Sunday, June 24, 2012

Tropical Storm Debby (2012)

Storm Active: June 23-27

Throughout mid-June, a trough of low pressure extending through the central Caribbean Sea caused limited shower activity across the regions of Cuba, Jamaica, and parts of Central America. By June 18, this trough had become associated with a low pressure center near the coast of Nicaragua, and more concentrated convective bursts soon appeared. Shear remained strong over the region, however, and no distinct circulation formed.

The system moved to the northwest over the following days, and the low associated with it dissipated. However, conditions gradually improved for development as it crossed into the Gulf of Mexico, causing widespread flooding in Cuba and southern Florida. On June 21, a well-defined low formed just west of the convection in the central Gulf of Mexico. Organization continued, and by June 23, a huge area of strong thunderstorm activity stretched from the Florida panhandle all the way to western Cuba. Later that day, a closed circulation formed, and the system was classified as a tropical cyclone. Having already attained gale force winds, it was named Tropical Storm Debby, with initial winds of 50 mph.

Shear out of the southwest kept all convection and tropical storm force winds to the east of the center overnight and into June 24. Additionally, the motion was a highly uncertain one, as multiple center and vortices were evident on satellite imagery. However, the general trend was a drift north, and conditions deteriorated in Florida as the outer bands of Debby swept across the coast.

The central pressure of Debby dropped on June 24, and the maximum winds increased, with the circulation becoming more symmetrical. At this time, Debby reached its peak intensity of 60 mph winds and a minimum pressure of 990 mb. However, the trend in shower activity was quite the opposite; the area near the center became completely devoid of convection by late that night, and all significant moisture was displaced towards eastern Florida. This lack of convection eventually caused the system to weaken.

Meanwhile, due to the presence of a powerful anti-cyclonic ridge to its north, Debby was nearly stationary, meandering in small loops, but making little overall progress in any direction over the next couple days. On June 26, a trough over the United States caught Debby and caused it to adopt a slow east motion. The only rain bands of Debby were still only to the northeast of the center, but flooding rains continued over portions of Florida, Georgia, and South Carolina that day.

That evening, the center of Debby made landfall in northwest Florida with 40 mph winds and quickly weakened to a tropical depression. Over land, the circulation of Debby became noticeably elongated from northeast to southwest, and the system adopted an unusual southeast motion. However, the center reformed farther east during the morning of June 27, causing a more rapid turn to the east. The cyclone exited the coast that morning. Its circulation was becoming too elongated to maintain tropical characteristics, however, and it was declared extratropical that afternoon. Debby's remnants initially achieved some organization on June 28, but dry air again permeated the low. It was absorbed a few days later.

Forming on June 23, Debby was the earliest fourth named storm of a season ever to form, surpassing the previous record set by Dennis in 2005, which formed on July 7. This record stood until the formation of Tropical Storm Danielle in 2016. Debby caused flooding throughout parts of the Caribbean and southeast U.S., causing 2 fatalities.

Tropical Storm Debby at peak intensity. Even at its best organization, the cyclone did not have convection circumnavigating the center.

Track of Debby.

Wednesday, June 20, 2012

Hurricane Chris (2012)

Storm Active: June 19-22

On June 17, a circulation began to form from a front situated over the western Atlantic. The low gradually deepened over the following day, and caused scattered shower activity in the area around Bermuda. As the low pressure center became disentangled from the front to its east, its circulation became better organized, through convection decreased.

By June 19, gale force winds were being generated near the low's center and the low assumed some tropical characteristics, though the center remained devoid of cloud cover. Later that day, as the system moved to the northeast, the northwest quadrant developed more significant convection, ultimately allowing it to be classified as Tropical Storm Chris.

Chris tracked generally eastward with no significant change in strength over the next day, but convection became more evenly distributed about the center. The motion of the system increased on June 20, and it underwent strengthening as outflow improved. During the morning of June 21, Chris began its turn to the north as it orbited a upper-level low to its north. By this time, a distinct eyewall and the beginnings of an eye had formed. As a result, the cyclone was upgraded to a hurricane, just above the 40°N latitude line. It soon reached its peak intensity of 75 mph winds and a pressure of 987 mb.

Chris began to move over cooler waters later that day, and weakened as its convection diminished, becoming a tropical storm again. It transitioned into an extratropical cyclone on June 22. Having formed into a tropical storm at 39.3°N, the cyclone was the second most northerly forming Atlantic storm on record. Forming on June 19, it also was among the earliest occurrences of a third named storm of the season in the Atlantic basin.

Hurricane Chris at minimal category 1 intensity. At its peak, Chris attained a distinct eye feature, despite only marginally favorable conditions.

Track of Chris.