https://phys.org/news/2018-05-nasa-alberto-rainfall-southeast-tennessee.html

Alberto formed out of a broad area of low pressure at the surface that was located over and around the Yucatan Peninsula. Because the area of low pressure was under the influence of a nearby upper-level trough, Alberto was designated as a subtropical storm by the National Hurricane Center (NHC) on the morning of Friday May 25, which is rather unusual as most subtropical storms form at higher latitudes. The storm initially formed just east of the Yucatan Peninsula.

A large subtropical ridge over the southwestern Atlantic steered Alberto on a northward track, and the storm brushed the far western tip of Cuba on Saturday May 26 before the center re-formed as it moved northward into the southeast Gulf of Mexico as a still minimum subtropical storm with maximum sustained winds of around 40 mph. As it moved north further into the Gulf, Alberto initially struggledto organize and intensify. The storm remained under the influence of an upper-level trough (elongated area of low pressure) with most of the active thunderstorms located well to the east of the center.