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2013 Atlantic Hurricane Season Birdseye Discussion #24

By: NCHurricane2009 , 3:57 AM GMT on June 25, 2013

...MONDAY JUNE 24 2013 11:55 PM EDT...
Pair of tropical waves moving across the Lesser Antilles is heading toward favorable upper winds developing in the western Caribbean Sea. Based on current observations and the forecast shown in computer model runs...this situation appears rather similar to the formation of last week's Tropical Stom Barry...and therefore I have upgraded the pair of tropical waves to a special feature. See special feature section below on potential tropical cyclone development in the western Caribbean region within the next 5 days.

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_24_2013_2345Z_zps51342180.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0600Z, and the 0739Z-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_24_2013_2345Z_zps3dd4db27.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).

Low-latitude upper ridge persists across much of the Atlantic tropics. Pair of tropical waves has continued westward across the Lesser Antilles...with the western of the two now in the eastern Caribbean. Upper ridge that has moved into the NW Atlantic (paragraph P2) has pushed the paragraph P7 and P4 upper vorticity southward such that much of the low-latitude upper ridging has de-amplified. The de-amplified portion of the low-latitude upper ridge is providing westerly shear across the tropical wave pair...and coupled with dry Saharan air advected westward by the 1034 mb center in paragraph P5 (see brown shading in lower-right of above thermo chart)...current development of this tropical wave pair is suppressed.

Meanwhile the western lobe of the low-latitude upper ridge is not quiet as de-amplified such that its anticyclonic outflow is enhancing an area of t-storms over the south-central Caribbean Sea. Coupled with tropical wave activity sliding toward such a t-storm cluster...this pattern is quiet similar to the pattern in paragraph P8 of discussion #15 just before last week's pre-Barry disturbance became a special feature on this blog. Therefore I have decided to upgrade this tropical wave pair to a special feature as well...especially considering that computer models insist on expanding the paragraph P7 Florida-area upper ridge into the W Caribbean in between the two paragraph P7 upper vortices (and I think some of this favorable W Caribbean upper ridging will also be a manifestation of the anticyclonic outflow presently over the south-central Caribbean t-storms).

CMC and GFS computer models support some kind of development in the W Caribbean...Yucatan...Bay of Campeche area by 180 hours. But with the models also showing the W Caribbean upper winds becoming quiet favorable between now and 120 hours...I think gradual tropical cyclone development in the W Caribbean could occur within the next 120 hours (5 days). Currently the paragraph P1 weather system is expected to have enough amplitude as to weaken the west extent of the paragraph P5 ridge...so it is possible this system gets pulled northward towards the Gulf of Mexico region in the coming days before turning west due to the ridge that builds behind the paragraph P1 weather system.

P1...Large frontal cyclone and upper trough is parked offshore of the west US coast. In the next days...a slowly-developing shortwave upper trough will soon eject eastward from this system while supporting another frontal cyclone. The early phases of this are beginning in the upper-left corner of the above chart with a 997 mb surface frontal depression over the Wyoming/Montana border.

P2...Upper trough persists near the east Canada coast and NW Atlantic...with its eastern divergence supporting a 998 mb frontal cyclone between Canada and Greenland...and with its western convergence supporting a 1021 mb surface ridge moving into Hudson Bay. Elsewhere over North America...western US upper trough is moving into the central US while its eastern divergence supports a 1000 mb frontal depression that has migrated NE from the Colorado/Kansas and into south-central Canada in the last 36 hrs. SE US upper vortex mentioned in the previous discussion has weakened into a shortwave upper trough becoming absorbed by aformentioned upper trough moving into central US. Warm air advection ahead of the 1000 mb south-central Canada frontal depression supports an upper ridge that has moved from the central US into the NW Atlantic in the last 36 hrs.

P3...Although an upper trough and associated surface frontal cyclone exited the picture from the NE Atlantic (paragraph P2 of the previous discussion)...the long frontal zone stretching several hundred miles to the southwest left some features behind including a 1013 mb frontal depression east of Newfoundland supported by the eastern divergence of the east Canada coast/NW Atlantic upper trough mentioned in paragraph P2 above. Since then....this 1013 mb depression has also exited the picture from the NE Atlantic...but its front leaves behind a 1020 mb depression SSE of Newfoundland now supported by the eastern divergence of the east Canada coast/NW Atlantic upper trough.

P4...Cut-off upper vortex N of the Cape Verde Islands (paragraph P3 of the previous discussion) and cut-off upper vortex in the open central Atlantic (paragraph P4 of the previous discussion) have merged into one large upper vortex in the open central Atlantic.

P5...Surface ridge dominates much of the open Atlantic basin. Its main center...currently 1034 mb...is NE of the Azores and remains generally deep-layered in nature. The 1034 mb surface center is supported by upper convergence NE of its upper-level center. This surface ridge continues to have a westward extension currently located across the W Atlantic...SE United States...Gulf of Mexico..and into east-central Mexico. This western extension is supported by upper convergence from a variety of upper features mentioned in paragraph P2...including west side of the SE US upper shortwave trough...east side of upper ridge that has moved into the NW Atlantic...and west side of upper trough along east coast of Canada/NW Atlantic.

P6...South fragment of tropical wave moving across Central America (mentioned in paragraphs P6 and P7 of the previous discussion) has moved into the eastern Pacific and therefore will no longer be mentioned on this blog. North fragment of tropical wave moving into the east Florida coast (mentioned in paragraph P7 of the previous discussion) has dissipated.

P7...Cut-off upper vorticity over the eastern Bahamas has during the past two discussions split into two upper vortices. One upper vortex has migrated southward from the waters S of Bermuda and into the central Bahamas while pushed by the paragraph P2 upper ridge moving into the NW Atlantic. Second upper vortex has retrograded across the Caribbean and into the Gulf of Mexico while orbiting around the persistent Florida-area upper ridge.

P8...See above special feature section for update on pair of tropical waves and overhead low-latitude tropical upper ridging mentioned in paragraph P8 of the previous discussion. Based on Meteosat-9 satellite animation over the last couple of days...it appears a tropical wave with on-off t-storm clustering has recently rolled off Africa and is currently south of the Cape Verde Islands as marked in the lower-right of the above atmo chart. Although it currently has a t-storm cluster below a favorable eastern lobe of low-latitude upper ridging...it appears to be headed into the dry air/westerly vertical shear environment mentioned in the above special feature section...I expect no development here in the short-term...

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

Reader Comments

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4. WunderAlertBot (Admin)
4:33 AM GMT on June 26, 2013
NCHurricane2009 has created a new entry.
3. zampaz
9:29 AM GMT on June 25, 2013
Thank you for your analysis NCHurricane2009.
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2. KoritheMan
7:14 AM GMT on June 25, 2013
Interesting setup that you highlight in the western Caribbean. I certainly didn't notice it. Now I'll be watching.
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1. nigel20
4:17 AM GMT on June 25, 2013
Thanks again for your in-depth blog post...I really appreciate it.
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