Locally heavy storms will threaten outdoor plans, slow travel and may cause damage in portions of the northeastern US into Saturday evening.
"Some of the storms will be nasty with gusty winds and heavy rain," according to AccuWeather Chief Meteorologist Elliot Abrams.
People spending time outdoors or on the road will need to keep an eye out for rapidly changing weather conditions.
There is the potential for some communities to pick up a quick inch or two of rain in as many hours. This sort of rainfall can lead to street and highway flooding.
Water may also rapidly rise in low-lying areas, especially where the ground is already saturated from recent downpours.
A localized number of the storms can also be strong and gusty. Some tree limbs may break, which may cause sporadic power outages. An isolated tornado cannot be ruled out.
Flight delays will mount as storms approach then diminish after the storms pass and cloud ceilings rise.
Burlington, Vermont; Binghamton and Albany, New York; Philadelphia and Harrisburg, Pennsylvania, and Washington, D.C., are among the cities at greatest risk for the heavy and gusty thunderstorms.
"The thunderstorms threaten to disrupt the start of the MLB baseball games in Philadelphia and Washington, D.C.," AccuWeather Senior Meteorologist Kristina Pydynowski said.
Lightning strikes outside of AccuWeather's headquarters in State College, Pennsylvania, on Saturday, August 12, 2017. (Photo/J.P. Tracey)
While the strongest thunderstorms are expected to erupt west of New York City, thunderstorms will still force residents and visitors to seek shelter during the evening.
As soon as thunder is heard, the risk of being struck by lightning is present.
"Barring a longer than normal game, the stormy weather should hold off until after the last out in the game between the Boston Red Sox and New York Yankees at Yankee Stadium."
The thunderstorms should also tend to weaken prior to reaching the New Jersey beaches and most of southern New England.
"In the Northeast, Sunday looks like the best bet for outdoor plans," Abrams said.
Cooler-than-average weather for the middle of August will settle over much of the region into next week.