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Typhoon Roke, known in the Philippines as Tropical Storm Onyok, was a persistent and powerful tropical cyclone that affected Japan, including some areas that had been damaged by another typhoon just a few weeks prior. It was the fifteenth named storm, the tenth severe tropical storm, the sixth typhoon of the 2011 Pacific typhoon season and overall, the 27th tropical cyclone to be monitored by the Japan Meteorological Agency during the year. ==Meteorological history== On September 8, the Joint Typhoon Warning Center started to monitor a tropical disturbance that had developed about to the northeast of Hagåtña, Guam. Unorganized deep convection was surrounding the disturbances developing low level circulation centre, in an area of low vertical windshear and improving outflow.〔 During that day the disturbance gradually developed further while moving westwards under the influence of a subtropical ridge of high pressure.〔 During September 9, as the system continued to move westwards, the Japan Meteorological Agency reported that the disturbance had developed into a tropical depression. Continuing to move westwards the system gradually developed further with the depressions low level circulation centre consolidating before it was declared Tropical Depression 18W by the Joint Typhoon Warning Center during the next day. Over the next two days, the system gradually drifted west and intensified slightly, prompting the Joint Typhoon Warning Center (JTWC) to issue a Tropical Cyclone Formation Alert (TCFA) on it.〔(【引用サイトリンク】url=http://vizagbom.blogspot.com/2011/09/jtwc-tropical-cyclone-formation-alert_11.html )〕 Convection gradually consolidated the LLCC and the JTWC initiated advisories on the system on September 11, designating it with ''18W''.〔(【引用サイトリンク】url=http://vizagbom.blogspot.com/2011/09/jtwc-tropical-cyclone-advisory-01_11.html )〕 The next day, the depression drifted into the Philippine Area of Responsibility (PAR) and the Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) initiated advisories on the depression, naming it ''Onyok''.〔(【引用サイトリンク】url=http://www.webcitation.org/61fF7WWL3 )〕 However, just as similar to Kulap, Onyok also exited the PAR in 6 hours from entering the region.〔(【引用サイトリンク】url=http://www.webcitation.org/61fFXGTRR )〕 In an advisory, the JTWC reported that there were at least two more vortices associated with the system, that caused an abrupt, erratic movement.〔(【引用サイトリンク】url=http://www.webcitation.org/61fVjdF76 )〕 However, being located in an area of warm sea surface temperatures and low vertical wind shear, the depression continued to strengthen and on September 13, the JMA upgraded the depression to a tropical storm and named it ''Roke''.〔(【引用サイトリンク】url=http://www.webcitation.org/61fUifcW0 )〕 On September 14, a Tropical upper tropospheric trough (TUTT) cell located approximately 05 degrees to the west of the system caused strong subsidence prompting the JTWC to downgrade Roke to a tropical depression.〔(【引用サイトリンク】url=http://www.webcitation.org/61h4FzMh5 )〕 However, because of favorable atmospheric conditions, Roke strengthened again, and the JTWC re-upgraded Roke to a tropical storm.〔(【引用サイトリンク】url=http://www.webcitation.org/61i2Rwh7D )〕 On September 16, the previously exposed LLCC was being re-consolidated with convection and Roke continued to strengthen again. Despite the upper low over the LLCC, Roke remained a warm-core tropical cyclone and the JTWC predicted that there were chances of Roke become a hybrid or a subtropical storm.〔(【引用サイトリンク】url=http://www.webcitation.org/61jieS1Be )〕 On continuing its west-northwestward movement, Roke eventually slowed down to under with a tongue of cloud-free air entering the LLCC from the west side. Due to a mid-level warm anomaly, the subtropical transition was taking place at an unusually slow rate.〔(【引用サイトリンク】url=http://www.webcitation.org/61juEtwHf )〕 Later, that day, Roke turned to the southwest and slowed down with convection consolidating and deepening near the LLCC. What began as a monsoonal depression with an elongated and weak LLCC was now more stronger and organized.〔(【引用サイトリンク】url=http://www.webcitation.org/61l412Vzg )〕 Also, the TUTT cell above the system started weakening and data from an ASCAT scatterometer pass revealed that the storm started to strengthen and the JTWC no longer expected a subtropical transition.〔(【引用サイトリンク】url=http://www.webcitation.org/61l4VP8HY )〕 On September 17, the JTWC reported that Roke developed a small, deep convective eye with an unusually large convective band surrounding the southern periphery of the storm. At that time, Roke was approximately east of Kadena Air Base, Japan with winds of over .〔(【引用サイトリンク】url=http://www.webcitation.org/61mnwjXHz )〕 As a result, the JMA upgraded Roke to a severe tropical storm.〔(【引用サイトリンク】url=http://www.webcitation.org/61moI3gQl )〕 However, Roke soon started become elongated around the northeast quadrant as a response to the strong westerlies ahead of a mid-latitude trough.〔(【引用サイトリンク】url=http://www.webcitation.org/61moU6Nx6 )〕 But this was not for too long. Roke quickly became organized again and developed an excellent equatoward outflow and continued to strengthen.〔(【引用サイトリンク】url=http://www.webcitation.org/61pqn2dkd )〕 Then, being located in an area of low vertical wind shear and abnormally high sea surface temperatures, Roke underwent rapid deepening and became a Category 1 typhoon on the SSHS with a maximum sustained windspeed of (1-min sustained).〔(【引用サイトリンク】url=http://www.webcitation.org/61pqzxWaH )〕 The JTWC later reported that Roke underwent ''Explosive intensification'', a more extreme case of rapid deepening that involves a tropical cyclone deepening at a rate of at least 2.5 mbar per hour for a minimum of 12 hours. Also, they added that Roke developed a eye and a good poleward outflow channel.〔(【引用サイトリンク】url=http://www.webcitation.org/61pr6Jnws )〕 On September 21, Typhoon Roke made landfall over Hamamatsu, Japan at about 5:00 UTC (14:00 JST).〔(【引用サイトリンク】url=http://www3.nhk.or.jp/news/html/20110921/t10015741001000.html )〕 Soon Roke started weakening as cloud tops started getting warmed up and eye diameter started to decrease. However, the system still maintained a near radial outflow and the convective structure continued to remain organized that kept Roke from dissipating rapidly.〔(【引用サイトリンク】url=http://www.webcitation.org/61rG722t4 )〕 Although Roke entered a de-intensification phase, it still had plenty of strength that posed a great threat to regions of Japan. Being located approximately southwest of Yokosuka, Kanagawa, the typhoon accelerated northeastward at approximately with winds of over (1-min sustained) being a Category 3 typhoon on the SSHS.〔(【引用サイトリンク】url=http://www.webcitation.org/61rGNc28H )〕 Being embedded in the baroclinic zone, Roke started its extratropical transition. Also, land interaction severely weakened the storm to a minimal Category 1 typhoon with winds of under (1-min sustained).〔(【引用サイトリンク】url=http://www.webcitation.org/61rqwpqZc )〕 Only six hours later, the storm further weakened and accelerated northeastward at approximately with rapidly dissipating deep convection completely sheared to the northeast of the LLCC. As a result, the JTWC ceased advisories on the storm, as it became fully extratropical.〔(【引用サイトリンク】url=http://www.webcitation.org/61rr7FsZT )〕 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「Typhoon Roke (2011)」の詳細全文を読む スポンサード リンク
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