6/20/17 - Heavy Rainfall Headed For Gulf Coast & First Ever "Potential Tropical Cyclone" Forms

Update: Invest 93L is now Potential Tropical Cyclone 3 in the Gulf. Potential Tropical Cyclone 2 is now Tropical Storm Bret, east of the Caribbean. We will have an updated post later this evening. 


Overview -  Invest 93L is disorganized this am, but the overall low level structure has improved in the last 24 hours. Surface wind analysis shows more of an elongated trough axis and not a well defined low as of yet. Strong convection has been firing over the western Caribbean sea, east of the main surface trough axis. There is currently a high chance of development, 80% within 48 hours and 90% through the next 5 days.

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Watches/Warnings - Please review the current watches and warnings below:

Intensity - The atmospheric setup in the Gulf of Mexico is not favorable enough at this time to allow for much intensification. At this time, guidance does not suggest anything more than a moderate tropical storm with winds likely staying below 60 mph. While it can’t be completely ruled out, there is a less than 10% chance this system reaches hurricane intensity.

Track - There has been a consensus in the guidance that 93L will generally track towards the west or northwest portions of the Gulf of Mexico by midweek. The forecasted steering flow is complicated as the models are trying to handle an upper level trough over the western Gulf of Mexico, building high pressure over the southwest Atlantic and the southwest U.S., and a trough of low pressure over the Great Lakes. There’s agreement that the surface trough associated with 93L will move WNW today and a surface low will likely form in the south central Gulf of Mexico within the next 24 hours. Once the system is in the central Gulf, the models diverge. The GFS takes the system NNW towards the LA coastline while the EURO/UKMET models turn the system west towards the middle Texas coastline. It appears the models have different views on how much influence the upper level trough over the Gulf of Mexico will have on the tropical system. The GFS has been slowly shifting westward towards the EURO/UKMET and right now it appears the GFS is not handling the steering pattern as well as some of the other guidance. All interests from the lower TX coast to SE LA should monitor the future track of this system as it’s not set in stone yet.

Latest "spaghetti" model plots.

Latest "spaghetti" model plots.

Alert Levels - We have issued high alert levels for the NW and North-Central Gulf of Mexico for the potential of heavy rain which may lead to flash flooding and the possibly of coastal flooding due to higher seas to the north and east of the center. We do not expect this to be a wind event. Heavy rainfall will be the primary threat.

Impacts - Regardless of development, the main impacts from this system will be heavy rainfall and the possibly of tropical storm force winds up to 50-60 mph. Rainfall amounts to the north and east of the center may reach 6+ inches and up to 10-12 inches in localized areas. Coastal areas from the middle Texas coast to SE LA should expect minor coastal flooding issues.

Latest rainfall forecast from the EURO model. Note, the highest rain totals will be north and east of the center.

Latest rainfall forecast from the EURO model. Note, the highest rain totals will be north and east of the center.

Conclusion - If you are a resident or have interests along the Gulf of Mexico, please continue to check in throughout this week for updates on this system as we will be here with the latest information.


Overview - The National Hurricane Center now has the option to name tropical systems when there is a high chance of development and the threat of tropical storm or hurricane force winds within 48 hours. These systems will be designated as “Potential Tropical Cyclones” (PTC) and the NHC will issue advisories just as they would on a real active system. Invest 92L was upgraded to Potential Tropical Cyclone 2 yesterday as it’s forecasted to become a tropical storm and bring ts force winds to the southern portions of the Lesser Antilles over the next 24-36 hours. Once the system reaches the Caribbean Sea, we expect the system to weaken back into an open wave due to increasing wind shear that it will encounter as it moves west.

Watches/Warnings - Tropical storm warnings are currently in effect, please review the image below.

Intensity - Based on the latest guidance, we expect this system to attain tropical storm status before weakening back into an open wave once it reaches the Central/Eastern Caribbean Sea on Wed/Thu due to increasing wind shear.

Track - The track forecast is fairly straightforward, the system will generally track towards the west-west northwest over the next couple of days generally towards the southern Lesser Antilles in the eastern Caribbean Sea. 

Alert Levels - Since there’s high confidence in the future development of this system, we have issued imminent alert levels for the southern half of the Lesser Antilles. Minor impacts are possible within the next 23-48 hours. Tropical Storm Warnings are in effect.

Impacts - Please review the image below for impacts as of the latest NHC advisory.

Conclusion - The fact that we have such a strong tropical wave with the potential to develop is very rare for mid June. It’s also historic in the fact that this is the first system the NHC has designated as a Potential Tropical Cyclone. The NHC is certainly doing a better job at informing the public when there’s a threat of a system developing and impacting land. It’s absolutely the right decision. You will now find information in the app on Potential Tropical Cyclones, look for the new blue storm icon in the overview and current storm sections.

We will have another discussion tomorrow. Thank you for using Hurricane Tracker and have a great week!