Hurricane Florence

Hurricane Florence was a powerful and long-lived Cape Verde hurricane that caused catastrophic damage in the Carolinas in September 2018, primarily as a result of freshwater flooding due to torrential rain. The sixth named storm, third hurricane, and the first major hurricane of the 2018 Atlantic hurricane season, Florence originated from a strong tropical wave that emerged off the west coast of Africa on August 30, 2018. The wave steadily organized, and strengthened into a tropical depression on the next day near Cape Verde. Progressing along a steady west-northwest trajectory, the system gradually strengthened, acquiring tropical storm strength on September 1. An unexpected bout of rapid intensification ensued on September 4–5, culminating with Florence becoming a Category 4 major hurricane on the Saffir–Simpson scale (SSHWS), with estimated maximum sustained winds of 130 mph (215 km/h). Strong wind shear then led to rapid weakening, and Florence weakened to tropical storm strength on September 7. Shifting steering currents led to a westward turn into a more suitable environment; as a result, Florence reintensified to hurricane strength on September 9 and major hurricane status by the following day. Florence reached peak intensity on September 11, with 1-minute winds of 150 mph (240 km/h) and a minimum central pressure of . An unexpected eyewall replacement cycle and decreasing oceanic heat content caused a steady weakening trend; however, the storm grew in size at the same time. Early on September 14, Florence made landfall in the United States just south of Wrightsville Beach, North Carolina as a Category 1 hurricane, and weakened further as it slowly moved inland under the influence of weak steering currents. Florence degenerated into a post-tropical cyclone over West Virginia on September 17 and was absorbed by another frontal storm two days later.

Early in the storm's history, the system brought squalls to the Cape Verde islands, resulting in minor landslides and flooding; however, overall effects remained negligible. With the threat of a major impact in the Southeastern and Mid-Atlantic United States becoming evident by September 7, the governors of North Carolina, South Carolina, Virginia, Georgia, and Maryland, and the mayor of Washington, D.C. declared a state of emergency. On September 10 and 11, the states of North Carolina, South Carolina, and Virginia issued mandatory evacuation orders for some of their coastal communities, predicting that emergency personnel would be unable to reach people there once the storm arrived. Though Florence made landfall as a greatly weakened Category 1 hurricane, winds associated with the tropical cyclone were strong enough to uproot trees and power lines, causing extensive power outages across the Carolinas. Furthermore, due to the slow motion of the storm, heavy rain fell throughout the Carolinas for several days. Coupled with a powerful storm surge, the rainfall caused widespread flooding along a long stretch of the North Carolina coast, from New Bern to Wilmington. Inland flooding from Florence inundated cities such as Fayetteville, Smithfield, Lumberton, Durham, and Chapel Hill. Most major roads and highways in the area experienced flooding, with large stretches of I-40, I-95, and US Route 70 remaining impassable for days after the storm's passage. Wilmington was cut off entirely from the rest of the mainland by the flooding. The storm also spawned tornadoes in several places along its path, including an EF2 tornado that killed one person in Virginia. Many places received record-breaking rainfall, with Florence setting maximum rainfall records from a tropical cyclone in both of the Carolinas. Overall, the storm caused $24.23 billion in damage, mostly in the Carolinas, and 54 deaths.

Meteorological history

On August 28, 2018, the National Hurricane Center (NHC) began monitoring a tropical wave—an elongated trough of low air pressure—over Western Africa for possible tropical cyclogenesis within the subsequent five days. As it progressed westwards under the influence of easterly trade winds, favorable environmental conditions, including ample moisture and low wind shear, enabled further organization of the wave and the development of broad shower and thunderstorm activity. Though the tropical wave lacked a well-defined low-level circulation center, the NHC began issuing advisories on the system as Potential Tropical Cyclone Six later that day as the system was threatening Cape Verde. Easterly trade winds propelled the disturbance along a west to west-northwest trajectory. Toward the end of August 31, the system's convective organization became sufficient for the NHC to upgrade the disturbance to Tropical Depression Six south of Santiago in Cape Verde. While the storm came under the steering influence of a strong subtropical ridge to the north the following day, moderate wind shear temporarily stunted development and displaced convection to the eastern side of the depression. Later, however, pronounced banding features developed around the circulation, prompting the NHC to upgrade the depression to Tropical Storm ''Florence'' at 0900Z on September 1.

Development of a small central dense overcast and a mid-level eye feature signified Florence's intensification to hurricane strength early on September 4, roughly west-northwest of Cape Verde. Shortly thereafter, the system unexpectedly rapidly intensified within a small area of low wind shear in an otherwise adverse upper-level environment; the hurricane's core structure, eye, and outer banding improved markedly, catching forecasters off-guard and intensifying beyond model outputs. On September 5, the tropical cyclone reached an initial peak intensity with 1-minute sustained winds of 130 mph (215 km/h) with a central pressure of , making it as a Category 4 hurricane on the Saffir–Simpson scale. Thereafter, increasing wind shear caused the hurricane to rapidly weaken to tropical storm strength by September 8. A building mid-level ridge halted Florence's northward movement, leading to a westward turn.

Environmental conditions became increasingly conducive to reorganization on September 8 as NOAA Hurricane Hunters began reconnaissance of the cyclone, with the shear decreasing and warm waters becoming deeper. Convective banding blossomed around the storm and a formative eye appeared on satellite imagery. The storm's central dense overcast became more defined, and a complete eyewall developed within its core. Florence reattained hurricane-status by 12:00 UTC on September 9, with the Hurricane Hunters observing sustained winds at the surface. Fueled by sea surface temperatures of , Florence rapidly reintensified overnight, and Convective bursts with frequent lightning surrounded the eyewall, giving rise to a well-defined wide eye. Expanding outflow ventilated the cyclone, enabling continued growth. The system rapidly re-achieved Category 4 intensity by 16:00 UTC on September 10, and Florence reached peak intensity at 18:00 UTC on September 11, with sustained winds of 150 mph (240 km/h) and a minimum central pressure of 937 mbar (hPa; 27.67 inHg). Steady weakening occurred thereafter due to an eyewall replacement cycle and a less favorable environment. At this point, the future track of the hurricane became increasingly uncertain as models predicted a collapse of steering currents.

Steady weakening continued as the hurricane approached North Carolina, and Florence fell below major hurricane status late on September 12. On the following day, steering currents collapsed, which caused Florence to slow down greatly while moving towards the North Carolina coast. At 11:15 UTC (7:15 a.m. EDT) on September 14, Florence made landfall just south of Wrightsville Beach, North Carolina as a Category 1 hurricane, with sustained winds of 90 mph (150 km/h) and a central pressure of . The hurricane's sluggish movement resulted in widespread, catastrophic rainfall throughout North and South Carolina. After making landfall, the tropical cyclone began to rapidly weaken due to the frictional effects of land, and Florence weakened to a tropical depression on September 16 before transitioning into an extratropical cyclone the following day. Florence's remnant low dissipated over Massachusetts on September 18. However, the remnants of Florence subsequently emerged into the Atlantic, before splitting into two separate storms. The system to the south would eventually become Subtropical Storm Leslie several days later.

Preparations

Cape Verde and Bermuda

Upon the designation of Potential Tropical Cyclone Six on August 30, the government of Cape Verde issued tropical storm warnings for the islands of Brava, Fogo, and Santiago. Domestic airlines cancelled 20 flights on August 31 and September 1; maritime travel was also suspended for this period. Mariners were advised to remain cautious of large swells around the islands, potentially reaching . Under the threat of damaging waves, the Autoridade Nacional de Proteção Civil evacuated 125 people, primarily elderly, from Furna and Rincão. Eleven military personnel were deployed to Rincão to assist in evacuations and preparations. Tropical storm warnings were discontinued on September 1, as the system progressed westward and no longer posed a threat to the archipelago.

In anticipation of adverse conditions, Norwegian Cruise Lines and Oceania Cruises adjusted itineraries for ''Norwegian Escape'', ''Norwegian Dawn'', and '' Sirena'' to avoid crossing the hurricane's path and not dock in Bermuda.

United States

As forecast models indicated an increasing threat to the Southeastern United States, North Carolina Governor Roy Cooper declared a state of emergency on September 7. Transportation rules for farmers were waived to enable faster harvesting. President Donald Trump declared an emergency in North Carolina, granting the state access to federal funds. An overnight curfew was established for Lumberton for the duration of the hurricane. The cost of hurricane preparation in Virginia were at US$10.8 million.

South Carolina Governor Henry McMaster followed suit on the next day. The South Carolina Emergency Management Division (SCEMD) and Harvest Hope Food Bank began mobilizing resources for potential recovery efforts. The SCEMD raised operation conditions to level 3 on September 9, and began preparations for the "possibility of a large-scale disaster", with forecasts showing Florence striking the state as a major hurricane. Local officials established overnight curfews for the cities of Aynor, Conway, Dillon, Myrtle Beach, and Surfside Beach to limit the number of people on the roads and enable effective emergency responses. The entirety of Horry and Marion counties also fell under curfews.

On September 8, Virginia Governor Ralph Northam also declared a state of emergency. On September 10, Maryland Governor Larry Hogan declared a state of emergency for the entire state, with the potential of "historic, catastrophic and life-threatening flooding in Maryland". On September 11, Washington, D.C. Mayor Muriel Bowser declared a state of emergency for the entire District of Columbia due to the "imminent threats on the people of D.C., including threats to health, safety and welfare" caused by Florence. On September 12, Georgia Governor Nathan Deal issued a state of emergency for the entire state.

Evacuation and closures

Mandatory evacuation orders for residents and tourists on Hatteras Island in Dare County began on September 10, with orders expanding to the rest of the county the following day. Evacuations along the rest of the Outer Banks and in Brunswick County went in effect on September 11. On September 10, Governor Henry McMaster ordered evacuations for the entire coastline of South Carolina, constituting roughly 1 million people. On September 10, Virginia Governor Ralph Northam ordered mandatory evacuations for low-lying coastal areas in the Hampton Roads and Eastern Shore regions effective September 11, constituting 245,000 people. The US Navy moved 30 ships stationed off the coast of Virginia farther out to sea, to protect the ships and the coastline.

In North Carolina, mandatory evacuations were issued on September 11 for Brunswick County, Carteret County, Craven County, Onslow County, Pamlico County, Tyrrell County, North Topsail Beach, Emerald Isle, Ocracoke Island

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