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Hurricane John, also known as Typhoon John, formed during the 1994 Pacific hurricane season and became both the longest-lasting and the farthest-traveling tropical cyclone ever observed. John formed during the El Niño of 1994–95〔(【引用サイトリンク】title=Cold and Warm Episodes by Season )〕 and peaked as a Category 5 hurricane on the Saffir–Simpson hurricane wind scale, the highest categorization for hurricanes. Over the course of its existence, it followed a 7,165-mile (13,280-km) path from the eastern Pacific to the western Pacific and back to the central Pacific, lasting 31 days in total.〔 〕 Because it existed in both the eastern and western Pacific, John was one of a small number of tropical cyclones to be designated as both a hurricane and a typhoon. Despite lasting for a full month, John barely affected land at all, bringing only minimal effects to the Hawaiian Islands and the United States military base on Johnston Atoll. Its remnants later affected Alaska. ==Meteorological history== The origins of Hurricane John were thought by the United States National Hurricane Center (NHC) to be from a tropical wave that moved off the coast of Africa on July 25, 1994. The wave subsequently moved across the Atlantic Ocean and Caribbean without distinction, before it crossed Central America and moved into the Eastern Pacific Ocean on or around August 8.〔〔 Upon entering the Eastern Pacific the wave gradually developed, before the NHC initiated advisories on the system and designated it as Tropical Depression Ten-E during August 11. The system was at this time moving westwards and located around to the south-southeast of Acapulco, Mexico.〔〔 Conditions were not ideal for development, but it quickly developed banding features and well-defined outflow, and was upgraded to a tropical storm and named John later that day.〔 A strong ridge of high pressure over the northeastern Pacific Ocean forced John westward, where upper level wind shear kept John a tropical storm. Intensity fluctuated considerably, however, as shear levels varied. More than once, shear cleared away most of the clouds above John and nearly caused it to weaken to a tropical depression.〔 However, after eight days of slow westward movement across the Pacific Ocean, shear lessened greatly on August 19, and John intensified significantly and was designated as a hurricane at 1700 PDT. During an eighteen-hour period between August 19 and August 20, John further strengthened from a weak Category 1 hurricane to a major Category 3 hurricane. Around 1100 PDT on August 20, it crossed into the central Pacific, the first of three basin crosses John would make.〔 After entering the central Pacific, John left the area monitored by the NHC and was instead monitored by the Central Pacific Hurricane Center (CPHC). As it moved slowly westward, Hurricane John continued to strengthen considerably in an increasingly favorable environment well south of the Hawaiian Islands; on 22 August John was designated a Category 5 hurricane on the Saffir–Simpson hurricane scale (the highest classification for hurricanes) and later that day (by Hawaii Standard Time) reached its peak winds of 175 miles per hour (280 km/h).〔 〕 Also on August 22 (by Hawaii Standard Time), John made its closest approach to the Hawaiian Islands, 345 miles (500 km) to the south. John had threatened to turn north and affect the islands days before, but the ridge of high pressure that typically shields the islands from hurricanes kept John on its southerly path. Nonetheless, heavy rains and wind from the outer bands of John affected the islands.〔 With the Hawaiian Islands behind it, John began a slow turn to the north, taking near-direct aim at Johnston Atoll, a small group of islands populated only by a United States military base. The storm slowly weakened from its peak as a Category 5 hurricane in the face of increasing shear, dropping down to a Category 1 hurricane with 90 miles per hour (145 km/h) maximum winds. On August 25 local time, John made its closest approach to the Johnston Atoll only 15 miles (24 km) to the north. On Johnston Atoll, sustained winds were reported up to 60 miles per hour (95 km/h), the equivalent of a strong tropical storm, and gusts up to 75 miles per hour (120 km/h) were recorded.〔 (Note that this report does not reflect changes made in post-season analysis.)〕 Clearing Johnston Atoll, John turned to the northwest and began strengthening again as shear decreased. On August 27 local time, John reached a secondary peak strength of 135 miles per hour (210 km/h), and shortly thereafter it crossed the International Date Line at approximately 22° N and came under the surveillance of the Guam branch of the Joint Typhoon Warning Center (JTWC). By crossing into the western Pacific, John also became a typhoon and was referred to as Typhoon John during its time in the western Pacific.〔 Immediately after crossing the Date Line, John again weakened and its forward motion stalled. By September 1, John had weakened to a tropical storm and was nearly motionless just west of the Date Line. There, John lingered for six days while performing a multi-day counterclockwise loop. On September 7, a trough moved into the area and quickly moved John to the northeast. John crossed the Date Line again on September 8 and reentered the central Pacific.〔 After reentering the central Pacific, John briefly reached a tertiary peak strength of 90 miles per hour (145 km/h), a strong Category 1 hurricane, well to the north of Midway Island. However, the trough was rapidly pulling apart John's structure, and the cold waters of the northern central Pacific were not conducive to a tropical cyclone. On September 10, the 120th advisory was released on the system, finally declaring John to have become extratropical approximately 1000 miles (1600 km) south of Unalaska Island.〔 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「Hurricane John (1994)」の詳細全文を読む スポンサード リンク
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