Monday, October 9, 2017

Hurricane Ophelia (2017)

Storm Active: October 9-15

Around October 6, an area of low pressure began to form along a stationary frontal boundary located over the eastern Atlantic. The next day, the system began to separate from the remainder of the frontal boundary, although it still displayed a long, curved, front-like band of convection emanating from the center. Slowly, it developed some subtropical characteristics as it drifted in the northeast Atlantic, moving little. By October 8, the low was on the verge of tropical or subtropical cyclone status and satellite data indicated gale-force winds near the center. Overnight, a region of shower activity persisted just east of the center. Available information pointed to winds just below tropical storm strength, so the system was designated Tropical Depression Seventeen. Banding features started to appear during the morning of the 9th, and the depression was upgraded to Tropical Storm Ophelia.

Initially, Ophelia was moving slowly to the north and northeast in a region of weak steering currents. Over the next day, however, a mid-level ridge built in northwest of the cyclone and it turned toward the southeast. Meanwhile, shear was diminishing and convection was able to wrap around the center, which allowed for some strengthening. The largest inhibitor to development was some dry air inside the circulation. Interaction with this dry air caused intensity fluctuations on October 10, but deeper convection completely enclosed the center that night. At the same time, an eye feature formed, and Ophelia strengthened more rapidly. During the afternoon of October 11, Ophelia reached hurricane strength, becoming the tenth consecutive tropical cyclone of the 2017 season to develop into a hurricane.

Steering currents collapsed later that day as well, leaving the system to drift slowly eastward overnight. The appearance of deeper convection near the center suggested that additional strengthening had occurred. Sea surface temperatures remained just lukewarm, but unusually cool upper atmospheric temperatures created a steep enough gradient to support intensification. On October 12, Ophelia reached category 2 status, an unprecedented achievement for a hurricane so far northeast that late in the hurricane season. The cyclone began to gradually accelerate east-northeast overnight, reaching an intensity of 105 mph winds and a pressure of 970 mb. The eye clouded over briefly the morning of the 13th, but this was a short-lived trend. Later that day the eye cleared out and became even better defined, with deep convection completely surrounding the center. As a result, Ophelia maintained its remarkable category 2 status even farther north and east.

The system was not finished, however. A final burst of intensification on October 14 brought Ophelia to major hurricane strength, and it reached a peak intensity of 115 mph winds and a pressure of 960 mb. In doing so, it became the easternmost major hurricane ever recorded. The gap between it and its predecessors was even more impressive in its latitude range, where it was 900 miles farther east than any previous major hurricane. Finally, early on October 15, much colder waters and higher shear began to weaken Ophelia and induce extratropical transition. Later that day, the storm became extratropical as it sped toward Ireland. The center made landfall in southwest Ireland during the morning of October 17, bringing damaging hurricane-force winds. Since the system was moving at over 40 mph, it quickly passed over Ireland and the UK. The post-tropical cyclone brought gale force winds all the way to Scandinavia before finally dissipating.

Hurricane Ophelia is shown above as a major hurricane near the Azores, an unprecedented event in Atlantic hurricane records dating back to 1851.

Ophelia was no longer a tropical cyclone when it reached Europe (triangle points) but it still brought hurricane-force winds to many parts of Ireland.

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