2013 Atlantic Hurricane Season Birdseye Discussion #15

By: NCHurricane2009 , 5:28 AM GMT on June 15, 2013

...SATURDAY JUNE 15 2013 1:28 AM EDT...
As paragraph P1 in the mid-latitudes discussion below describes...an upper ridge persists over the United States...which has been promoting shearing upper vorticity features (such as the upper trough mentioned in paragraph P7) over June's climatologically favored Caribbean and Gulf of Mexico areas thanks to the relatively lower pressures southeast of the upper ridge. However as computer models have been predicting...this shearing upper vorticity is becoming replaced by a western fracture of low-latitude upper ridging. See paragraph P8 below for info on potential Bay of Campeche tropical development below this favorable fracture of the upper ridge during the next week.

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_14_2013_2345Z_UPDATED_zps6db05a01.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0000Z, and the 0116Z-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_14_2013_2345Z_zpsa7c99869.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).

P1...Main component of upper trough and surface frontal system originating from western Canada is currently over eastern Canada with a 1007 mb surface frontal depression...with western convergence of the upper trough supporting surface ridging over Hudson Bay. However...the bulk of the upper vorticity of this system remains behind over western Canada/western US where its eastern divergence supports surface western US front and associated Great Plains t-storm activity. Prior low-level warm air advection ahead of this system promoted an upper ridge over the United States...but based on looking at the lastest US drought monitor and surface temp map I would say this upper ridge currently appears bolstered by the hot and dry air mass associated with a drought over the interior US. Meanwhile...a fragment of the aforementioned western Canada/western US upper vorticity dove SE around the crest of this upper ridge 7 days ago...where we now have an upper trough and associated 1001 mb surface frontal cyclone zooming across the north-central Atlantic. 2 days ago...yet another fragment of the western Canada/western US upper vorticity also dove SE around the crest of the upper ridge...where we now have an eastern US upper trough supporting a 1020 mb ridge over the Great Lakes with its western convergence...and with its eastern divergence supporting an intensifying 999 mb frontal cyclone that has moved from the NE US into the NW Atlantic during the last day. In the next 48 hours...the bulk of the upper vorticity over western Canada/western US will evolve into an east-west trowal to the north of the upper ridge...and then the trowal will swing east while supporting yet another frontal cyclone that will eject eastward from the central US.

P2...NE Atlantic upper anticyclone persits midway between the Canary Islands and Azores while supported by low-level warm air advection ahead of the east-moving 1001 mb frontal cyclone in the north-central Atlantic mentioned in paragraph P1 above.

P3...Upper trough shifting eastward across the far NE Atlantic during the previous discussion is making landfall in western Europe. Attendant frontal cyclone is moving into the British Isles...and has deepened from 1004 mb to 997 mb while once again tapping into eastern divergence of the upper trough. Western convergence of this upper trough supports surface 1020 mb ridge in the far north Atlnatic near the south tip of Greenland.

P4...Cut-off upper vortex persists in the open central Atlantic.

P5...Surface ridge dominates much of the open Atlantic basin. Its main center...currently 1028 mb...is now supported by convergence at the SE quad of a brand new NW Atlnatic upper anticyclone. This upper anticyclone has developed thanks to warm air advection ahead of the 999 mb NW Atlc frontal cyclone mentioned in paragraph P1 above. This surface ridge continues to have a westward extension across the northern Gulf of Mexico and onto the Texas coast (with 1014 mb center) thanks to southeastern upper convergence of the paragraph P1 United States upper ridge.

P6...Tropical upper ridge moving into northern Mexico in the previous discussion has now merged with the prominent upper ridge over the United States mentioned in paragrpah P1.

P7...Upper vortex over the Florida Straits has opened up into an upper trough while temporarily trying to link with the mid-latitude eastern US upper trough mentioned in paragraph P1 above. The mid-latitude eastern US upper trough will soon bypass this upper trough...rendering this upper trough cut-off to the southeast of the strong United States upper ridge (also mentioned in paragraph P1). With the United States upper ridge acting as a blockade against any other 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 tropical upper ridge mentioned in paragraph P8 below.

P8...Low-latitude upper ridging has been covering the eastern tropical Atlantic over the last several days...with the west end of this upper ridge fracturing into the Caribbean Sea in the wake of the gradually weakening paragraph P7 upper trough. As paragraph P8 of the previous discussion mentioned...thunderstorms continue to be enhanced over the south-central Caribbean and parts of Central America due to upper outflow at the west end of this Caribbean upper ridge fracture. Tropical wave crossing the Lesser Antilles into the eastern Caribbean Sea mentioned in paragraph P9 of the previous discussion is currently positioned from Hispaniola...thru the open Caribbean waters...and into NW Venezuela. This tropical wave is tracking toward the aforementioned south-central Caribbean thunderstorms. Coupled with the fact that computer models insist on shifting the favorable Caribbean upper ridge fracture westward into the Bay of Campeche (BOC) as this tropical wave also tracks toward that area...perhaps their is potential for BOC tropical cyclone development next week as suggested by the 18Z cycle of GFS...CMC...and Euro models. Things that will cause the Caribbean upper ridge fracture to shift west into the BOC include the gradual dissipation of the cut-off upper trough mentioned in paragraph P7 coupled with a southward-digging upper trough associated with amplifying 999 mb frontal cyclone mentioned in paragraph P1. However I am a bit skeptical of this potential BOC tropical development at the moment as the above atmo chart suggests the tropical wave is about to enter shearing upper southwesterlies ahead of the paragraph P7 upper trough. I also beleive the 18Z cycle of the GFS model was initialized with too amplified of a favorable Caribbean upper ridge fracture (for instance the 18Z upper-level wind field showed SSW vector over the central Bahamas whereas the above atmo chart's upper-level wind barbs show the vectors over the central Bahamas more from the SW). As I wrote this...the more recent 00Z cycles of models appear better initialized...but those model runs were not yet complete to see whether or not they now downplay the BOC development potential as a result of being initialized with a less amplified Caribbean upper ridge fracture.

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

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