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Hurricane Otto produced days of torrential rain over much of the northeastern Caribbean in October 2010. Otto originated as a subtropical cyclone lingering north of Puerto Rico on October 6, and transitioned into a tropical storm the next day, the fifteenth of the 2010 hurricane season. Accelerating toward the northeast, Otto strengthened into a Category 1 hurricane on the Saffir–Simpson scale on October 8, attaining peak winds of 85 mph (140 km/h). The storm began weakening due to incompatible surroundings and became extratropical west of the Azores on October 10. Otto was the first Atlantic tropical cyclone on record to transition from a subtropical storm since Tropical Storm Laura in 2008. Drifting near the northeastern Caribbean for several days, Otto and its precursor disturbance brought prolonged rainfall to the Leeward Islands, the Virgin Islands, and Puerto Rico, triggering widespread flooding and numerous mudslides. Damage from the storm—in particular to roads, property and infrastructure—exceeded $22 million (2010 USD), but there were no fatalities. After recurving toward the northeast, Otto proceeded across the open Atlantic without affecting any other landmasses. ==Meteorological history== In late September, a large area of disturbed weather associated with two tropical waves formed just east of the Lesser Antilles. The disturbance drifted very slowly west-northwestward, inhibited by strong wind shear that eventually caused the westernmost wave to dissipate. Albeit weak, an elongated remnant trough, or area of low pressure, persisted for several days, stalling over the extreme eastern Caribbean Sea as a nearby upper-level cyclonic vortex retrograded to its north.〔 By October 5, the trough had drifted northward into a more favorable atmospheric environment over the Virgin Islands, which allowed the lowest pressures to extend to the surface. The low became well defined, interacting with the adjacent upper vortex to produce a wide convective band—a concentrated region in which strong showers and thunderstorms can form—over the northeastern Caribbean. Over the next day, the system continued to acquire a prominent subtropical structure: it developed a markedly larger wind radius than typically seen in pure tropical cyclones. Satellite observations also revealed that although the lower wind circulation was distinct, it had become intertwined with the cyclonic vortex aloft to its southwest, confirming the hybrid nature of the system. The National Hurricane Center (NHC) thus classified the system as a subtropical depression at 06:00 UTC on October 6, when it was 265 mi (425 km) north-northwest of San Juan, Puerto Rico.〔 The depression slid slowly northwestward between the contiguous upper vortex and a large high-pressure region over the central Atlantic. A region of lighter wind shear ahead, as well as an anticipated weakening of the upper cyclone, prompted the NHC to introduce the possibility of a tropical transition.〔 Later, satellite observations showed a rapid improvement in the depression's structure; convective banding wrapped completely around the broad inner wind field, which produced gusts to 65 mph (110 km/h). Accordingly, the NHC upgraded the depression to Subtropical Storm Otto at 21:00 UTC on October 6, about 215 mi (345 km) northeast of Grand Turk. Although satellite images continued to display a classical subtropical cyclone, with Otto's center and the vortex aloft nearly collocated, data from a Hurricane Hunters aircraft indicated a weak warm convective core was developing within the mid levels of the circulation—a feature normally present at the upper levels of tropical cyclones. Moreover, a contraction of the large wind field reaffirmed that Otto was entering the final stages of its tropical transition. Although convective activity briefly weakened overnight, weakening shear and considerably warmer sea surface temperatures permitted small patches of thunderstorms to refire on the morning of October 7. As Otto meandered northward, temperature contrasts from forecast models indicated that the warm core within the circulation had ascended to the upper levels of the cyclone. In consequence, a burst of deep, tropical convection with extreme cloud top temperatures of approximately −112° F (−80° C) occurred over the center. Having shed the last of its subtropical characteristics, Otto became a warm-core system and was operationally declared tropical at 1200 UTC that day. Over the course of October 8, Otto began to accelerate to the northeast under the increasing influence of a vertically deep trough off the US East Coast.〔 Conditions aloft remained conducive, and the storm's convection deepened symmetrically over the center to form a large, well-defined central dense overcast. By 1200 UTC, Otto's winds had reached 75 mph (120 km/h) while a mid-level eyewall began to form, prompting the NHC to upgrade the storm to a Category 1 hurricane south of Bermuda. Further strengthening ensued as the newly formed hurricane proceeded over the warm waters of the central Atlantic; microwave imagery revealed the eye, though obscured, was vertically well established, marking Otto's peak strength with estimated winds of 85 mph (140 km/h). Upon peaking in intensity, Otto had become fully embedded within the deep-layered flow to its southwest.〔 Racing northeastward, the hurricane entered an area of progressively cooler waters and adverse upper atmospheric conditions, which eroded its cloud pattern and disrupted the circulation. With maximum winds dropping below 70 mph (110 km/h), Otto was reduced to a tropical storm late on October 9. Convective activity came to a near halt due to relentless wind shear and a lack of tropical moisture, leading specialists to conclude the storm was entering an extratropical transition. The next day, the cool dry air infiltrated the weak warm core, and Otto began to develop frontal banding features. With these characteristics, Otto became an extratropical cyclone on October 10, and the NHC discontinued advisories on the storm. The post-tropical system decelerated near the Azores over the next week, where it eventually degenerated into a remnant low that recurved sharply southeastward before completely dissipating west of Morocco on October 18.〔 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 Otto (2010)」の詳細全文を読む スポンサード リンク
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