2012 Atlantic Hurricane Season Birdseye Discussion #148

By: NCHurricane2009 , 3:27 AM GMT on November 01, 2012

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...WEDNESDAY OCTOBER 31 2012...11:30 PM EDT...
The remnant gale of Sandy has continued to weaken while drifting northward into southeastern Canada...and is no longer producing significant weather. The Appalachian Mountains in West Virginia remain under a winter weather advisory...see www.nws.noaa.gov for hazards associated with this advisory.

Elsewhere...tropical or subtropical cyclone formation is possible during the next 120 hours (5 days) in two areas. See paragraph P4 in the tropical belt discussion for potential tropical cyclone development in the southern Caribbean. See paragraph P2 for potential subtropical cyclone development in the open eastern Atlantic.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1922Z-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).

...MID-LATITUDES DISCUSSION...
P1...The remnant surface low of Sandy continues weakening below non-divergent upper vortex. The surface low and upper vortex are shifting northward into SE Canada about the east side of the central US upper trough finally pushing into the Great Lakes. The upper vortex has left behind an upper trough over the SE US and Gulf of Mexico that is merging with central US upper trough. Vast convergence west of both upper troughs supports Gulf of Mexico and SW US surface ridging. Immense low-level warm air advection ahead of Sandy's large circulation continues supporting a large north Atlantic upper anticyclone. Surface ridge offshore of Canada (currently 1025 mb) is becoming supported by the western convergence of the paragraph P3 upper trough...and surface ridge also persists over Hudson Bay in Canada.

P2...Deep-layered low pressure system/upper vortex persists in the eastern Atlantic at a location south of the Azores. Even though this system is centered over mild water temps of 23 to 24 deg C...t-storm activity has become stronger and better organized in the last 24 hours...which indicates the cold core upper vortex of the system is cold enough for instability over these water temps. Therefore...the NHC tropical weather outlook may soon flag this area...and I may release a special update in between full blog updates if this system proceeds toward subtropical cyclone formation. 120-hour outlook of this system is complex...with the system currently trapped southeast of deep-layered ridging consisting of both the north Atlantic upper anticyclone and surface ridge offshore of Canada both mentioned in paragraph P1. As the remnant of Sandy has continued to weaken...the low-level warm air advection ahead of the remnants has weakened such that the north Atlantic upper anticyclone should soon de-amplify...allowing this deep-layered low to shift east while merging with the paragraph P3 upper trough. However by the end of 120 hours...all models agree that low-level warm air advection ahead of the next frontal system will re-amplify the north Atlantic upper anticyclone...causing the paragraph P3 upper trough to re-amplify east of the upper anticyclone...in turn strengthening western convergence on the back side of the paragraph P3 upper trough such that the surface ridge currently offshore of Canada re-strengthens. In essence...the re-amplification of the north Atlantic upper anticyclone and strengthening surface ridge cuts-off a portion of the deep-layered low that retrogrades westward such that subtropical cyclone formation is possible once again if the current deep-layered low does not develop.

P3...Upper trough in the NE Atlantic persists in relatively lower pressures east of the the north Atlantic upper anticyclone in paragraph P1. Currently its eastern divergence supports a 1005 mb surface frontal depression over Morocco along the warm front extending from the paragraph P2 deep-layered low.

...TROPICAL BELT DISCUSSION...
P4...Sprawling east-west tropical Atlantic upper anticyclone is now centered over the northern Lesser Antilles. Upper divergence on the NW quad of the upper anticyclone continues supporting Caribbean surface troughing that has shifted from the eastern to the central Caribbean. T-storm activity has become better organized around the surface troughing while under the favorable outflow of the tropical Atlantic upper anticyclone..and although their is no computer model support for development...this favorable upper wind config is shown in the models to last for the next 120 hours. Therefore...this area should be watched for tropical development...and the track of this system depends on if and when development occurs. Over the next 120 hours...their will be surface ridge weaknesses that will try to draw the system east...and surface ridges that try to draw the system west. Models agree that cold fronts extending from Sandy and the paragraph P1 upper troughing will first create a ridge weakness to the NE...while the Gulf surface ridge in paragraph P1 persists to the NW while supported by convergence on the back side of the paragraph P1 upper troughing. Models then eject the paragraph P1 upper trough NE...and likewise the Gulf surface ridge supported on the back side of the upper trough. Quickly...the models come in with the next frontal upper trough before 120 hours is over...with western convergence of this upper trough re-building a Gulf surface ridge to the NW...and eastern divergence of this upper trough re-creating another surface ridge weakness to the NE.

P5...Relatively higher pressures southeast of the paragraph P2 deep-layered low supports relatively new upper ridge near the Cape Verde Islands mentioned in paragraph P4 of the previous discussion.

P6...Surface trough heading toward the Lesser Antilles has been removed from TAFB maps...but interestingly their is a t-storm complex on satellite imagery SE of the Lesser Antilles. Tropical latitude surface troughing in the vicinity of the cold front of the paragraph P2 deep-layered low persists. 1016 mb ridge west of the surface troughing and NE of the Lesser Antilles has weakened to a 1015 mb center north of the Lesser Antilles while becoming exposed to upper divergence SE of the paragraph P1 upper troughing and NW of the paragraph P4 upper anticyclone. 1012 mb ridge to the east of the surface troughing and toward the west coast of Africa has weakened to 1011 mb due to upper divergence on the SE quad of the paragraph P2 deep-layered cyclone overspreading the area.

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