WxWatcher007

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.

The ICON has gained my tentative respect this season.

I don’t either. These are vastly different run to run differences—to be expected as you know.

This is a really good point, and is a good place for a reminder that usually CAG systems are slow to develop and are relatively lower ceiling at least initially because they can be so broad. Michael was an exception to the rule. Turning to the GFS…it looks like the eastern trough is enough to take it north and then NE across FL, but then a ridge rolls over the northern U.S. and traps it from escaping OTS immediately in advance of another trough that could kick or draw north. Just one of many solutions but I think the Gulf and East Coast should be watching this one closely. This looks like a favorable intensification environment if a low can build a well-organized structure.

The TC genesis signal looks right on the edge of 7 days judging by the ensembles. While I think the CAG (Central American Gyre) signal is real and we have a good chance of something forming, I’d say we need more time to lock that signal.

Severe geomagnetic storm underway!

With a Kp 8 too now

For the aurora folks—now sitting at a Kp of 7 and Bz is south.

@GaWx I know 99L and PTC 8 didn’t complete tropical genesis, but the pattern has been ripe for development and I think it’s becoming even more conducive with a possible CAG setting up next week and maybe beyond. Unlike frontal boundaries, these regions are purely tropical, moisture laden, and don’t necessarily have the shear issues. That said, anything trying to pop in a CAG would need time to develop, and given the broader eastern CONUS pattern it’s unclear if anything substantial can happen before areas are drawn north by the continued troughing we’ve seen. The homebrew regions of the Gulf, western Caribbean, and southeast coast is where my focus is the next two weeks.

Worst of it definitely being taken out on NC, with the heaviest rain now just offshore.

NHC notes that the GFS is a little fast.