2012 Atlantic Hurricane Season Birdseye Discussion #39
...JULY 1 2012...9:20 AM EDT...
As we push into July...Atlantic tropics have quieted with all areas of interest from the previous discussion diminishing.
...ATMOSPHERIC FEATURES BIRDSEYE CHART...
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0000Z, and the 0123Z-released HPC 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...
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).
P1...Western North America surface frontal system (paragraph P1 of discussion #38) has since moved rapidly eastward across southern Canada...and merged with frontal system over the eastern US (paragraph P2 of discussion #38) at both the surface and upper-levels. At the surface...there are a variety of pressure centers below 1000 mb from eastern Canada to the waters SE of Greenland (marked in the above charts). An east-west front extends across the United States...and another front extends SW-NE across the western Atlantic Ocean where the remnant low of Debby (located NNE of Bermuda) is still embedded as of 0000Z TAFB. Surface 1018 mb ridge over the eastern US...once supported by upper convergence on the back side of this system's upper vorticity...has continued shifting southeast and is now a 1016 mb ridge centered in the SE Gulf of Mexico. Finally...west Gulf of Mexico cut-off upper low stemming from this weather system several days ago has moved into Texas.
P2...Upper ridge over the western Atlantic and south Greenland from the previous discussion has been split in three areas by mass cool air advection behind the complex frontal system in paragraph P1 above. The norhtern half is an upper anticyclone near south Greenland...the middle is an upper anticyclone in the open central Atlantic...and the southern is near Cuba and the Bahamas.
P3...Large upper trough in the north-central Atlantic (and its surface frontal cyclone) from the previous discussion has moved NE into Europe...and the surface frontal cyclone's tailing cold front is marked in the upper-right corner of the above charts. This upper trough has left behind a cut-off upper trough retrograding southwestward around the central Atlantic upper anticyclone mentioned in paragraph P2 above. The west end of this cut-off features an upper vortex south of the Azores...and it appears split flow upper divergence between the vortex and the flow going into the cut-off upper trough has causd a weak surface trough south of the Azores as of 0000Z TAFB. Finally...yet another cut-off upper trough was left E of Bermuda in the past days (in paragraph P4 of the last few discussions). This is now a cut-off upper vortex E of Bermuda whose tail end reaches into the SE Caribbean. The SE Caribbean fragment of this upper vorticity will soon retrograde westward about the southernmost upper anticyclone mentioned in paragraph P2.
P4...Open Atlantic surface ridge still has a strong center....which is now 1032 mb and west of the Azores as of 0000Z TAFB. The 1032 mb center was supported by upper convergence behind the upper trough mentioned in paragraph P3 above and upper convergence ahead of the central Atlantic upper anticyclone mentioned in paragraph P2 above. Now that the central Atlantic upper anticyclone is becoming vertically aligned with the 1032 mb center...the 1032 mb center may begin weakening.
...TROPICAL BELT DISCUSSION...
P5...Upper ridge over the southern Gulf of Mexico has undergone changes since the previous discussion. The remnant of Debby...part of the complex frontal system in paragraph P1...had cool air advection behind it such that upper troughing dug to the east of this upper ridge...which utlimately pushed the upper ridge into the western Gulf of Mexico. Meanwhile...upper divergence between the north boundary of this upper ridge and south boundary of the upper troughing triggered a surface trough trailing from the remnant of Debby. While the upper ridge retrograded into the west Gulf...it provided enhanced outflow over the surface trough that triggered a short-lived tropical disturbance that was mentioned in the tropical weather outlook of the National Hurricane Center. Now that this disturbance has made landfall in south Texas and NE Mexico...tropical development is no longer possible here.
P6...Cut-off upper vorticity in the eastern Caribbean was mentioned as a dissipating feature in the previous discussion (paragraph P8...discussion #38)...when in fact it continued to linger while retrograding westward around the upper ridge in paragraph P5 (that is...when that upper ridge was stronger and larger). This upper vorticity is now an inverted upper trough over the Yucatan and southern Gulf of Mexico.
P7...As a fragment of the upper vorticity in paragraph P6 retrograded westward out of the Caribbean...a small upper ridge in the southern Caribbean built it its wake. A tropical wave in the area (paragraph P10...discussion #38) interacted with the upper divergence of the small upper ridge to produce t-storms over the Panama area. The tropical wave has recently move into the eastern Pacific...while the small upper ridge continues to provide local outflow for storm activity in the Panama area.
P8...Expansive east Atlantic upper ridge continues. In conjunction with the surface ridge in paragraph P4 and southernmost upper anticyclone in paragraph P2...deep-layered easterly flow exists across much of the Atlantic tropics that is advecting African desert dry air (brown shading in the above thermo birdseye chart) westward. All embedded upper vorticity in this east Atlantic upper ridge has dissipated.
P9...Tropical wave southwest of the Cape Verde Islands in the previous discusison was a special feature on this blog and was briefly upgraded to Invest 97-L by the Naval Research Laboratory (NRL) of the US Navy. The tropical wave was successful in fighting off dry desert air thanks to enhanced poleward outflow provided by embedded upper vorticity in the paragraph P8 upper ridge. The upper vorticity dissipated...leaving the tropical wave to struggle against moderate easterly vertical shear on the south side of the paragraph P8 upper ridge...albiet split upper flow on the southwest quadrant of the same upper ridge helped the tropical wave gain more t-storm activity. As of this writing...the tropical wave is nearing the Lesser Antilles and is no longer a special feature while struggling in southerly vertical shear from the upper vorticity mentioned towards the end of paragraph P3.
P10...A poorly-defined tropical wave has been added by TAFB since the previous discussion....located midway between the Cape Verde Islands and the Lesser Antilles while struggling with dry air mentioned in paragraph P8. The western lobe of the paragraph P8 upper ridge has been inflated by latent heat release of the tropical wave in paragraph P9...and the eastern lobe of the paragraph P8 upper ridge has been inflated by latent heat release of the vigorous tropical wave in paragraph P11...with new upper vorticity forming in between the eastern and western lobes as a result. This tropical wave also remains suppressed by this upper vorticity.
P11...Yet another vigorous tropical wave has rolled off of western Africa...and is now located over and south of the Cape Verde Islands as of 0000Z TAFB. Its t-storm activity latent heat release has inflated the eastern lobe of the paragraph P8 upper ridge...this inflation allowing the tropical wave to begin carving out its own supportive upper outflow structure in this upper ridge. With supportive upper outflow allowing the tropical wave to fight off dry air mentioned in paragraph P8...coupled with low shear from deep-layered easterly flow also mentioned in paragraph P8...this tropical wave may become the next feature to watch for potential tropical development.