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Hurricane Bertha was both the longest-lived and easternmost developing July tropical cyclone on record. The second named storm, as well as the first hurricane and major hurricane of the 2008 hurricane season, Bertha originated as a tropical wave over western Africa on July 1. After emerging into the eastern Atlantic, favorable environmental conditions allowed the wave to organize into a tropical depression two days later. Early on July 3, the depression intensified into a tropical storm, and by July 7, the system had acquired enough organization to be considered a Category 1 hurricane. Turning towards the northwest, a period of rapid deepening ensued thereafter. Bertha intensified into a major hurricane—a Category 3 or higher on the Saffir–Simpson hurricane wind scale—at 1800 UTC and further intensified to reach its peak intensity with winds of 125 mph (205 km/h) three hours later. A period of substantial weakening began early on July 8 as the system entered a region of higher wind shear, though it attained a secondary peak as a Category 2 hurricane on July 10. Shortly thereafter, the system entered an eyewall replacement cycle while simultaneously tracking over cooler ocean waters; this caused Bertha to weaken to a tropical storm by July 13. Moving northeast, southeast, and eventually resuming its northeast motion, the system attained hurricane intensity once again very briefly before transitioning into an extratropical cyclone on July 20. The extratropical low was absorbed by a larger system the following day. Following formation, Bertha produced light precipitation across Cape Verde. Several days later, preceding its track across a large portion of the Atlantic, the system brought several inches of rain to Bermuda. Tropical storm-force winds caused minimal damage in the form of broken tree limbs and downed power outages; however, no fatalities were reported. Large swells impacted the East Coast of the United States as the hurricane curved out to sea, resulting in two fatalities; in addition, one swimmer was never found and is presumed dead. Strong rip currents along the coastline of North Carolina injured four while at least sixty required rescuing; farther north, in New Jersey, at least 57 people had to be rescued. In Delaware, at least 55 people were injured. ==Meteorological history== Hurricane Bertha was first identified as a broad area of low pressure accompanying a tropical wave over western Africa in late June 2010. Tracking generally west-northwestward, the system emerged into the eastern Atlantic Ocean on July 1. Steady development took place as convection – thunderstorm activity – consolidated around its center, and spiral banding became better established. At 0300 UTC on July 3, the wave and associated low-pressure area was deemed sufficiently organized to be designated as Tropical Depression Two while centered roughly 220 mi (350 km) south-southeast of the Cape Verde Islands. At this time, the National Hurricane Center (NHC) noted that the depression displayed intense convection near the center and increasingly pronounced banding features in the northwestern portion of the circulation. Additionally, the organization mentioned that the global models performed well in predicting the tropical cyclogenesis of Bertha, with the Global Forecast System (GFS) forecasting development of Bertha a week out. Six hours later, the depression attained gale-force winds, and was subsequently upgraded to Tropical Storm Bertha after satellite estimates from both the Satellite Analysis Branch (SAB) and Tropical Analysis and Forecast Brach (TAFB) supported an intensity of 40 mph (55 km/h).〔 Moving west-northwestward around the southern periphery of a mid-level ridge situated over the central Atlantic, Bertha briefly stopped intensifying as cloud tops associated with the system warmed; despite this, banding features remained well-defined. However, the intensification process began shortly thereafter as a burst of deep convection developed atop the cyclone's center. The system was located within an environment conducive for strengthening, although it was noted in the 5:00 p.m. AST (2100 UTC) forecast discussion that Bertha would soon be entering an area of cooler sea surface temperatures. Continuing towards the west-northwest, the tropical storm remained consistent in its intensity through the overnight hours of July 4, characterized at the time with a new burst of convection developing atop Bertha's center. Early the following day, satellite imagery revealed a ragged appearance in association with Bertha as it passed over sea surface temperatures near 77 °F (25 °C), values below the threshold needed to sustain a tropical cyclone. However, over the following hours, satellite imagery revealed a slightly better organized Bertha as the system entered an area of warmer sea surface temperatures. During the afternoon hours of July 6, a series of microwave imagery depicted Bertha's low-level circulation tilted to the southwest of its mid-level center. Additionally, an eye-like feature became apparent, an indication that Bertha was gathering strength. A deep ring of convection surrounded this eye feature, and upper-level outflow spread towards the west. The system continued to intensify over the following hours, and given Bertha's microwave imagery appearance on July 7, the NHC upgraded the system to Category 1 hurricane status on the Saffir–Simpson Hurricane Wind Scale, the first of the season. At this time, the NHC predicted a peak intensity just below Category 2 hurricane status as an approaching trough produces high vertical wind shear began to impede on the system's development after 48 hours. Despite this, Bertha continued to intensify, and began a period of rapid intensification during the afternoon hours of July 7. During this time, Bertha intensified 50 mph (85 km/h) in a 15-hour period. At 5:00 p.m. AST (2100 UTC), Bertha reached its peak intensity as a strong Category 3 hurricane with winds of 125 mph (205 km/h) and a minimum barometric pressure of 952 mbar (hPa; 28.11 inHg). After reaching peak intensity, satellite imagery revealed a rapid degradation in Bertha's structure. The well-defined eye previously observed had become cloud-filled and ragged, and microwave imagery evidenced that the western portion of the eyewall had eroded. This rapid weakening was likely due to the hurricane encountering an area of higher wind shear, cooler sea surface temperatures, and dry air entrainment. The advisory issued at 1100 a.m. AST (1500 UTC) dropped Bertha's maximum sustained winds to 100 mph (155 km/h), although it was noted that this could be conservative. Further weakening occurred over the next 24 hours as Bertha encountered unfavorable conditions for strengthening. However, after a decrease in wind shear, Bertha intensified to attain Category 2 hurricane status on July 10. While performing a gradual northward turn, Bertha fluctuated in intensity for several days while maintaining hurricane intensity. By July 13, Bertha had weakened to a tropical storm while located a few hundred miles to the southeast of Bermuda. Turning northward before dipping southeastward, Bertha remained a tropical storm until July 18, at which time it was upgraded to a hurricane once again. It remained at this intensity until unfavorable conditions led to subsequent weakening on July 20. Bertha weakened to a tropical storm and transitioned into an extratropical cyclone shortly after. Its extratropical remnants persisted for the following 24 hours as they moved northeastward into the northern Atlantic, about midday between the island of Newfoundland and the Azores. 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 Bertha (2008)」の詳細全文を読む スポンサード リンク
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