattered to possibly widespread instances of flooding,” the WPC said.
As of Monday morning, a flood watch in effect from Tuesday afternoon through Wednesday morning covered parts of Bucks, Chester, Delaware, Montgomery and Philadelphia counties.
The Lehigh Valley was not yet included in the watch, but Martrich said heavy rain certainly will target this area.
“It’s not good news for Musikfest, I’ll tell you that,” he said.
(1/6) Conditions become much more active this week. Here is a thread on what we can expect.
— NWS Mount Holly (@NWS_MountHolly) August 5, 2024
The latest briefing package covering all of these impacts can be found here:#NJwx #PAwx #MDwx #DEwx https://t.co/JiD09ByGTv
Debby’s impact as the week unfolds
As of early Monday, Debby was a hurricane making landfall along the Gulf Coast of Florida. It is expected to bring potentially historic rainfall across southeast Georgia and the coastal plain of South Carolina, the National Hurricane Center said.
What’s unclear is how much rain we could see in the region as a result of the storm.
“This will affect us, if not directly, then at least it will be indirectly,” Martrich said.
The National Weather Service said confidence in the forecast is lower than average for the long term, "mainly due to uncertainty with the evolution and track of Debby.”
The Lehigh Valley should see an impact from bands of showers and storms that will spin off Debby and lift toward the region, with rain likely beginning Wednesday that should stay in our forecast for the rest of the week.
“There are suggestions that Debby will emerge over the Mid-Atlantic by this weekend," the latest forecast discussion said.
"A better indication on specific impacts and the evolution of Debby is likely to occur over the next several days once more information becomes available.”
After very warm temperatures to kick off the week, the rest of the period is expected to see highs in the 70s and potentially some dry weather returning to the area by Sunday.
