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Typhoon Irma, known in the Philippines as Typhoon Anding, was a powerful typhoon that struck the Philippines in November 1981. The twenty-fifth named storm and fourteenth typhoon of the 1981 Pacific typhoon season, Irma originated from an active monsoon trough to the east of the Philippines. The cyclone slowly developed as it moved westward. Following an increase in organization, the system was first classified on November 18 and was subsequently upgraded into a tropical storm on the next day. After passing near Guam, Irma continued to deepen, and was estimated to have attained typhoon intensity early on November 21. The intensification rate accelerated thereafter, and on the afternoon of November 22, Irma reached its peak wind speed of . After maintaining this intensity for 16 hours, Irma weakened considerably due to interaction with the mountainous terrain of the Philippines. On the morning of November 24, Irma moved ashore northeast of Manila, with winds of . The storm rapidly deteriorated overland, but was still believed to have been a typhoon when it emerged into the South China Sea. Typhoon Irma then began to re-curve towards the northwest while weakening; the cyclone was estimated to have obtained extratropical characteristics on November 26. Affecting an area already severely impacted by Typhoon Hazen, Typhoon Irma brought significant damage and flooding to the Philippines, especially in the province of Camarines Norte. Additionally, a storm surge was noted in four towns in the Camarines Sur province, resulting in the deaths of 137 people. The nearby village of Benagaspasan was nearly demolished, where 47 fatalities occurred. In all, 595 were killed due to Irma. A total of 482,678 persons were directly affected by Typhoon Irma. Irma destroyed or damaged 119,233 dwellings, which left nearly 40,000 homeless. A total of 24,137 families or 141,974 individuals left their homes, including 57,198 that sought emergency shelter. Overall, damage totaled to $63.3 million (1981 USD). ==Meteorological history== Typhoon Irma originated from an active monsoon within the vicinity of Micronesia. The second of three storms to form within this region in mid-November 1981, the cyclone was first noted on November 10 as a "zone of strong convection activity". Although the zone was well-organized, there was initially little to no evidence of a low-level circulation. However, a weak circulation was detected on a few days later, and on November 15, the system was situated to the east of Ponape as satellite imagery indicated that convection was developing. During the next three days, thunderstorm activity waxed and waned as the disturbance moved north and then west. During this time, the disturbance was located east of Typhoon Hazen. By November 18, shower activity had improved in both coverage and organization. That afternoon, the Joint Typhoon Warning Center (JTWC) issued a Tropical Cyclone Formation Alert (TCFA) for the disturbance. Within two hours, the Japan Meteorological Agency (JMA) began to track the system. On the morning of November 19, a Hurricane Hunter aircraft reported winds of , prompting the JTWC to classify the system as a tropical depression.〔 After passing north of Guam, Irma was upgraded into a tropical storm by both agencies. Around this time, the JTWC expected that Irma would pass south of a front and then turn southwest.〔 Tropical Storm Irma began to deepen more rapidly, and on November 20, the JMA upgraded Irma into a severe tropical storm.〔 Thereafter, Irma turned west as a subtropical ridge built north and northwest of the storm, which protected Irma from feeling the effects of strong wind shear.〔 At 1800 UTC on November 20, the JTWC upgraded Irma into a typhoon.〔 Later that evening, a Hurricane Hunter aircraft reported winds of and a pressure of .〔 Following the formation of a eye,〔 the JMA declared that Irma attained typhoon status at 0000 UTC on November 21;〔 subsequently, the system passed south of a second cold front. By 0900 UTC that day, rapid deepening to pressures below was anticipated by the JTWC.〔 At 1800 UTC on November 21, the JMA raised the intensity of the typhoon to 〔 while the JTWC reported that Irma reached winds of , equivalent to a Category 3 hurricane on the United States-based Saffir-Simpson Hurricane Wind Scale (SSHWS). Midday on November 22, a Hurricane Hunter airplane reported a pressure of . Based on this the JTWC upgraded Irma into a super typhoon.〔 Meanwhile, data from both the JTWC and JMA suggested that Irma reached its peak intensity, with the former reporting winds of and the latter reporting winds of .〔 On that day, the Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) also started to monitor the storm and assigned it with the local name ''Anding''.〔〔 Irma maintained super typhoon intensity for 16 hours before gradually weakening due to the storm's close proximity to the mountainous terrain of the Philippines. After turning northwest towards a break within the subtropical ridge, Irma moved ashore around 0900 UTC on November 24, roughly northeast of Manila.〔 At the time of landfall, both agencies estimated winds of , equal to Category 2 intensity on the SSHWS.〔 Although the JTWC downgraded Irma to a tropical storm that afternoon just before entering the Lingayen Gulf and the South China Sea,〔 the JMA maintained Irma at typhoon intensity throughout the storm's passage of the Philippines.〔 Ten hours later, a Hurricane Hunter aircraft investigated Irma and noted that Irma was poorly organized, with most of the convection sheared off to the north of the center. Influenced by a trough east of Asia, Irma began to re-curve into the Luzon Straits on November 25.〔 Around this time, the JMA downgraded Irma into a severe tropical storm. Early on November 26, the JMA reported that Irma had transitioned into an extratropical cyclone.〔 About 24 hours later, Irma merged with a cold front in the Ryukyu Islands.〔 On the evening of November 27, both PASAGA and the JMA ceased monitoring Irma.〔〔 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 Irma (1981)」の詳細全文を読む スポンサード リンク
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