2012 Atlantic Hurricane Season Birdseye Discussion #124

By: NCHurricane2009 , 10:54 AM GMT on October 04, 2012

...OCTOBER 4 2012...6:55 AM EDT...
An outage persists with GOES-E satellite imagery in the last ten days. GOES-W has been extended to cover much of the view in the two birdseye charts below. However...the east edge of the temporary 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.

Tropical Storm Nadine moving northeastward across the Azores this morning while becoming increasingly indistinct on satellite imagery within the cold front cloud band of a non-tropical system (paragraph P3) coming in from the west. Therefore...Nadine should become non-tropical later this afternoon after pulling away from the Azores. A tropical storm warning remains in effect for the Azores...but will be dropped later today after weather conditions improve. 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 tropical depression fifteen...then Tropical Storm Oscar...in the last 24 hours. Oscar should continue turning northward into the open Atlantic. See Oscar special feature section below for additional details on this system.


This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0000Z, and the 0128Z-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.


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).

Fairly excited about my previous track forecast...which correctly had a righward bias with respect to NHC's such that the center passes over the central Azores. Therefore...my track forecast in Figure 1 is a continuation of my previous...which still has an ever-so-slight rightward bias with the updated NHC track forecast at 5 AM EDT. This is further supported by the slight rightward angle that the most recent segment of NHC recorded storm track has with respect to the 5 AM EDT NHC track forecast. Nadine is currently hooking northward within the east side of the paragraph P3 weather system...and will sooner or later merge with the cold front of the system. In fact...she no longer has her own distinct cloud field and is mixed in with the cold front's cloud band. Therefore...I do agree with the NHC on Nadine becoming non-tropical by 12 hours...and also agree with Nadine maintaining her current strength thru her transition to non-tropical as she gets supportive upper divergence on the east side of the paragraph P3 upper trough.

Figure 1: My forecast for Tropical Storm Nadine generated at 5 AM EDT this morning.

Impact swath in Figure 1 is based on extrapolating the 5 AM EDT tropical storm wind radius along my forecast track. No longer mentioning enhanced rainfall within the impact swath as her cloud/precip field is no longer separable from that of the cold front's. Therefore...their will be rainfall both inside and outside of the impact swath...all associated with the cold front and not directly associated with Nadine.

The strong tropical wave in the eastern Atlantic...Invest 96-L...has continued to be enhanced by upper outflow of paragraph P5 East Atlantic upper ridge such that it has strengthened progressively into Tropical Storm Oscar. The tropical storm is moving northward into a break in the subtropical ridge induced by the paragraph P3 weather system...between the paragraph P4 low-level ridge to the NE and paragraph P5 1024 mb low-level ridge to the NW. As such...the tropical storm has already left the favorable upper ridge that allowed for its genesis...and is suffering from westerly vertical shear on the north side of this upper ridge. The sheared structure is well-defined in satellite imagery this morning...with a circular storm mass displaced eastward from the surface swirl center.

The NHC solution in Figure 2 is to soon hook Oscar eastward in westerly flow on the south side of the paragraph P3 weather system. The NHC intensity forecast shows Oscar maintaining strength or getting a little stronger despite the shear...as the NHC track allows Oscar to move ahead of the paragraph P3 upper trough and take advantage of eastern divergence supplied by the upper trough. Based on the 00Z GFS model's representation of the SW lobe of the paragraph P4 low-level ridge (which would seem to me to block eastward motion of Oscar for about 24 more hours)...and the fact that the NHC recorded storm track has a leftward angle with respect to the NHC track forecast...my track forecast in Figure 2 has quiet a leftward bias with respect to the NHC's. As such...I prefer to weaken Oscar in the westerly shear as my track forecast keeps him just west of the favorable eastern divergence of the paragraph P3 upper trough that would otherwise help him. The models...the NHC..and I agree that Oscar should dissipate into a surface trough in the next 36 to 48 hours as Oscar loses his identity within the vast low pressure field of the paragraph P3 weather system.

Figure 2: My forecast for Tropical Storm Oscar generated at 6 AM EDT this morning.

Impact swath in Figure 2 is based on the tropical storm wind field shown in the NHC 5 AM EDT Oscar advisory package...because I think this wind field well-represents the sheared nature of the storm. The wind field is extrapolated along my forecast track to generate the swath. The swath is more symmetric about the storm track toward the end of the forecast because a NE-tracking tropical storm in a westerly shear environment has its impacts occur symmetrically about the storm track.

P1...A shortwave upper trough continues entering the top-left corner of the above atmo chart from W Canada. Its western convergence supports a strong surface ridge over the NW US and W Canada delivering unseasonably cold air. Its eastern divergence supports surface frontal activity. The Canadian 993 mb frontal cyclone has weakened due to the strength of the aforementioned surface ridge...and now the dominant feature on the front is a 1004 mb depression over the central US. This frontal depression is delivering bouts of winter weather across the northern edge of the US and southern edge of Canada.

P2...Major upper trough over central North America remains split. Western convergence of the southern split is driving dry air over the SW US and W Gulf of Mexico. The eastern divergence of the northern split continues driving a frontal cyclone eastward across north Canada that is moving offshore and toward Greenland (cyclone's surface cold front is seen in top-center of above atmo chart). Eastern divergence of the southern split is driving a 1014 to 1016 mb frontal cyclone that has moved NNE into the Great Lakes from the eastern US. Easterly flow from the paragraph P6 W Atlantic upper ridge converges with the southerly flow ahead of the southern split upper trough...this upper convergence driving a surface 1021 mb ridge over the eastern US.

P3...Deep-layered cyclone moving eastward across the north Atlantic and toward Tropical Storm Nadine. The upper-layer of the cyclone remains an upper trough axis while the surface center has strengthened from 996 to 992 mb in the last 24 hrs...perhaps as the surface center continues to tap into eastern upper divergence of the upper trough. However...the surface center remains tucked below the less-divergent upper trough axis itself...so expect the surface center to not undergo significant strengthening or weaken.

P4...Upper trough continues moving east from the Atlantic high seas and into western Europe. Western convergence of the upper trough continues driving NE Atlantic surface ridge.

P5...Central tropical Atlantic upper vortex persists...while its SW portion has broke off into a retrograding upper vortex moving across Caribbean Sea in the last 48 hours while steered by W Atlantic upper ridge in paragraph P6. NW convergence of the upper vortex supports 1024 mb W Atlantic surface ridge and a slot of dry air. In relatively higher pressures east of this upper vortex...upper ridge remains built across the eastern tropical Atlantic...further supported by t-storm latent heat release Tropical Storm Oscar

P6...W Atlantic upper ridge persists while supported by low-level warm air advection ahead of the paragraph P2 Great Lakes surface frontal cyclone.

P7...Tropical wave nearing the Lesser Antilles in the previous discussion is now crossing the islands into the eastern Caribbean Sea this morning. Its t-storm activity has reduced...and is suppressed from tropical development by SW vertical shear from the paragraph P5 central Atlantic upper vortex.

P8...By tracking a westward-moving cluster of t-storms in Meteosat-9 infrared satellite...I have continued marking a suspect tropical wave which I believe this morning is positioned SW of the Cape Verde Islands and well SE of Tropical Storm Oscar.

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

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