A weather system over the southeastern Gulf of Mexico could bring heavy rain to the southeastern U.S. this week. An upper level low over the eastern Gulf of Mexico could transfer enough kinetic energy down to the lower troposphere to spin up a low at the surface. Air flowing around the eastern side of the low is contributing to upper level divergence over Florida. The divergence enhanced rising motion over Florida and rain fell over parts of the southern and central portions of that state.
The weather system is forecast to move slowly northward during the next several days. The Sea Surface Temperatures in the southeastern Gulf of Mexico are 24°C to 26°C. There is enough energy in the upper levels of the water to support the formation of a tropical cyclone. The upper level low will create southerly winds which will cause moderate vertical wind shear. The shear will inhibit development, although those winds could contribute to upper level divergence to the east of the weather system. Upper level divergence could allow the surface pressure to decrease and a low pressure system could form at the surface. The National Hurricane Center (NHC) issued a special Tropical Weather Outlook on Sunday afternoon on the weather system. NHC indicated the probability was 40% that a tropical or subtropical cyclone could form during the next five days.
Guidance from numerical models suggest that the weather system will move slowly northward over the eastern Gulf of Mexico during the next few days. Counterclockwise rotation around the low will transport moist air northward on the eastern side of the low. The moist air combined with upper level divergence will create the potential for locally heavy rainfall over the southeastern U.S. Heavy rain could result in floods in some locations.
A complex weather system near the Bahamas is forecast to move westward and it will bring gusty winds and locally heavy rain to parts of the Bahamas and South Florida during the weekend. The circulation is strongest in the middle and upper troposphere. An upper level low is centered near the Bahamas. Showers and thunderstorms are occurring north and east of the upper low. There is not a distinct center of circulation in the lower troposphere or at the surface. There is a small upper level ridge to the east of the upper low and the ridge is producing some upper level divergence which is pumping mass away to the east of the system.
The system will move through an environment that is only marginally favorable for the development of a tropical cyclone. It will move over water where the Sea Surface Temperature is near 26°C. So, there is potentially enough energy in the upper ocean to support the development of a minimal tropical cyclone. The upper low and the ridge to the east are southerly winds near the Bahamas and westerly winds southeast of the Bahamas. Those winds are causing strong vertical wind shear. The winds are weaker near the center of the upper low, but there are no thunderstorms in that region at the current time. If a surface low were to develop under the center of the upper low, then there would be the possibility of some slow development. A second, possible scenario is that a subtropical cyclone develops north and east of the upper low where the showers and thunderstorms are forming.
The National Hurricane Center (NHC) issued a special Tropical Weather Outlook on this system at 10:45 a.m. EDT on Friday. NHC indicated that “no significant development” is expected and it gives a 0% probability of the formation of a tropical cyclone.
The upper level low is forecast to move south-southwest over the northwestern Caribbean Sea during the next 72 hours. The surface and lower parts of the system are forecast to move across the Bahamas toward South Florida during the weekend. Since the showers and thunderstorms are occurring north and east of the upper low, this could bring gusty winds and locally heavy rain to parts of the Bahamas and South Florida during the weekend. Some of the humid air on the northeastern periphery of the system could be pulled toward the Carolinas ahead of an approaching cold front. The moist air could enhance rainfall in eastern South Carolina and eastern North Carolina when the cold front moves through those places and lifts the air.