Sunday, August 24, 2014

Hurricane Cristobal (2014)

Storm Active: August 23-29

On August 16, some scattered thunderstorms developed in association with a broad low pressure system situated over the central tropical Atlantic, about halfway between the western coast of Africa and the Caribbean. No further organization occurred until around August 19, when convection became a little more concentrated in association with the system. As the low approached the Leeward Islands on August 21, it remained poorly defined, but began to generate gale force winds. Land interaction limited development over the next day while the low continued west-northwest just to the north of Puerto Rico and Hispaniola. However, on August 23, the system slowed in forward speed and turned northwest towards the Bahamas. That afternoon, though the circulation remained somewhat broad, banding on the north and east sides of the circulation improved to the point that advisories were initiated on Tropical Depression Four.

Some wind shear was affecting the system, but ocean waters near the Bahamas were very warm, and deep convection gradually increased near the center of circulation. By the morning of August 24, the depression had strengthened into Tropical Storm Cristobal. Over the next day, the system moved slowly northward, bringing sustained heavy rain to portions of the Bahamas. Though shear from the north exposed the circulation of Cristobal during the early morning of August 25, the center reformed southeast of its former position, bringing it closer to the convective canopy, and allowing modest strengthening through that morning.

During that day, the system meandered slowly to the north and east, moving away from the Bahamas. Meanwhile, though thunderstorm activity developed closer to the center, Cristobal's overall satellite presentation remind disorganized. The tropical storm was interacting with a frontal boundary, giving the associated convection a more linear than circular pattern. Despite this, winds increased that night and Cristobal became a category 1 hurricane. The system acquired a faster and more definite northward motion on August 26. Atmospheric conditions became more favorable over the next day, allowing Cristobal to develop a more organized, albeit asymmetric, structure. By the morning of August 27, the cyclone had developed a partial eyewall in the northwest semicircle. Though shower activity to the south and east was still scarce, small intensification accompanied this improvement in structure.

Around noontime, Cristobal passed well to the west of Bermuda, bringing scattered showers, gusty winds, and dangerous ocean conditions to the island. Influenced by mid-latitude winds, the system then began its turn towards the northeast, accelerating rapidly. At the same time, the cyclone assumed a more symmetrical appearance. As the hurricane raced to the north and east over the next day, it acquired an eyewall and even an intermittent eye feature during the afternoon and evening of August 28. Cristobal reached its peak intensity that night above 40°N, with 85 mph winds and a minimum pressure of 970 mb.

That evening, however, the system moved over much cooler water, and began extratropical transition as it moved northeast past Nova Scotia with a forward speed of nearly 50 mph. By the morning of August 29, all remaining convection was displaced well to the north of the center. Further, the wind field had broadened, indicating that the cyclone was no longer tropical. The low that had been Cristobal maintained powerful winds for several days, and eventually affected Iceland.

Hurricane Cristobal reached its peak intensity less than a day before extratropical transition, briefly developing a well-defined eye.

Cristobal recurved off of the east coast of the United States, and did not have a significant impact on any landmasses as a tropical cyclone.

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