The unnamed storm dropped 20 inches of rain on Carolina Beach and more than 19 inches near Southport, all in just 12 hours. But projections for the storm only called for up to eight inches — so the storm caught public officials and residents off guard.
That made it a 1000-year storm, although Steve Pfaff with the National Weather Service said the Cape Fear Region has seen at least nine multi-hundred-year rain events since Hurricane Floyd in 1999.
"The extreme events are becoming more frequent compared to what we typically would see over longer periods,” Pfaff said.
This event was particularly difficult to forecast, it started as a non-tropical low-pressure system, and potentially could have become a tropical storm prior to moving onshore.
Instead, Pfaff said the main area of low pressure broadened and directed small areas of low pressure toward the Cape Fear Region. This created a "fire hose" of intense thunderstorms across the area for several hours, according to Pfaff.
As a National Weather Services' rainfall map indicates, that intense storm activity was highly localized, with significant variance between neighboring areas.
For example, the Wilmington International Airport, north of the city, only got four inches of rain. That’s just 18 miles from the apparent center of the storm in Carolina Beach, and it got 16 less inches of rain. Likewise in Brunswick County, Bolivia saw much more rain than Leland or Shallotte, each about 15 miles away.
Warm ocean temperatures added fuel to the fire, and strong onshore winds hitting the shoreline upped the intensity of the thunderstorms. Incredible rainfall rates were observed during this time, and some of the 12 hour rainfall totals were unfortunately historic. At Carolina Beach, it is estimated that this event was a 1-in-1000-year event for a 12-hour period.
Related: Carolina Beach Mayor says crews are out assessing the damage from Tropical Cyclone 8
It should also be noted that this does not imply that a similar event will not happen for another thousand years — there is a chance any given year that extreme rainfall events can occur (by the same logic, communities that haven't seen a major storm event in recent years are not "due" for one).
The Cape Fear Region continues to recover from the storm, with more than a dozen roads in Brunswick County closed because of flooding or sinkholes.
