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Severe Tropical Cyclone Narelle was a Category 4 cyclone in early January 2013 that brought light rains to areas in South Australia suffering from a drought and heat wave. On 4 January, a tropical low developed within a monsoon trough over the Timor Sea. Over the following several days, the system gradually tracked westward and intensified, being classified Tropical Cyclone Narelle on 8 January. Turning southward into a region of low wind shear, Narelle intensified into a severe tropical cyclone on 9 January. Over the following two days, the cyclone's structure fluctuated, temporarily featuring an eye, before it maintained its organisation and intensified further on 11 January. The storm attained its peak intensity later on 11 January as a Category 4 cyclone with winds of 185 km/h (115 mph). The following day, Narelle passed approximately northwest of Exmouth as it moved on a south-southwesterly course. The system steadily weakened and ultimately fell below tropical cyclone strength on 15 January well to the west of Geraldton. Early in the storm's existence, Narelle brought strong winds, heavy rain, and high winds to many areas in Indonesia. More than 10,000 homes were flooded and many others were damaged by thunderstorms. A total of 14 people were killed by the storm, and 17 others were listed as missing. In Western Australia, scattered strong thunderstorms caused minor damage and produced a possible tornado. ==Meteorological history== On 4 January, a weak area of low pressure developed within a monsoon trough near Timor. The following day, the Joint Typhoon Warning Center (JTWC) began monitoring the system for possible development into a tropical cyclone. Traveling westward, the system was forecast to intensify as it moved into an area highly favouring tropical cyclogenesis with very warm waters (with sea surface temperatures of ) and low wind shear. Additionally, a nearby anticyclone provided good outflow for the system. Over the following two days, deep convection gradually built around the low and on 7 January, the Tropical Cyclone Warning Centre (TCWC) in Darwin designated the system as Tropical Low 05U, at which time the storm was situated roughly south-southeast of Sumba, Indonesia. By this time, the system was tracking west-southwestward around a subtropical ridge, which would dictate the track of the storm for the remainder of its existence.〔 Later on 7 January, the JTWC issued a Tropical Cyclone Formation Alert for the system, indicating that further development of the low into a significant tropical cyclone was anticipated. Just seven hours after this, the JTWC classified the system as a tropical storm and began issuing advisories. Through the morning of 8 January, weak wind shear hindered development of the system. After enough convection wrapped around the centre of circulation, the Australian Bureau of Meteorology classified the low as Tropical Cyclone Narelle, the second named storm in the western region during the 2012–13 season.〔 Shortly thereafter, intensification quickened as a central dense overcast formed and prominent banding features consolidated. Following the development of an eye early on 9 January, the Bureau of Meteorology upgraded Narelle to a severe tropical cyclone, with winds estimated at 120 km/h (75 mph).〔 Over the following day, Narelle's intensity leveled out as it encountered moderate wind shear. Once the shear relaxed, the system resumed strengthening. With conditions more favourable, Narelle redeveloped an eye and its outflow improved. Late on 11 January, Narelle is estimated to have attained its peak intensity with winds of 185 km/h (115 mph) and a barometric pressure of 930 mbar (hPa; 27.46 inHg). Operationally, the storm was believed to have been slightly stronger, peaking as a Category 5 cyclone on the Australian scale. It was not until a post-storm assessment that the Bureau of Meteorology found Narelle to have been a weaker system at its peak.〔 At the same time, the JTWC assessed the storm to have attained one-minute sustained winds of 215 km/h (130 mph), ranking it as a Category 4-equivalent cyclone on the Saffir–Simpson hurricane scale. Hours after Narelle reached peak intensity, increasing wind shear caused the storm's eyewall to erode and the outflow to become somewhat restricted. By the afternoon of 12 January, the storm's structure had significantly degraded, with the eye no longer apparent and a marked decrease in cold cloud tops. Later that day, the cyclone made its closest approach to Western Australia, passing approximately northwest of Exmouth.〔 Despite shear eventually lightening up, the storm's southerly course brought it over cooler waters, preventing restrengthening. Most of the deep convection shifted to the western side of Narelle's circulation, though its centre remained well defined. By the evening of 13 January, the storm had weakened below severe tropical cyclone strength.〔 Rapid weakening ensued on 14 January, as the effects of cooler waters and dry air caused the deep convection to dissociate into an area of shallow stratocumulus clouds. Narelle failed to redevelop deep convection and weakened below tropical cyclone status early on 15 January, prompting the Bureau of Meteorology to issue its final bulletin on the cyclone.〔 The system was last observed about west of Geraldton, where it continued southward away from Australia.〔 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「Cyclone Narelle」の詳細全文を読む スポンサード リンク
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