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Hurricane Neki was the final tropical cyclone of the 2009 Pacific hurricane season. It developed on October 18 as an unusually large disturbance from a trough south of Hawaii. Moving northwestward, it slowly organized at first due to its large size. After reaching hurricane status on October 21, Neki intensified at a much faster rate and peaked with winds of 125 mph (205 km/h). It later turned to the north and north-northeast and weakened due to hostile conditions. While passing through the Papahānaumokuākea Marine National Monument, Neki was downgraded to a tropical storm after the center became exposed from the deepest convection. It caused little impact in the island chain. After stalling and executing a small loop, Neki resumed its northward track and dissipated on October 27. ==Meteorological history== The origins of Hurricane Neki were from a surface trough that persisted near the equator in the central Pacific Ocean in the middle of October 2009. A weak tropical disturbance became evident in the trough on October 15, and three days later the system began developing curved bands of convection on its northern and southern periphery. This created an unusually large gyre for the region. Following the formation of a well-defined circulation, it is estimated the system developed into Tropical Depression Three-C late on October 18, about 730 mi (1175 km) south of Ka Lae, Hawaii. Upon developing into a tropical cyclone, the storm was moving west-northwestward, influenced by a ridge to its north.〔 It was located over an area of warm sea surface temperatures and moderate wind shear, which favored gradual intensification. The convection diminished during a diurnal cycle before redeveloping the next day. Maintaining an unusually large size, the depression slowly organized, gradually separating from the trough from which it developed. On October 19, the CPHC upgraded it to Tropical Storm Neki, and shortly thereafter the storm turned toward the northwest.〔 By the next day, the cyclone resembled the structure of a monsoon depression typically found in the western Pacific Ocean. However, the structure began to more resemble a tropical cyclone after the outermost convection diminished and the thunderstorms around the center increased. Following the development of a banding-eye feature, Neki intensified into a hurricane early on October 21 about 625 mi (1010 km) southwest of Honolulu, Hawaii, or about 335 mi (535 km) east-southeast of Johnston Atoll.〔 After reaching hurricane status, Neki began rapidly intensifying as it turned northward, due to an approaching upper-level trough to its north.〔 An anticyclone aloft provided favorable outflow, which contributed in the strengthening. Early on October 22, Neki reached its peak winds of 125 mph (205 km/h) about 215 mi (345 km) northeast of Johnston Atoll, based on estimates from satellite imagery using the Dvorak technique. Afterward, the trough that influenced the hurricane's track also began restricting westerly outflow and increasing wind shear, which caused a steady weakening trend. It maintained major hurricane status – a Category 3 on the Saffir-Simpson Hurricane Scale – for about 24 hours, during which the track turned toward the north-northeast.〔 The weakening and deterioration of the storm's structure became more marked on October 23 after the thunderstorms failed to persist over the center. While approaching the Papahānaumokuākea Marine National Monument, Neki weakened to tropical storm status.〔 Continued wind shear exposed the circulation from the convection, although further weakening was slow to occur. On October 24, Neki made its closest approach to land after passing within 13 mi (21 km) of the uninhabited Necker Island. Its forward motion slowed due to a building ridge to the north, causing the storm to execute a small loop.〔 Despite the shear, Neki was initially able to continue developing thunderstorms, although cooler water temperatures resulted in further weakening. The storm resumed its northward motion after the ridge receded to the east, and on October 26 Neki weakened to a tropical depression once the circulation decoupled from the thunderstorms. The next day it dissipated as the center became elongated ahead of an approaching cold front.〔 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「Hurricane Neki」の詳細全文を読む スポンサード リンク
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