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Atlantic Tropical Action 2012 - Part I


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Saharan Air Layer or SAL

An area of dry dusty air traveling East to West from the Sahara Desert in Africa across the Atlantic Ocean that can sometimes reach Miami Fla.. I have seen it many times living down there most of my life.They can often make spectacular sunrises and sunsets.

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Looks like two Cape Verde lows in the MDR..

The GFS appears to be doing a poor job with realistically propagating this easterly wave after initiating it. There will be the passage of the convectively active phase of an eastward propagating atmospheric Kelvin wave in the upcoming week over this region, however the solution of the GFS doesn't appear to be doing a good job. The figure below is a time-lon plot of TRMM 3B42 rain rates and GFS 850 hPa southerly total winds. You can see in the GFS forecast (below black line) that it initiates this easterly wave at the coast of West Africa. While this type of circulation does develop during CCKW passages at this region, the GFS forecast appears to be over-doing it a bit, especially during the time of year. But to be seen!

rain_v.africa.total.30.5N-15N.gif

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Tropical wave interacting with trough to it's NE and anticyclone aloft to it's east is generating decent convection. Low level vorticity has increased over Hispaniola, but there's little mid level energy associated to it. There's substantial shear, especially to it's west...although it might become a player in the E GoM after it crosses FL/FL straits.

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Tropical wave interacting with trough to it's NE and anticyclone aloft to it's east is generating decent convection. Low level vorticity has increased over Hispaniola, but there's little mid level energy associated to it. There's substantial shear, especially to it's west...although it might become a player in the E GoM after it crosses FL/FL straits.

Looking at GFS 200-850mb shear forecast from FSU experimental cyclone genesis site out to a week, and then 250 mb and 850 mb winds from GFS ensembles, and NAEFS beyond, if anything got into the Gulf, it wouldn't face extremely hostile conditions just based on deep shear. Never know when something from the mid-latitudes might make it down, along with systems of tropical origin. Not really expecting anything, looking at OLR maps on CPC site (5 and 15 day means) I'd expect favorable MJO conditions to return in August, or just before the climatologically favored uptick in activity. Not the most sophisticated way at working with the MJO, extrapolating recent OLR maps, I know, but I'm not in Jorge and Don territory for amateur smartness.

250 mb winds aren't all that bad anywhere in the basin really at 10 days, the shear is really more about 850 mb winds, and those are strongest North of South America.

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Sure its July, and as normal, Atlantic tropics aren't very busy. But my typical glass full optimism, 50 Kj/cm^2 TCHP now from offshore Corpus Christi to just offshore South Louisiana, and another stripe of the 50s offshore Charley territory of Gulf coast South Florida.

On a side note, reading some Holland, predicted and empirical suggestion the biggest Delta Intensity/Delta T is between 26 and 28 to 29º SST, near 30mb MPI per degree, with a sharp decrease in increasing MPI with SST above 29º. When it is slow, I occupy myself with reading. I myself wonder often about SST as compared to TCHP, which clearly inherently assumes upwelling, as it relates to faster moving cyclones or smaller areal extent, which would have less time to suffer from upwelling. Wada (2007) would seem to disagree, at least for Chinacanes.

2012186go.jpg

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Sure its July, and as normal, Atlantic tropics aren't very busy. But my typical glass full optimism, 50 Kj/cm^2 TCHP now from offshore Corpus Christi to just offshore South Louisiana, and another stripe of the 50s offshore Charley territory of Gulf coast South Florida.

On a side note, reading some Holland, predicted and empirical suggestion the biggest Delta Intensity/Delta T is between 26 and 28 to 29º SST, near 30mb MPI per degree, with a sharp decrease in increasing MPI with SST above 29º. When it is slow, I occupy myself with reading. I myself wonder often about SST as compared to TCHP, which clearly inherently assumes upwelling, as it relates to faster moving cyclones or smaller areal extent, which would have less time to suffer from upwelling. Wada (2007) would seem to disagree, at least for Chinacanes.

2012186go.jpg

Yes it seems when storms develop over colder water, they can survive over colder water, however when they develop over warmer SSSTs and then move over colder SSTS they sometimes fall apart. This is especially true in the EPAC where storms weaken rapidly when they hit the cooler SSTs.

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Sure its July, and as normal, Atlantic tropics aren't very busy. But my typical glass full optimism, 50 Kj/cm^2 TCHP now from offshore Corpus Christi to just offshore South Louisiana, and another stripe of the 50s offshore Charley territory of Gulf coast South Florida.

On a side note, reading some Holland, predicted and empirical suggestion the biggest Delta Intensity/Delta T is between 26 and 28 to 29º SST, near 30mb MPI per degree, with a sharp decrease in increasing MPI with SST above 29º. When it is slow, I occupy myself with reading. I myself wonder often about SST as compared to TCHP, which clearly inherently assumes upwelling, as it relates to faster moving cyclones or smaller areal extent, which would have less time to suffer from upwelling. Wada (2007) would seem to disagree, at least for Chinacanes.

...and guess where the biggest dI/dT occurs in the Atlantic?

post-29-0-51228900-1341695734_thumb.png

Image caption reads "Maximum increment of the maximum sustained winds (km/6h) for tropical cyclones that have occurred in the Atlantic from 1851 to 2000"...a good deal of that probably is a consequence of the warm eddy that spins off the current loop to the W or SW...which this year is strong and will be in a prime spot for the heart of the season near the Tamaulipas and S TX coast...the problem is that it might left untouched, especially if a stronger Niño develops.

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OK, so what's next?

If the CFS is right, might be a shot late next week (and into the week of 7/22) and getting something going (shear considerations aside) and then again in August as the MJO nudges around more favorable.

Shear is the bigger wildcard...if that doesn't subside much, could be quiet outside of any homebrew off of the US coast or a rogue mll/ull spinning down to the surface in the Central Atlantic for a while.

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There's an outside chance at some sloppy mess from the cold front along the Gulf over the weekend or early next week, but nothing more than a rain maker even if it does form.

Well, more from my usual natural glass full optimism than actually believing it, it'd appear we are 3 days away from a sub-tropical depression off Delaware, per 12Z CMC. 1014 mb, probably not what Josh wants.

BTW, I remember another developing Nino year and a non-tropical system making it to the Gulf, and Danny in 1997 was a solid Cat 1 at landfall.

1997DannyNOLARadar.PNG

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ULLs pinched off the westerly flow...TUTTs still attached and not closed (trough)

The features show up really well on a Dynamic Tropopause pressure map. You can see the upper level features that have been cutoff as the upper level anticyclone that was dominating the Eastern United States has moved offshore and the upper level impulses have folded underneath. There is widespread westerly upper level flow (at the tropopause level) across the Atlantic basin. Thus, there is little chance outside of the Gulf for any sort of tropical development over the next 5-7 days under this regime.

254zwcz.png

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