Tornadoes touched down in Delaware and on New York’s Long Island on Thursday, August 20, as a potent severe-weather system brought rotating thunderstorms, torrential rain and widespread flash flooding to the northeastern United States.
One of the most serious storms struck Dover, Delaware. During the event, the National Weather Service described a confirmed tornado over Dover as large and extremely dangerous, prompting an unusually urgent Particularly Dangerous Situation tornado warning. Damage was reported while the storm was still underway.
@MaxVelocityWX Someone in front of the Motel in Dover Delaware had a dash cam as the tornado hit. pic.twitter.com/k6yp3IhaQL
— Tyler (@LunarHarv3st) August 21, 2026
By Friday, NWS meteorologists were conducting a formal damage survey around Dover. Preliminary reports documented damaged buildings, including a motel that lost its roof, along with fallen trees and other structural damage. Dover’s state of emergency was lifted Friday morning as cleanup continued.
Waterspout Becomes Tornado on Long Island
Several hours later, another dramatic storm developed along the southern coast of Long Island.
A waterspout over the Atlantic moved ashore at Atlantic Beach, becoming a tornado as it crossed the coastline. The National Weather Service confirmed the tornado Friday after reviewing radar, video and damage information.
The tornado tore through the Sun and Surf Beach Club, damaging or destroying dozens of cabanas and throwing debris across the property. One person suffered minor injuries.
DELAWARE TORNADO: Drivers in Delaware had an ominous scene as #tornado warned stormed swept through the Northeast on Thursday.
— WeatherNation (@WeatherNation) August 21, 2026
What would your reaction be if you saw this on the road? pic.twitter.com/uqpDWca5DC
The same storm system also produced widespread torrential rainfall. Flooded roads stranded motorists across parts of New York and New Jersey, while sections of major transport routes, including the Long Island Expressway in Queens, were inundated. Emergency crews in Jersey City rescued dozens of people from flooded vehicles.
What Fueled the Tornadoes?
The outbreak developed as a strong cold front and associated surface low encountered an exceptionally warm and moisture-rich air mass along the East Coast.
Warm, humid air near the surface provided substantial instability, while winds changing in speed and direction with height created the vertical wind shear necessary for thunderstorms to organize and rotate.
An approaching disturbance higher in the atmosphere supplied additional lift, helping thunderstorms intensify as they moved through the Northeast.
At the same time, the atmosphere contained abundant moisture. That allowed storms to produce intense rainfall alongside the tornado and damaging-wind threat, creating a dangerous combination of severe convection and flash flooding.
The Atlantic Beach tornado also demonstrates how coastal severe weather can evolve rapidly. A rotating column beneath a thunderstorm can develop over water as a waterspout and retain its circulation after crossing the shoreline, at which point it is classified as a tornado.
By Friday, the severe-weather system had moved away, leaving damage surveys, debris removal and infrastructure repairs underway across the affected areas
