A tornado watch is in effect from Delaware to Philadelphia to New York City to upstate New York as the Northeast braces for several rounds of severe thunderstorms Tuesday afternoon and evening.
In New Jersey, multiple tornado warnings were issued on Tuesday afternoon.
At least two tornadoes have been reported so far, one in northeast Pennsylvania, and the second in northwestern New Jersey.
Besides tornadoes, the storms are forecast to bring damaging wind gusts up to 70 mph, large hail and rainfall rates above 1 inch per hour.
Flash flooding poses a major threat to a large swath of the Interstate 95 corridor, from Philadelphia to New York City to Connecticut.
Further west and south, severe thunderstorm watches are in effect from Kentucky to Pennsylvania, including the cities of Charleston, West Virginia, Cincinnati, Ohio, and Pittsburgh, Pennsylvania. Flooding is also expected in Tennessee.
More than 1,700 flights have been canceled Tuesday ahead of the storms, with airports in New York City, Philadelphia and Washington, D.C., seeing the biggest impacts. Ground stops were issued at airports in New York City, D.C., Boston, and Baltimore.
New York City Mayor Zohran Mamdani is urging New Yorkers to "exercise caution" on Tuesday.
"Go inside if there’s thunder, heavy rain, or strong winds," he said on social media. "If you live in a basement apartment, know your exits and be ready to move to a higher floor if heavy rain begins."
Tuesday's anticipated flooding comes just days after New York City was inundated with pounding rain that flooded streets on Saturday.
Iowa flooding
Meanwhile, severe weather also brought dangerous flooding to Des Moines, Iowa, on Monday night.
Nearly two dozen cars were stranded on roads and five people were rescued, according to the Des Moines Police Department.
"We simply ask everyone to slow down, pay attention to changing conditions and make safety the priority," said Des Moines Police Chief Michael McTaggart.
ABC News' Melissa Griffin contributed to this report.