Tropical Development Likely in the Gulf of Mexico this Weekend

After a June void of any tropical cyclones in the Atlantic, there is finally a system worth discussing right now, dubbed Invest 92L. The system is currently located over the southeastern U.S. and will progress southward into the northern Gulf of Mexico by the middle of the week, where the National Hurricane Center is giving it an 80% chance of forming into a tropical cyclone by Saturday.

Five Day Tropical Weather Outlook issued at 8am EDT on July 8, showing 92L tracking south over Georgia. (NHC)

92L generated from a non-tropical mesoscale low that formed over the foothills of the Rocky Mountains on the Fourth of July, and has since tracked southeast to its current position over central Georgia. It currently does not contain any convection, as the flow around the low is quite broad and still decoupled with its upper-level counterpart over southeast Alabama. This low is currently progressing southeastward in tandem with a decaying frontal boundary to the north, and then move southward into Florida and the eastern Gulf of Mexico tomorrow night as a ridge begins to build towards the west, at which point convection may begin to fire.

Imagery of the mesolow over Georgia and unassociated tropical convection surrounding it. (NOAA GOES-EAST Imagery)

As 92L progresses into the Gulf of Mexico, intensification is very likely. Condition across the region are favorable for the development of tropical convection. Sea surface temperatures are at 31C, which sits about 2C above normal and is more than warm enough to sustain a tropical cyclone. Wind shear is currently low at less than 10kts overall, the surrounding environment is expected to be quite moist, and upper-level divergence is expected to be high. In addition, oceanic heat content values along the Loop Current are extremely high, so if 92L tracks a little bit farther south than anticipated, then it could intensify further.

Selected Image. If missing, image may be unavailable
Oceanic heat content map of the Atlantic Basin, showing OHC values of about 150kJ/cm^2 along the Loop Current. (OSPO OHC Graphics)

Over the past several days, there was a split on the track for 92L. The EURO model was persistent on bringing the storm farther south and west towards the central or northwestern Gulf Coast under a ridge over the Rockies as a bonafide tropical storm or minimal hurricane. The GFS model, on the other hand, kept it closer to shore and farther east, not allowing for development and moving northeast under the influence of a trough over the Great Lakes. Since then, the models have come into better agreement on track, falling more in-line with the EURO solution. The trough is expected to be weaker and the ridge is forecast to be stronger, so 92L is now predominantly forecast to miss the connection with the trough and travel farther west instead. A more western track allows for more time over water, and hence more time to strengthen. The system should travel west under the ridge until it begins to build towards its east by this weekend, which will cause it to take a gradual northerly turn. At this point, models are indicating that the most likely landfall point will be somewhere along the Texas or Louisiana Gulf Coasts over the weekend. Some models, such as the EURO itself, have a near-hurricane strength storm moving onshore between Galveston and Port Arthur, TX, on Saturday evening, while the GFS has a tropical depression moving onshore in the same general area on Friday night. Afterwards, the system is expected to progress northwards across eastern Texas and eventually into the Midwest where it will fizzle out. Keep in mind that these model forecasts are not set-in-stone and are subject to change.

Regardless of formation and where landfall occurs, heavy rainfall is expected along the Gulf Coast from tomorrow to the weekend. On average, 2-5 inches of rain can be expected across the southeastern U.S. with isolated totals as high as 7-8 inches. The Florida Gulf Coast, in particular, may see the most rain, as the system will be broader and slower-moving near the area. Rainfall totals will only be higher than these where the system makes landfall, which is still unknown despite the agreement in the models today. Also expect very rough seas and gusty winds along coastal areas through the weekend across the Gulf Coast.

Day 9 image not available
1-7 day Quantitative Precipitation Forecast over the CONUS, showing 2-5″ of rain across the southeastern U.S. from 92L. (WPC)

If this system does attain a name, it would be Barry. Adhere to the National Hurricane Center and your local weather officials for the latest information on Invest 92L. More articles will be written as the situation progresses, so stay tuned.

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