For the fourth year in a row, a pre-season tropical or subtropical cyclone has formed over the Atlantic basin. At 11:00 a.m. EDT Friday, the National Hurricane Center (NHC) initiated advisories on Subtropical Storm Alberto over the Northwestern Caribbean. Alberto is expected to emerge into the Gulf of Mexico on Saturday, where it will likely find environmental conditions more favorable for strengthening.

As of 11:00 a.m. EDT, newly-named Subtropical Storm Alberto was centered near 19.7°N 86.8°W, and was moving north-northeast at about 6 mph. Maximum sustained winds were 35 knots (40 mph), with an estimated minimum pressure of 1005 mb. Visible satellite imagery indicates that Alberto still has multiple circulations, but the circulation was sufficiently well defined for NHC to classify as a subtropical storm. Based on a ship report of tropical storm force winds, the storm has been named. Since Alberto has a large radius of maximum winds and the circulation center is currently exposed to view, it has been classified as subtropical rather than tropical. An Air Force reconnaissance aircraft is scheduled to investigate Alberto later today.

Environmental conditions are currently only marginally favorable for intensification. Although sea surface temperatures are a warm 28°C (82.4°F), wind shear remains fairly strong – above 25 knots. Alberto is currently located in a fairly moist mid-level environment, with relative humidity values near 70 percent. As Alberto emerges into the central Gulf of Mexico, wind shear is expected to decrease to less than 15 knots, but Alberto will be moving over cooler waters and into a drier environment during that time. The current NHC forecast calls for Alberto to make landfall near Biloxi, Mississippi, though this is still a bit uncertain. Most of the impacts from Alberto will occur on the stronger east side, where heavy rains are expected.

The official NHC forecast calls for Alberto to become a 65-mph tropical storm before landfall. Alberto is likely to transition into a tropical cyclone as it moves into a lower shear environment. However, though unlikely, it is not out of the question that Alberto could become a minimal hurricane if it fights off dry air and is able to develop a core. The 00z ECMWF model shows this possibility, deepening Alberto 983 mb before landfall. May Atlantic hurricanes are extremely rare, with the most recent being Alma in 1970. Only four have been recorded since reliable records began in 1851. There has never been a landfalling United States hurricane during the month of May on record.

A tropical storm watch has been issued for the northeastern Yucatan Peninsula and the western tip of Cuba. Even though Alberto may become stronger than previously anticipated, the primary threat remains heavy rain. Most of the heaviest rains will occur east of the center. Residents of the Northeastern Yucatan Peninsula, western Cuba, Southeastern United States and Gulf Coast east of Louisiana should closely monitor the progress of Alberto.

I will be back with another blog on Alberto tomorrow.