WxWatcher007

The thread gets renamed, and I try to keep the latest advisory info in the title until landfall.

Much like in the Gulf, shear vector and storm motion matter a lot in how much shear a TC actually encounters. It looks like a shift in shear direction has now given this the space to organize. Just look at visible satellite from yesterday vs now. Tail Doppler shows that the LLC and MLC are pretty well aligned. That likely means the organizational trend (not necessarily intensity, yet) is poised to pick up the pace—if alignment holds.

A couple things also stand out on that GFS run. The first is the presence of a pretty significant Predecessor Rain Event (PRE) in north GA/eastern TN/western NC. The second is a significant wind field of TS winds, even along the southeast coast. That kind of onshore flow could cause some flooding issues as well.

I uninstalled this week. It’s not like nights are 75/71 now. I haven’t had a low above 63° since 9/1.

I don’t think dry air is likely to be a major inhibitor (but watch for it still given the theme of the season) because I don’t think we’re going to get enough shear in the Gulf given storm motion to impart much before there’s a well organized inner core. Unlike other storms, even if there’s a last minute increase, which didn’t weaken storms like Beryl and Francine, this one will be moving quite fast near the coast. Not much time to weaken imo. To me, the things that could keep this in check wind wise (and currently I think “high end” 2 seems to be the floor) are: 1) too much time organizing the next 48 hours and establishing an aligned vortex, which could be done with the current southwesterly shear in the Caribbean and/or 2) Early ERCs that promote the storm to expand substantially and become inertially stable, but with a much broader wind field. In fact, I think the earlier RI happens the more likely 2 becomes. To be sure still potentially higher end in this scenario, with surge impacts being enhanced along the west coast of Florida and peak wind impacts blunted some in the Big Bend/Panhandle. Still a lot of uncertainty for something less than 72 hours out.

Really high end RI. Honestly it’s impressive that both the EPAC and Gulf could see rapidly intensifying hurricanes just a few days apart.

It may be trying to get to the surface but I think it’s going to be hard to get a read without recon, and it may take a while given the southwesterly shear. Cayman Islands radar could be helpful tonight as the process takes its first shot at it. https://www.weather.gov.ky/radar

Thanks for reminding people, and not that anything I say matters, but for folks reading—this could be a high impact event, and we have not just posters but probably a lot of lurkers that will be reading this. Not that anyone should be making decisions based on what’s said here lol (always follow official sources, etc) but for people posting I just ask that we set aside any wish casting, down playing, or non-contextualized posts (for example, posting an image of a hurricane model without analysis) as this comes together. Obviously stuff happens but let’s try to stay on track. There’s an opportunity to learn a lot here the next few days about tropical genesis, the development of inner core structures, and how TCs interact with troughing/deep layer shear, and that discussion gets lost in poor posts. tl;dr I sound like a prude lol but let’s be responsible and thoughtful in our posts as people will likely be seriously impacted by this one.

PTC Nine will be designated at 11am.

The NHC in the 8am outlook is telegraphing a PTC designation by 11am to issue watches/warnings for Cuba and Mexico.

This was the first cone for what became Michael—also a system that came from a CAG. But I should also add that Michael (obviously) was the exception to the rule. Few Atlantic CAG TCs become major hurricanes, for many of the reasons discussed here.

I think the ceiling for this is less related to shear and more to how organized it can become before reaching the Gulf. While the environment in the Gulf doesn’t look pristine from an intensification standpoint, I think some of the higher end potential (not necessarily the GFS solutions but rather the middle ground between GFS/Euro) can be realized if this isn’t a broad gyre type system in that timeframe. The loop current in the Gulf is awfully impressive and I don’t know if moisture is going to be a huge inhibitor. The impact of shear could also be lessened if it’s aligned with storm motion. Just my .02.

It may be another day or two until things are settled.

Euro won’t be anywhere as strong as the outlier GFS, but it will come in stronger than the 00z run.

Like @purduewx80 said earlier, these runs illustrate how wide the envelope of solutions still is. Looking at the 500mb trend and there is none really. The trough is kind of all over in placement, and there’s a huge difference in impacts and impact locations as a result. The only thing that seems to be in better focus is that Florida looks like the primary landfall risk zone currently.

Not sure how 96L isn’t classified.

Given the current discussion in the main thread, the increasing confidence in a TC developing, and the threat of U.S. impacts within the next 7 days, I think it's time to break out discussion of our current area of interest in the western Caribbean into a separate thread. Northwestern Caribbean Sea and Gulf of Mexico: A broad area of low pressure is likely to form by the early to middle part of next week over the northwestern Caribbean Sea and the adjacent portions of Central America. Thereafter, gradual development of this system is possible, and a tropical depression could form as the system moves slowly to the north or northwest over the northwestern Caribbean Sea and across the Gulf of Mexico through the end of next week. Regardless of development, this system is expected to produce heavy rains over portions of Central America during the next several days. * Formation chance through 48 hours...low...near 0 percent. * Formation chance through 7 days...medium...60 percent. We've been tracking this for a while, and as I mentioned before our favorable homebrew region pattern that led to several invests off the East Coast and Hurricane Francine in the Gulf due to stalled frontal boundaries and trough interaction has evolved this week to a Central American Gyre (CAG) pattern characterized by broad cyclonic flow over the eastern Pacific, Central American land mass, and western Caribbean. The result is a growing amount of vorticity which we're starting to see in the region. This is an analysis at 850mb. As a trough digs into the region, we get a favorable setup for upper divergence, which aids the development of convection, which will likely continue to pulse until we can start seeing a complex of storms become more persistent. It's unclear if today's convection is the start of this process. TCs that come out of CAGs usually start as broad systems that slowly develop. That's partly a function of being in a broader cyclonic flow. However, once the TC establishes itself, depending on the intensification environment they can have a variety of upper bound or lower bound ceilings. There's strong cross guidance support in both the operational models and ensembles that something develops in the Western Caribbean or Gulf in the coming days, and is drawn north toward the U.S. coast. There are a lot of options on the table. First, with intensity, it's unclear how quickly any potential TC will organize to take advantage of what looks like a favorable environment for intensification. The GFS on balance has been more aggressive, while the Euro has been least aggressive. Secondly, with track, while it looks like the central and eastern Gulf are looking most likely to be in a possible landfall zone, there are questions about what happens with the steering pattern both before and after a landfall. The general pieces on the board are identified--a western ridge and eastern U.S. trough, but it's unclear how timing and amplitude will shake out and influence the eventual track. Here's a trend gif at 500mb looking at the GFS and Euro respectively. Bottom line is there is a lot of uncertainty with this system. While genesis is likely, we still have questions on eventual intensity, landfall location, and overall track afterward, which could impact the central, southern, or eastern sections of the country. Given the broad and likely moisture laden characteristics of the system, surge and rainfall are likely to be significant impacts. Folks all along the Gulf coast should be watching this closely.

Agree. I think that’s going to make where the system develops—on the western or eastern side of the Yucatán—really critical. An eastern solution could take it up the east coast, whereas something in the central Gulf could be a real disaster with inland momentum getting halted leading to a moisture bomb somewhere.

It’s not bad to mix in a few of these days from time to time.

Ensembles. You treat the operational runs as extensions of ensembles at this stage imo—just one solution in the greater whole. It’s always a good idea before looking at the specific outcomes of these runs to take a step back and analyze the steering and development/intensification environment first.

Vertical instability sits near climatological norms in the homebrew regions of the Gulf, EC, and Caribbean, but remains well below normal (but rising) in the tropical Atlantic.

My peak season forecast may go down in flames, but my pattern recognition has been pretty good lol.

While it’s worth watching a possible one off in the dead tropical Atlantic portion of the MDR and perhaps something weak in the central Atlantic for TC genesis, obviously the western Caribbean is the place to pay closest attention. The homebrew signal I’ve been talking about since late August has evolved over the last week. Originally, the signal was for genesis potential off the SE coast and in the Gulf due to stalled frontal boundaries from anomalously strong late summer troughs. That led to our three invests, one which hit NS as a non tropical cyclone, one which became a PTC but fell just short of a tropical designation, and one that helped seed what became Hurricane Francine. Now we’re looking at a CAG signal, which as I’ve said before is a more tropical genesis pathway than what we formerly had. These can spin up one (most likely) or two TCs. While the ceilings are usually low, this environment seems like it has higher end potential given the extent of OHC, instability, and low wind shear—one area of the cool neutral ENSO that did come to fruition from the hyperactive seasonal forecasts. Everything remains on the table, and I think anyone in the Gulf and to a lesser extent folks on the EC should be paying attention to this.