Tropical Storm Alberto (2006) - Meteorological History

Meteorological History

In early June 2006, an area of convection persisted across Central America and the western Caribbean in association with a broad, nearly stationary trough of low pressure. Thunderstorms increased and became more concentrated on June 8 after a tropical wave moved into the western Caribbean, and an upper-level low to its west increased outflow over the system. The disturbance moved slowly north-northwestward, and development was initially inhibited by marginally favorable upper-level winds and land interaction. The system gradually organized, and by June 10 a circulation formed with sufficiently organized convection for the National Hurricane Center to classify it Tropical Depression One. At this point the storm was located about 140 miles (225 km) south of the western tip of Cuba.

The depression tracked to the northwest through the Yucatán Channel into an area of increased wind shear, which left the center exposed and elongated. Despite its poor structure, the system maintained strong winds in its eastern semicircle. The depression intensified into Tropical Storm Alberto early on June 11 about 260 miles (420 km) southwest of the Dry Tortugas, based on Hurricane Hunters' reports of flight level winds of 50 mph (80 km/h) in a few convective bands. Upon becoming a tropical storm, the low-level circulation had become better defined, though forecasts predicted the wind shear would increase, preventing significant strengthening of the storm. One forecaster at the National Hurricane Center remarked the system resembled a subtropical cyclone. However, deep convection developed and built westward against the wind shear as the overall organization improved. At the same time Alberto turned northeastward under the influence of an approaching trough. On June 12, the circulation abruptly reformed under the area of deepest convection, which coincided with the storm's passage over the loop current; consequentially, Alberto quickly strengthened to reach peak winds of 70 mph (115 km/h) about 220 miles (350 km) west-northwest of Tampa, Florida.

Though it was projected to track over cooler waters and stay in an area of increased shear, forecasters at the National Hurricane Center predicted Alberto would attain hurricane status and make landfall at that intensity. The storm maintained peak intensity for about 18 hours, and while accelerating northeastward, Alberto's convection diminished as the cloud pattern became elongated. On June 13, dry air became entrained in the circulation, leaving the center exposed from the convection and the wind field greatly broadened. A partial eyewall developed in the western semicircle of the center; however, winds were well below hurricane force. Alberto continued to weaken, and made landfall at about 1630 UTC on June 13 with 45 mph (75 km/h) winds in Taylor County, Florida, about 50 miles (80 km) southeast of Tallahassee.

The storm maintained a well-organized structure and banding features over land, while continuing to produce winds of tropical storm force as it moved into Georgia. Early on June 14, the storm weakened to tropical depression status while located near the city of Millen, Georgia. Alberto began to lose tropical characteristics soon thereafter, and about six hours after weakening to a tropical depression it transitioned into an extratropical cyclone. Late on June 14 it accelerated northeastward to emerge into the Atlantic Ocean, and on June 15, it entered the area of responsibility of the Canadian Hurricane Centre. While over open waters, Alberto's remnants began to re-intensify; later that day, the extratropical remnant low attained winds of 65 mph (105 km/h) and a pressure of 969 mbar while a short distance south of Nova Scotia. At this time, the low presented a well-defined comma structure. After passing near Sable Island, the remnants of Alberto crossed the Avalon Peninsula of Newfoundland on June 16. The extratropical storm turned to the east-northeast and later to the east as it continued its rapid forward motion, and on June 19 the remnants of Alberto merged with an approaching cold front near the British Isles.