Around September 14, a non-tropical low formed in the northeastern Atlantic, at around 45 ° N latitude. Unusually, it moved slowly south-southeastward over the following couple of days and then took a turn toward the east. This brought it over at least somewhat warmer water, and some more cloud cover developed near the center. By September 18, based on information from satellite imagery and Portugal-based radar, the system had developed a warm-core and a small, but well-organized convective pattern. As with some northeastern Atlantic cyclones from previous years, the tiny warm-core was still contained in a larger extratropical cyclone. A combination of these factors led to the naming of Subtropical Storm Alpha*, with maximum sustained winds estimated at 50 mph.
With Alpha's formation, 2020's parade of storms continued at a ridiculous pace. Alpha was the 22nd named storm, the earliest, and only second, 22nd storm ever recorded, after Wilma of 2005 which formed on October 17 of that year. After completing the hurricane names list for a given year, the Greek alphabet is used to name cyclones. 2020 was only the second year this was ever required, again after 2005. This wasn't the only strange thing about Alpha. Just a few hours after classification, the storm made landfall in central Portugal, with winds of 50 mph and a minimum pressure of 996 mb. Only Vince of 2005 had made landfall in Europe as a tropical or subtropical cyclone before in recent history, though many cyclones reach Europe after becoming extratropical.
After landfall, the low-level circulation was quickly weakened by its encounter with mountainous terrain, though this did not prevent heavy downpours from occurring in Portugal and western Spain. Less than 12 hours after operationally being classified a subtropical storm, Alpha became extratropical. Its remnants dissipated over northern Spain the next day.
*Note: Though operationally classified on September 18, the post-season analysis in 2021 indicated that Alpha in fact had become a subtropical storm the previous day.
The above images shows Subtropical Storm Alpha just before landfall in Portugal.
The precursor to Alpha spent several days in the northeast Atlantic as an extratropical cyclone (triange points above) and only became subtropical briefly (square points).
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