Tropical Impacts Likely Along The Gulf Coast Next Week!

As of this afternoon a broad surface low has developed in the western Caribbean. Pressure continues to slowly drop and confidence is high that this low will become a tropical system in the Gulf of Mexico over the next few days. The National Hurricane Center (NHC) is keeping a close eye on this system and has given the low an 80% chance of development into a tropical cyclone over the next five days and a 30% chance of development within 48 hours.

Western Caribbean/southern Gulf of Mexico being monitored by the NHC

What happens early next week? Why?

Numerical guidance is still split on the movement of this low early next week. There are two possible scenarios once the low moves into the southern Gulf of Mexico by Monday: (I) the low moves northwestward towards the coast of Texas, or (II) the low moves northeastward towards the coast of Alabama/Florida. The track of the low is heavily dependent upon the position of the mid-level ridge across the southwestern United States (that may build eastward), the strength and position of the Bermuda High, and the evolution (amplification or deamplification) of the trough digging across the eastern United States next week.

Texas scenario:

The European model is showing the low pressure developing in the southern Gulf of Mexico by Monday and moving towards the west-northwest. This particular scenario is due to the the trough not being as elongated towards the northern Gulf, which does not create a weakness along the southeastern coast. The European actually shows the mid-level ridge across the southwestern United States building eastward across the northern Gulf of Mexico. This would act as a barrier (protecting Alabama and Florida from a direct impact) meaning the low would move northwest or west-northwest. This track would cause the greatest impacts along the coast of Mexico and Texas (by Wednesday). There would be impacts from Louisiana to Florida as well, however. Deep tropical moisture would stream into the area increasing heavy rain chances in these areas and rough seas along the coast. There could even be some coastal flooding near Louisiana and Texas due to the cyclonic rotation of this low. Heavy rain would also be likely across parts of Texas and Mexico. The European has been consistent with its westward path and low-end intensity, however, it should be noted: the European has had a slight trend further northwest and stronger with the low over the past few runs.

European 500mb map (Wednesday morning)

The 12km NAM is similar to the European but slightly further north. This scenario is worst case scenario because it meanders the low in the northern Gulf of Mexico, which would cause flooding rain across the coastal areas of Louisiana and Texas.

12km NAM potential rainfall map (through early next week)

This solution would also bring in tropical moisture to coastal areas of Mississippi, Alabama, and western Florida so heavy rainfall would be possible in these areas. Along with heavy rainfall, is the possibility of coastal flooding and beach erosion (especially for Mississippi, Louisiana, and eventually Texas) as this scenario would generate a strong onshore flow regardless of the intensity of the low.

12km NAM 10m wind speed map (Wednesday morning)

Alabama/Florida scenario:

The GFS-Parallel and Canadian (which have been consistent in their path, but have slowly adjusted slightly westward) show the low pressure moving towards the north-northeast as it approaches the coast of Alabama/Florida. (This guidance actually indicates a landfall just west of Panama City, Florida.) This particular scenario the GFS-Parallel and Canadian are painting is due to the the trough digging into the eastern United States remaining elongating, which creates a weakness along the southeastern United States. This also prevents the mid-level ridge across the southwestern United States from building eastward; creating a highway between southwestern ridge and Bermuda, which would steer the system into Florida by Tuesday night/Wednesday. This would mean the southeast (Alabama, Florida, Georgia, and South Carolina) would have the greatest impacts by the system; likely causing flooding across much of Florida and the Southeast. This scenario would also wrap some deep moisture into parts of the coastal areas of Mississippi and Louisiana, but the greatest coverage of convection would be in Florida.

GFS-Parallel potential rainfall map (through Thursday morning)

Along with heavy rainfall, is the possibility of coastal flooding and beach erosion for Florida and Alabama as this scenario would generate a strong onshore flow. It should be noted the GFS-Parallel and Canadian are much deeper with the low as it approaches the southeast (likely a tropical storm), but numerical guidance strength this early in the game should be taken with a grain of salt.

GFS-Parallel 500mb map (Tuesday afternoon)

How should you plan for this and confidence level:

The guidance is split on the intensity and track of this low after Monday, but confidence is high of a tropical depression developing in the southern Gulf of Mexico by Monday. Regardless of the eventual track of the system, impacts are possible from this system across most of the coastal regions along the Gulf Coast. If you live anywhere along the Gulf Coast (Florida to Texas), make sure you stay abreast to this fluid forecast and keep checking back for updates as the system’s movement becomes more certain.

Which scenario is most likely: Texas impact or Florida impact?

I believe the European (and to an extent the NAM) guidance is most realistic at this point, which would cause a more northwestward track. This would cause the greatest impacts in Louisiana and Texas; however, impacts would still be realized in Florida, and coastal areas of Alabama and Mississippi. I want to reiterate that track confidence is low. Everyone along the Gulf Coast needs to keep an eye on this system over the next 48-72 hours. (A concern of mine is the European has shown a tendency as of late to over amplify the ridges across the south. This is something I will keep a close eye on.)

An update will be provided tomorrow!