2013 Atlantic Hurricane Season Birdseye Discussion #21

By: NCHurricane2009 , 7:23 AM GMT on June 21, 2013

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...FRIDAY JUNE 21 2013 3:24 AM EDT...
Barry dissipates into a remnant low over east-central Mexico.

Elsewhere...an upper ridge is expected in the vicinity of Florida as detailed in paragraph P7 below...and their is a slight possibility the north end of the Caribbean tropical wave (also mentioned in paragraph P7) could interact with the favorable upper winds of this upper ridge in the next 72 hours. However...their is no computer model support for tropical development in this area at this time...and surface pressures in the region are forecast to be high due to upper convergence on the east side of a central United States upper ridge mentioned in paragraph P1.

Upper winds will also be favorable below the central Atlantic low-latitude upper ridge mentioned in paragraph P8. However computer models show no tropical development with any tropical waves to pass below the upper ridge...and Saharan dry air in the region also makes conditions unfavorable.

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_20_2013_2345Z_zps78bbb978.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0000Z, and the 0130Z-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_20_2013_2345Z_zpse6c80208.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...A couple of new mid-latitude features have entered the scope of this discussion from the upper-left corner of the above charts in the last 48 hours. First is an upper trough and attendant 999 mb surface frontal cyclone from northern Canada that has recently crossed Hudson Bay (with western convergence of this upper trough also supporting a 1026 mb surface ridge over southern Hudson Bay). Second is a western US upper trough with attendant surface frontal cyclone...with an upper ridge over the central US developing due to warm air advection ahead of the frontal cyclone. A fragment of this western US upper trough has tracked into the SE US as a shortwave.

P2...Upper trough over eastern US and eastern Canada is moving into the NW Atlantic. Eastern divergence supports a surface frontal cyclone that has moved from Newfoundland to the Atlantic high seas in the last 24 hrs while it has deepened to 984 mb. Western convergence of this upper trough supports 1027 mb surface ridge that has moved from the Great Lakes to the waters offshore of Nova Scotia. Low-level warm air advection ahead of the 984 mb frontal cyclone supports upper ridge that has built into the north Atlantic from the W Atlantic in the last 24 hrs.

P3...Cut-off upper vortex N of the Cape Verde Islands persists.

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 1034 mb...is located in the vicinity of the Azores while currently supported by upper convergence between easterlies south of the N Atlantic upper ridge in paragraph P2 and southerlies east of the paragraph P4 upper vortex. This surface ridge continues to have a westward extension into the Gulf of Mexico (with a current 1019 mb center) while supported by convergent upper NW flow west of the paragraph P1 SE US shortwave...and convergent NW flow east of the paragraph P1 central US upper ridge (this upper convergence may be also enhanced by the robust outflow on the north side of Barry adding resistance against the convergent upper NW flow). In the low-levels (700 to 850 mb)...CIMSS still shows that the west extent of the surface ridge goes all the way into Mexico...with the Mexico portion of the ridge steering Barry westward further into Mexico.

...TROPICAL BELT DISCUSSION...
P6...Central America and parts of Mexico continue to be dominated by upper-level anticyclonic ridge in part associated with the outflow structure of former tropical cyclone Barry. As mentioned in paragraph P5...the weakening remnant low of Barry is being steered further west into Mexico by the west extent of the low-level ridge discussed in that paragraph.

P7...Cut-off upper vortex persists over the eastern Bahamas. Tropical Wave over Puerto Rico/E Caribbean in the previous discussion is currently located over Hispaniola and the central Caribbean...with surface convergence from the tropical wave and eastern upper divergence of the upper vortex supporting occasional t-storm clouds over Hispaniola...E Bahamas...and nearby W Atlantic waters. As mentioned in paragraph P1...a shortwave upper trough has arrived into the SE US...with a new Florida upper ridge expected to form in relatively higher pressures between the SE US shortwave and the eastern Bahamas upper vortex. In turn...a fragment of the upper vortex will retrograde SW around the Florida upper ridge. Because of this...the south half of the tropical wave will become suppressed by the retrograding upper vortex...but watching the north end of this tropical wave to see if it interacts with the more favorable upper winds beneath the expected Florida upper ridge. However...their is no computer model support for tropical development in this area at this time...and surface pressures in the region are forecast to be high due to the west extent of the paragraph P5 surface ridge.

P8...Low-latitude upper ridge persist in the central tropical Atlantic. Tropical wave SW of the Cape Verde Islands in the previous discussion is currently below this low-latitude upper ridge in the waters midway between the Cape Verdes and Lesser Antilles. Tropical wave rolling off Africa in the previous discussion is now passing south of the Cape Verde Islands and still has an associated t-storm cluster. Meanwhile...westward expansion of dry air continues in the lower-right of the above thermo chart...perhaps advection of Sahara Desert air via the south side of the paragraph P5 ridge. Even though the first of the two above-mentioned tropical waves is currently below the favorable upper winds of the central Atlantic low-latitude upper ridge...this dry air is suppressing this tropical wave...so perhaps the second of the two tropical waves south of the Cape Verde Islands will eventually lose its t-storm cluster to this dry air. Currently...no computer models suggest development from either of these two tropical waves as they slide beneath the central Atlantic low-latitude upper ridge.

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