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Severe Tropical Cyclone Gwenda was tied for the most intense Australian tropical cyclone on record, with a barometric pressure of 900 hPa (mbar). Forming out of a tropical disturbance over the Arafura Sea on 2 April 1999, the precursor to Gwenda tracked slowly westward and gradually became more organised. On 4 April, the system developed into a Category 1 cyclone and was named Gwenda. It began to undergo explosive intensification the following day, and in a 30-hour span ending early on 7 April, the storm's maximum 10-minute sustained wind speed increased from 75 km/h (45 mph) to 225 km/h (140 mph) and its barometric pressure decreased to 900 hPa (mbar). The Joint Typhoon Warning Center reported that the storm had peaked as a high-end Category 4 equivalent on the Saffir–Simpson Hurricane Scale. Increasing wind shear and an acceleration in forward speed caused Gwenda to quickly weaken. Less than 18 hours after peaking, the storm made landfall roughly east of Port Hedland, Western Australia with winds of 100 km/h (65 mph). After moving ashore, Gwenda abruptly stalled before dissipating on 8 April. Although it was once an extremely intense cyclone, the factors that caused its deterioration also prevented significant damage. Rainfall from the storm peaked at . Minor structural damage was reported, and only localised flooding was recorded. Following its usage, the name Gwenda was retired at the end of the season. ==Meteorological history== Severe Tropical Cyclone Gwenda originated from a weak tropical disturbance that formed on 1 April over the Arafura Sea. Drifting westward, the system gradually became better organised, and early on 2 April, the Australian Bureau of Meteorology classified it as a tropical low. Over the following two days, the low continued to mature; on 4 April, the Bureau of Meteorology upgraded it to a Category 1 cyclone and named it Gwenda.〔〔 Around the same time, the Joint Typhoon Warning Center (JTWC) issued a Tropical Cyclone Formation Alert as deep convection became concentrated around the centre of circulation and the system's outflow significantly improved. Located within an environment of low to moderate wind shear, the storm was expected to intensify. By 5 April, the JTWC began issuing advisories on Gwenda, classifying it as a weak tropical storm and designating it as Cyclone 32S. Tracking southwest in response to a subtropical ridge to the south,〔 Gwenda began to rapidly intensify.〔 Its forward motion significantly decreased as it turned due south before curving towards the southeast,〔 and in a 30-hour span, maximum winds around the centre of the storm increased from 75 km/h (45 mph) to 225 km/h (140 mph). The barometric pressure decreased by 90 hPa (mbar), making Gwenda one of the fastest intensifying storms on record. At the end of the intensification phase on 7 April, the Bureau of Meteorology classified the storm as a Category 5 cyclone, the third of the season, with a pressure of 900 hPa (mbar).〔 The JTWC also reported a substantial increase in intensity, classifying Gwenda as a high-end Category 4 equivalent on the Saffir–Simpson Hurricane Scale with 1-minute sustained winds of 240 km/h (150 mph).〔 Upon attaining peak intensity, Gwenda displayed a well-defined eye surrounded by deep convection.〔〔 At this time, some monitoring satellites estimated that it had attained winds of 260 km/h (160 mph), equivalent to a Category 5 hurricane.〔 While Gwenda was active, the Bureau of Meteorology stated that its intensity peaked with winds of 215 km/h (125 mph) and a pressure of 915 hPa (mbar). Hours after attaining this intensity, increasing wind shear began to impact the cyclone, causing convection to become elongated and the eye less defined.〔 Rapid weakening commenced as Gwenda turned southeastward towards the Pilbara coastline.〔 The cyclone continued to deteriorate as it approached Western Australia, with convection displaced ahead of its centre.〔 In addition to the wind shear, Gwenda's forward speed suddenly increased, leading to further disorganisation.〔〔 Late on 7 April, the centre of Gwenda made landfall as a Category 2 cyclone roughly east of Port Hedland with winds of 100 km/h (65 mph).〔〔 The JTWC estimated the storm to have been slightly stronger at landfall, with winds near 120 km/h (75 mph).〔 Shortly after moving inland, the JTWC issued their final advisory on the weakening storm.〔 The Bureau of Meteorology continued to monitor Gwenda as it abruptly stalled just onshore. However, convection associated with Gwenda continued to stream southeastward due to high wind shear. The storm's remnants persisted for several hours before dissipating early on 8 April.〔 The Australian Bureau of Meteorology uses 10-minute sustained winds, while the Joint Typhoon Warning Center uses one-minute sustained winds. The Bureau of Meteorology's peak intensity for Gwenda was 225 km/h (140 mph) 10-minute sustained, or 260 km/h (160 mph) one-minute sustained.〔 The JTWC's peak intensity for Gwenda was 240 km/h (150 mph) one-minute sustained, or 220 km/h (130 mph) 10-minute sustained.〔〔 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 Gwenda」の詳細全文を読む スポンサード リンク
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