Thunderstorms capable of producing flooding rain, damaging wind and frequent lightning strikes into Tuesday night will target a zone in the Northeast and South, home to more than 70 million people.
Drenching, gusty and locally severe storms will reach from Maine to Florida.
Some of the metro areas in the Northeast, from Washington, D.C., to New York City and Boston, will be hit by drenching or gusty storms for the second evening in a row.
The storms will affect heavily populated areas of the south including around Charleston, South Carolina; Charlotte and Raleigh, North Carolina; Jacksonville, Florida; Richmond, Virginia, and Savannah, Georgia.
The storms have the potential to cause major disruptions to outdoor activities and travel.
As the storms roll through the major metro area airports, the risk of wind shear can be significant enough to aircraft to result in a ground stop. The most likely time for airline delays will be during the afternoon and evening hours as storms reach peak intensity.
Delays at Newark Airport, New Jersey, mounted to four hours Monday evening as storms rolled through. Weather-related delays extended from Washington Dulles and Reagan National airports to Baltimore, Philadelphia, Newark and New York's LaGuardia and JFK airports on Tuesday.
Wind gusts with a few individual storms can be strong enough to knock down trees, damage roofs and cause power outages.
Enough rain could fall to cause flooding of basements and small streams on a regional basis.
The storms will bring wind-swept downpours that will pose hazards for those traveling on the roads. At the height of the storms, water can flow across flood-prone stretches of roadways and settle in poor drainage areas. Visibility can suddenly drop to unsafe levels for driving at highway speeds.
As the storms develop and rapidly approach locations, they can produce lightning strikes with little notice. If you can hear thunder, you are at risk for being struck by lightning. Seek shelter immediately as storms approach.
A small number of the storms can also bring damaging hail to a few communities, while a small fraction of the strongest storms can also produce a short-lived tornado.
During Wednesday, the risk of locally drenching and strong thunderstorms will continue at the beaches from New England to the mid-Atlantic and South. Heavy storms are also forecast for much of the Florida Peninsula.
As the storms continue along the Atlantic Seaboard and over parts of the South into the middle of the week, a push of unseasonably cool and less humid air will expand over the Midwest and into the Appalachians.
A modified version of this air will spill into the South and along the Atlantic Seaboard during the middle to latter part of the week.
Autumn officially starts at 10:29 p.m. EDT on Monday, but it will not feel like autumn in some parts of the U.S.
After storms clipped Chicagoland early Sunday, drier air will filter into the area for the rest of the week.
A brief warmup is in store for residents of the Northeast this weekend before more fall-like conditions return.
The weekend will conclude with a couple of showers throughout the area on Sunday, but more favorable conditions will mark the start of the workweek in Detroit.
In keeping with tradition, temperatures will continue their up-and-down cycle during the second half of September around New York City.
Drier and more tranquil weather will move into the Atlanta area for the upcoming week.