Discussion: A short wave trough from the Pacific diving southeastward toward the Gulf of Mexico the past 2 days has enhanced convection in the southeast Gulf of Mexico, caused an area of low pressure to form and invite this disorganized feature north-northeastward the past day or so. NOAA/NHC determined this system is a subtropical storm given wind speed observations near or greater than 40 mph in squalls east of the storm center.
Alberto is a subtropical storm due to the relative cold air environment northwest of the storm. As Alberto becomes more organized and creates more organized convection the heat release from the convection will erode the cool air aloft north of the storm and Alberto will gain full tropical characteristics likely tomorrow afternoon.
Normally, sea surface temperatures of 81-82F/27-28C are required to sustain a tropical cyclone in the North Atlantic basin. The forecast track by NOAA/NHC takes Alberto over marginally warm waters of the east-central Gulf of Mexico. Surface temperatures warm to 83F/28C south and southeast of Louisiana therefore some intensification of Alberto is likely prior to landfall.
The trek over marginally warm waters and slower development has caused NOAA/NHC to lower their intensity forecast of Alberto slightly from forecasts issued yesterday.
The primary operational models (GFS and ECM) take Alberto into the Alabama coast late Monday or Monday night. The ECM is slower and NOAA/NHC respects that forecast delaying landfall until 1AM Tuesday in the vicinity of Mobile, AL as a moderate-strength tropical storm.
The tendency of the official NOAA/NHC track is slightly east and a little weaker compared to yesterday.
The potential for sustained tropical storm force wind is high (>70%) for coastal Mississippi, Alabama and gar west coast of the Florida Panhandle Monday/Monday night as Alberto gains strength and becomes a fully tropical episode.
The primary issue with Alberto remains heavy rain. The NOAA/NHC rainfall forecast is adjusted to indicate 6-10 in. of rain possible into southern Alabama Sunday night into Tuesday.
Alberto is a slow-mover, still a depression as far north as Kentucky Wednesday night.
Fig. 1-2: The NOAA/NHC Alberto-related rainfall forecast and flash flood risk forecast.
Fig. 3: Satellite view of ragged looking Subtropical Storm Alberto.
Fig. 4: Gulf of Mexico sea surface temperatures.
Fig. 5: Tropical cyclone model tracks.
Fig. 6: Tropical cyclone model intensity forecast. Note one model, HMNI indicates minimal hurricane force prior to landfall.
Fig. 7: NOAA/NHC tropical storm force wind risk profile for Alberto.