The former cold front has now turned into a warm front and is moving northward. There have been several rounds of heavy showers and thunderstorms thus far today, and another round is developing late this afternoon and will continue into the evening. The highest chances for a thunderstorm will be in the Poconos, Lehigh Valley, and Central New Jersey from this point through early Monday Morning (closer to the forcing mechanism to produce lift)...but a thunderstorm can form just about anywhere with the ample moisture and instability in place with any other mini trigger such as old outflows.
A Bermuda High sets up shop off the coast and develops a hot southwest flow. This will increase the daytime high temperatures further which will likely mean most areas flirt with or exceed 90 degrees on Monday and Tuesday. Humidity leading to high dew points in the upper sixties to lower seventies will put heat indices into the 95 to 100 degrees range. The National Weather Service has issued an excessive heat warning for Monday into Tuesday. On Monday and Tuesday, scattered afternoon and evening showers and thunderstorms will be possible, especially on old outflow boundaries or any other weak impulse that tries to ride on top of the ridging. Tuesday Evening into Wednesday will likely have more widespread activity as a cold front is closer to the region to act as a triggering mechanism. The cold front will be slow to move through and thus the humidity and thunderstorm chances remain for Wednesday. Thunderstorms during this humid and hot time frame will likely provide only momentary relief from the heat.
On Wednesday, Tropical Storm Beryl or the remnants of the system will be turning up the coast. At this moment, the most likely scenario is that the cyclone turns out to sea once it gets to North Carolina. But this is not set in stone and it will be dependent on how fast it turns north-northeast after making landfall around Georgia and Florida later tonight. This could at the very least increase the tropical moisture ahead of the cold front Tuesday and Wednesday perhaps making for a bit more widespread thunderstorm activity and heavier rains than would normally be the case.
Just know that any thunderstorm during the next several days will be slow moving with weak steering in place and with ample moisture, these storms could drop several inches of rain in localized locations leading to dangerous flash flooding. In addition, some thunderstorms will be capable of wet microbursts of damaging wind gusts and large hail.