Saturday, October 13, 2012

Hurricane Rafael (2012)

Storm Active: October 12-17

On October 5, a tropical wave emerged off of Africa, but remained weak for the next several days as it traversed the eastern Atlantic. The system gradually moved over warmer waters and increased in shower activity. By October 9, the system had a well-defined low pressure center associated with it. Shear out of the west still impacted the low, but atmospheric conditions improved over the following few days.

Rain and windy conditions began to affect the Lesser Antilles and surrounding areas during the day of October 12. At this time, the convection was becoming concentrated at the center of circulation, but was still somewhat displaced to the east. Later that day, aircraft indicated that the cyclone had developed a closed center, and was thus classified Tropical Storm Rafael. At the time of its formation, the convection was still distributed linearly along the former trough boundary, and the circulation remained slightly elongated. However, the thunderstorm activity was very vigorous; there were widespread areas of heavy squalls and tropical storm force wind gusts.

Rafael moved generally to the north-northwest over the following day, and very slowly organized, with a more defined region of cold cloud tops appearing near the center during the afternoon of October 13. This initiated a period of strengthening as the center moved closer to the Virgin Islands. The system passed close to the northeastern Caribbean islands late that night with maximum winds of 50 mph as the cyclone continued its trek north.

On October 14, Rafael took a slight turn towards the northwest as the ridge over the north-central Atlantic strengthened, slowing as it did so. By this time, the cyclone had assumed a more symmetric appearance, and on October 15, the circulation finally achieved gale force winds on all sides of the center, and was near hurricane intensity. Later that night, a flare up of very strong convection appeared at the center, prompting the upgrade of Rafael to a Category 1 hurricane.

Early on October 16, the system began to accelerate northward in the flow of a trough emerging off of the U.S. coast, and vertical shear increased. Despite the intense shear, however, outflow remained remarkably healthy in all quadrants, and Rafael strengthened further, reaching its peak intensity of 90 mph winds and a pressure of 969 mb that morning. By the evening, the cyclone was approaching Bermuda as an impressively large cyclone.

The system made its closest approach to the island that night, and continued to accelerate to the north-northeast, moving away from the island at over 25 mph. Early on October 17, Rafael's circulation assumed an extratropical appearance, with a very large area of gale force winds and bands extending many hundreds of miles from the center. However, the hurricane maintained a small amount of deep convection near the center until that afternoon, at which time is was pronounced extratropical, still producing hurricane-force winds as an extratropical low. The low continued northeast before combining with another powerful system over the north Atlantic the next day.

Rafael as a Category 1 hurricane moving north into open waters.

Track of Rafael.

No comments: