Subtropical Storm Alberto formed over the northwestern Caribbean Sea on Friday morning. The National Hurricane Center (NHC) designated an area of low pressure as Subtropical Storm Alberto on Friday morning based on data from buoys and ship reports. At 5:00 p.m. EDT on Friday the center of Subtropical Storm Alberto was located at latitude 19.4°N and longitude 86.3°W which put it about 85 miles (135 km) south-southeast of Cozumel, Mexico. Alberto was moving toward the east at 2 m.p.h. (3 km/h). The maximum sustained wind speed was 40 m.p.h. (65 km/h) and there were wind gusts to 50 m.p.h. (80 km/h). The minimum surface pressure was 1005 mb.
A Tropical Storm Watch has been issued for the portion of the U.S. coast from Indian Pass, Florida to Grand Isle, Louisiana including New Orleans. The government of Mexico issued a Tropical Storm Watch for the portion of the coast from Tulum to Cabo Catoche. The government of Cuba issued a Tropical Storm Watch for the province of Pinar del Rio.
The circulation around Subtropical Storm Alberto was asymmetrical. The low level center of circulation was located just to east of the Yucatan Peninsula. The strongest thunderstorms were occurring in a band located about 100 miles (160 km) east and north of the center. Flow around an upper level trough over the Gulf of Mexico was producing westerly winds which were blowing toward the top of the circulation. Those winds were causing strong vertical wind shear which was the reason why the thunderstorms were occurring well to the east of the center of circulation.
Subtropical Storm Alberto will move through an environment marginally favorable for intensification during the next 24 to 36 hours. Alberto will move over water where the Sea Surface Temperature is near 28°C. So, there is sufficient energy in the upper ocean to support intensification. However, the upper level trough will continue to cause moderate to strong vertical wind shear during the next day or so. The wind shear will inhibit intensification. Some gradual strengthening is possible. The winds are weaker near the axis of the upper level trough. If Alberto moves under the axis of the trough when it reaches the northern Gulf of Mexico, then the wind shear will decrease. Alberto could strengthen more quickly if that happens. There is a chance that Alberto could reach hurricane intensity. If more thunderstorms form closer to the center of circulation, then NHC could change the designation of Alberto to a tropical storm.
Subtropical Storm Alberto is moving around the western end of a large high pressure system over the Atlantic Ocean. The high is steering Alberto slowly toward the north-northeast. A general motion toward the north is forecast during the next day or so. When Alberto gets farther north, the upper level trough could steer it more toward the north-northwest. There is a chance that the steering currents could weaken when Alberto nears the Gulf Coast. Thus, there is much more uncertainty about the track forecast after that time.
The greatest risk with Subtropical Storm Alberto will be locally heavy rain and the potential for flooding. Most of the heavy rain is likely to fall north and east of the center. Much less rain is likely to fall from the western side of Alberto. The coast of the Gulf of Mexico is very susceptible to storm surges. The water level will rise along the eastern and northern coasts of the Gulf of Mexico where the winds blow the water toward the shoreline.
A cyclone is likely to form over the Gulf of Mexico during the upcoming weekend. A broad area of low pressure at the surface is currently centered over the Yucatan Peninsula. The area of low pressure is currently designated as Invest 90L. The circulation around the low pressure system is not well organized at the current time. The center of the surface low is over the Yucatan Peninsula. Showers and lower clouds are occurring near the center of the low. Stronger thunderstorms are occurring on the eastern side of the low over the northwestern Caribbean Sea. Sustained winds of 20 m.p.h. to 30 m.p.h. (30 km/h to 50 km/h) were blowing across the northwestern Caribbean Sea. The winds were weaker over land near the center of circulation.
An upper level trough over the Gulf of Mexico was producing strong westerly winds which were blowing over the top of the surface low. Those winds were causing strong vertical wind shear and the wind shear was one of the reasons why the stronger thunderstorms were occurring east of the center of circulation. Sinking motion in the western portion of the upper level trough was bringing drier air to the surface and the drier air was inhibiting the formation of thunderstorms in the western side of the surface low.
The National Hurricane Center (NHC) indicated in a Special Tropical Weather Outlook at 2:00 p.m. EDT on Thursday that there is a 70% probability of the formation of a subtropical or tropical depression during the next 48 hours. NHC has tentatively tasked a reconnaissance aircraft to investigate the low pressure system on Friday afternoon if necessary.
The wind speeds are slower near the axis of the upper level trough. If the surface low pressure system moves under the axis of the upper level trough, then there would be less vertical wind shear and a cyclone could form. If thunderstorms develop near the center of circulation after the center moves over the northwestern Caribbean Sea or southeastern Gulf of Mexico, then NHC would likely designate the system as a tropical depression. If the thunderstorms develop farther away from the center of circulation and the circulation does not exhibit a tropical appearance, then NHC could classify the system as a subtropical depression. NHC would issue advisories on the cyclone even if it is designated a subtropical depression.
There is a strong high pressure system over the Atlantic Ocean and the high is likely to steer the surface low toward the north. The Sea Surface Temperature of the water in the southeastern Gulf of Mexico is near 27°C. So, there is enough energy to support the formation of a tropical cyclone. Most of the stronger thunderstorms are likely to continue to form in the eastern side of the circulation because of the vertical wind shear and drier air to the northwest of the surface low. The low pressure system could slowly organize into a tropical storm during the weekend.
Heavy rain and the potential for flooding are the greatest risks with this low pressure system. There will be some storm surge along the eastern and northern coasts of the Gulf of Mexico as counterclockwise rotation around the low blows water toward the shore.