cieldumort
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As has been noted in the General Long Range Forecast Lounge, modeling has been trending warmer and warmer on the development of a Central American Gyre over this coming weekend that spins up an Atlantic side TC early next week.
As of 9/18/0z, global modeling is plenty compelling enough to start a lounge on this as-of-yet, only modeled system.
Central American Gyres are large, closed areas of low pressure that have two peak seasons: May through June, and then again September through November. As their name suggests, they are roughly centered over Central America.
There are two distinct types of CAGs: nonbaroclinic and baroclinic. Nonbaroclinic CAGs are by far the most common and are associated with an upper-level high. Baroclinic CAGs are far less common, and are characterized by an upper-level trof. The exact type of CAG can have large implications for the future location of TC genesis and track of any TC born from the parent broad area of low pressure. Most baroclinic CAGs form well north of where of where most nonbaroclinic CAGs do. Both types produce very heavy to extreme rainfall events, particularly along the Central American coastline.
Over this coming weekend, an upper-level trough will drop far south into the GOM, forcing rising air across the western Caribbean and lowering pressures generally throughout this region, especially near or along our seemingly ever-present quasi-stationary coastal front, which itself is expected to slide into Central America and the northwestern Caribbean by then. By early next week, this ULL is likely to split, allowing an upper-level anticyclone to track further west and possibly colocate with the nascent area of surface low pressure near or over Central America, thus further increasing the potential for tropical cyclone genesis or perhaps already by this time, just increasing favorable conditions for continued strengthening.
Should the above play out as now most global models prognosticate, an area of tightening low pressure, possibly a TC, will be forming on the eastern to northeastern side of the CAG or along/just south of the front, likely in the northwestern Caribbean, with steering currents that might favor a north to northeast track.
Alternate solutions range from development more along the north to northwestern portion of the CAG (far less likely, but possible), only East Pac TC development (also far less likely, but possible), and no TC development at all (less likely, but somewhat possible).
ECMWF ensemble implied TC development odds in the western to northwestern Caribbean over the next 10 days are already over 70%.
As of 9/18/24 1:30AM EDT, the date and time of original entry, this area of low pressure is only a modeled forecast, and does not yet have an Invest tag. Should a disturbance form from this that does get Invest tagged, the title will be updated accordingly.
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cieldumort
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0z models are coming in hot tonight. We still do not have even as much as a broad area of low pressure, let alone Invest or depression, so all of this should be taken with a pound of salt. However, conditions in the NW Caribbean and Gulf next week could be extraordinarily favorable for anything that wants to and does form.
19/0z Globals
GFS: Apparent TD or monsoon depression in the NW Caribbean by 12Z Tuesday. Tropical Storm in NW Caribbean by 0z Wednesday. Cat 1 by 12Z Wednesday in NW Caribbean tracking northwest. Cat 2/3 by 06Z Thursday in the Yucatán Channel, tracking northwest. Begins slowing down and gradually rounding more to the north and probably Cat 4 by 12Z Friday in the southern Gulf of Mexico. Maintains Cat 4+/- into Saturday while slowly tracking north, while also now a large high-end Major. This is potentially a wrecking ball of a surge-maker at this point. 0z Monday 30th, Tropical Storm conditions begin battering the coasts of eastern Louisiana, Mississippi, Alabama and westernmost Florida panhandle. Begins feeling the tug to the northeast and a landfall somewhere around Port St. Joe, Florida predawn Tuesday the 1st of October as a 959+/-mb large hurricane with some probably very significant storm surge. Cuts across north Florida/SE Georgia and plops offshore of South Carolina Tuesday afternoon, tracking northeast just offshore.
ICON: Seems to delay TC genesis to predawn Tuesday Sep 24, tracking wnw across the Yucatán and into the Bay of Campeche, heading towards eastern Mexico through the end of run. Still over water at the end of run at 12Z Thursday Sep 26, never stronger than a tropical storm up to this point.
GDPS: Apparent TD or monsoon depression off the coast of Nicaragua/Honduras 12Z this coming Monday. Sloppy Tropical Storm by 12Z Tuesday in the NW Caribbean, tracking north-northwest. In the Yucatán Channel 06Z Wednesday Cat 1. Large Cat 1/2 in the east-central Gulf 06Z Thursday. Landfall as a large apparent Cat 2 somewhere about the far western Fl panhandle Thursday afternoon/night.
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cieldumort
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0z/19 Ensemble members by and large are fairly stout and mostly cluster around a track towards Florida. Several members however delay development and/or stay weak, with a track more towards the western Gulf.
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cieldumort
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Unlike the 0z ensembles, the 0z shows a large spread, with perhaps some signal for delayed development and an overall greater risk for the western to central Gulf. Florida is still well in the mix.
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cieldumort
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Today's 12Z and ensembles are somewhat similar to yesterday's with the GEFS favoring earlier and more easterly development and subsequent stronger TCs that trend into the north to northeastern Gulf, and the ECENS development still a bit more delayed with a bias towards the northern to western Gulf. But, there is also arguably more of a shifting of the ensembles towards the members and not the other way around.
9/20/12z members
9/20/12z members
It is my personal read of the layout that should there be TC genesis out of this, which I would place at about 90% odds within 7 days (presently 50% ), it will most likely occur along or east of the eastern coasts of Central America and/or the Yucatán, possibly as far north as the Yucatán channel region, whereas the still advertises several solutions, including the operationals, developing a TC in the southwestern Gulf.
Just where TCG occurs is likely to have an outsized influence on future track and intensity.
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