2013 Atlantic Hurricane Season Birdseye Discussion #74

By: NCHurricane2009 , 7:57 AM GMT on August 21, 2013

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...WEDNESDAY AUGUST 21 2013 3:57 AM EDT...
Atlantic tropics remain quiet even as we push into the later part of August. However...compared against the 1966 to 2009 climatology...the 2013 season is ahead of schedule with the number of tropical storms (http://www.nhc.noaa.gov/climo/images/cum-average_ Atl_1966-2009.gif). But it is also worth noting this season is behind the number of average hurricanes by this date.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Aug_21_2013_0115Z_zpsc4d1b9f0.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0000Z, and the 0123Z-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 Aug_21_2013_0115Z_zps970e5359.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...Next upper trough and associated surface frontal cyclone in the mid-latitude westerlies is entering the upper-left corner of the above charts from Canada's Hudson Bay.

P2...Shortwave upper trough and associated surface frontal cyclone previously in the high seas SSE of Greenland is now in the NE Atlantic moving into western Europe. The shortwave upper trough previously supporting surface frontal cyclone offshore of the NE US is moving into the north-central Atlantic while the cyclone deepens to 1003 mb...but the bulk of this shortwave continues to be associated with cool air advection behind frontal cyclone that has moved across southern Greenland. It is interesting to observe the 1003 mb frontal cyclone continues to produce strong thunderstorms...but this activity is supported by non-tropical means via upper divergence ahead of the upper shortwave. Western convergence of the upper shortwave supports 1021 mb eastern US surface ridge as well as intensifying 1020 mb surface ridge that has moved into Atlantic Canada. What is left of eastern US upper trough is now upper vortex centered over Illinois and upper trough over Texas and northern Mexico. Low-level warm air ahead of the aforementioned upper shortwaves and upper vortex supports northern Gulf upper anticyclone...western Atlantic upper anticyclone...and NE Atlantic upper anticyclone shifting into western Europe.

P3...Cut-off upper trough south of the Azores has moved into the Canary Islands in advance of the easternmost shortwave upper trough moving into western Europe mentioned in paragraph P2.

P4...Surface ridge dominating much of the open Atlantic is anchored by western Atlantic 1021 mb center supported by eastern convergence of paragraph P2 western Atlantic upper anticyclone...and 1022 mb center just south of the Azores supported by northeastern convergence of paragraph P6 eastern Atlantic upper ridge. In conjunction with south side of the eastern Atlantic upper ridge...the south side of this surface ridge continues advecting dry Saharan air from Africa as seen by low-latitude brown shading in the above thermo chart.

...TROPICAL BELT DISCUSSION...
P5...Upper vorticity persists from the western Caribbean and southern Florida...into the western Atlantic waters between Bermuda and Puerto Rico...extending into the tropical waters just west of the remnant of Erin.

P6...To the southeast of the upper vorticity mentioned in paragraph P5 above...large eastern Atlantic low-latitude upper ridge persists. This upper ridge has expanded into much of the Caribbean in the wake of the weakening upper vorticity.

P7...Tropical wave previously in the western Caribbean has moved into the southwestern Gulf of Mexico and has absorbed what was left of former disturbance Invest 92-L mentioned in paragraph P1 of the previous discussion.

P8...Tropical wave previously moving into the eastern Caribbean is now entering the central Caribbean waters SW of Haiti and SE of Jamiaca. During the past afternoon and earlier this evening...it produced a flare up of thunderstorms supported by outflow of paragraph P6 Caribbean upper anticyclone...and in turn latent heat release inflated the upper anticyclone such that relatively lower pressures adjacent to the inflation has supported the formation of a weak upper vortex over the Lesser Antilles. About 4 and a half days ago...this tropical wave left behind what is now the surface trough approaching the southern Lesser Antilles. Will be watching this tropical wave and surface trough to see how they interact with favorable Caribbean upper anticyclone...especially considering their was prior computer model support for the surface trough to develop as it moved in the eastern Caribbean as mentioned during the intro statements of discussions #72 and #71.

P9...Remnant low of Erin previously midway between the Cape Verde Islands and northern Lesser Antilles is moving toward the northern Lesser Antilles but has weakened further into a surface trough in a hostile environment of southwesterly shear ahead of paragraph P6 upper vorticity and dry Saharan air mentioned in paragraph P4.

P10...Tropical wave with a broad area of cyclonic turning...formerly classified as disturbance Invest 94-L when it was impressive earlier and currently located southwest of the Cape Verde Islands...has lost thunderstorm activity in the past 24 hours while ingesting dry Saharan air to the northwest mentioned in paragraph P4.

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