Turning northwest toward the United States, a second phase of rapid intensification ensued that day into September 10 with Florence regaining Category 4 strength.

[4] On this day, the system split in two, with the northern one ultimately developing into Florence and the southern portion later becoming Tropical Depression Nineteen-E in the Eastern Pacific.

[1] Favorable environmental conditions, including ample moisture and low wind shear,[5] enabled further organization and development of broad shower and thunderstorm activity.

Lacking a well-defined center but posing an immediate threat to Cape Verde, the NHC began issuing advisories on the system as Potential Tropical Cyclone Six later that day.

[9] Toward the end of August 31, convective organization became sufficient for the NHC to mark the formation of Tropical Depression Six as the system passed south of Santiago in Cape Verde.

[16][17] Development of a small central dense overcast and a mid-level eye feature signified that Florence achieved hurricane strength early on September 4, roughly 1,240 miles (2,000 km) west-northwest of the Cape Verde islands.

[21] The hurricane's core structure and outer banding improved markedly, catching forecasters off-guard and intensifying beyond model outputs.

Sustained winds rose to 130 mph (215 km/h) and its pressure fell to 950 mbar (hPa; 28.05 inHg); this ranked it as a Category 4 hurricane on the Saffir-Simpson scale.

[26][29] Weather models became increasingly consistent on the storm's future track, leading to greater confidence in a major impact to the Southeastern United States.

[30] This threat was enhanced by the downstream effects of Typhoon Jebi's extratropical remnant influencing a ridge off the eastern United States which, in turn, forced a trough away from Florence faster than initially anticipated.

[31] This trajectory proved climatologically unusual, with United States hurricane impacts primarily originating farther south and west of Florence's position on that day.

[37] The system rapidly achieved Category 4 intensity by 16:00 UTC, with reconnaissance aircraft recording surface winds near 130 mph (215 km/h) and a pressure of 946 mbar (hPa; 27.93 inHg).

[37] Hurricane Florence achieved its initial peak intensity late on September 10 with sustained winds of 140 mph (220 km/h) and a pressure of 940 mbar (hPa; 27.76 inHg).

Extensive outflow became established over the cyclone, extending northwest and east, providing ample ventilation and deformation which enabled Florence to continue expanding.

A strengthening trough moving inland over the Pacific Northwest amplified ridging over the Northeastern United States and western Atlantic Ocean, steering Florence to the west-northwest.

Ample atmospheric moisture combined with strong upward lift from the anticyclone atop Florence yielded an environment conducive to widespread torrential precipitation.

[49] Additional fluctuations in the hurricane's core resulted in erratic movement, including a brief stalling period approximately 100 mi (155 km) east-southeast of Wilmington.

[50] Trudging west, the eye of Florence ultimately made landfall near Wrightsville Beach at 11:15 UTC on September 14 as a Category 1 hurricane with winds of 90 mph (150 km/h) and a central pressure of 956 mbar (hPa; 28.23 inHg).

[54] Although the center of Florence progressed inland over South Carolina, offshore convective available potential energy values of 1,000–2,000 J/kg and strong mid-level winds continued fueling the aforementioned rainbands.

Minimal diabatic heating stemming from the hurricane's lack of a thermal gradient kept the threat of tornadic storms low, with the primary driving force being ample atmospheric moisture.

[57] Small-scale training supercells—series of severe storms that continuously develop, track across, and dissipate over the same areas—developed between Morehead City and Wilmington during the overnight hours of September 14–15.

The heaviest rains shifted to South Carolina early on September 16; estimated rainfall rates reached 2 to 3 in (51 to 76 mm) per hour in Dillon, Marion, and Marlboro counties.

[1] Heavy rains propagated north along with the circulation center; however, rainbands extended from Virginia to South Carolina through September 17 with a narrow band of convection pivoting along the eastern slopes of the Appalachian Mountains.