2012 Atlantic Hurricane Season Birdseye Discussion #153
...TUESDAY NOVEMBER 6 2012...4:32 PM EDT...
Slight chance of subtropical cyclone development in the open eastern Atlantic remains possible as highlighted in paragraph P4 of the mid-latitudes discussion.
See paragraph P2 in the mid-latitudes discussion for statement on what appears to be an imminent threat of a nor'easter impacting the same areas in the northeastern United States hit by last week's Hurricane Sandy. Formation of this nor'easter is expected in the next 24 hours...and while it will bring gusty winds...it is not expected to be as severe as Hurricane Sandy. This nor'easter is not expected to gain tropical characteristics.
...ATMOSPHERIC FEATURES BIRDSEYE CHART...
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1200Z, and the 1336Z-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...Eastern lobe of strong gale offshore of the west coast of North America has entered the upper-left corner of the above atmo chart from western Canada. Western lobe of the gale remains offshore. Currently...warm air advection ahead of both lobes supports highly-amplified west coast upper ridge whose eastern convergence supports a 1030 mb western US surface ridge. The back side of the eastern lobe is providing cool air advection...resulting in a shortwave upper trough diving SE from central Canada. In the next 24 hours....this shortwave upper trough will re-enforce the larger paragraph P2 upper trough...see paragraph P2 for how the re-enforced upper trough creates a nor'easter. It is then expected the remainder of the gale offshore of western North America will pivot into the western US in the wake of the nor'easter.
P2...Upper trough over the central US has moved into the eastern US... consisting of an upper vortex now over the Maine/Canada border and another upper vortex over western North Carolina. In the last 24 hours...eastern divergence of the upper trough has intensified the 1008 mb western Atlantic surface frontal depression into 994 mb while moving NE into Newfoundland. This same upper divergence has intensified a 1014 mb frontal depression into 1012 mb while it has moved ESE into the SE US. The depression was pushed ESE by the 1019 to 1024 mb surface ridge that has pivoted into the central US and eastern Canada supported by the western convergence of the upper trough. See statement in paragraph P1 on how this upper trough is expected to be energized by a shortwave upper trough from central Canada. In the next 24 hrs...the energized upper trough will support the rapid genesis of a surface non-tropical gale offshore of the Carolinas and along the front extending from what is now the 994 mb depression. This strong gale maybe what is now the 1012 mb SE US frontal depression...or alternatively this strong gale will absorb it. Either way the strong gale is expected to track NE parallel to the US coast...and therefore it will be called a "nor'easter." Unfortunately...the nor'easter is expected to impact areas hit by last week's Hurricane Sandy with gusty winds...with rain and snow showers also possible. However...this nor'easter is not expected to be as strong as Sandy.
P3...Large upper trough pushing into the western Atlantic has split into two SW-NE tilted upper troughs...one east of Greenland and a second in the open central Atlantic. 990 mb surface frontal depression over southern Greenland in the previous discussion has moved east with the first of the two upper troughs...and has weakened to 993 mb with a lack of divergence directly below the upper trough axis. Eastern divergence of the open central Atlantic upper trough supports widespread cloudiness. Relatively higher pressures between both upper troughs is currently where the north Atlantic upper ridge in the previous discussion thrives. Finally...the north Atlantic surface ridge (currently 1037 mb) has strengthened in the western convergence of the paragraph P4 upper trough.
P4...Large eastern Atlantic upper trough persists. Surface 1013 mb depression has moved ENE from the Canary Islands into Morocco in the last 24 hours. Low-level warm air advection ahead of what is expected to be a nor'easter mentioned in paragraph P2 will keep the north Atlantic upper ridge mentioned in paragraph P3 amplified...causing the east Atlantic upper trough to stay amplified east of the upper ridge axis...in turn strengthening western convergence on the back side of the upper trough axis such that the surface ridge currently in the north Atlantic (mentioned in paragraph P3) remains strong. In essence...the amplified north Atlantic upper ridge and strong surface ridge cuts-off a portion of the surface cold front extending from the 1013 mb low...and a portion of the east Atlantic upper trough...that all retrogrades westward such that subtropical cyclone formation is possible.
...TROPICAL BELT DISCUSSION...
P5...Sprawling tropical Atlantic upper anticyclone continues covering the waters east of the Lesser Antilles and the Caribbean Sea. Surface trough below the sprawling upper anticyclone...located midway between the Lesser Antilles and Cape Verde Islands...has dissipated in the last 24 hrs. As seen in the above thermo chart...dry air continues to whirling within the upper anticyclone.