Thursday, September 11, 2014

Hurricane Edouard (2014)

Storm Active: September 11-19

On September 7, a tropical low emerged off of the coast of Africa, already showing signs of organization as it moved west. Though a broad circulation was evident in association with the system from the beginning, convection remained decentralized through the next few days. On September 8, the system passed to the well south of the Cape Verde Islands, with minimal impacts. At the same time, the low began a gradual turn toward the northwest, exploiting a weakness in the Bermuda High. Upper-level winds prevented development through September 10. Thereafter, shear abated, allowing the low to acquire organization. By the morning of September 11, the appearance of banding features and a better-defined circulation merited the classification of the system as Tropical Depression Six.

Overnight, denser convection developed near the center, and the cyclone was upgraded to Tropical Storm Edouard. Meanwhile, vertical shear kept the center near the southwestern edge of the convective canopy. The circulation of Edouard gained definition over the next day, leading to some modest intensification as the central pressure dropped and the outflow improved. Even though September 13, however, dry air continued to enter the system from the south, fighting the development of a central dense overcast. But upper-level winds continued to become more favorable and waters were anomalously warm, resulting in continued strengthening. During the morning of September 14, an eye made a brief appearance on visual imagery, and Edouard was upgraded to a category 1 hurricane.

During that day, only the entrainment of dry air, which disrupted the formation of a full eyewall, prevented the rapid intensification of the cyclone. Still, the central pressure dropped considerably that evening and overnight. By the morning of September 15, Edouard had become a category 2 hurricane. Later that day, the system began to navigate around the western edge of a subtropical ridge and assumed a more poleward motion. Edouard developed a larger and more symmetric eye during the afternoon while rain bands extended farther from the center, especially on the western side of the circulation. Overnight, the cyclone lingered just below major hurricane strength.

During the morning of September 16, Edouard strengthened into the first major hurricane of the 2014 Atlantic season, and in doing so reached its peak intensity of 115 mph winds and a central pressure of 955 mb. Meanwhile, the storm made its closest approach to Bermuda, passing just over 400 miles to the east as it began to curve towards the north and northeast that evening. As it encountered less favorable thermodynamic conditions, Edouard slowly decreased in convection and weakened. However, the circulation remained vigorous through September 17 as the system accelerated toward the northeast. That afternoon, Edouard's convective banding structure briefly became concentric, when an inner eyewall and a larger circular rain band beyond it. This resulted in a relatively gentle pressure gradient out from the center. Therefore, though the central pressure of the cyclone was quite low, its winds were only that of a category 1 hurricane.

As Edouard moved over progressively cooler water during the next day, however, the eyewall began to decay and gradual weakening continued. By late morning on September 18, the system had reached the north edge of a mid-level ridge, and was heading due east. It became a tropical storm that afternoon. Over the next day, wind shear increased significantly, stripping all convection from the circulation and displacing it to the southeast. By the afternoon of September 19, Edouard had become post-tropical.

The above image shows Hurricane Edouard on September 16, shorting after becoming the first major hurricane of the 2014 season.

During its time as a tropical cyclone, Edouard did not affect any landmasses.

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