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Tropical Cyclone Helen was the first tropical cyclone to bring gale-force winds to Darwin, Australia since 1985. The fourth named storm of the 2007–08 Australian region cyclone season, Helen developed out of a weak area of low pressure in late December over the Top End region of Australia. Generally tracking westward, the system eventually intensified into a tropical cyclone and was given the name Helen on 2 January. By this time, it was situated over the Joseph Bonaparte Gulf and was beginning to retrograde eastward. Late on 4 January, the storm made landfall near Channel Point with winds of 95 km/h (60 mph) though rapidly weakened to a tropical low within 12 hours. Gradually accelerating, the remnants of Helen moved over the Gulf of Carpentaria before striking land again on 6 January. The system was last noted over the Cape York Peninsula on 7 January. From late December through 6 January, Helen and its precursor low produced significant rainfall over the Northern Territory, generally amounting between . One person drowned in the Victoria River after his car was swept away in a flood. As a tropical cyclone, Helen produced significant wind gusts across the Top End, peaking at 120 km/h (75 mph), downing thousands of trees. In Darwin, roughly 15,000 people were without power due to the storm, more than 100 of which remained so four days after the storm. Overall losses from the storm reached A$1.3 million (US$1.1 million) with an additional A$1 million (US$882,000) in cleanup costs. ==Meteorological history== As early as autumn 2007, long-rage forecast models indicated that a La Niña would develop by December of that year. In general, this event results in increased sea surface temperatures near Australia. Following this, a strong Madden–Julian oscillation phase took shape, leading to the development of Tropical Cyclone Melanie off the coast of Western Australia and an area of low pressure over the Top End by 28 December. Situated over land, the system initially embedded within a disorganised trough and to intensify as it slowly tracked eastward. By 30 December, it separated itself from the trough and travelled towards the west. The following day, the interaction between the two systems allowed the low to significantly deepen, attaining a barometric pressure of 993 mbar (hPa; 29.32 inHg). This strengthening was short-lived as wind shear over the low increased, displacing convection from its centre. By 2 January, the weak low moved over the Joseph Bonaparte Gulf where it slowly developed over the following day.〔 Once over water, the Joint Typhoon Warning Center (JTWC) designated the system as Tropical Depression 09S. As organisation improved, a mid-level subtropical ridge over Western Australia pushed the system westward, away from the Kimberley coast. Steadily strengthening, the low attained gale-force winds near its centre during the morning of 4 January and was subsequently named Helen by the Bureau of Meteorology. Shortly thereafter, a strong westerly monsoon flow to the north caused Helen to turn eastward, back towards land. Intensification continued up until landfall, by which time Helen had attained Category 2 status on the Australian tropical cyclone intensity scale. Maximum ten-minute sustained winds reached 95 km/h (60 mph) and the storm's barometric pressure decreased to 975 mbar (hPa; 28.79 inHg).〔 The JTWC assessed Helen to have been slightly weaker, with peak winds estimated at 85 km/h (50 mph).〔 Around 10:00 pm local time on 4 January, the centre of Tropical Cyclone Helen made landfall near Channel Point. As it moved ashore, the storm developed an eye; however, this feature began breaking apart once overland and the eyewall merged into the system's feeder bands. Roughly 12 hours after landfall, Helen weakened to a tropical low before moving over the Gulf of Carpentaria late on 5 January. Due to an increase in forward motion, the system was unable to regenerate sufficient convection to be reclassified a tropical cyclone before making a second landfall along the Cape York Peninsula.〔 Once overland again, the remnants of Helen abruptly slowed and were last noted on 7 January in the same region.〔 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 Helen (2008)」の詳細全文を読む スポンサード リンク
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