Historic Flooding Rainfall with Potential Tropical Cyclone Eight: September 15-16, 2024

Historic rainfall occurred across the Cape Fear Region of southeastern North Carolina on September 16, 2024.  Gauges and automated radar estimates showed that 12 to 20 inches of rain fell in only two days, creating severe flash flooding affecting Carolina Beach, Southport, Bolivia, and Boiling Spring Lakes.  Although this system never became a named tropical system, observed weather impacts including strong winds, heavy rain, and flash flooding were similar to tropical storms and hurricanes of the past.

Potential Tropical Cyclone Eight was an area of low pressure that developed off the Carolina Coast on September 13, 2024.  While it initially developed along a stalled front, over several days the system began to draw energy from the warm ocean surface.  As winds increased, the low was given a "Potential Tropical Cyclone" categorization late in the afternoon of September 15, indicating that conditions could support its evolution into a tropical or subtropical storm.  A Tropical Storm Warning was issued for the Carolina coastline for the expectation of these weather conditions. 

While the system displayed some tropical characteristics at times, Hurricane Hunter aircraft sent to investigate the storm found it never developed a symmetric wind circulation and it maintained horizontal temperature contrasts not consistent with the structure of tropical storms.

Regardless of the nature of the storm, Potential Tropical Cyclone Eight brought historic rainfall and flash flooding to parts of Brunswick and southern New Hanover counties.  Storm total rainfall totals of 12 to 20 inches were recorded within a 25-mile wide stripe running from Carolina Beach and Southport through Bolivia, the Green Swamp, and ending south of the Delco community in eastern Columbus County.  The majority of this rain fell within a 12 hour window between 5:00 am and 5:00 pm on Monday, September 16.  Flash flooding quickly developed in Carolina Beach during the morning hours, then shifted northwestward following the heaviest rainfall rates as the center of Potential Tropical Cyclone Eight shifted onshore.

Gauge-measured rainfall in excess of 12 inches within a 12 hour period is expected to occur, on average, once every 200 years across coastal southeastern North Carolina.  A few spots may have had rainfall amounts as large as 18 inches within a 12 hour period, approaching the kind of event expected to occur, on average, once every 1000 years.  These estimates are calculated in NOAA Atlas 14, a reference document that shows the climatological recurrence of heavy rainfall events.

A study conducted at the North Carolina Institute for Climate Studies predicts increased frequency of future heavy rainfall events as a consequence of climate change.  Warmer air holds more moisture, therefore a warming climate can support heavier rainfall.  By the year 2075, extreme rainfall events could become 25% heavier due to climate change.

Multiple roads were closed due to floodwaters and some roads were physically washed out by the immense volume of floodwater.  Some major highways that were closed included:

• NC Highway 133 near Daws Creek Road SE, south of Wilmington
• US 421 (Carolina Beach Road) in Carolina Beach between Goldsboro Ave to Atlanta Ave
• NC Highway 211 washed out in Southport near Dosher Cutoff
• NC Highway 211 at St. James Dr SE
• US 17 near Governor's Rd SE
• US 17 near Sellers Rd NW in Supply
• US 17 Business Route near Benton Rd in Bolivia
• NC Highway 87 near Fertilizer Rd near Riegelwood

Widespread flooding across Carolina Beach. Video provided by Sharon Carlson.

Flooding along Fort Fisher Blvd in Kure Beach. Photo by Lee Snead.

Over three feet of floodwater in Carolina Beach.  Photo by Ashley MacBride

Carolina Beach, NC

Flooding on Danford Road at NC Highway 87, east of Bolivia, NC.  Photo provided by the Brunswick County Sheriff's Office

Rainfall Totals

Gauge-measured totals across southeastern North Carolina and northeastern South Carolina.  These originate from a variety of networks including NWS ASOS, FAA AWOS, CoCoRaHS, NWS cooperative observers, CWOP, and Weather Underground.

Extreme flooding developed across portions of Brunswick County and lasted for days.  A river gauge installed at the Lockwood Folly River at NC Highway 211 recorded its second highest stage on record, 19.06 feet, only 1.7 feet below the record set back in 2018 during Hurricane Florence. 

Winds

Even though this system never became a full-fledged tropical cyclone, wind gusts over 50 mph were recorded in a number of locations. While most of these higher winds occurred near the Cape Fear coastline in association with the heavy rain squalls racing onshore, a second area of strong northerly winds gusting to 45-50 mph developed during the afternoon well inland from Lumberton to Dillon to Florence.  This appears to be as cool, dry air was pulled into the western periphery of the storm's circulation, promoting mixing of stronger winds down from aloft.

Scattered reports of wind damage were received, mostly to trees and power lines.

Tree blown down across Shoreline Drive East in Sunset Beach.  Photo provided by the Sunset Beach Police Department

Tree blown down on a house in Carolina Beach, shared by Dorothy Pagan

Page Author: Tim Armstrong
Last Updated: September 19, 2024