The National Weather Service in Sterling, Va., confirmed that at least three tornadoes touched down Tuesday in St. Mary’s and Calvert counties amid an outbreak of severe weather that targeted the Mid-Atlantic associated with Tropical Storm Isaias.

One of the tornadoes was on the ground for more than seven miles according to the National Weather Service, which is investigating the tornadoes. Final ratings and wind estimates will be made available later Wednesday or on Thursday.

Two of the tornadoes occurred in St. Mary’s County. The first, in the southern part of the county near Point Lookout, was given a preliminary rating of EF0 on the 0 to 5 Enhanced Fujita scale. It touched down about 6:28 a.m. shortly after sunrise. Winds were estimated at up to 80 mph inside a narrow funnel, which was on the ground for just under a mile.

The other St. Mary’s County twister, preliminarily rated an EF1, caused damage near Piney Point, which is about 15 miles south of Leonardtown. It was on the ground for about seven miles between 6:30 and 6:43 a.m. Winds were estimated at 100 mph.

A third tornado occurred as a waterspout made landfall in Calvert County just to the east of Huntington. It was on the ground for 2.2 miles between 7:33 and 7:37 a.m. The twister was given a preliminary rating of EF1 with peak winds of 90 mph.

That tornado moved ashore and caused tree damage in the Willow Beach Colony neighborhood just north of the Breezy Point Campground, tracking 2.2 miles before dissipating.

Part of a larger tornado outbreak

The tornadoes were part of an outbreak of dozens that swarmed the Mid-Atlantic and Delmarva Peninsula as Tropical Storm Isaias rode up the East Coast.

The National Weather Service issued more than 100 tornado warnings Monday night into Tuesday as Isaias unleashed destructive, and at times deadly, twisters that left paths of damage from North Carolina to New Jersey.

The siege began when multiple tornadoes touched down Monday night west of Wilmington, N.C., causing damage near the town of Bolivia. Two tornadoes were on the ground simultaneously. Doppler radar was able to detect debris lofted by the twin funnels. Another tornado struck northwest of Wilmington in the town of Leland.

A continuous barrage of rotating supercell thunderstorms continued to feed into Isaias during its entire journey up the Mid-Atlantic.

Two people were killed when a tornado ripped through a mobile home community in Windsor in northeast North Carolina about 2:30 a.m. Tuesday. At least 10 homes were destroyed.

Then, about 3 a.m. Tuesday, a significant tornado moved across the North Carolina border into Virginia, hitting Suffolk County, where it produced EF1 damage. This was part of the same storm complex that tracked through Windsor earlier.

Around the same time, another tornado, rated EF2, was in progress near Courtland in Southern Virginia.

The Weather Service office in Wakefield also confirmed an EF2 tornado that tracked through Southampton County, Va., about that time.

A fourth tornado in Southeast Virginia, rated EF1, then swept through James City County at 4:13 a.m.

Later Tuesday morning, tornadoes ravaged areas farther north. The National Weather Service office in Mount Holly, N.J., confirmed six tornadoes: two on the Delmarva Peninsula, two in southern New Jersey, and two in southeast Pennsylvania.

How do tropical cyclones produce tornadoes?

It’s not unusual for a tropical cyclone to produce tornadoes. The change of wind speed and direction with height resulting from a cyclone’s inflow and outflow can cause individual thunderstorms and downpours in the feeder bands to rotate.

In tropical cyclones, winds near the surface spiral counterclockwise into the storm and exit clockwise aloft. That shear is occasionally enough to spin up tornadoes by the dozen.

An outbreak of 118 tornadoes from Florida to Pennsylvania, heavily concentrated in Virginia, occurred with remnants of Hurricane Ivan in 2004.