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Atlantic Tropical Action 2012 - Part II


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It is interesting that, despite the models’ adamancy about a NE track over E Cuba / the Bahamas, climatology (CLP5) and the BAMD--which typically performs better with these slow-moving, late-October Caribbean systems, as it did with Wilma 2005--suggests a NNW track and a FL threat now that the system is likely to make its closest approach to the United States on or before 25 October. Although an initial NE drift seems likely after a few days, the highly progressive pattern suggests short-wave ridging will quickly build back in about a few days later, in the wake of the trough axis off E Canada...mainly due to the Pacific pattern favoring a deep West-Coast trough during that time frame. Given the likelihood that the system will be in the neighborhood on or before 25 October, I think a FL threat cannot be discounted...particularly if a low-level vortex consolidates farther west and becomes the primary vortex. I am having a hard time buying the idea that the system will split into two separate vortices...despite what the models indicate. The split may merely be convective feedback, a byproduct of the fact that the system may be large and messy...making a single vortex difficult to initialize. I am tending to argue that a single vortex--as in the ECMWF--is more likely to consolidate S of Jamaica and then drift NNW for a few days before turning NE...with a stall or a turn back to the NNW or NW probable after that time. The upcoming pattern is actually a bit similar to that of 14-18 October 1950...when Hurricane King threatened FL. Then, as now, we had a strong Greenland vortex, a progressive wavelength, and a strong West-Coast trough / Plains-based ridge with a strong surface gradient off the Southeast. Of course, in 1950, the wavelength was not quite as amplified...but the similarities between the ECMWF and the 1950 pattern are striking in some respects. Due to this, I also believe this system may surprise us and become more intense than what some people are anticipating...King 1950 actually began as a very broad, disorganized monsoonal gyre, yet actually became smaller over time and developed a tight center...and, of course, bombed out as it curved NNW into South FL. Note that the models showing the split take the Western vortex toward S FL and the eastern vortex over the Bahamas / out to sea...while in 1950 forecasters initially expected King to bend NE, out to sea, due to the effects of a Canadian trough to the NE. Instead, ridging built back in and forced King to curve from NNE to N and then NNW. I am not saying we will see a repeat of King...but the set-up bears watching.

Interestingly, King also split into two systems as it neared FL, with the Gulf (western) vortex becoming Hurricane Love.

Another question is whether the GFS and ECMWF ensembles are overestimating the upper-level divergence and vorticity off the East Coast by day five. The models tend to turn 99L more NE due to the influence of a cut-off upper low or retrogressive short-wave trough that moves SSW toward FL and the W Caribbean, thereby undercutting what is otherwise a solidly broad but somewhat weak mid-level ridge. The spaghetti plot of the 00Z NCEP ensembles shows fairly substantial divergence as to how far SSW and how deep the cut-off low will be. A faster movement and weaker depth would lead to a position farther SSW in the Caribbean, leaving a stronger ridge to the north and likely imparting a N or NNW movement to 99L--assuming, of course, that 99L moves more slowly within days 2-5. In that case, S FL would face more of a King-like threat from 99L, which would likely benefit from an outflow channel imparted by the upper low. On the other hand, a faster 99L and a broader, deeper cut-off low in days 2-5 would support a NE track over E Cuba, in line with the operational GFS and ECMWF models. However, since upper lows have recently tended to have been analyzed somewhat too deeply over the W Caribbean, I would tend to support a blend of the two possibilities, with 99L moving slowly W through day 2, slowly curving NE thereafter, and then turning back N over east-central Cuba by days 4-5. Then, depending upon the depth of the ridge and the amplitude / progression of the Rockies trough, 99L would pose a threat to either S FL (as a TC) or the Carolinas / Mid-Atlantic / New England (as a warm-seclusion-type event, possibly). We shall see, but at the moment I am leaning toward S FL.

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Maybe I am grasping at straws, but I am still not completely convinced that the 00Z models are handling the likelihood that 99L will be weaker, slower, and farther west through day 2. So I would not eliminate the S-FL threat yet until we see a few more 00Z and 12Z model cycles. Models have been overdeveloping many tropical cyclones this season. The King 1950-type option is not yet out the window, though it was always less than 50% in terms of probability.

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Seriously. We can't catch a break.

I cannot count how many times the actual tracks have been east of what climatology would indicate for the respective time of year.

Just look at the model consensus vs. the red climatological model. In any other year this system might have been a decent FL threat.

Scrap 2012. We have had the same trend since 2009.

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Wow. Come on guys. You guys give up now? just because tthe 00z models of a storm that hasn't developed yet and has a very broad low level center show OTC? This year has really taken a toll on everyone.

I have not given up, but at some point--if a few additional model cycles continue the current trend--I will. The main issue this year has always been the strength of the East-Coast trough and the suppression of upper-level anticyclones, leading to strong shear across the Caribbean basin.

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Insult to injury (if 99L recurves): the latest intensity models are more bullish than ever and now take the system up to Cat-2 intensity (85 kt) over the open W Atlantic. :lmao:

But interestingly, many of the other models show 99L lingering in the S Caribbean through day 5--a possible indication of support for a slower, weaker evolution and a NNW path toward S FL.

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00z CMC has a major phase with the Trof and the end result is some sort of apocalyptic hybrid-bomb over the DC area.

Which is exactly what Hazel 1954 was-- an October cyclone that formed in the Caribbean and then shot N to rake DC, NYC, and other major I95 cities as an extremely severe extratropical cyclone. Multiple cities-- including DC-- had official, sustained hurricane winds.

The Hazel echoes in these runs are very interestin'.

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