Tropical Storm Alpha (2005) - Meteorological History

Meteorological History

Alpha's origins were from a tropical wave that developed near the Windward Islands on October 20. Satellite images indicated that a low pressure center associated with the tropical wave formed near Barbados and moved west-northwest with increasing convective activity. In an area of light wind shear, the convection increased and Doppler weather radar data from Puerto Rico detected a well-defined cyclonic circulation. On October 22, the area of low pressure organized into Tropical Depression 25, southeast of Hispaniola. Shortly thereafter, satellite imagery indicated that a closed circulation had developed, and the associated convection had started banding. Later that same day, the depression had organized enough to be upgraded to Tropical Storm Alpha; this was the first time the National Hurricane Center had to use a Greek name for an Atlantic hurricane.

When Alpha came within the Doppler weather radar range of Puerto Rico, the radar suggested that an eyewall-like feature had developed. Alpha was tracking along the southwest edge of a subtropical ridge. With nearby Hurricane Wilma's large circulation, Alpha was experiencing strong southerly flow from Wilma. Alpha, with its small circulation, was then faced with the mountainous terrain of Hispaniola, which led forecasters to believe Alpha was soon to dissipate. Shortly after Alpha reached its peak intensity on October 23 its wind decreased. While convection remained in bands, the low level circulation was disrupted by land. This left the center ill-defined and difficult to locate.

Late on October 23, Alpha made landfall in Hispaniola, quickly decreasing in intensity as it did so. After making landfall, the storm weakened, leaving it just between tropical storm and tropical depression status. Because of the weakening, and the strong southerly flow from nearby Hurricane Wilma, it was hard to determine whether a low-level circulation was present. However, satellite imagery suggested that a new center had developed over open waters to the north of Hispaniola. It was downgraded to a tropical depression early the next day, now re-emerging over open waters. The storm soon developed an elongated center of circulation which indicated that the system was weakening. On October 24 the low-level center had completely dissolved, and only a small area of convective activity persisted. Thus the system had dissipated, and was a remnant low pressure system when the National Hurricane Center issued their last advisories of Alpha. Shortly thereafter, the remnant low was absorbed into the circulation of Hurricane Wilma on October 25.