- Where it is now: At around 75°W, low in the southwestern Caribbean, and moving off the Caribbean coast of Colombia
- Where it will be: The wave/moisture axis will be along the Nicaragua coast on Thursday and near the Yucatan Peninsula this weekend. However, the precise placement of an organized disturbance forming from this wave will depend on finer details with its initial development, and that at the moment is quite unclear. A fast-developing system in the western Caribbean is more likely to move north into the Gulf as a result of trough. Its track if it does develop in the Eastern Pacific or Bay of Campeche is a little more unclear since that would be a little further out in the model guidance, though northwesterly tracks seem to be favored in those cases.
- Model support: GFS organizes a tropical cyclone this weekend in the western Caribbean. ICON on board with something very disorganized going into the Gulf. ECMWF and CMC not on board with development on the Atlantic side and have generally shown not much of anything happening, but the two have somewhat flirted with the possibility of a disturbance in the Bay of Campeche or Gulf of Tehuantepec in a few recent model runs. A small handful of EPS members show weak development in and around the Gulf of Honduras. The GEFS is more enthusiastic, with several members showing a tropical storm in the western Caribbean by early next week.
- What to watch for: The strength of the eastern Caribbean ridge, northerly placement of vorticity, and the intensity of offshore convection between 13-16°N especially between now and Friday. A weaker ridge and stronger convection could pull the system away from Central America and increase the likelihood of a tropical cyclone developing.
Composite of infrared satellite data, total precipitable water (both from SSEC RealEarth) and NHC/TAFB surface analysis
This wave and its future have dominated short-range and medium-range tropical discussion for the Atlantic this month (details in the short- to mid-range models thread and the waves thread, where it is "Wave #1"). After great anticipation, this wave is now beginning to move into the southwestern Caribbean, where it and a monsoon trough are teaming up to some disorganized convection this afternoon.
There have been a great deal of posts talking about longer-term model runs (pretty much just the GFS) that show a hurricane moving up the Gulf. However, anything of the sort of flavor depicted by the GFS hinges on the next few days. Model guidance is in agreement that this system will continue to be convective (GFS, ECMWF for tonight), which is unsurprising given the several days of troughiness aloft dragging moisture northwards through the western and central Caribbean. Out until about tomorrow afternoon, the models appear pretty similar, with the vorticity maximum hanging out around Panama and a band of enhanced vorticity to the north, which would probably be associated with some band of deep convection at around 12°N that could be ongoing Wednesday morning into the afternoon. However, there is a relatively slight, but possibly meaningful 100 mi difference in the center of the vorticity maximum between the GFS and the ECMWF, with the ECMWF being further south. It may be also worth noting that the CMC shows very little concentrated enhancement of vorticity. The GFS brings the system the farthest north of the three models, followed by the ECMWF, and then the CMC. Coincidence? Perhaps not.
Also a point of consideration is that the strength of the ridge centered over Puerto Rico; a stronger ridge would promote more easterly flow, preventing the disturbance from lifting as far north in response to the trough in the Gulf of Mexico. As has been the case for several days, the GFS shows the weakest ridge (compare with the ECMWF). In both guidance suites, the forecast strength of ridge hasn't changed considerably, though the GFS seems to have gradually trended towards a slightly stronger ridge. That said, the GEFS has also trended slightly stronger with the Gulf trough.
However, I think one of the most critical factors for the fate of this disturbance is the amount and intensity of convection towards the northern end of the wave. While things aren't too structurally different between the models tomorrow morning, things change beginning that evening. The GFS shows an area of robust, deep, and concentrated convection at 15°N Wednesday evening and then does so again Thursday afternoon and evening. The effect this has on the disturbance is quite noticeable. The first convective burst causes an increased area of low-level vorticity, amplifying the wave and dragging the whole system a bit northward/northwestward. The second convective burst repeats this process and really sets the storm into motion, continuing into Friday morning and helping to form a closed mid-level circulation that serves as a pivotal step to getting a tropical cyclone formed in the western Caribbean.
The ECMWF has something akin to the first convective burst Wednesday evening (though a bit weaker), but fails to produce as much offshore convection as the GFS on Thursday. Without the convective aid and pressure falls needed to save the disturbance from a tangle with Central America, the ECMWF brings the weak system into Nicaragua. Hardly anything is depicted by the model in the western Caribbean and Gulf of Honduras on Saturday. The convection on the GFS, on the other hand, launches the disturbance north of 15°N, putting it in a position to develop within the western Caribbean.
As a result of this discrepancy, both the ECMWF and CMC put the disturbance that tangles the disturbance with Central America. Though a trough this weekend over Texas and the Gulf of Mexico may help to lift some moisture and convective bits into the Bay of Campeche, the entwining of the system with Mexico and Central America would make tropical cyclogenesis a bit more tricky and complicated. (As an aside, it may be worth noting that the GEFS has trended a bit stronger with that trough).
Given the amount of troughs forecast to repeatedly fly through the Gulf, the intensity of a future tropical cyclone headed that way will likely be dependent on the ability for the system to drag along the anticyclone that will initially be moving along with it in the Caribbean. This, again, is dependent on the amount and intensity of offshore convection, which would be needed to produce diabatic heating of the upper-troposphere and reinforce ridging aloft (compare the positioning of outflow aloft on Friday morning between the GFS and ECMWF). While differences in future modeled intensity and the finer details of the environment in the Gulf could be important, that would all hinge on whether this system can, quite literally, get off the ground in the first place.
Yet another case of a trigger-happy in the early season western Caribbean, combined with some possible convective feedback issues cropping up once again? Time will tell.