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Tropical Storm Bret was the second named storm of the 2011 Atlantic hurricane season. Bret formed along the southwestern periphery of a weather front north of the Bahamas on July 17. At first, the storm moved little and gradually strengthened in response to favorable upper-level conditions, reaching peak sustained winds of 70 mph (110 km/h). Steering currents in the area subsequently became better established, and Bret turned toward the northeast only to encounter a substantial increase in vertical wind shear. Despite the shear, the storm maintained a well-defined wind circulation for several days, with intermittent bursts of thunderstorms near its center. By July 22, Bret had been devoid of strong thunderstorm activity for several hours, prompting the National Hurricane Center to discontinue public advisories when it was located about 375 miles (605 km) north of Bermuda. Since Bret remained over the open Atlantic for most of its existence, its effects on land were limited. While moving little, the storm produced inclement weather and widespread cloudiness over much of the north-central Bahamas. Squalls off the eastern coast of Florida generated rough seas along coastlines, injuring a number of people. Although it stayed well offshore, the storm enhanced tropical moisture over Bermuda, causing beneficial rainfall in dry areas. ==Meteorological history== In mid-July, 2011, a broad upper trough dropped southward over the northwest Atlantic, supporting a cold front that extended westward across Bermuda to inland over Georgia. The front produced a large area of light showers to its north, with its westernmost component remaining quasi-stationary over northeastern Florida. On July 16, a surface low developed along the decaying boundary, just off the coast, generating an area of sporadic convection north of the Bahamas. Although a wind circulation was initially absent and surface pressures were relatively high, the low later became better organized under abating shear conditions. At 2100 UTC on July 17, the National Hurricane Center (NHC) declared it a tropical depression, after reconnaissance confirmed the presence of a closed circulation center about 100 mi (160 km) northwest of Great Abaco Island. It strengthened into Tropical Storm Bret just three hours later, owing to a quick increase in winds and deep central convection. Situated along a weakness in the subtropical ridge, Bret drifted very slowly southward during the initial stages of its existence.〔 Though traces of dry air approached it from the west, the cyclone continued to strengthen, as prominent bands of deep thunderstorms tightened around it eastern semicircle. Satellite images displayed a disorganized eye-like feature on July 18, suggesting a rather sharp increase in strength. Indeed, an additional reconnaissance flight into the cyclone found peak surface winds of around 70 mph (110 km/h), just below hurricane strength. Following its peak, Bret began to accelerate toward the northeast in response to building high pressure in the area. It fluctuated little in intensity for several hours, although a combination of high wind shear and a lack of tropical moisture inhibited further development. By July 19, the circulation center had become exposed and devoid of deep convection, and the storm weakened to 50 mph (85 km/h) winds upon moving through the increasingly hostile environment. Despite the unfavorable conditions, Bret retained this intensity for the next couple of days as it briefly slowed, with a distinct low-level circulation and a few patches of persistent thunderstorms over its southwestern quadrant. Early on July 20, the heavily sheared cyclone began to reaccelerate within the deepening southwesterly wind flow. Over the next day, Bret continued to deteriorate in organization; however, a brief decline in the upper winds allowed intermittent bursts of convection to redevelop south of the exposed center. Bret eventually weakened to a tropical depression over cool ocean temperatures early on July 22, once again lacking significant convection while increasing in forward speed. Forecasters at the NHC noted that Bret remained "a maverick tropical cyclone by refusing to dissipate despite experiencing very hostile wind shear conditions," with ship data indications of prevailing strong winds. By 1500 UTC, however, the circulation had become ill defined, prompting the NHC to declassify Bret as a tropical system about 375 mi (605 km) north of Bermuda. During the next several hours, the remnant low of Bret continued to move northeastward out into the Atlantic, until it dissipated on June 23.〔 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「Tropical Storm Bret (2011)」の詳細全文を読む スポンサード リンク
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