2013 Atlantic Hurricane Season Birdseye Discussion #17

By: NCHurricane2009 , 1:30 AM GMT on June 17, 2013

...SUNDAY JUNE 16 2013 9:30 PM EDT...
Southern Caribbean tropical disturbance has become better organized and as a result has been upgraded to Invest 93-L. However...the consolidation of the disturbance's upper-level anticyclonic outflow and low-level cyclonic spin has occured at a location further southwest than I previously anticipated...and as a result is interacting with the Central American landmass moreso than I previously thought it would. Therefore I now believe it has a lower chance of developing into a tropical cyclone before crossing the Yucatan...and has a very low probability of having its circulation emerge over the Bay of Campeche as its newly-formed circulation should track straight west from its current position over Honduras. The only reason I am currently keeping Invest 93-L a special feature is that despite the circulation being over Honduras that the NHC may find a closed surface circulation and sufficiently strong winds in the offshore rainbands to declare this a tropical cyclone within the next 24 hours. Another possibility is that strong enough t-storms develops in one of the offshore rain bands with enough latent heat release to slightly relocate the upper-level anticyclonic outflow just offshore...with surface pressure drops below a relocated outflow causing the low-level circulation to regenerate offshore within the next 24 hours. Regardless of further development...heavy rainfall with flooding potential is expected over Honduras...Belize...Guatemala...southeastern Mexico...and the Yucatan Peninsula of Mexico. See special feature section below for details on Invest 93-L. Visit www.nhc.noaa.gov in the event 93-L becomes a tropical cyclone with associated warnings during the next 24 hours.

As promised in my final 2012 hurricane season birdseye discussion...I have begun to release post-storm reports for the 2012 Atlantic Hurricane Season which includes evaluations of how my storm forecasts (issued on these birdseye discussions) compared with that of the official forecasts from the National Hurricane Center. As these post-storm reports come out...they can be viewed on my other blog thread at www.wunderground.com/blog/MIHurricane2009.

 photo Jun_16_2013_2015Z_zps864c5e7f.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1942Z-released WPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

 photo Jun_16_2013_2015Z_zps6fee2a99.png
This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

1009 mb surface low near the coast of Costa Rica mentioned previously in this special feature section has dissipated...leaving the thunderstorms to consolidate with the more northerly positoned tropical wave axis that is currently marching into the western Caribbean Sea and Honduras. Despite the northward shift of the thunderstorms...they have remained focused at locations further south and further west than I previously anticipated they would be at this point. As a result...the latent heat release of these t-storms has generated an upper-level anticyclonic center in the Caribbean upper ridge further SW than I thought as shown by the black "X" over eastern Honduras in Figure 1b and by the blue H near eastern Honduras in the above atmo chart. Visible satellite imagery this past afternoon confirms a low-level low pressure circulation is spinning up over eastern Honduras as a result of surface pressure drops due to the outflow of the relatively new upper-level anticyclonic center.

Despite the circulation consolidating over land and hence reducing development potential...see the intro statement of this discussion as to why I am maintaining this as a special feature on this blog. I previously used the June 14 18Z GFS upper-level wind forecast shown in Figure 1a to upgrade this system to a special feature...predicting that on 1200Z Monday the thunderstorms and low-level spin would be focused near or below the black "X" west of Jamaica and over open water as that "X" represented where GFS showed the anticyclonic center of the Caribbean upper ridge consolidate. Instead as shown by today's GFS model initialization in Figure 1b the Caribbean upper ridge now has two anticylonic centers (shown by two black "X" marks)...one over northern south America...and the other near eastern Honduras. With this initialization...as Figure 1b also shows...today's GFS model now predicts that on 1200Z Monday that the anticyclonic center over eastern Honduras dissiapted in the face of the paragraph P5 Yucatan upper trough while the one over northern south America gets displaced westward (to the south of Jamaica) thanks to the amplifying upper trough of the 983 mb cyclone mentioned in paragraph P1. By dissipating the upper anticyclone currently over eastern Honduras by 1200Z Monday...the GFS model run in Figure 1b I think is not giving enough credence to the tremendous t-storm latent heat release backing that upper anticyclone...and in fact I think their is a chance this upper anticyclone could completely displace the paragraph P5 Yucatan upper trough (but if GFS in Figure 1b is correct that the Yucatan upper trough instead wins out...this would reduce the rainfall potential over the Yucatan and southeastern Mexico).

As the caption of Figure 1 concludes...the circulation of this disturbance has formed further southwest than I previously thought. Now with the circulation formed...it should track straight west thanks to deep-layered ridge axis in northern Gulf of Mexico mentioned in paragraph P4...and thanks to another surface ridge to develop behind forecast Ohio Valley frontal cyclone mentioned in paragraph P1. With the westward track beginning at a location further south than previously thought...it should now track over mainland southeast Mexico later on rather than the Bay of Campeche waters...so I currently believe tropical cyclogenesis potential over the Bay of Campeche from this system later on (if it doesn't develop in the next 24 hours) has gone out the window.

 photo Jun_16_2013_300mb_GFS_for_Invest_93L_zpsb5aaa4ba.png
Figure 1: The image with label (a) is the upper-level 18Z GFS computer model run from June 14. The images with label (b) is the upper-level 12Z GFS computer model run from today. All black Xs represent an anticyclonic center of the Caribbean Sea upper ridge. I previously predicted using image (a) that the circulation of this disturbance would develop near or below the black X west of Jamaica and over open water by 1200Z Monday. Instead as shown by the top-right image (b)...on 1200Z Sunday (today) we have an anticyclonic center much further southwest and near eastern Honduras where the circulation of this disturbance has in reality developed (easterly wind barb over Honduras in the top-right image (b) is how I spotted the anticyclonic center over eastern Honduras). The loss of Honduras easterly wind barbs in the bottom-right image (b) shows that this particular model run loses the eastern Honduras upper anticyclone by 1200Z Monday.

P1...Main component of upper trough and surface frontal system originating from western Canada is currently about to leave the east Canada coast with a deep-layered 995 mb center. As anticipated during the last few discussions...the bulk of the upper vorticity of this system has become an east-west trowal (see east-west blue-dashed line in upper-left corner of above atmo chart). The trowal is expected to soon swing east...but the associated surface frontal cyclogenesis that was expected to occur over the central US by now has been delayed in models for another 48 hours and is now expected to occur over the Ohio Valley. Regardless...southeastern divergence of the upper-level trowal supports central US frontal activity...with low-level warm air advection ahead of this frontal activity continuing to support United States upper ridge (albeit this upper ridge has recently been pushed south into the southern states and northern Gulf of Mexico as the aforementioned east-west trowal has pushed in). Meanwhile...a fragment of the upper vorticity that is now this east-west trowal dove SE around the crest of this upper ridge 9 days ago...where we now have an upper trough and associated 1000 mb surface frontal cyclone zooming across the northeastern Atlantic NNE of the Azores and toward western Europe. 4 days ago...yet another fragment of the upper vorticity also dove SE around the crest of the upper ridge...where we now have an upper trough moving across the W Atlnatic whose western convergence supports 1023 mb ridge that recently moved offshore from the eastern US...and whose eastern divergence supports a relatively new 1014 mb frontal depression NE of Bermuda and an intensifying 982 mb frontal cyclone that recently crossed Newfoundland and into the Atlantic high seas SW of Greenland (this frontal cyclone will shortly absorb the 995 mb frontal depression mentioned in the early part of this paragraph).

P2...NE Atlantic upper anticyclone has been pushed further south to a location NW of the Cape Verde Islands thanks to amplificaiton of northeastern Atlantic upper trough mentioned in paragraph P1 above.

P3...Cut-off upper vortex persists in the open central Atlantic.

P4...Surface ridge dominates much of the open Atlantic basin. Its main center...currently 1031 mb...is now supported by upper-level convergence between easterlies streaming south of a north-central Atlantic upper anticyclone and southerlies steraming east of the paragraph P3 upper vortex. The north-central Atlantic upper anticyclone is a result of warm air advection ahead of the 983 mb frontal cyclone mentioned in paragraph P1 above. This surface ridge has had a westward extension into the Gulf of Mexico over the past days (and currently this extension has a 1019 mb center). This extension was due to southeastern upper convergence of the paragraph P1 United States upper ridge...and because the upper ridge has recently shifted southward and stacked with the extension...we now effectively have a deep-layered ridge axis in the northern Gulf of Mexico tonight. Furthermore...the 1023 mb center offshore of the eastern US also mentioned in paragraph P1 has recently joined this extension. This extension remains a bit split off from the aforementioned main 1031 mb center due to southward-digging cold front extending from the 983 mb frontal cyclone.

P5...Cut-off Upper trough over the western Caribbean in the previous discussion is now over the Yucatan Peninsula. With the United States upper ridge in paragraph P1 acting as a blockade against any injections from mid-latitude upper troughs...this cut-off upper trough over the next days will gradually diminish (as all cut-offs without injections do) while becoming squeezed between the United States upper ridge and the upper ridge of tropical disturbance Invest 93-L.

P6...Elsewhere in the Atlantic tropics...the Caribbean Sea is dominated by the low-level low pressure circulation of tropical disturbance Invest 93-L and upper-level anticyclonic ridge supported by the latent heat release of the immense thunderstorms of the disturbance. Low-latitude tropical upper ridging meanwhile remains in the eastern Atlantic. As of 1800Z this evening...the NHC TAFB added a weakly-defined tropical wave east of the southern Lesser Antilles as marked in the bottom-center of the above atmo chart. Not sure if this tropical wave is the same one I suspected existed in paragraph P11 of discussion #13 which I subsequently removed by discussion #15 because of the lack of its existence in prior TAFB maps. This weakly-defined tropical wave is inactive while currently in unfavorable upper winds in the gap between the aformentioned Caribbean Sea upper-level ridge and aforementioned low-latitude eastern Atlantic upper ridge.

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