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Subtropical Storm Andrea was the first named storm and first subtropical cyclone of the 2007 Atlantic hurricane season. It developed out of a non-tropical low on May 9 about 150 miles (240 km) northeast of Daytona Beach, Florida, three weeks before the official start of the season. After encountering dry air and strong vertical wind shear, Andrea weakened to a subtropical depression on May 10 while remaining nearly stationary, and the National Hurricane Center discontinued advisories early on May 11. Andrea was the first pre-season storm to develop since Tropical Storm Ana in April 2003. Additionally, the storm was the first Atlantic named storm in May since Tropical Storm Arlene in 1981. The storm produced rough surf along the coastline from Florida to North Carolina, causing beach erosion and some damage. In some areas, the waves eroded up to 20 feet (6 m) of beach, leaving 70 homes in danger of collapse. Offshore North Carolina, high waves of 34 feet (10 m) and tropical-storm-force winds damaged three boats; their combined nine passengers were rescued by the Coast Guard, although all nine sustained injuries. Light rainfall was also reported in some coastal locations. Damage was minimal, but six people drowned as a result of the storm. ==Meteorological history== In early May, an upper-level trough dropped southward through the western Atlantic Ocean, forcing a back-door cold front—a cold front that moves southwestward ahead of a building surface ridge to its north or northeast—southward. For several days, forecast models had anticipated for the trough to evolve into a closed low pressure area, and on May 6, a frontal low with a large and well-defined circulation developed about 90 miles (140 km) east of Cape Hatteras. The low maintained scattered convection around its circulation center, and in conjunction with the strong high pressure to its north, a very tight pressure gradient produced gale force winds near the coastline. The extratropical storm tracked southeastward and later turned to the southwest while steadily deepening; on May 7, it attained hurricane force winds. With a lack of tropical moisture, its corresponding convection was minimal and scattered. The National Hurricane Center first mentioned the possibility of tropical cyclogenesis on May 8, while the storm was located about 230 miles (370 km) east-southeast of the South Carolina coastline. Its associated convection had steadily increased as it tracked slowly westward at 5–10 mph (8–16 km/h). The system changed little in organization throughout the day, though by the following morning, hurricane specialists indicated the low was acquiring subtropical characteristics as it tracked over progressively warmer waters.〔 Early on May 9, a Hurricane Hunters flight into the system revealed winds of 45 mph (70 km/h) and a flat thermal core, which indicated the system was neither warm-core nor cold-core. In addition, satellite imagery indicated a consolidation of the convection near the center, as well as hints of upper-level outflow and a contraction of the radius of maximum winds from more than 115 miles (185 km) to about 70 miles (120 km). Based on the observations and the hybrid structure of the system, the National Hurricane Center classified the low as Subtropical Storm Andrea at 1500 UTC on May 9 about 150 miles (240 km) northeast of Daytona Beach, Florida. During a subsequent analysis of the storm, researchers estimated that the storm had transitioned into a subtropical cyclone nine hours earlier.〔 As Andrea developed before June 1—the traditional start of hurricane seasons in the Atlantic Ocean—it became the first pre-season storm since Tropical Storm Ana in April 2003. Additionally, the storm was the first Atlantic named storm in May since Tropical Storm Arlene in 1981. Upon first becoming a subtropical cyclone, Andrea was embedded within a large, nearly stationary deep-layer trough, resulting in a westward movement. Drifting over sea surface temperatures of no more than 77 ° F (25 °C),〔 the organization of the system deteriorated with a significant decrease in convection. By early on May 10, much of the associated weather was located to the east of the cyclone within a band of moderate convection due to a brief spell of westerly vertical wind shear. The center of circulation had become disorganized, with several small cloud swirls within the larger circulation. This disorganization of the center, combined with increasing wind shear and dry air suppressing convective activity, caused it to begin weakening later that morning. By 1500 UTC on May 10, only a few thunderstorms remained near the center, and thus the NHC downgraded Andrea to subtropical depression status. Though a few intermittent thunderstorms persisted over the eastern semicircle, the depression remained disorganized and weak; the National Hurricane Center discontinued advisories early on May 11, after it had been without significant deep convection for 18 hours about 80 miles (125 km) northeast of Cape Canaveral, Florida. Later on May 11, convection re-fired over the center as the system drifted south-southeastward, though it lacked sufficient organization to qualify as a tropical cyclone. By May 12, shower activity had organized greatly to the east of the center, and the National Hurricane Center remarked that a small increase in convection would result in the formation of a tropical depression. It accelerated east-northeastward away from the continental United States without redeveloping, and after passing over cooler waters, the remnants of Andrea merged with an approaching cold front on May 14.〔(【引用サイトリンク】url=ftp://ftp.met.fsu.edu/pub/weather/tropical/Outlook-A/2007060109.ABNT20 )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Subtropical Storm Andrea (2007)」の詳細全文を読む スポンサード リンク
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