2012 Atlantic Hurricane Season Birdseye Discussion #120

By: NCHurricane2009 , 5:47 PM GMT on September 29, 2012

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...SEPTEMBER 29 2012...1:50 PM EDT...
An outage persists with GOES-E satellite imagery in the last five and a half 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 became a hurricane yesterday...subsequently weakening back to a strong tropical storm in the early morning. Even though I was previously forecasting Nadine to begin weakening today (special update #119A and full discussion #119)...the tenacious cyclone has instead regained hurricane strength as of 11 AM EDT. The cyclone is expected to track slowly north in the Atlantic subtropics for the next few days. See Nadine special feature section below for details.

As paragraph P1 in the mid-latitudes discussion highlights...the next upper trough in the mid-latitude westerlies is driving the formation of an impressive surface frontal low over Texas. In the next 12 hours...weather from this feature will begin spreading into the Gulf of Mexico...but no tropical development is expected. However...similar to Invest 93-L in discussion #110...this system for the next days could be capable of significant weather across the US Gulf coast...SE US...and along the east US coast. See details of 93-L in discussion #110 for the kinds of impacts a system like this could deliver.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0600Z, and the 0729Z-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...
Nadine's previous intensification episode ended when the east side of the paragraph P6 C Atlc upper trough imparted southerly vertical shear across the storm...causing her to weaken to a strong tropical storm this morning. I was previously expecting the shear to continue until dissipation (my previous dissipation time was 11 PM Mon). Clearly in Figure 1...I am now keeping the cyclone alive well past 11 PM Mon...because of her recent re-intensification into hurricane strength at 11 AM EDT this morning. Despite being over waters less than 26 deg C...satellite imagery in Figure 2 shows Nadine with impressive t-storms at her core with a small eye. Her more symmetrical satellite appearance suggests the shear is reducing as her latent heat release is causing the shearing C Altc upper trough to amplify into an upper vortex. The paragraph P3 upper trough is about to pass to the north and NE of Nadine. This suggests enhanced upper outflow channels into the developing upper vortex to the SW and upper trough to the NE in the next 24 hours. This extremely favorable upper wind configuration causes me to forecast bullish strengthening into a strong category 1 hurricane in the next 24 hrs...quiet more bullish than the 11 AM EDT NHC forecast. The last time we saw rapid intensification at this location was category 2 Hurricane Gordon during discussion #82...but that was over waters above 26 deg C. With Nadine being above waters cooler than 26 deg C...I prefer to stay away from suggesting category 2 strength.

The 12Z GFS model shows 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 by 60 hours (11 PM Mon)...so I forecast a brisk weakening rate by that time. I slow the weakening rate by 84 hours (11 PM Tue) as the GFS 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 agree with the NHC that Nadine will become a non-tropical remnant low supported by the eastern divergence of the incoming paragraph P2 upper trough. I show no weakening between 11 PM Tue and 11 PM Wed due to the support from the upper trough's divergence.


Figure 1: My forecast for Hurricane Nadine generated early this afternoon.


Figure 2: Infrared satellite image of Hurricane Nadine taken during the late morning by Meteosat-9 (1200Z)

Nadine is currently located southwest of the Azores and further north than what my previous forecasts predicted. And given that Nadine's forward speed has doubled from 7 to 14 mph since I last forecasted 36 hrs ago...my updated forecast track in Figure 1 is a northward shift from my previous. Nadine is moving northward into a developing narrow ridge weakness associated with the 990 mb frontal cyclone in paragraph P3...between paragraph P4 ridge the NE and what is now the 1025 mb paragraph P3 ridge coming in from the NW. I agree with stalling the motion of Nadine by late Sunday and all of Monday as she becomes trapped between these two ridges. I do not agree with the GFS model's and NHC's SW drifting motion by that time...as such a motion in my opinion will be blocked by a third ridge to the west supported by the W convergence of paragraph P6 C Atlc upper trough. After the 1025 mb ridge passes by to the north...the NHC and models show Nadine reacting to a strong frontal cyclone supported by the incoming paragraph P2 upper trough. Because of the SW drift shown by the NHC and GFS model...Nadine is further south and hence travels more east in those solutions while getting caught on the south side of the frontal cyclone. Because I don't agree with the SW drift...my solution would have Nadine getting caught in the east side of the frontal cyclone...which would swing Nadine more north than east as I show in Figure 1.

Impact swath in Figure 1 is based on extrapolating the 11 AM EDT tropical storm wind radius along my forecast track...then shrinking the swath a bit to represent the weakening later in the forecast.

...MID-LATITUDES DISCUSSION...
P1...In the last 36 hours...deep-layered vortex over SE Wyoming has merged with next upper trough in the mid-latitude westerlies. This upper trough is already splitting...with the northern half driving a W Canada frontal cyclone (cyclone's warm front marked in top-center of above atmo chart) whose warm air advection is driving an upper anticyclone over Manitoba. Southern half of upper trough is over the western US...which has sheared off a great bulk of moisture from Eastern Pacific Tropical Cyclone Norman into the SW US upper ridge. Latent heat release from this moisture amplified the SW US upper ridge while the upper ridge has shifted across Texas and N Mexico. Along the front trailing from the NE US 1012 mb low (mentioned in paragraph P2)...split flow upper divergence between this amplified upper ridge and west US upper trough is driving a new and impressive frontal cyclone over Texas. With the immense moisture from Norman wrapped into this frontal cyclone...flood watches are posted across south Texas...spreading into Louisiana and Mississippi. For the next couple of days...potential exists for flood watches to continue spreading across the US Gulf coast region and SE US. 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.

P2...Shortwave upper trough moving across Hudson Bay in the previous discussion has become amplified to the east of the Manitoba upper anticyclone mentioned in paragraph P1 above. The upper trough is now moving into E Canada and the NE US. The surface cyclone it supported has dissipated. Instead...it has intensified the central US 1018 mb frontal depressions (paragraph P1 discussion #119) into a 1012 mb frontal depression that has moved into the NE US. Western convergence of this upper trough now supports a chunk of a former Great Lakes surface ridge (paragraph P3 discussion #119)...which are the 1021 to 1022 mb centers over the central US in the above atmo chart.

P3...Upper trough over eastern North America has finally shifted into the NW Atlantic and is headed eastward for the Atlantic high seas. The upper trough's eastern divergence continues supporting a frontal cyclone...which has moved offshore from Canada and past the south tip of Greenland while intensifying from 996 to 990 mb in the last 36 hours (it bottomed to 988 mb 12 hours ago). Split flow upper divergence between SW flow ahead of this upper trough and NW flow entering the central Atlantic upper trough (paragraph P6) supports a relatively new 1020 mb frontal depression in the NW Atlantic. The upper trough's western convergence supports a chunk of a former Great Lakes surface ridge (paragraph P3 discussion #119)...which are the 1025 mb centers over Atlantic Canada in the above atmo chart. Western convergence of this upper trough used to drive an eastern US surface ridge...but what is left of this surface ridge is now a 1017 mb center over the Florida panhandle now supported by eastern convergence of the Texas/N Mexico upper ridge in paragraph P1 above. To the east of that upper ridge...cut-off upper trough over the E Gulf to W Caribbean now stretches from coastal NC to the W Caribbean.

P4...Deep-layered ridge in the NE Atlantic...featuring a surface 1028 mb center over the Azores...persists.

P5...Amplified upper trough just offshore of Europe has finally exited the picture in the last 36 hours...with its eastern divergence supporting an impressive surface cyclone that has moved into Spain and Portugal.

...TROPICAL BELT DISCUSSION...
P6...Upper vorticity over the SE Caribbean...and upper ridge cell over the W Atlantic and Puerto Rico...have rapidly de-amplified into zonal upper westerlies across the entire Caribbean and W tropical Atlantic. De-amplification of the upper flow was due to coastal NC-to-W Caribbean cut-off upper trough (paragraph P3) pushing in. Central Atlantic upper trough persists SW of Hurricane Nadine...and its eastern divergence drove an impressive t-storm cluster and new surface trough in the central tropical Atlantic in the last 36 hours. However...SW vertical shear ahead of this upper trough will prevent this t-storm cluster from developing into a tropical cyclone. In relatively higher pressures southeast of this upper trough...upper ridge has built from the W coast of Africa as evidenced by upper-level cloud motions around paragraph P11 and P12 tropical waves.

P7...Surface trough in Bay of Campeche has dissipated in last 36 hours thanks to eastern convergence of paragraph P1 Texas/N Mexico upper ridge. This upper convergence supports a slot of dry air across the W edge of the Caribbean...SE Mexico...and northern Central America seen in the above thermo chart.

P8...Tropical wave moving across the central Caribbean Sea in the previous discussion is now in the W Caribbean. It is producing scattered t-storms over the central Caribbean....Jamaica...Cuba...and the E Bahamas thanks to eastern upper divergence of paragraph P3 coastal NC-to-W Caribbean upper trough. This same upper divergence mechanism is producing a new surface trough just north of the Bahamas.

P9...Surface trough NE of the Lesser Antilles in the previous discussion is now passing north of Puerto Rico...and is being affected by the immense shear of the W tropical Atlantic zonal upper westerlies mentioned in paragraph P6.

P10...Eastern Atlantic surface ridge just NW of the Cape Verde Islands has eroded and dissipated thanks to Nadine's low-level low pressure field to the north.

P11...Tropical wave W of the Cape Verde Islands is entering the tropical waters midway between the Cape Verdes and Lesser Antilles. It continues producing a t-storm cluster while enhanced by upper outflow of upper ridge building from W Africa mentioned in paragraph P6.

P12...Satellite imagery shows that a tropical wave with cyclonic turning and large amounts of t-storms has emerged from W Africa into the Atlantic tropics in the last 36 hours. NHC TAFB positioned this tropical wave just east of the Cape Verde Islands as of 0600Z TAFB this morning. Similar to the tropical wave in paragraph P11...this tropical wave is enhanced by upper outflow of upper ridge building from W Africa mentioned in paragraph P6.

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6. WunderAlertBot (Admin)
12:44 AM GMT on October 01, 2012
NCHurricane2009 has created a new entry.
5. TrevUsh
2:28 PM GMT on September 30, 2012
Thanks for taking your time to write that informative reply. I'll keep an eye on the Atlantic the whole way.
Member Since: September 30, 2012 Posts: 0 Comments: 1
4. NCHurricane2009
5:13 AM GMT on September 30, 2012
Quoting TrevUsh:
Hey Guys,
Please excuse my lack of terms here: I'm scheduled to sail a smallish yacht from Panama to Florida some time in October. My question to you guys is:
What do you see happening with the systems moving through?
Do you think the peak of the season has passed?
How do you view October compaired to previous years?
Any help is greatly appreciated.

I find myself more comfortable with the day-to-day forecasting of tropical and non-tropical weather than predicting the climatology of a given season or for a few weeks out. However...I will give this a shot...

What I have observed since Isaac's time is that upper troughs in the western part of the Atlantic basin have become unseasonably strong...promoting vertical shear that generally has been disrupting development here. An El Nino watch was given during early September. Strong upper troughs in the western half of the Atlantic are consistent with an El Nino regime...so I would tend to suggest that it is more likely the upper troughs are going to get stronger for the rest of the season. Therefore...your yacht trip is more likely to be free of tropical cyclone headaches...

But I would still keep an eye on the tropics as you get closer to your yacht trip's time...
Member Since: September 15, 2009 Posts: 447 Comments: 3623
3. TrevUsh
4:12 AM GMT on September 30, 2012
Hey Guys,
Please excuse my lack of terms here: I'm scheduled to sail a smallish yacht from Panama to Florida some time in October. My question to you guys is:
What do you see happening with the systems moving through?
Do you think the peak of the season has passed?
How do you view October compaired to previous years?
Any help is greatly appreciated.
Member Since: September 30, 2012 Posts: 0 Comments: 1
2. NCHurricane2009
6:08 PM GMT on September 29, 2012
Quoting wxchaser97:
Thanks NC09, I bring Nadine up to 80mph but she could get stronger than 80mph.

Yeah...I choose to go 90 as I show in Figure 1...can't wait to see what happens here...
Member Since: September 15, 2009 Posts: 447 Comments: 3623
1. wxchaser97
6:01 PM GMT on September 29, 2012
Thanks NC09, I bring Nadine up to 80mph but she could get stronger than 80mph.
Member Since: March 16, 2012 Posts: 127 Comments: 7928

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