2012 Atlantic Hurricane Season Birdseye Discussion #152
...MONDAY NOVEMBER 5 2012...8:20 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 at 48 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 1800Z, and the 2013Z-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 is entering 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 western US surface ridge. For the next 48 hours...models show cold air driven in by the back side of the eastern lobe energizing the paragraph P2 upper trough. See paragraph P2 for how the energized paragraph P2 upper trough creates a nor'easter. The models then pivot the remainder of the gale into the western US in the wake of the nor'easter.
P2...Upper trough over the central US consists of an upper vortex now over SE Canada and upper trough extending to the SW. SE US 1013 mb surface frontal depression has moved offshore into the western Atlantic while intensifying to 1008 mb as the depression has taken advantage of eastern divergence of the upper trough. 1023 mb South Dakota surface frontal depression 24 hours ago has dived SE into Missouri while intensifying to 1014 mb in the same upper divergence. The depression was pushed SE by the 1023 to 1027 mb surface ridge from central Canada formerly supported by the western convergence of the paragraph P3 upper trough...and now supported by western convergence of this upper trough. See statement in paragraph P1 on how this upper trough is expected to be energized. By 48 hours...all models agree that strengthening upper divergence on the east side of 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 1008 mb depression. Because the strong gale is expected to track NE parallel to the US coast...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 is now entirely offshore. Divergence on the east side of the upper trough supports 990 mb frontal depression that has lifted NNE from Newfoundland toward southern Greenland in the last 24 hours...while the 995 mb center approaching southern Greenland in the previous discussion has been absorbed by this 990 mb center. Low-level warm air advection ahead of the 990 mb center is supporting an upper ridge over the North Atlantic. North Atlantic surface ridge (currently 1035 mb) is strengthening in the western convergence of the paragraph P4 upper trough.
P4...Large eastern Atlantic upper trough persists. Surface 1011 mb depression south of the Azores in the previous discussion has moved ENE into the Canary Islands. 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 aforementioned 1011 mb low and 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...remains suppressed by dry air whirling within the upper anticyclone.