2012 Atlantic Hurricane Season Birdseye Discussion #129

By: NCHurricane2009 , 10:13 AM GMT on October 10, 2012

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...OCTOBER 10 2012...6:20 AM EDT...
An outage persists with GOES-E satellite imagery in the last several days. GOES-W has been extended to cover much of the view in the two birdseye charts below. However...the east edge of the GOES-W scan has a bias for showing cold cloud tops that are not actually present. Therefore...I have patched the east side of the atmospheric birdseye chart with Meteosat-9 grafts. The east side of the thermodynamics birdseye chart is left unrepaired...so be mindful that the moisture content on the east side of this chart has a positive bias due to the false illusion of cold cloud tops.

See paragraph P4 for statement on disturbance Invest 97-L pulling northeastward from the Bahamas.

Attention continues turning to tropical wave Invest 98-L en route to the Lesser Antilles. Computer models suggest tropical cyclone formation potential as the wave moves into the eastern Caribbean area by 72 to 120 hours...but the tropical wave must first survive a current onslaught of westerly vertical shear. See paragraph P5 for additional details on this feature.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0600Z, and the 0724Z-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...Upper troughing over North America is being re-enforced by cool air advection from strong surface frontal cyclone that has intensified from 998 to 994 mb while moving from NE North Dakota to southern Hudson Bay in the last 24 hours. Western convergence of this upper troughing is supporting a new central US surface ridge (currently 1025 mb). 1009 mb frontal depression moving NE across Newfoundland in the previous discussion has rapidly intensified to 977 mb with the support of eastern divergence from its shortwave upper trough. This intense depression clipped the southern tip of Greenland in the last 24 hours...and is now just east of Greenland. Previous central US surface ridge (currently 1027 to 1020 mb) has shifted eastward into SE Canada and the eastern US while becoming associated with the western upper convergence of 977 mb gale's shortwave upper trough.

P2...What is left of NE Atlantic deep-layered cyclone is a surface and upper-level trough over and just NE of the Azores. The upper trough has gained SW-NE tilt while becoming squeezed by amplifying W Atlantic upper ridge in paragraph P4. Western convergence of this upper trough is supporting a 1028 mb surface ridge that has shifted from the W to central Atlantic.

...TROPICAL BELT DISCUSSION...
P3...Central tropical Atlantic upper vortex...still extending into the eastern Caribbean...is now a SW-NE tilted upper trough now linked with SW-NE upper trough in paragraph P2. In relatively higher pressures west of the upper trough...a western Caribbean upper ridge persists whose upper outflow earlier triggered an impressive t-storm cluster over Nicaragua...Honduras...and adjacent Caribbean waters. Yet another upper ridge persists in relatively higher pressures east of this upper trough...located in the eastern tropical Atlantic. This eastern tropical Atlantic upper ridge is de-amplified by the aforementioned central tropical Atlantic upper trough...and by upper vortex W of the Cape Verde Islands that appears to have de-amplified into an upper trough. Even though I have no satellite-derived 200 mb (upper wind) barbs in this area from the GOES-E satellite outage...I am using the adjacent wind barbs and the curvature of the cloud band SE of the Cape Verde Islands to deduce the aforementioned upper trough W of the Cape Verde Islands. I surmise the cloud band SE of the Cape Verde Islands is supported by the eastern divergence of this upper trough.

P4...W Atlantic upper ridge has amplified due to warm air advection ahead of 977 mb and 994 mb gale centers mentioned in paragraph P1. Surface disturbance Invest 97-L (now a 1012 mb low) is pulling NE from the Bahamas while steered by SW flow ahead of the 977 mb gale's W Atlantic cold front. Satellite imagery suggests 97-L and the surface front are gradually melding together...the band of weather associated with both overspreading Bermuda this morning. With the W Atlantic upper ridge shown to persist in computer model runs...I am watching to see if this band of weather gains any tropical organization under the outflow of the upper ridge in the next days.

P5...Tropical wave Invest 98-L with 1008 mb low pressure spin is currently approaching the Lesser Antilles..and has not gotten any better organized in the last 72 hours. It continues to be enhanced by upper outflow of paragraph P3 eastern tropical Atlantic upper ridge. As described in that paragraph...the upper ridge has de-amplified such that zonal shearing upper westerlies have increased across the tropical wave. The CMC...Euro (ECMWF)...GFS...and NOGAPS models insist on tropical cyclone formation from this system as it enters the eastern Caribbean region in the 72 to 120 hr timeframe. A study of this evening's 00Z GFS shows that the SW-NE upper trough in paragraph P3 should be diminishing during that timeframe...allowing the upper ridge over the tropical wave to expand and support such development. First waiting to see how well the tropical wave survives the current and unfavorable westerly vertical shear. If the tropical wave turns out to be in good shape as we approach the 72 hr timeframe...then I will be upgrading it to a special feature on this blog.

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