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2013 Atlantic Hurricane Season Birdseye Discussion #16

By: NCHurricane2009 , 6:01 AM GMT on June 16, 2013

...SUNDAY JUNE 16 2013 2:00 AM EDT...
A tropical disturbance has developed this past afternoon in the southern Caribbean below a favorable western fracture of low-latitude upper ridging. Because of the forecast evolution of the upper ridge fracture...I am now expecting a high probability of tropical cyclone formation either in the western Caribbean Sea as early as late Monday...or potentially later in the week after this system crosses the Yucatan into the Bay of Campeche. Interests in Central America should monitor this system in case it does not develop further north and instead goes west into their area with plenty of rainfall potential. Interests in the Yucatan...Bay of Campeche...and east-central Mexico should monitor this situation for possible tropical depression or tropical storm development. See special feature section below for additional details on this situation.

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_15_2013_2045Z_zps3d39e378.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1924Z-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_15_2013_2045Z_zps3ed2545d.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).

As paragraph P8 in the previous discussion mentioned...upper outflow at the west end of the current Caribbean Sea upper ridge continues to enhance t-storms over parts of Central America and the south-central Caribbean Sea where we now have a 1009 mb surface low near the coast of Costa Rica. Tropical wave also mentioned in paragraph P8 of the previous discussion is arriving into the central Caribbean and with its surface convergence it appears to have enhanced this area of t-storms to the degree that the National Hurricane Center introduced this system into their Tropical Weather Outlook this evening. The strongest computer model support continues to be with the GFS which shows eventual development later on when this tropical wave moves into the Bay of Campeche. The CMC and Euro are also suggestive of some development...but on the weakish side while only showing a weaker Bay of Campeche low pressure area while they favor a more eastern Pacific solution.

While studying the June 14 18Z GFS model run during the previous discussion...I claimed that I believed the model was initialzied with too amplified of a Caribbean upper ridge while citing a SSW upper wind vector over the central Bahamas when my 00Z atmo chart at the time was showing more of a SW upper wind vector over the central Bahamas. The problem with that comparison was I was comparing an 18Z initialization to 00Z wind vectors...and indeed scrolling that 18Z GFS model 6 hours ahead (to 00Z) showed it accurately matching that 00Z atmo chart nearly spot-on. In fact...that June 14 18Z GFS model run 24 hours out is still proving quiet accurate when comparing it to the above upper-level wind barbs in the above 18Z atmo chart. Therefore I am relying on the GFS upper-level wind model to give a prognosis on what could happen with this disturbance. As such the following is my outlook on this disturbance...

One scenario is that the thunderstorms simply consolidate around the aforementioned 1009 mb surface low such that the latent heat release causes the anticyclonic core of the Caribbean upper ridge to consolidate at a more southward location. In such a scenario...the disturbance would then spend little time over water...move into Central America...and then move into the eastern Pacific perhaps realizing the CMC and Euro suggestions of eastern Pacific activity. By studying the GFS upper-level wind forecast...the GFS suggests that by 1200Z Monday that the anticyclonic core of the Caribbean upper ridge will instead shift west and north such that it lands in the open western Caribbean Sea to the east of the Yucatan Peninsula. It appears the west shift of the upper ridge would be due to the dissipation of the paragraph P5 upper trough and due to the southward digging of the upper trough associated with the amplifying 996 mb frontal cyclone in paragraph P1. It appears the north shift of the upper ridge would be due any latent heat release of t-storms along the more northerly positioned tropical wave axis...and due to warm air advection ahead of the forecast central US frontal cyclone mentioned at the very end of paragraph P1. Moreover...the GFS's forecast western Caribbean upper anticyclone is made more impressive by an enhanced eastern outflow channel into a new cut-off upper vortex to develop from the 996 mb frontal cyclone's upper trough. Therefore I see it highly likely that this disturbance by 1200Z Monday will have consolidated northwestward and below the impressive western Caribbean upper anticyclone...with possible surface tropical cyclone formation just east of the Yucatan as early as very late on Monday. After Monday...models show a strong surface ridge developing behind the forecast central US frontal cyclone...and such a ridge would steer this west across the Yucatan...across the Bay of Campeche...and into east-central Mexico. GFS suggests that the favorable upper ridge core moves west with the disturbance through that time as the upper ridge becomes directly related with the t-storm latent heat release of this system.

P1...Main component of upper trough and surface frontal system originating from western Canada is currently over eastern Canada with a 1001 mb surface frontal depression...with western convergence of the upper trough supporting a surface ridge 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 front and associated thunderstorms pushing into the central US. Low-level warm air advection ahead of this central US front supports United States upper ridge. Meanwhile...a fragment of the aforementioned western Canada/western US upper vorticity dove SE around the crest of this upper ridge 8 days ago...where we now have an upper trough and associated 1002 mb surface frontal cyclone zooming across the northeastern Atlantic to the north of the Azores and toward western Europe (western convergence of this upper trough now supports surface ridge near the S tip of Greenland mentioned in paragraph P3 of the previous discussion...which is currently 1023 mb). 3 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 upper trough moving into the W Atlnatic whose western convergence supports 1020 mb ridge that moved from the Great Lakes to the eastern US...and whose eastern divergence supports a brand new 1008 mb frontal depression just north of Bermuda and an intensifying 996 mb frontal cyclone that has moved across Newfoundland and toward southern Greenland in the last day (this frontal cyclone will shortly absorb the 1001 mb frontal depression mentioned in the early part of this paragraph). In the next 24 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 south of the Azores and west of the Canary Islands while pushed southward by 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 1027 mb...is now supported by convergence at the SE quad of a relatively new NW Atlantic upper anticyclone. This upper anticyclone has developed thanks to warm air advection ahead of the 996 mb frontal cyclone mentioned in paragraph P1 above. This surface ridge had a westward extension into the Gulf of Mexico over the past days (and currently this extension has a 1018 mb center). This extension is due to southeastern upper convergence of the paragraph P1 United States upper ridge...however this extension has recently been split off from this ridge due to southward-digging cold front extending from the 996 mb frontal cyclone.

P5...Cut-off Upper trough over the Florida Straits in the previous discussion is now in the western Caribbean. 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 the tropical disturbance mentioned in the above special feature section.

P6...Elsewhere in the Atlantic tropics...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 while now associated with the tropical disturbance discussed in the above special feature section.

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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