2012 Atlantic Hurricane Season Birdseye Discussion #121

By: NCHurricane2009 , 12:44 AM GMT on October 01, 2012

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...SEPTEMBER 30 2012...8:50 PM EDT...
An outage persists with GOES-E satellite imagery in the last seven 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.

Hurricane Nadine maintaining high-end category 1 strength while looping counter-clockwise in the Atlantic subtropics. It is now apparent the Azores are likely to get a strike from Nadine later this week...and therefore interests here should carefully monitor the progress of the storm this week. Since the Azores previously received direct weather from Nadine on September 19 to 21...this will be their second event with this cyclone. See the Nadine special feature section below for details.

As paragraph P1 in the mid-latitudes discussion highlights...a significant upper trough in the mid-latitude westerlies is driving an impressive surface frontal cyclone moving east across the southern US. Its frontal boundary is producing weather in the Gulf of Mexico...but no tropical development is expected. However...some hazardous weather remains possible with this system. See paragraph P1 in the mid-latitudes discussion for details.

A tropical wave in the eastern Atlantic is becoming better organized under favorable upper winds...and the favorable upper winds are forecast by models to persist with the wave over the next days. However...the low pressure spin of the tropical wave so far is not organized enough for imminent tropical cyclone formation. If the low pressure spin indeed becomes better orgainzed...I will be upgrading this to a special feature on this blog. For now...see paragraph P8 in the tropical belt discussion for statement on this tropical wave.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1929Z-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...HURRICANE NADINE...
Fairly excited about my previous intensity forecast...which enjoyed 100% accuracy in the last 24 hours while precisely predicting the rate at which Nadine would hit 90 mph max winds today. Nadine continues thriving in a peninsula of favorable upper outflow/upper divergence between the paragraph P3 upper trough passing to the NE and paragraph P5 C Altc upper vortex to the SW. My updated intensity forecast in Figure 1 is similar to my previous...but showing slightly less weakening than my previous due to the fact that Nadine has been holding her strength today a little better than I previously thought. Weakening appears imminent...as the 18Z GFS model insists Nadine's favorable upper outflow becoming squashed out by rather hostile...zonal shearing upper westerlies on the SW side of the paragraph P3 upper trough in the next 24 hours (Monday)...so I forecast a brisk initial weakening rate that makes me fall below the 5 PM EDT NHC intensity forecast. I slow the weakening rate by Tuesday as the 18Z GFS still shows a shortwave upper ridge ahead of the paragraph P2 weather system coming in from the NW...so I speculate that the upper ridge would reduce shear...and or Nadine taking some advantage of split flow upper divergence between the flow around the upper ridge and departing zonal upper westerlies. By the end of the forecast...I stop weakening Nadine 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 GFS model...I firmly believe Nadine will be non-tropical by 96 hours (Thursday) as she will be well-embedded in the eastern divergence of the upper vortex and racing NE into much cooler waters that should cause her to lose her vertical warm core. On the other hand...the NHC prefers delaying the transition to non-tropical to 120 hours (Friday).


Figure 1: My forecast for Hurricane Nadine generated at 7 PM EDT this evening.

Nadine is currently located southwest of the Azores...performing a counter-clockwise loop while drifting SW and southward in between the paragraph P4 ridge to the NE...paragraph P3 ridge to the NW...and paragraph P5 ridge to the west. I previously did not believe the current SW and south drift was going to happen due to the presence of the paragraph P5 ridge. In hindsight...the paragraph P4 and P3 ridges are stronger than the paragraph P5 ridge...with those two ridges turning Nadine west such that it slammed into the eastern wall of the paragraph P5 ridge. After it slammed into the ridge this afternoon...it is now turning straight southward as seen on satellite animation this evening...thanks to that ridge's eastern northerly flow. With the straight south motion currently observed...I agree with the NHC track forecast on a slow south motion for the next 24 hours. The NHC and models drift Nadine east between 24 and 48 hrs...but given that the 18Z GFS shows all ridges having equal strength and opposing influence by that time...I prefer to keep Nadine instead stationary...creating a westward bias in my position by 48 hours.

For the longer-range...the NHC and models show Nadine reacting to a strong frontal cyclone supported by the incoming paragraph P2 vortex. My previous track forecast had a NE bias relative to NHC for the timeframe that Nadine intersects the frontal cyclone...which meant that my previous solution had Nadine getting caught in the east side of the cyclone such that it tracks more north than east (and this solution caused me to be far north...or left...of the NHC solution). Now...I have a slight W bias relative to NHC for the timeframe that Nadine intersects the frontal cyclone...which now means that my updated track forecast in Figure 1 has Nadine getting caught on the south side of the cyclone such that it tracks more east than north (and now my solution is a little right of the NHC solution). My updated track forecast in Figure 1 now has Nadine's center passing closer to the central Azores...while the NHC's track forecast has Nadine's center passing closer to the western Azores.

Impact swath in Figure 1 is based on extrapolating the 5 PM EDT tropical storm wind radius along my forecast track. Although my impact swath for Wednesday and Thursday barely covers the western Azores and heavily-envelopes 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 be monitoring this situation carefully.

...MID-LATITUDES DISCUSSION...
P1...Major upper trough over western North America continues sliding eastward. Western convergence of the upper trough is driving clearing skies and dry air over Texas...as well as a western US surface ridge. Upper trough's northern half driving a frontal cyclone from W Canada eastward (surface features of the cyclone seen in top-left of above atmo chart). Warm air advection ahead of this frontal cyclone is driving an upper ridge that has shifted from Manitoba to southern Hudson Bay in the last 24 hrs. Southern half of upper trough is driving an impressive frontal cyclone moving east across the southern US from Texas (evaluated at 1001 mb as of 1929Z). Flood watches are posted across parts of Louisiana and Mississippi as of this writing. For the next couple of days...potential exists for flood watches to continue spreading across the US Gulf coast region and SE US. Warm air advection ahead of the frontal cyclone is driving an upper ridge that has shifted from Texas to the Gulf of Mexico in the last 24 hrs. Southerly flow ahead of the frontal cyclone will be in directional vertical shear with respect to westerly flow across the upper ridge...so if enough instability develops from daytime heating...severe t-storm and or tornado watches may also be required in the next couple of days. A tornado watch is currently in effect for parts of Louisiana...Mississippi...Alabama...and the Florida panhandle...and tornado warnings within the watch have been issued. Residents across the SE US and US Gulf coast should visit www.nws.noaa.gov and or listen to local media for latest info on hazardous weather from this system.

P2...Upper trough over E Canada and NE US has amplified further into an upper vortex thanks to amplified upper ridges ahead of the paragraph P1 weather system to the west. Surface 1012 mb frontal depression over the NE US has intensified into a 1003 mb frontal cyclone while taking advantage of eastern peripheral divergence of the upper vortex. Western convergence of this upper vortex supports 1019 to 1024 mb surface ridge centers that have shifted from the central US and into eastern Canada in the last 24 hrs...as well as a slot of drying air wrapping in behind the 1003 mb frontal cyclone.

P3...Upper trough continues moving east across the Atlantic high seas. The upper trough's eastern divergence continues supporting a frontal cyclone that has passed north of Hurricane Nadine...and is exiting the picture while headed for NW Europe. The upper trough's western convergence supports a greater-than-1028 mb ridge center just offshore of Newfoundland. W Caribbean cut-off left behind by this upper trough days ago has been moved to paragraph P6 of the tropical belt discussion below.

P4...Impressive ridge in the NE Atlantic has weakened from 1028 to 1026 mb in the last 24 hours.

...TROPICAL BELT DISCUSSION...
P5...Central tropical Atlantic upper trough/vortex persists SW of Hurricane Nadine. Central Atlantic surface trough & t-storm cluster it generated with its eastern divergence 24 hrs ago has dissipated. However...it has generated a new 1022 to 1023 mb W Atlantic surface ridge with its western convergence. In relatively higher pressures southeast of this upper trough...upper ridge has built across the eastern tropical Atlantic.

P6...W Caribbean tropical wave (discussion #120 paragraph P8)...W Caribbean cut-off upper trough (discussion #120 paragraph P3)...and surface trough passing north of Puerto Rico (discussion #120 paragraph P9) have all combined to make complex weather in this area. The W Caribbean cut-off upper trough is flanked by two upper ridges. The northwestern upper ridge extends into the W Atlantic and is driven by warm air advection ahead of the paragraph P2 frontal cyclone. The southeastern upper ridge has developed in relatively higher pressures SE of the cut-off upper trough and spans the east Caribbean. Upper convergence between the NW upper ridge and cut-off upper trough supports a slot of dry air where the tropical wave is located. Split flow upper divergence between the cut-off upper trough and SE upper ridge supports stormy weather across Jamaica...Cayman Islands...eastern Cuba...Haiti...the eastern Bahamas...as well as the surface trough that has moved from N of Puerto Rico to N of Haiti in the last 24 hrs. Most impressive feature of cut-off upper trough is a well-defined upper vortex spinning in the W Caribbean tonight.

P7...Tropical wave midway between the Cape Verdes and Lesser Antilles in the previous discussion has seen an increase in t-storms while supported by enhanced upper outflow of paragraph P5 East Atlantic upper ridge. However...it is about to enter hostile southerly vertical shear produced by east side of paragraph P5 Central Atlantic upper trough.

P8...Satellite imagery continues showing an eastern Atlantic tropical wave with cyclonic turning in its t-storm clouds such that TAFB assigned it a surface low pressure spin today. NHC TAFB positioned this tropical wave just southwest of the Cape Verde Islands as of 1800Z TAFB this afternoon. Similar to the tropical wave in paragraph P7...this tropical wave is enhanced by upper outflow of paragraph P5 East Atlantic upper ridge. Models show this upper ridge remaining in place while re-enforced by this tropical wave's t-storm latent heat release...so tropical cyclone formation from this system is possible in the next days. It initially appears such a tropical cyclone would first track west while steered by paragraph P4 and P5 Atlantic surface ridges...and then get pulled northward into the open Atlantic by widening weakness between the two ridges generated by paragraph P2 frontal cyclone.

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4. WunderAlertBot (Admin)
8:12 AM GMT on October 02, 2012
NCHurricane2009 has created a new entry.
3. nigel20
1:33 AM GMT on October 01, 2012
Thanks NC!
Member Since: November 6, 2010 Posts: 12 Comments: 8486
2. wxchaser97
1:15 AM GMT on October 01, 2012
Thanks NC09! The end is near with Nadine and I pretty well agree with your forecast. I am writing a blog on the longest lived Atlantic hurricanes and my usual tropical update tomorrow.
Member Since: March 16, 2012 Posts: 127 Comments: 7972
1. MAweatherboy1
1:12 AM GMT on October 01, 2012
Thanks NCH09!
Member Since: February 11, 2012 Posts: 84 Comments: 8047

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