Tuesday, September 4, 2012

Hurricane Michael (2012)

Storm Active: September 3-11

On September 1, a trough of low pressure formed in the eastern Atlantic. Over the next day, it began to interact with an upper-level low, the resulting union producing a wide area of isolated showers activity. Later on September 2, a surface low formed at the southern edge of the trough, accompanied by a small area of dense overcast.

Though upper-level winds were initially unfavorable, the circulation organized fairly quickly, and by September 3, the convection had increased enough for the low to be designated Tropical Depression Thirteen.

Up to that point, the system had been moving slowly west to west-southwest as a dip in the jet stream prevented it from accelerating significantly. After formation, Thirteen began to drift northwestward, and eventually northward in the wake of a trough to its north.

Some shear was evident on the west side of the circulation through September 4, but the compact system maintained its integrity and increased slightly in deep convection that day, keeping the center of circulation close to the most intense thunderstorm activity. As a result, the cyclone was upgraded to Tropical Storm Michael.

Overnight, due to the approach of an anticyclone from the west, the tropical storm turned to the northeast. However, its forward speed was still quite slow for a cyclone of its latitude, as it was also hemmed in by the Bermuda high to its east. As the low to Michael's north moved away, shear diminished, and allowed Michael to steadily strengthen through September 5. By the afternoon of that day, an eye feature had made a brief appearance, but it was quickly replaced by a central overcast. These factors supported an intensity near hurricane strength that evening.

During the evening, Michael's center contracted, and the cyclone underwent rapid intensification, bringing the cyclone to major hurricane strength by the morning of September 6, the first of the season. That afternoon, the system had reached its peak intensity of 115 mph winds and a pressure of 964 mb. Michael had expanded somewhat by this time, and had an extremely well-defined eye. However, as the cyclone continued to move northeast, sea surface temperatures began to decline, and Michael began to gradually weaken.

On September 7, Michael gradually made a turn to the northwest, but remained in an area of weak steering, and moved slowly, still maintaining Category 2 intensity for the next day. On September 9, the ridge to Michael's north strengthened considerably, and the cyclone turned toward the west, and even west-southwest that evening. The eye was still prominent, but convection was degrading by this time, especially in the northwest quadrant. Therefore, Michael weakened to a category 1 hurricane.

On September 10, Michael navigated around the western edge of the ridge to its north, and made a sharp turn to the north over the following day. Around the same time, shear increased sharply in the vicinity of Michael, partly due to the outflow of Tropical Storm Leslie. The eye disappeared for the last time, and Michael weakened to a tropical storm. By September 11, all convection had been ripped away from the system by upper-level winds, and the system was declared extratropical that afternoon, and absorbed the next day.

Michael at peak intensity as a low-end Category 3 hurricane.

Track of Michael.

No comments: