2012 Atlantic Hurricane Season Birdseye Discussion #128

By: NCHurricane2009 , 8:25 AM GMT on October 09, 2012

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...OCTOBER 9 2012...4:30 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.

In the western part of the Atlantic tropical basin...continuing to watch the surface trough of Invest 97-L (paragraph P4)...a surface tropical low near Costa Rica (paragraph P6)...and the melding together of a western Atlantic upper ridge (paragraph P4) and western Caribbean upper ridge (paragraph P3). The surface trough of Invest 97-L has entered hostile westerly vertical shear associated with the paragraph P1 weather system...and therefore should not develop. The Costa Rica surface low should soon make landfall across Central America and enter the eastern Pacific. With no more tropical development potential in the western Atlantic basin expected...this is my last statement on this area in the intro section of my blogs.

In the central part of the Atlantic tropical basin...the t-storms associated with the central Atlantic upper vortex (paragraph P3) have dwindled in the last 24 hours. Tropical development here was never anticipated due to the t-storms being associated with an upper feature rather than a surface feature.

Attention is turning to the eastern part of the tropical Atlantic basin...where a tropical wave has been upgraded to Invest 98-L. Computer models suggest tropical cyclone formation potential as the wave moves into the Caribbean area by 96 to 120 hours...but the tropical wave must first survive an onslaught of westerly vertical shear expected before that timeframe. See paragraph P8 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 1800Z, and the 1930Z-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...984 mb surface gale and its supporting upper trough moving across Greenland are exiting the above atmo chart from the top-center. Despite the departure of this upper trough...upper troughing over North America is being re-enforced by cool air advection from yesterday's 1002 mb Canadian frontal depression (now 1006 mb over E Hudson Bay) and another Canadian frontal depression that has entered the picture...currently 998 mb over NE North Dakota. Eastern divergence of this upper troughing has supported a new frontal depression offshore of the eastern US which has rapidly zipped NE across Newfoundland at 1009 mb. This 1009 mb depression's cool air advection has carved out its own shortwave upper trough...and yesterday's strong central US surface ridge (currently 1025 to 1026 mb) is shifting eastward while becoming associated with the western convergence of this new upper shortwave trough.

P2...Deep-layered cyclone in the eastern open Atlantic is slowly shifting toward Europe. Upper-levels of this system continues to be marked by large upper trough. Western convergence of this upper trough is supporting a 1028 mb W Atlantic surface ridge. What is left of NE Atlantic surface ridge from paragraph P3 of previous discussion #127 is becoming assimilated into the W Atlantic surface ridge. Surface center of the deep-layered cyclone...supported by eastern divergence of the upper trough...is moving slowly NNE in the waters well north of the Azores.

...TROPICAL BELT DISCUSSION...
P3...Central tropical Atlantic upper vortex persists...still extending to a smaller upper vortex near Haiti and the Dominican Republic. In relatively higher pressures west of both upper vortices...a western Caribbean upper ridge has built. Yet another upper ridge persists in relatively higher pressures east of these upper vortices...located across the eastern tropical Atlantic. The east end of this eastern tropical Atlantic upper ridge is de-amplified by an upper vortex that has been dropped off by paragraph P2 upper trough (Even though I have no satellite-derived 200 mb (upper wind) barbs in this area from the GOES-E satellite outage...the upper vortex continues to be confirmed by Meteosat-9 water vapor imagery at a location W of the Cape Verde Islands).

P4...W Atlantic upper ridge persists in advance of large-scale paragraph P1 upper troughing. Disturbance Invest 97-L over the Bahamas...supported by the upper outflow of this upper ridge...has seen more impressive curved t-storm bands in the last 24 hours. However...the surface low has been downgraded to a surface trough...and the disturbance has drifted westward while steered by a merger of the central US surface ridge (paragraph P1) and W Atlantic surface ridge (paragraph P2). On this track...the disturbance is moving into hostile westerly vertical shear delivered by paragraph P1 upper troughing...and therefore I continue to not have a special feature section on this blog for 97-L.

P5...Intermittent disturbed weather across the Bay of Campeche...southern Gulf of Mexico...and Florida remains supported by eastern divergence of paragraph P1 upper troughing. Surface forcing for this area of weather is also coming from cold front extending from 1009 mb depression in paragraph P1...and coming from surface troughs in the Bay of Campeche (one of which is a northern fracture from tropical wave in paragraph P6 below).

P6...Tropical wave moving into the western Caribbean in the previous discussion has fractured into two areas. Its northern end is contributing to weather discussed in paragraph P5 above. Its southern end is a 1010 mb tropical low pressure near Costa Rica and Panama that is producing t-storms with the aid of upper outflow from paragraph P3 W Caribbean upper ridge. Although this is a very favorable upper wind configuration for tropical cyclone development...the tropical low is about to continue westward into Central America and eventually into the eastern Pacific. Perhaps it will eventually become the next eastern Pacific tropical cyclone (eastern Pacific activity is not covered on this blog).

P7...I had been tracking a suspect tropical wave...which in the previous discussion I placed in the waters between the Lesser Antilles and Cape Verde Islands. Because the associated t-storm cluster has disappeared since 1200Z October 5...and because the NHC TAFB has not added this wave to their maps....I am cancelling this wave from my analyses.

P8...Tropical wave with 1008 mb low pressure spin in the eastern Atlantic...entering the waters midway between the Cape Verde Islands and Lesser Antilles...has not gotten any better organized in the last 48 hours...but has been upgraded to tropical disturbance Invest 98-L in the last 24 hours. It continues to be enhanced by upper outflow of paragraph P3 eastern tropical Atlantic upper ridge...and so far has managed to avoid oppressive effects of nearby upper vortex that have de-amplified the east end of this upper ridge. This is because the tropical wave is well southwest of this upper vortex. Based on animation of this evening's computer models...this tropical wave has about 24 hours to develop before encountering hostile westerly vertical shear by 48 hours delivered by the pair of cut-off upper vortices mentioned in paragraph P3. Unlike previous nights...the CMC...Euro (ECMWF)...GFS...and NOGAPS models are all suggesting tropical cyclone formation from this system as it enters the Caribbean region by 96 to 120 hrs. A study of this evening's 00Z GFS shows that the shearing cut-off upper vortices should be diminishing by that time...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 expected onslaught of shear. If the tropical wave turns out to be in good shape as we approach the 96 hr timeframe...then I will be upgrading it to a special feature on this blog.

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2. WunderAlertBot (Admin)
10:13 AM GMT on October 10, 2012
NCHurricane2009 has created a new entry.
1. wxchaser97
2:59 AM GMT on October 10, 2012
Thanks NC09.
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