2012 Atlantic Hurricane Season Birdseye Discussion #126

By: NCHurricane2009 , 4:11 AM GMT on October 07, 2012

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...OCTOBER 7 2012...12:11 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...disturbed weather south of Bermuda has been intensifying and is now upgraded to Invest 97-L. This disturbed weather has developed in part due to a western Atlantic upper ridge (paragraph P7 below and paragraph P8 of previous discussion #125). Meanwhile...upper outflow of a southern Caribbean upper ridge has supported intermittent t-storms in the south-central Caribbean...Panama..Costa Rica...and a portion of the eastern Pacific (paragraph P6 below and paragraph P7 of previous discussion #125). The surface low of Invest 97-L...the surface tropical waves in paragraphs P9 and P10...and the melding together of the southern Caribbean and western Atlantic upper ridges shown in models...suggest the potential for some sort of broad tropical disturbance to emerge in this area...although there is no specific computer model support at this time. I believe such a broad tropical disturbance would drift westward while steered by a merger of the 1033 mb central US surface ridge (paragraph P1) and developing west Atlantic surface ridge (paragraph P3).

In the eastern part of the tropical Atlantic basin...a tropical wave that has recently emerged from Africa is becoming better organized. See paragraph P12 below for details on its window of opportunity.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1926Z-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 vortex over south-central Canada has absorbed all shortwave upper troughs to the south and east mentioned in paragraph P2 of previous discussion #125. This upper vortex...along with the 1004 mb surface depression below it and 1000 mb depression to the east...have all shifted NE into eastern Canada in the last 24 hrs. The 1004 mb and 1000 mb centers have intensified to 994 and 993 mb...respectively...while tapping into eastern divergence supplied by the upper vortex. Western convergence of this upper vortex continues supporting strong central US surface ridge (now 1033 mb) that continues driving in unseasonably cold air. This western upper convergence also supports a band of dry air in northern Mexico and the western Gulf of Mexico.

P2...Surface 1010 mb low north of Bermuda in the previous discussion has dissipated.

P3...Deep-layered cyclone is shifting from the central to eastern open Atlantic. Upper-levels of this system continues to be marked by impressive upper trough recently becoming re-enforced by Atlantic Canada shortwave mentioned in paragraph P2 of previous discussion #125. Western convergence of this upper trough is supporting a gradually developing W Atlantic surface ridge...as the eastern US surface ridge (paragraph P2 previous discussion #125) and 1020 mb surface ridge offshore of Newfoundland (paragraph P2 previous discussion #125) combine. Surface center of the deep-layered cyclone is maintaining strength below 988 mb as it taps into eastern upper divergence of the upper trough. This strong surface center is moving into the Azores this evening.

P4...Based on Meteosat-9 animation over the last day...shortwave upper trough heading toward western Europe in the previous discussion (marked in upper-right corner of above atmo chart) has made it to the British Isles. Western convergence of the upper trough activity in this area continues driving NE Atlantic surface ridge....which now extends hundreds of miles SW to a 1012 mb center. This extension is supported by upper convergence between eastern tropical Atlantic upper ridge in paragraph P6 and upper trough in paragraph P3.

P5...During the previous discussion...remnant non-tropical low of Nadine was turning eastward toward the British Isles while hitching a ride with paragraph P4 shortwave upper trough. Meteosat-9 infrared satellite animation over the last day suggests the remnant low lost its identity before reaching land.

...TROPICAL BELT DISCUSSION...
P6...Central tropical Atlantic upper vortex persists...still extending to a smaller upper vortex near Jamaica and Haiti. Upper convergence on west side of both upper vortices supports pocket of W Caribbean dry air. As both upper vortices gradually weaken (as all cut-off upper vortices do)...a southern and western Caribbean upper ridge continues building in their wake. Another round of t-storms across the south-central Caribbean...Panama..Costa Rica...and a portion of the eastern Pacific is supported by outflow of this building upper ridge. Yet another upper ridge persists in relatively higher pressures east of these upper vortices...located across the eastern tropical Atlantic. This eastern tropical Atlantic upper ridge is split in half by cut-off upper vortex delivered by paragraph P3 upper trough.

P7...W Atlantic upper ridge is shifting southward in advance of large-scale paragraph P1 upper vortex pushing in. Disturbed weather south of Bermuda (supported by split flow upper divergence between this upper ridge and paragraph P6 central tropical Atlantic upper vortex) has likewise shifted southward toward the northern Caribbean Islands and eastern Bahamas. Outflow of the upper ridge is further enhancing the t-storm activity of this disturbed weather...which has caused its upgrade to disturbance Invest 97-L. However...the t-storm activity has been intermittent rather than persistent...and the surface low pressure area (now 1007 mb) is to the southeast of the t-storm cluster rather than under it. These reasons...along with lack of computer model support...are why I am not upgrading this disturbance to a special feature on this blog.

P8...A surface trough and t-storm activity in the southern Gulf of Mexico and Bay of Campeche was mentioned in paragraph P9 of previous discussion #125...supported by eastern divergence of southernmost shortwave upper trough in paragraph P2 of previous discussion #125. With all such shortwave upper troughs now absorbed by paragraph P1 upper vortex...this area of weather is now supported by eastern divergence supplied by the large-scale upper vortex. Although the surface trough in the southern Gulf and Bay of Campeche has diminished due to building 1033 mb central US surface ridge (paragraph P1)...there is another surface trough being marked over eastern Florida today.

P9...Tropical wave moving into the central Caribbean in the previous discussion is now entering the western Caribbean. The northern half of the wave is suppressed by pocket of dry air mentioned in paragraph P6...while the southern half maybe aiding in the t-storm activity over the south-central Caribbean...Panama..Costa Rica...and a portion of the eastern Pacific described in paragraph P6.

P10...Tropical wave moving across the Lesser Antilles in the previous discussion is now in the eastern Caribbean Sea. It is suppressed by non-divergent and shearing upper westerlies on the south sides of the two upper vortices mentioned in paragraph P6. All of the t-storms it produced yesterday remains left behind...supported by the eastern divergence of the easternmost upper vortex. While these t-storms remain curved and organized at a location just NE of the Lesser Antilles...this organization is occurring about the easternmost upper vortex rather than the surface tropical wave. However...there is a surface trough below the easternmost upper vortex...perhaps a northern fracture left behind by this tropical wave.

P11...I had been tracking a westward-moving t-storm cluster in Meteosat-9 infrared satellite animation...and marking it as a suspect tropical wave. Although the t-storm cluster has disappeared since 1200Z October 5...I am still marking the suspect tropical wave for continuity's sake...which I believe this evening is positioned in the open tropical Atlantic midway between the Cape Verde Islands and Lesser Antilles.

P12...The tropical wave that moved offshore from Africa in the previous discussion is becoming better organized and has developed a 1010 mb low pressure spin while passing south and SW of the Cape Verde Islands. It is becoming enhanced by upper outflow of paragraph P6 eastern tropical Atlantic upper ridge. Based on animation of this evening's 1800Z GFS model...this tropical wave should continue west...and has about 72 hours to develop before encountering hostile westerly vertical shear by 96 hours delivered by the pair of cut-off upper vortices mentioned in paragraph P6.

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2. WunderAlertBot (Admin)
3:56 AM GMT on October 08, 2012
NCHurricane2009 has created a new entry.
1. wxchaser97
4:19 AM GMT on October 07, 2012
Thanks NC09!
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