UPDATED, Thursday 6 p.m.: Personnel from the National Weather Service office in Wakefield, Virginia conducted a damage survey at Flipper’s Arcade in Grandy earlier today, and determined that it was a gustnado that hit the building Wednesday morning.
The event was spawned as an unusual weather pattern for mid-summer along the Outer Banks and eastern North Carolina that caused flash flooding in a number of locations this week.
Low pressure systems repeatedly moving along a stalled frontal boundary over eastern North Carolina, allowed tropical moisture to flow across the area that’s produced showers and thunderstorms with heavy rainfall.
In a statement issued Thursday afternoon, the weather service said as a band of moderate to heavy rain with embedded thunderstorms was moving through the region, the tail end of the system moved through Grandy.
Security video courtesy Wiseguys Pies shows the phenomena forming at 7:21 a.m. just behind the building on the other side of U.S. 158, hitting the southeast corner of the arcade, throwing debris in the air and also causing powerlines overhead to spark.
Photos from the arcade show part of the roof was damaged and a front window was blown out. No injuries were reported.
Based upon the video, it would seem likely that the damage was caused by a tornado. However, the swirl of wind is actually moving in the opposite direction of the band of the thunderstorm cell. So as result, this is not a tornado.
The radar shows about five minutes before the damage, an enhanced area of east-to-southeast winds along Currituck Sound near Grandy at around 45 mph at 7000 ft.
Meanwhile at the surface the winds, from local observations were from the north-northeast at 15 to 20 mph.
It is likely that a combination of easterly winds aloft mixing to the surface, the frictional interaction between and the sound and land, and the prevailing north-northeast flow was responsible for generating the low level swirl that is termed a gustnado.
Based upon the damage to the arcade, the winds likely gusted to between 60 and 70 mph before quickly dissipating.
So then what was the swirl of wind that caused the damage?
A gustnado is a relatively small whirlwind which forms as an eddy in thunderstorm outflows. They do not connect with any cloud-base
Rotation and are not tornadoes.
Since their origin is associated with cumuliform clouds, gustnadoes are classified as thunderstorm wind events.
Gustnadoes form due to non-tornadic straight-line wind features in the downdraft (outflow), specifically within the gust front of strong thunderstorms. Gustnadoes tend to be noticed when the vortices loft sufficient debris or form condensation clouds to be visible, although it is the wind that makes the gustnado, similarly to tornadoes.
Gustnadoes do not have anything in common with tornadoes structurally or dynamically in regard to vertical redevelopment, intensity, longevity, or formative process, as tornadoes are associated with mesocyclones within the inflow (updraft) of the storm, and not the outflow.
It is important to note that although not classified as a tornado, gustnadoes can produce damage consistent with that of an EF-0 or low end EF-1 tornado or roughly in the 70 to 90 mph range.
Heavy rainfall floods roads, impacts businesses
Rainfall amounts topped six inches in many locations in Currituck and Dare counties, with flash flood warnings issued for lower Hatteras Island, Ocracoke and all of Currituck County earlier this morning.
That’s on top of all the rain many locations have received since strong to severe thunderstorms hit on Sunday.
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The National Park Service reported at 10 a.m. there was significant ponding of water on some flat/poorly drained beach front areas near South Point on Ocracoke and that 75 percent of the Ocracoke Campground and the entire Cape Point Campground were under water.
Parts of N.C. 12 were flooded in the typical spots along the Pea Island section, especially the Canal Zone. Flooding along the roads and roadside ditches in all the Hatteras Island villages and in some locations between the villages.
An areal flood advisory for Hatteras and Ocracoke islands was issued as rain continued to fall this afternoon.
With a strong onshore flow, a high risk of rip currents is posted for all beaches. So, everyone stay out of the ocean today.
A flash flood watch remains in effect for Hatteras and Ocracoke islands.
The chances of heavy rainfall are forecast to decrease on Thursday, but showers and thunderstorms will remain with us until at least the weekend.
National Weather Service forecast for Nags Head, as of Wednesday 12:30 p.m.: