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Hurricane Dennis (1999)
Hurricane Dennis was a North Atlantic hurricane that affected The Bahamas and parts of the Mid-Atlantic and Northeast during the 1999 Atlantic hurricane season. The fifth tropical cyclone, fourth tropical storm, and third hurricane of the season, Dennis originated from a tropical wave that passed north of the Leeward Islands in mid-to-late August. Moving west-northwest, the wave organized into a tropical depression on August 24. Tracking just north of Grand Turk that same day, the depression was upgraded to a tropical storm just several hours later. Positioned on the eastern end of an elongated trough, Dennis was embedded within an area of high wind shear. However, despite this, the storm strengthened into a hurricane on August 26, and then further into Category 2 hurricane status on August 28. Moving in an erratic motion off the North Carolina coastline, Dennis became entangled within a cold front that caused dry air to impact the circulation, thus weakening the storm to a tropical storm. On August 30, Dennis made landfall along the Outerbanks of North Carolina, resulting in tropical storm-force sustained winds and hurricane-force gusts in the area. Rapidly weakening, Dennis weakened into a tropical depression over the central portion of North Carolina, and was absorbed within a larger extratropical low on September 8, while located over Canada.
==Meteorological history==
On August 17, a tropical wave emerged off the western coast of Africa. 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 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 0000 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 1200 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 0600 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 1200 UTC, Dennis was upgraded to a Category 2 hurricane and reached peak winds of 105 mph (165 km/h), though its lowest barometric pressure was recorded until 0600 UTC on August 30. Despite this intensity, the hurricane's eye was extraordinarily large, up to 30-40 mi (50-65 km) wide, and several fixes from the Hurricane Hunters did not indicate the present 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 1800 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 1200 UTC on September 5. The cyclone drifted erratically even overland, turning northeast and eventually north before dissipating over New York at 1800 UTC on September 7. Two days later, the low was absorbed into a larger cyclone.〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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