Subtropical Storm Alberto

Subtropical Storm Alberto formed in the western Caribbean this morning. Alberto will track northward into the Gulf of Mexico through the holiday weekend; wreaking havoc across much of the Southeast in the form of flooding, storm surge, tornadoes, and high winds (see Fig. 1).

Fig. 1: National Hurricane Center Forecast

At this hour, Subtropical Storm Alberto has maximum sustained winds of 40 mph and moving to the E at 2 mph. Alberto is expected to transition from a subtropical cyclone to a tropical cyclone over the weekend as environmental conditions become more favorable. “Subtropical” essentially is a hybrid between a mid-latitude cyclone (cold core) and a tropical cyclone (warm core). Just because the named cyclone is a “subtropical” entity at this time, it needs to be taken extremely seriously because the same impacts as a tropical storm or low-end hurricane can be felt and are expected across parts of the Southeast.

There are high shear values across the southern Gulf of Mexico and Caribbean, which is causing Alberto to have a unique satellite appearance. Much of the convection (thunderstorms) is east of the center of the storm (see Fig. 2). This is of importance because this convection will move into Florida and other parts of the Southeast–causing flash flooding. Another important factor that may enhance flooding is a building high to the north of Alberto. This high may act to ‘trap’ Alberto across the Gulf States early next week. Widespread heavy rainfall is possible (see Fig. 3) in which some areas may see 8-14″ of rainfall. All areas east of the Mississippi River across the Southeast have a chance to see flooding due to Alberto from this weekend into at least mid-week next week.

Fig. 2: Current Satellite Imagery

Fig. 3: WPC Rainfall Forecast Through 7 Days

Over the next 36-48 hours, Alberto will continue to move northward. Tropical storm impacts will be felt by Sunday morning for the Gulf Coast States and Alberto should be close to land by Monday. Alberto will slowly continue to increase in intensity during this time period as environmental conditions becomes more favorable for intensification (less shear and anomalously warm waters in the northern Gulf) allowing to the transition to a warm core high end tropical storm or low-end hurricane.

A Tropical Storm Watch is now in place for portions of the northern Gulf Coast of the United States. This extends from Indian Pass, Florida, westward to Grand Isle, Louisiana. Please begin to prepare for tropical impacts from this system if you live along the Gulf Coast. Updates will be provided as needed.

Fig. 4: Current Tropical Storm Watches