Monday, August 29, 2016

Hurricane Hermine (2016)

Storm Active: August 28-September 3

On August 18, a tropical wave just southwest of the Cape Verde Islands began to display scattered shower activity. The system remained rather broad and disorganized during its trek westward across the Atlantic for most of the following week. Throughout much of this period, the wave and associated low were little more than an large swirl of sparse clouds with limited convection farther south. This was due to the influence of the Saharan air mass to the north. Organization increased some around the 22nd and 23rd as the low passed through the Lesser Antilles, but a well-defined circulation did not yet develop. In fact, organization decreased markedly over the following several days, as the convection became scattered across many of the islands of the Caribbean away from the center. It was not until the system passed just south of the Florida Keys on August 28 that it finally acquired the status of Tropical Depression Nine.

The location of the center of circulation remained difficult to spot on satellite imagery through the next day, but convection increased overall, particularly to the south of the center. This caused heavy rains for much of western Cuba. Organization increased markedly on August 30 and the subsequent overnight period: a large area of very deep convection developed over the southeastern Gulf of Mexico surrounding the center and the central pressure dropped appreciably. This did not immediately correspond to an increase in maximum winds, but aircraft data collected the afternoon of August 31 indicated that the system had finally strengthened into Tropical Storm Hermine.

By this time, the cyclone had assumed a track toward the north-northeast due to the influence of a trough over the southeastern United States. At the same time, atmospheric conditions improved, allowing Hermine to take advantage of the very warm Gulf waters and intensify quickly. That evening, the storm developed more organized banding features, with a huge band extended from northwest to southeast of the center. Shortly afterward, this band began to affect the Florida panhandle. By the morning of September 1, heavy rain was moving across western Florida as far south as Tampa. An eyewall appeared later that morning and completed its circumnavigation of the center that afternoon. Hermine became a category 1 hurricane soon after. A few hours later, the cyclone reached its peak intensity of 80 mph winds and a central pressure of 984 mb and made landfall in the Florida panhandle, causing storm surges of several feet, strong winds, and over 5 inches of rain for many areas.

Hermine weakened to a tropical storm overnight and move inland over Georgia by the morning of September 2. The cyclone traversed South Carolina that afternoon and entered North Carolina that evening. All the while, it weakened and gradually lost tropical characteristics. This did not prevent it from causing flooding rains from the Carolinas north to the Delmarva peninsula by the morning of September 3. Around this time, Hermine became post-tropical and moved east-northeast back over water. There it reintensified some and developed winds near hurricane force. While storm surge remained a threat to the coast, the system moved farther away from land over the next day, lessening direct impacts. Early on September 5, Hermine changed course, moving first slowly northward, and then toward the west-northwest by the afternoon. Though it remained post-tropical, the system generated some shallow convection to the north and west of the center, bringing continued shower activity to coastal New England. The circulation began to spin down on the 6th, and while it moved a little closer to the coast, impacts diminished. By September 7, the weakening cyclone had switched direction and was moving generally east-northeast. It dissipated shortly after.

The above image shows Hermine shortly after it became a hurricane.

Hermine continued to affect the U.S. east coast even after transitioning to a post-tropical cyclone (post-tropical track points are indicated by triangles).

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