Initially not anticipated to transition into a tropical cyclone, the low gradually tracked south-southeastward for several days with little development.

[3][4] Alpha originated from a large, extratropical low-pressure area, which developed over the Northeastern Atlantic Ocean on 14 September.

[1] By this time, the extratropical cyclone had a very large radius of gale-force winds expanding over 500 km (270 nmi; 310 mi) from its center of circulation.

[1] Alpha accelerated to the northeast, and a combination of radar imagery from Portugal, scatterometer passes, and satellite-derived wind data revealed Subtropical Storm Alpha had peaked around 00:00 UTC on 18 September, just about 417 km (225 nmi; 259 mi) off the coast of Portugal, while the storm was producing 1-minute sustained winds up to 80 km/h (50 mph).

[1][8] Alpha maintained its intensity up to its landfall about 17 km (11 mi) south of Figueira da Foz, Portugal, around 18:40 UTC that day.

[9] After landfall, the small low-level circulation associated with Alpha began to quickly decay, as the storm moved inland, and the cyclone weakened to a subtropical depression at 0:00 UTC on 19 September.

[10] Winds due to Alpha caused widespread power outages, uprooted trees, and damaged dozens of vehicles.

[3] In Spain, orange warnings were also raised by the State Meteorological Agency (AEMET) for the Spanish autonomous communities of Madrid, Extremadura, Aragon, and Catalonia as Alpha moved into Portugal late on 18 September, citing a risk of heavy rain, hail, and strong wind gusts.

[2] Castilla–La Mancha's news agency reported that uprooted trees and minor floods had occurred in the community during Alpha, while several water rescues were carried out around midday of 19 September.

[20] Alpha was the earliest 22nd Atlantic tropical or subtropical storm on record, surpassing the old mark of October 17, set by Hurricane Wilma in 2005.