A significant storm system moving across the eastern United States is expected to bring torrential rain, flash flooding, and severe thunderstorms to parts of the Northeast and Mid-Atlantic through early Friday morning, while cooler and less humid air from Canada promises relief heading into the weekend, according to AccuWeather meteorologists.
Flash flood risk zones: Over 40 million affected
According to AccuWeather, a “one-two punch” of an approaching cold front and a jet stream disturbance is expected to produce a swath of heavy rain from eastern Pennsylvania, eastern Maryland, far northern Virginia, and northern Delaware, northward through the lower Hudson Valley of New York, including New York City, and into Connecticut, Rhode Island, and parts of Massachusetts.
This region—home to approximately 43 million people—may receive 2 to 4 inches of rain, with localized amounts up to 8 inches, according to the weather agency’s forecast. Rainfall at this intensity could overwhelm storm drains and cause urban flash flooding, disrupt travel on highways like Interstate 95, and lead to subway flooding in major cities like New York.
Rainfall of this magnitude can result in rapid rises on small streams and significant runoff in poorly drained areas, AccuWeather warned.
Severe storms from Pennsylvania to South Carolina
AccuWeather also forecasts severe thunderstorms with damaging wind gusts and localized flooding Thursday across a stretch from southern Pennsylvania and southern New Jersey, down through Delaware, Virginia, North Carolina, and into South Carolina.
Although storms with flash flood potential will be scattered throughout this region, the greatest rainfall concentration is expected across the northern tier of the storm zone, especially into Thursday evening, AccuWeather said.
By Friday, isolated strong storms may reach farther south along the Atlantic coast, including southern Georgia.
Drenching rain expands from Midwest to Northeast
Heavy downpours that began Wednesday night in central Indiana, northern Ohio, northwestern Pennsylvania, western and central upstate New York, and even parts of southern Ontario, are moving eastward through Thursday, continuing to saturate already-soaked ground, according to AccuWeather.
Canadian high pressure brings relief
After the storm exits, high pressure from central Canada will push into the Northeast and Mid-Atlantic, replacing the muggy summer air with cooler, drier conditions by the weekend.
AccuWeather notes that typical highs for this time of year range from the 80s to low 90s, with lows in the 60s to low 70s. This weekend, however, daytime highs will range from the 60s in the mountains to the low 80s in I-95 corridor cities like Philadelphia, Baltimore, Newark, and Washington, D.C.
Nighttime lows will dip into the 40s in mountainous regions of New York, Vermont, and New Hampshire, with 60s expected across most urban areas along I-95. Some mountain locations could even see temperatures fall into the 30s, according to AccuWeather.
Coastal winds and flooding risk
A stiff northeast breeze, driven by the pressure difference between the Canadian high and a storm developing along the Southeast coast, may affect coastal New England and the mid-Atlantic, AccuWeather Senior Meteorologist Dave Dombek warned.
This onshore wind could stir rough surf and rip currents, and push water levels 1–2 feet above normal, leading to minor flooding at high tide in low-lying coastal communities, such as Cape Cod, Atlantic City, and Ocean City, Maryland.