2012 Atlantic Hurricane Season Birdseye Discussion #123

By: NCHurricane2009 , 7:34 AM GMT on October 03, 2012

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...OCTOBER 3 2012...3:40 AM EDT...
An outage persists with GOES-E satellite imagery in the last nine days. GOES-W has been extended to cover much of the view in the two birdseye charts below. The east edge of the temporary GOES-W scan has been adjusted such that its previous bias for showing false cloud tops has been mitigated...and therefore the east edge of the two birdseye charts below are left unrepaired by me. However...I added a Meteosat-9 graft in the lower-right corner of the atmospheric features chart...which better shows a suspect tropical wave that has emerged from Africa (paragraph P8).

Tropical Storm Nadine continuing eastward...and should soon turn northeastward toward the Azores and hit with tropical storm conditions later today. A tropical storm warning remains in effect for the Azores...so preparations in this area should be complete or be completed by this morning. Up to the minute latest info on Nadine...including status of warnings...can be found under the public advisory of Nadine under www.nhc.noaa.gov. Also see Nadine special feature section below for details.

Tropical wave Invest 96-L in the eastern Atlantic has become very well organized...and could become a tropical depression or tropical storm at anytime later today. See Invest 96-L special feature section below for details.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1918Z-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).

...SPECIAL FEATURE...TROPICAL STORM NADINE...
Nadine has weakened a bit more in the last 24 hours. Her satellite appearance showed weaker t-storm activity (perhaps due to the cool waters she is over). The t-storm activity also appeared sheared slightly eastward from the center...perhaps as upper northwest winds from the upper ridge ahead of the paragraph P3 weather system moved in. Very recently...the t-storm activity appears to be stronger...perhaps as Nadine is beginning to take advantage of the incoming upper ridge. I speculate that the upper ridge is reducing the shear/supporting her upper outflow...and or Nadine is taking some advantage of split flow upper divergence between the flow around the upper ridge and departing zonal upper westerlies. Little to no weakening is also supported by the end of the forecast...as she transitions into a non-tropical low supported by the eastern divergence of the incoming paragraph P2 upper vortex. After examining Nadine's relationship with the upper vortex in the 00Z GFS model...I firmly believe Nadine will be non-tropical by 42 hours (5 PM Thursday) as she will be well-embedded in the eastern divergence of the paragraph P3 upper trough while racing NE into much cooler waters that should cause her to lose her vertical warm core. With the aforementioned atmospheric mechanisms suggesting little to no weakening thru transition to non-tropical...I do not show any weakening of Nadine as shown in Figure 1. This is also the solution supported by NHC at 11 PM EDT (albiet they slightly weaken Nadine to 45 mph max winds as she becomes non-tropical).


Figure 1: My forecast for Tropical Storm Nadine generated at 2 AM EDT this morning.

Nadine is currently located southwest of the Azores...currently moving east as she responds to westerly flow on the SE quad of the surface cyclone mentioned in paragraph P3. Nadine will eventually hook more northward as the east side of the cyclone pulls her in. Previously I had agreed with the NHC track forecast...and the NHC track forecast has not changed in the last 24 hours. However this time around...as seen in Figure 1...I have a slight rightward bias relative to the NHC's 11 PM EDT track forecast. This is because the most recent segment of the NHC recorded storm track in Figure 1 shows a straight eastward motion rather than the beginnings of a NE track as the 11 PM EDT NHC track forecasts suggests. This means I am forecasting the center of Nadine to be very near or over the central Azores by early Thursday...while the NHC forecasts the center to weave between the western and central Azores.

Impact swath in Figure 1 is based on extrapolating the 11 PM EDT tropical storm wind radius along my forecast track. Although my impact swath for later today and Thursday only covers the central Azores...a slight shift in track one way or the other could easily change this. Therefore...it is important to emphasize that all of the Azores should have acted on the tropical storm warning....which is in effect for all of the Azores. See www.nhc.noaa.gov Nadine public advisories for latest statements on Azores tropical storm warnings.

...SPECIAL FEATURE...TROPICAL WAVE INVEST 96-L...
Satellite imagery continues showing an eastern Atlantic tropical wave with cyclonic turning in its t-storm clouds such that TAFB continues assigning it a surface low pressure spin. NHC TAFB positioned this tropical wave well west-southwest of the Cape Verde Islands as of 1800Z TAFB last afternoon. This tropical wave is continuing to be enhanced by upper outflow of paragraph P5 East Atlantic upper ridge. Moreover...this upper ridge remains in place while re-enforced by this tropical wave's t-storm latent heat release...so tropical cyclone formation from this system appears imminent...especially as the tropical wave has become very well-organized. Therefore I continue to assert that tropical cyclone formation is very likely sometime today.

It appears that this tropical wave is already turning northwestward toward the widening low-level ridge weakness associated with the paragraph P3 weather system. Therefore...expect this system to recurve northward into the open Atlantic waters.

...MID-LATITUDES DISCUSSION...
P1...A shortwave upper trough is entering the top-left corner of the above atmo chart from W Canada. Its eastern divergence supports a vigorous 993 mb surface frontal cyclone.

P2...Major upper trough over central North America has split. Western convergence of the splitting upper trough is driving dry air over the SW US and W Gulf of Mexico...a 1017 mb ridge over Texas...and a 1018 mb ridge just south of Canada's Hudson Bay. The upper trough's northern split is driving a frontal cyclone eastward across Canada (cyclone's surface cold front with 1002 mb depression is seen in top-center of above atmo chart). Southern split of the upper trough is now a cut-off upper vortex over the TX/LA/AK/OK area...whose eastern divergence is driving an impressive surface frontal cyclone moving NE across the eastern US (evaluated at 1005 mb as of 1800Z).

P3...Deep-layered cyclone over the NE US and eastern Canada is shifting eastward into the north Atlantic and toward Tropical Storm Nadine. The upper-layer of the cyclone is now an amplified upper trough axis while the surface center has strengthened from 1000 to 996 mb in the last 24 hrs. With the surface center now beneath the less-divergent upper trough axis itself...expect the surface center to begin weakening. Western upper convergence of the upper trough supports a 1018 mb surface ridge over the NE US.

P4...Upper trough continues moving east across the Atlantic high seas and is nearing western Europe. Western convergence of the upper trough now drives the 1026 mb NE Atlantic surface ridge mentioned in paragraph P4 of previous discussion #122.

...TROPICAL BELT DISCUSSION...
P5...Central tropical Atlantic upper trough/vortex persists SW of Tropical Storm Nadine...and its SW portion has broke off into a retrograding upper vortex moving across the E Caribbean while steered by W Atlantic upper ridge in paragraph P6. Western convergence of the upper trough/vortex supports 1024 mb W Atlantic surface ridge. In relatively higher pressures southeast of this upper trough/vortex...upper ridge remains built across the eastern tropical Atlantic...further supported by t-storm latent heat release from special feature Invest 96-L.

P6...W Caribbean cut-off upper vortex has lost its identity as the TX/LA/OK/AK upper vortex in paragraph P2 moves in from the NW. W Atlantic upper ridge persists to the east of this...and is propped up by mass low-level warm air advection ahead of the paragraph P2 eastern US surface frontal cyclone. All stormy weather in the W Caribbean area (once supported by split flow upper divergence between the dissipated W Caribbean upper vortex & the upper ridge) has become focused along the cold front of the eastern US cyclone.

P7...Tropical wave midway between the Cape Verdes and Lesser Antilles in the previous discussion is nearing the Lesser Antilles. It continues to produce t-storm activity...supported by upper divergence on the east side of paragraph P5 central Atlantic upper trough. Expect no development from this tropical wave as it gets a dose of southerly and or westerly vertical shear from the upper trough.

P8...Satellite imagery suggests the next tropical has emerged from the west coast of Africa (see lower-right of above atmo chart). The associated t-storm cluster shows some signs of organization...but appears to be biased to the west of the wave axis due to some easterly vertical shear on the south half of the paragraph P5 east Atlantic upper ridge.

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