Hurricane Alberto (2000) - Meteorological History

Meteorological History

A mesoscale convective complex, or large circular area of thunderstorms, developed in the Ethiopian Highlands of Africa on July 28. The complex moved west-southwestward through the continent, waxing and waning until persisting along a tropical wave on August 2. The next day, the wave emerged into the Atlantic Ocean from Guinea. Once over the open Atlantic Ocean, the wave quickly developed and became Tropical Depression Three later that day. The depression moved to the west-northwest and was upgraded to Tropical Storm Alberto early on August 4. Alberto continued to strengthen, but moved to cooler waters late on August 5 and weakened briefly. However, the storm strengthened again early on August 6, and it was upgraded to hurricane status, as an eye developed in its centre. The upgrade was accompanied with a brief westward turn. However, Alberto continued to move to the west-northwest later that day, reaching its first peak intensity of 90 mph (150 km/h) on August 7.

A vigorous upper-level low developed west of Alberto on August 7 and August 8. This caused an increase in vertical shear, weakening the hurricane down to a tropical storm on August 9. The low also caused the storm to turn to the northwest. However, on August 10, Alberto became better organised and was upgraded to hurricane status again. It then moved in a gradual curve towards the north and northeast through a break in a subtropical ridge between August 11 and August 12. Alberto made its closest approach to Bermuda on August 11, passing about 345 mi (555 km) east of the island. The strong storm became a Category 3 major hurricane on August 12 and reached its second and highest peak intensity of 125 mph (205 km/h), and a 60 mi (95 km) wide eye was observed. Alberto was an unusual storm in that it reached its peak intensity at a high latitude, north of 35˚N, after it had re-curved. The hurricane began to weaken due to increasing upper-level westerlies on August 13 and August 14, while moving east-northeastward. Alberto was downgraded to a tropical storm on August 14.

As early as August 10, computer models anticipated the hurricane to accelerate to the northeast and become extratropical within three days, but this did not materialise. A westerly trough that had been influencing Alberto’s motion outran the storm, and a strong ridge developed to the north and west, causing the storm to turn abruptly to the south on August 15, and to complete a large loop over the open Atlantic. Alberto turned to the southwest on August 16 and to the west on August 17. The storm then took a sharp turn toward the northwest as a large, slow-moving mid-level trough was carving out over the eastern United States. Alberto began to strengthen, and reached hurricane status for the third time on August 18. The hurricane continued to turn to the north on August 19 and to the northeast on August 20 and August 21. During this time, Alberto reached a third peak intensity of 105 mph (165 km/h) on August 20, and a 70 mi (110 km) wide eye was observed. Operationally, Alberto reached a peak intensity of 110 mph (175 km/h), but after reanalysis, it was reduced to 105 mph (165 km/h).

Hurricane Alberto began to weaken on August 22 as it accelerated into higher latitudes. It was downgraded to a tropical storm early on August 23. Initially, it was forecast to become extratropical on August 22, but a little burst of colder cloud tops enabled Alberto to remain tropical for a longer time, persisting into August 23, while it moved into a very high latitude at 53˚N. The weakening storm finally became extratropical late on August 23, while accelerating to the north-northeast, passing near Iceland on August 24. Winds dropped below gale-force, as the centre turned to the east-northeast on August 25. Alberto dissipated about 85 mi (140 km) east of Jan Mayen later that day.