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Typhoon Bolaven, known in the Philippines as Typhoon Julian, was regarded as the most powerful storm to strike the Korean Peninsula in nearly a decade,〔 with wind gusts measured up to . Forming as a tropical depression on August 19, 2012 to the southwest of the Mariana Islands, Bolaven steadily intensified as it slowly moved west-northwestward in a region favoring tropical development. The system was soon upgraded to a tropical storm less than a day after formation and further to a typhoon by August 21. Strengthening became more gradual thereafter as Bolaven grew in size. On August 24, the system attained its peak intensity with winds of 185 km/h (115 mph) and a barometric pressure of 910 mbar (hPa; 26.87 inHg). Weakening only slightly, the storm passed directly over Okinawa on August 26 as it began accelerating toward the north. Steady weakening continued as Bolaven approached the Korean Peninsula and it eventually made landfall in North Korea late on August 28 before transitioning into an extratropical cyclone. The remnants rapidly tracked northeastward over the Russian Far East before turning eastward and were last noted on September 1 crossing the International Dateline. Although Bolaven struck the Ryukyu Islands as a powerful typhoon, damage was less than expected. Relatively few buildings were damaged or destroyed across the region. The most significant effects stemmed from heavy rains, amounting to , that caused flash flooding and landslides. One person drowned on Amami Ōshima after being swept away by a swollen river. In mainland Japan, two people drowned after being swept away by rough seas. In South Korea, 19 people were killed by the storm. Many buildings were damaged and approximately 1.9 million homes were left without power. Losses in the country reached ₩420 billion (US$374.3 million), the majority of which was due to destroyed apple orchards. Significant damage also took place in North Korea where at least 59 people were killed and 50 others were reported missing. Additionally, 6,700 homes were destroyed. Offshore, nine people drowned after two Chinese vessels sank. ==Meteorological history== On August 18, an area of showers and thunderstorms associated with a trough formed about west-southwest of Guam. Over the following day, a low-level circulation developed within the trough. Tracking slowly northeastward into a region of warm sea surface temperatures, low wind shear, and favorable divergence, continued development was anticipated.〔 Later on August 19, the Joint Typhoon Warning Center (JTWC) issued a Tropical Cyclone Formation Alert as the system was anticipated to develop further. Hours later, the Japan Meteorological Agency (JMA) classified the low as a tropical depression. The JTWC followed suit early on August 20, designating the system as Tropical Depression 16W. Following the development of convective banding features along the southern side of the low, both the JMA and JTWC upgraded the depression to a tropical storm, with the former assigning it the name ''Bolaven''. By this time, the storm began turning northwestward in response to a subtropical ridge south of Japan. Later on August 20, microwave imagery from the Tropical Rainfall Measuring Mission satellite depicted a weak eye-like feature. Early on August 21, the JMA upgraded Bolaven to a severe tropical storm, with maximum estimated winds at 95 km/h (60 mph). Throughout the day, a large central dense overcast developed around the low-level circulation and banding features became more prominent, especially over the southern half of the storm. However, the northwestern quadrant of Bolaven struggled to organize as quickly due to moderate wind shear produced by a nearby upper-level anticyclone. Due to the improved structure, both the JMA and JTWC upgraded Bolaven to a typhoon during the latter half of August 21. Gradual intensification ensued over the following days as the storm became increasingly organized. A second anticyclone developed over the center of Bolaven later that day and enhanced the cyclone's poleward outflow. Although subsidence and wind shear increased along the northern edge of the storm on August 23, the system's outflow allowed it mitigate the negative effects ahead of it. Due to the storm's large size, it began turning towards the north-northwest along the subtropical ridge on August 24, earlier than anticipated. During this brief turn, the center of Bolaven crossed 135°E, entering the area of responsibility of the Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA). As such, the administration assigned the typhoon with the local name ''Julian''. Later that day, a well-defined, wide eye developed within the central dense overcast and several additional feeder bands formed along the south side of the circulation. Based on the improved structure, the JTWC estimated that the system attained one-minute sustained winds of 215 km/h (135 mph), equivalent to a Category 4 on the Saffir–Simpson Hurricane Scale. By the morning of August 25, Bolaven began to undergo an eyewall replacement cycle. Despite the slightly degrading structure, the JTWC estimated the storm to have intensified slightly, attaining one-minute winds of 230 km/h (145 mph). On August 25, Bolaven began to interact with Typhoon Tembin, which was located over the South China Sea, causing Tembin to execute a slow counter-clockwise loop. An outer eyewall became more apparent late on August 25 with a clear second ring of deep convection surrounding the original eye. Similar to the JTWC, the JMA continued to indicate that Bolaven was intensifying through early on August 26. At that time, the JMA estimated the typhoon to have reached its peak intensity with winds of 185 km/h (115 mph) and a barometric pressure of 910 mbar (hPa; 26.87 inHg). As the system approached Okinawa, radar imagery showed a wide eyewall surrounding a small, but well-organized wide inner eyewall. Shortly before 1500 UTC on August 26, the center of Bolaven passed directly over Okinawa. At the time, the JTWC assessed the system to have had one-minute sustained winds of 195 km/h (120 mph) while the JMA estimated the winds to be 175 km/h (110 mph). Early on August 27, the storm's inner eyewall collapsed as the eyewall replacement cycle finished, with the new eye estimated to be about in diameter. In addition to its unusually large eye, the storm itself was large, spanning approximately . However, microwave satellite imagery indicated an overall weakening of the western side of the storm. Accelerating northward, Bolaven maintained a well-defined outflow due to a large tropical upper-tropospheric trough to its southeast and a mid-latitude trough to the northwest. As the storm moved northward over the Yellow Sea, atmospheric conditions became increasingly hostile, with significantly lower sea surface temperatures and high wind shear.〔 During the overnight of August 27–28, the typhoon brushed South Korea as a weakening cyclone. Convection on the west side of the storm diminished and its feeder bands began to collapse. Increasing shear started taking its toll early on August 28 as convection became displaced from the center of circulation, leaving part of the southwestern quadrant exposed. This also indicated that Bolaven had begun to undergo an extratropical transition as it approached the Korean Peninsula. Following structural weakening, the JMA and JTWC downgraded Bolaven to a severe tropical storm and tropical storm, respectively. Hours before moving onshore in North Korea, the majority of the convection had moved over land while the circulation and the center itself had only stratocumulus clouds covering it. Around 1500 UTC on August 28, Bolaven made landfall in North Korea with winds of 100 km/h (65 mph). Rapidly moving towards the northeast, the storm became fully embedded within a baroclinic zone near the China–North Korea border later that day. The JMA continued to monitor Bolaven as a tropical cyclone until early on August 29, at which time the system was situated over the southern region of the Russian Far East. The extratropical remnants later turned eastward and were last noted on September 1 crossing the International Dateline. 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 Bolaven (2012)」の詳細全文を読む スポンサード リンク
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