Hurricane Dennis caused flooding in North Carolina and the Mid-Atlantic states in early September 1999, which would later be compounded by Hurricane Floyd. The fifth tropical cyclone of the season, Dennis developed from a tropical wave to the north of Puerto Rico on August 24. Originally a tropical depression, the system moved west-northwestward and strengthened into a tropical storm despite unfavorable wind shear. The storm became a hurricane by August 26. After striking the Abaco Islands, conditions improved, allowing for Dennis to strengthen into a Category 2 on the Saffir–Simpson scale by August 28. Around this time, Dennis began to move parallel to the Southeastern United States. Early on August 30, the storm peaked with winds of 105 mph (165 km/h). By the following day, steering currents collapsed and the storm interacted with a cold front, causing Dennis to move erratically offshore North Carolina. Wind shear and cold air associated with the front weakened Dennis to a tropical storm on September 1 and removed some of its tropical characteristics. Eventually, warmer ocean temperatures caused some re-strengthening. By September 4, Dennis turned northwestward and made landfall in Cape Lookout, North Carolina, as a strong tropical storm. The storm slowly weakened inland, before transitioning into an extratropical cyclone over western New York on September 7.
In the Bahamas, Dennis produced moderate winds, rain, and storm surge on San Salvador, Crooked Island, Eleuthera, and Abaco Islands, resulting in damage to roofs and coastal properties. Dennis brought waves to the east coast of Florida, causing minor erosion and four drowning deaths. The waves left severe erosion and coastal flooding along the Outer Banks of North Carolina. An deep channel created along Highway 12 isolated three towns on Hatteras Island. In Carteret, Craven, and Dare counties, the storm damaged at least 2,025 homes and businesses to some degree. Heavy rainfall produced by the storm in eastern North Carolina was generally beneficial due to drought conditions, but some crops were damaged. Two indirect deaths occurred in Richlands during a weather-related car accident. Similar inland flooding occurred in northern and eastern Virginia. A tornado in Hampton severely damaged five apartment complexes, three of which were condemned completely, as well an assisted living facility; about 460 people were forced to evacuate from the buildings, and as many as 800 vehicles may have been damaged. Overall, damage in North Carolina and Virginia totaled about $157 million. Generally minor flooding occurred in the Mid-Atlantic and New England.
Meteorological history
A tropical wave emerged into the Atlantic from the west coast of Africa on August 17. Tracking steadily westward, the wave remained devoid of significant convection until August 21, when associated shower and thunderstorm activity increased a few hundred miles northeast of the Leeward Islands. Over the course of the next two days, the development of a low-level circulation was noted, though a reconnaissance aircraft failed to locate the presence of a surface low-pressure area on August 23. Subsequent surface observations indicated the formation of a circulation at the surface, and the wave acquired enough organization to be designated as a tropical depression at 00:00 UTC on August 24, while centered 220 mi (355 km) east of Turks Island. Data from a secondary reconnaissance aircraft and ship reports indicated intensification, and the depression was upgraded to Tropical Storm Dennis at 12:00 UTC that same day accordingly. Located at the tail-end of a stationary trough and in an environment of unfavorable wind shear, the system was ill-defined and asymmetric. Despite the unfavorable environment, data from the Hurricane Hunters indicated that Dennis had intensified into a Category 1 hurricane by 06:00 UTC on August 26.
Tracking west-northwestward in advance of a trough over the eastern United States, the system did not resemble a typical hurricane on satellite imagery, with a low-level center outside of the deepest convection. The system turned towards the northwest and simultaneously slowed in motion by August 27 as a second mid-latitude trough passed to its north. Though wind shear remained unfavorable initially, it began to lessen on August 28 as an anticyclone developed aloft. At 12:00 UTC, Dennis was upgraded to a Category 2 hurricane on the Saffir–Simpson scale and reached peak winds of 105 mph (165 km/h), though its lowest barometric pressure was recorded until 06:00 UTC on August 30. Despite this intensity, the hurricane's eye was large, up to 30-40 mi (50–65 km) wide, and several fixes from the Hurricane Hunters did not indicate the presence of one at all. The system also became unusually large, with its radius of maximum sustained winds extending up to 70-85 mi (110–130 km) wide. Following peak intensity, Dennis accelerated towards the northeastward in response to the secondary trough, barely missing the Outer Banks. By August 31, steering currents collapsed and the hurricane began to aimlessly drift east of Cape Hatteras, North Carolina.
Though the upper-level trough advanced eastward away from the hurricane, a trailing cold front became intertwined with Dennis, forcing dry air into the circulation in addition to creating a hostile upper-level environment. On September 1, the system weakened below hurricane intensity, with the National Hurricane Center (NHC) noting that the storm could be as much an extratropical as a subtropical or tropical cyclone. Thereafter, a building ridge over the eastern United States forced the storm southward across slightly warmer ocean temperatures. As a result, banding features became better defined despite low convective tops as viewed on radar and in satellite imagery. On September 3, the high drifted eastward into the Atlantic, forcing Dennis to turn northwestward. A formative eyewall was observed on September 4, and Dennis reached a secondary peak intensity with winds of 70 mph (110 km/h) by 18:00 UTC. Three hours later, the system moved ashore the Cape Lookout National Seashore in eastern North Carolina at this intensity. Continuing inland, Dennis weakened to a tropical depression over central North Carolina at 12:00 UTC on September 5. The cyclone drifted erratically even overland, turning northeast and eventually north before dissipating over New York at 18:00 UTC on September 7. Two days later, the low was absorbed into a larger cyclone.
Preparations The erratic motion of Dennis resulted in the issues of several tropical cyclone warnings and watches. Alerts from this hurricane were issued starting on August 24, at which time a tropical storm warning was put it place for the southeast Bahamas and Turks and Caicos Islands, simultaneously, a tropical storm watch was also issued for the central Bahamas. Less than 24 hours, the tropical storm watch was upgraded to a tropical storm warning, while there was also an additional hurricane watch. All watches and warnings within the Bahamas were discontinued by late August 28.
Watches and warnings in the United States began on August 27, with a hurricane watch being issued from Sebastian Inlet to Fernandina Beach in Florida. A tropical storm warning was also issued for much of the same area several hours later. As Dennis began turning northward, the threat of the storm striking Florida lessened, which resulted in discontinuations of the watches and warnings. Watches and warnings were issued from South Carolina to Virginia, beginning with a hurricane watch from north of Savannah, Georgia, to Surf City, North Carolina. The watches and warnings were adjusted in accordance to the storm's changes in intensity and erratic movement. In South Carolina, officials opened about 13 shelters in the Charleston area, but just 40 people sought refuge in them. Governor Jim Hodges did not order evacuations, but encouraged residents in coastal areas to remain vigilant.
As Dennis made its initial approach to North Carolina, state officials urged nearly 150,000 coastal residents to prepare for the storm. Local officials ordered the evacuation of tourists and approximately 22,000 residents on Hatteras and Ocracoke islands. New Hanover County closed its courts, offices, and schools on August 30. The American Red Cross opened two emergency shelters in Wilmington. Airplanes at Seymour Johnson Air Force Base in Goldsboro were flown to Ohio.
Impact
Dennis left $157 million in damage and six deaths, with four in Florida due to drowning in high surf and two in North Carolina as a result of a weather-related car accident. In North Carolina and Virginia, insurance claims for damaged property totaled $60 million. Agricultural losses in the two states reached about $37 million. The heavy rain from Dennis staged a catastrophic flood disaster wrought by Hurricane Floyd about two weeks later.
Bahamas Dennis brought tropical storm and hurricane-force winds to the Bahamas. In Grand Bahama, a weather station reported winds of while other areas reported winds between . A reading and storm tides above normal occurred as the center of the storm moved across Abaco Island on August 28. The only official rainfall total from the Bahamas was at Eleuthera and Abaco. Dennis caused moderate damage across the Bahamas. On Abaco Island, the rain caused heavy flooding and storm surge washed out roads. Dennis also caused considerable damage to trees and boats. Widespread power outages were also reported. However, there were no reports of deaths or injuries and damage totals from the Bahamas are unavailable.
Southeastern United States In Florida, Dennis caused minor beach erosion as far south as Broward and Palm Beach counties. Storm tides swamped six boats in Boca Raton and the Hillsboro Inlet. While located offshore, the storm brought winds up to with gusts reaching in Jacksonville, while a weather station in St. Augustine reported a gust. Dennis dropped very light rainfall in Florida, amounting to only at Jacksonville International Airport. The hurricane also brought storm tides between above normal in some areas, though only minor beach erosion occurred. Overall, rip currents generated by Dennis resulted in four fatalities, with one in St. Johns County.
The state of Georgia reported wind gusts and only a trace of rain. In South Carolina, numerous weather stations reported winds between and gusts reaching hurricane force. Rainfall up to fell in some areas while buoys offshore reported tides above normal. Minor to moderate beach erosion was reported from Charleston to Colleton County. Damage in South Carolina was limited to downed trees and scattered power outages.
North Carolina
Dennis brought tropical storm-force winds with gusts up to hurricane-force to the North Carolina coast. In Oregon Inlet, there were winds, while Cape Hatteras and Wrightsville Beach reported gusts between . A weather station reported wind gusts and a barometric pressure reading of . When Dennis made landfall on September 4, it brought tropical storm-force winds to much of eastern North Carolina, including winds at Cherry Point. Storm tides above normal were reported along the North Carolina coast. Because Dennis was a slow moving storm, it produced heavy rains across eastern North Carolina. Precipitation peaked at in Ocracoke, while rainfall between fell elsewhere in the eastern parts of the state.
The heavy rains knocked down power lines near Wilmington, leaving 56,000 residents without electricity. In Brunswick County, a beachfront home collapsed in Ocean Isle Beach. New Hanover County experienced about $217,000 in losses. Two indirect deaths occurred in North Carolina due to a weather-related car accident in Richlands.