2013 Atlantic Hurricane Season Birdseye Discussion #14

By: NCHurricane2009 , 1:24 AM GMT on June 14, 2013

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...THURSDAY JUNE 13 2013 9:25 PM 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 vortex 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 paragraphs P8 and P9 below for details. Other than tonight's 18Z GFS computer model which shows tropical cyclone formation in the western Caribbean and Bay of Campeche by 180 hours...computer model runs are otherwise not showing tropical cyclone development below the forecast western fracture of the upper ridge. Given that the GFS model has recently hinted at potential...given that the Caribbean is the climatological spot for Atlantic tropical cyclones in June...and given that we have tropical wave activity sliding underneath the favorable western fracture of the upper ridge (as discussed in paragraph P9)...will be watching the Caribbean area over the next 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.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Jun_13_2013_2045Z_zps1fcba742.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1930Z-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.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Jun_13_2013_2045Z_zps5b9d82c1.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).

...MID-LATITUDES DISCUSSION...
P1...Main component of upper trough and surface frontal system originating from western Canada is currently over Hudson Bay and eastern Canada with a 1005 mb surface frontal depression...with western convergence of the upper trough supporting 1026 mb surface ridge just SW of Hudson Bay. However...the bulk of the upper vorticity of this sytem remains behind over western Canada/western US where its eastern divergence supports surface western US front and 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 now 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 6 days ago...where we now have a NW Atlantic upper trough and associated 1000 mb deep-layered frontal cyclone. 24 hrs ago...yet another fragment of the western Canada/western US upper vorticity also dove SE around the crest of the upper ridge...which is supporting a severe-weather-producing 1000 mb surface frontal cyclone that has moved from Minnesota to the NE US in last day. In the next 72 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 either from the Great Lakes or from the central US area.

P2...Central Atlantic upper anticyclone is shifting eastward into the NE Atlantic while supported by low-level warm air advection ahead of the east-moving 1000 mb deep-layered frontal cyclone in the NW Atlantic mentioned in paragraph P1 above.

P3...Upper trough regime over the north-central Atlantic is finally shifting eastward across the far NE Atlantic and toward Europe. Attendant 994 mb frontal cyclone near the south tip of Greenland has likewise shifted east into the far NE Atlantic while weakening to around 1004 mb while it remains directly below the non-divergent environment of the upper trough regime. Western convergence of this upper trough regime supports surface 1017 to 1020 mb ridge that has lifed off the east Canada coast into the far north Atlantic.

P4...Cut-off upper vortex far SE of Bermuda has shifted ENE into the open central Atlantic while accelerating in SW flow ahead of the larger-sized NW Atlantic upper trough mentioned in paragraph P1.

P5...Surface ridge dominates much of the open Atlantic basin. Its main center...currently 1028 mb...is now supported by convergence at the SW quad of the paragraph P4 upper vortex. It continues to have a westward extension across the northern Gulf of Mexico and into eastern Texas (with 1019 mb center) thanks to upper convergence on the southeast quad of the paragraph P1 United States upper ridge.

...TROPICAL BELT DISCUSSION...
P6...As the paragraph P7 upper vortex shifts westward...tropical upper ridge in the western Gulf of Mexico area is being pushed westward into northern Mexico.

P7...Upper trough over the Bahamas in paragraph P7 of the previous discussion has evolved into a westward-moving upper vortex over the Florida Straits as it gets steered around the much larger United States upper ridge mentioned in paragraph P1 above.

P8...Tropical wave moving across the south-central Caribbean Sea in the previous discussion is currently moving across Central America. As mentioned in this tropical wave's previous discussion (paragraph P9 of discussion #13)...because the paragaraph P7 upper vortex has lifted northward and now westward out of the way...this has allowed the west end of the tropical upper ridge (referred to in paragraph P9 below) to expand westward toward this tropical wave. Enhanced upper outflow of this upper ridge's west end continues to enhance t-storms in the eastern part of this tropical wave...which currently extend across parts of Central America and into the south-central Caribbean.

P9...Tropical wave mentioned in paragraph P10 of discussion #13 is currently crossing the Lesser Antilles into the eastern Caribbean Sea. Possible tropical wave mentioned in paragraph P11 of discussion #13 I estimate is currently midway between the Cape Verde Islands and Lesser Antilles based on continuity since then...but I may simply drop this tropical wave from future discussions if the NHC TAFB continues to not add it to their TAFB surface maps. Low-latitude upper ridging has been covering the eastern tropical Atlantic over the last several days...and as paragraph P8 above mentions....the west end of this upper ridge is building over the Caribbean Sea in the wake of departing paragraph P7 upper vortex. An upper anticyclonic core just east of the Lesser Antilles appears to be associated with this westward expansion of the upper ridge...with the upper outflow of this core appearing to enhance thunderstorms in the vicinity of the two tropical waves mentioned in this paragraph.

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