2013 Atlantic Hurricane Season Birdseye Discussion #41

By: NCHurricane2009 , 2:15 PM GMT on July 13, 2013

...SATURDAY JULY 13 2013 10:20 AM EDT...
Still watching the remnants of Chantal currently tracking northwest toward the Carolinas. Visible satellite imagery this morning suggests the system is developing a low-level circulation just to the north of its thunderstorm cluster. Regardless of development...expect heavier weather to move into the Carolinas in the next 24 hours. See Chantal special feature section below for additional details.

Due to apparent choking on dry air...I have cancelled the tropical wave southwest of the Cape Verde Islands as a special feature on this blog. See paragraph P10 for update statement on this tropical wave.

 photo Jul_13_2013_0915Z_zps74f32092.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0600Z, and the 0726Z-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 Jul_13_2013_0915Z_zps8164ef6f.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).

South end of the remnant tropical wave of Chantal is heading across the western Caribbean and Central America...and will soon be crossing southeastern Mexico. It is the north end of the remnant tropical wave that is more interesting while maintaining a cluster of thunderstorms currently north of the western Bahamas in the outflow of an upper ridge that exists due to relatively higher upper-level pressures between paragraph P2 southern upper trough fragment and paragraph P4 upper vortex SE of Bermuda. The Naval Research Laboratory site of the US Navy considers this system as Invest 96-L...but a statement on the site also indicates that Chantal and 96-L are the same system.

Visible satellite imagery suggests a low-level circulation is developing on the north side of the thunderstorm cluster. The system is tracking northwestward toward the Carolinas while steered by paragraph P2 1025 mb Great Lakes surface ridge. Once this system makes landfall in the next 24 hours...I will drop it as a special feature on this blog. Regardless of whether or not this system spins up into a tropical cyclone before landfall...expect heavier weather to move into the Carolinas.

P1...Next upper trough and surface frontal system continues entering the upper-left corner of the above atmo charts from western Canada.

P2...Upper trough previously over the northern US and eastern Canada has split into one upper trough moving by southern Greenland and a second cut-off upper trough over the Gulf of Mexico and eastern US. Eastern divergence of both upper trough fragments supports a lengthy front extending from the SE US...north-northeastward to the waters east of Greenland (with a 1016 mb frontal depression developing over Maryland). Western convergence of the northern upper trough fragment supports 1025 mb ridge over the Great Lakes...SE Canada...and eastern US. Upper ridge offshore of eastern North America ahead of both upper trough fragments has also split into two...with one upper anticyclone to the SE of Greenland and another anticyclone offshore of the NE US. The National Hurricane Center (NHC) just highlighted a small area in the northeastern Gulf of Mexico where a surface low could form from the eastern divergence of the southern upper trough fragment. Such a surface low would be close to shore and move northwestward into land quickly while steered by the above-mentioned 1025 mb ridge such that I believe any subtropical or tropical cyclone development from this system is unlikely.

P3...Western US upper anticyclonic ridge has shifted eastward into the central US.

P4...Upper trough previously in the NE Atlantic high seas is moving into western Europe...but its southwest end leaves behind a new cut-off upper vortex just west of the Azores. Eastern divergence of this upper trough supports lengthy front from the open central Atlantic extending NNE into the British Isles (a 1018 mb depression is located west of the Azores...just to the southeast of the new upper vortex...and along this front). In the last six days...a fragment of this upper trough has split southeastward and is currently the upper vortex over the eastern Azores (and a southwest portion of this upper trough fragment has evolved into what is now the upper vortex SE of Bermuda).

P5...Upper vortex over the Florida Straits has become absorbed by southern upper trough fragment mentioned in paragraph P2.

P6...Surface ridge dominates much of the open Atlantic basin. Its northern Gulf of Mexico extension currently with a 1015 mb center was formerly supported by southeast convergence of paragraph P3 central US upper ridge...but this Gulf portion is now dissipating due to incoming paragraph P2 weather system. Remainder of the open Atlantic portion of this surface ridge has split into two due to the front mentioned in paragraph P4. One portion is a 1025 mb center NE of Bermuda supported by eastern convergence of paragraph P2 NE US upper anticyclone. The other portion extends from the vicinity of the Cape Verde Islands northward into western Europe.

P7...Upper troughing persists previously in the Gulf of Mexico has been absorbed byt southern upper trough fragment mentioned in paragraph P2.

P8...Anticyclonic upper ridging in the eastern half of the Atlantic persists and remains expanded into the the Caribbean. This upper ridging also continues to have a low-latitude axis present over the Cape Verde Islands extending into W Africa. Upper trough vorticity persists in the south-central Caribbean (and also midway between the Cape Verdes and Lesser Antilles as mentioned in paragraph P9 of the previous discussion) such that the above-mentioned low-latitude axis is split from the Caribbean portion. The Caribbean portion of the low-latitude upper ridging extends from Central America northeastward towards the remnants of Chantal. What's left of what was an embedded SW-NE oriented string of upper vorticity in this upper ridging is now an escaping upper vortex over NW Spain. Days ago the south end of all the upper ridging mentioned in this paragraph (in conjunction with the south end of the paragraph P6 surface ridge) advected dry Saharan air from Africa...large swaths of which still remain as shown by brown shading in the above thermo chart. Since this upper ridging developed a low-latitude axis over the Cape Verde Islands that created upper outflow and resulting moistening lift over the ocean surface...the supply of dry Saharan air is mitigated as indicated by the current shades of white and blue toward Africa in the lower-right of the above thermo chart.

P9...Surface trough previously northeast of the Lesser Antilles is moving westward while steered by southwest corner of paragraph P6 surface ridge. The surface trough is now currently north of Puerto Rico and remains largely inactive while suppressed below paragraph P4 upper vortex SE of Bermuda with the exception of the north end of the surface trough that has t-storms due to split flow upper divergence between northerlies west of the upper vortex and easterlies south of the paragraph P2 upper anticyclone offshore of the NE US.

P10...Tropical wave southwest of the Cape Verde Islands...previously a special feature on this blog...has lost t-storm activity due to ingestion of dry Saharan air mentioned in paragraph P8. It is below a favorable environment of low shear and enhanced outflow of low-latitude upper ridge axis also mentioned in paragraph P8...but until this environment assists the tropical wave against the dry air...tropical cyclone development is not expected from this tropical wave.

P11...Vigorous tropical wave with curved t-storm bands west of its axis is entering the favorable low shear and enhanced outflow environment below paragraph P8 low-latitude upper ridge axis as it exits the African coast into the Atlantic tropics. Even though this tropical wave is showing early signs of impressiveness...it may not develop due to possible later ingestion of dry air as we have recently seen with the tropical wave in paragraph P10.

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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