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Typhoon Dolphin (2015)
Typhoon Dolphin was a powerful tropical cyclone that impacted the Mariana Islands, specifically Guam and the Northern Mariana Islands, in mid-May 2015. Forming as the eighth tropical depression of the annual typhoon season, Dolphin was first recognized as a tropical disturbance on May 3 over the eastern Caroline Islands. The system was upgraded to a tropical depression three days later, until it was classified as a named tropical system on May 9. Subsequently, the typhoon underwent rapid deepening to a Category 5 super typhoon. Afterwards, the typhoon began to weaken.
==Meteorological history==
Late on May 4, the Joint Typhoon Warning Center (JTWC) began monitoring an area of deep convection approximately 300 km (185 mi) southwest of Pohnpei. Although the attendant low-level circulation was ill-defined, microwave imagery revealed several fragmented rainbands wrapping into the center of the disturbance, and environmental conditions were expected to favor further development over the coming days. Drifting east-northeastward, the disturbance steadily organized as shower and thunderstorm activity continued to coalesce about a broad area of low pressure, and the JTWC issued a Tropical Cyclone Formation Alert early on May 6 as a result. At 12:00 UTC that same day, the Japan Meteorological Agency (JMA) highlighted the formation of a tropical depression approximately 300 km (185 mi) southwest of Pohnpei. As low-level banding continued to become better defined, the JTWC initiated advisories on Tropical Depression Seven at 21:00 UTC. Following formation, the depression turned eastward, steered by westerly flow along the equator. Deep convection continued to develop over the low-level circulation, albeit limited to the northwest quadrant due to persistent wind shear, prompting the JTWC to upgrade the system to a tropical storm at 15:00 UTC on May 8. At 12:00 UTC the next morning, the JMA followed suit, designating the cyclone as Tropical Storm Dolphin.
Upon being upgraded to a tropical storm, Dolphin executed a turn to the north-northwest under the influence of a building subtropical ridge to the cyclone's north. Although moderate southeasterly wind shear initially hindered further organization, a track parallel to the shear vectors mitigated the unfavorable effects, allowing an eye feature to become visible on microwave imagery by early on May 11. Upper-level outflow began to expand toward the north and south as upper-level winds slackened and a persistent central dense overcast feature developed over the low-level center. At 00:00 UTC on May 12, the JMA upgraded Dolphin to a severe tropical storm, while the JTWC upgraded the cyclone to a typhoon. By 06:00 UTC on May 13, the JMA further upped Dolphin to a typhoon. Amid a continued favorable environment, a pinhole eye approximately 10 km (6 mi) to 19 km (12 mi) in diameter became evident on satellite imagery, leading the JTWC to upgrade Dolphin to the equivalent of a Category 2 hurricane on the Saffir–Simpson hurricane wind scale (SSHWS) by 15:00 UTC. Continuing on a general west-northwest to northwest track, the intensification trend was soon halted by a combination of moderate southerly wind shear and dry air from the west, causing the eye to become obscured on conventional satellite imagery. On May 15, vertical wind shear once again lessened; tight low-level bands wrapped into a large 51 km (32 mi) eye, prompting the JTWC to upgrade Dolphin to an upper-end Category 3 equivalent on the SSHWS. The overall structure of the cyclone continued to improve, and by 03:00 UTC on May 16, it harbored 1-minute sustained winds of 185 km/h (115 mph). This rapid deepening process continued, and 24 hours later, the JTWC upgraded Dolphin to a Category 5 super typhoon, the third super typhoon of the season. After maintaining that intensity for 12 hours, Dolphin weakened to a Category 4 super typhoon. Six hours later, it weakened to a Category 4 typhoon after maintaining super typhoon intensity for 30 hours. Over the next few days, Dolphin weakened further, until the JTWC issued its final warning on May 19. However, the JMA still tracked Dolphin as a tropical system until the following day, when Dolphin was declared to have become extratropical on May 20. Its extratropical remnants was then absorbed by another developing extratropical cyclone north of it on May 24.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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