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WxWatcher007

Hurricane Barry

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With NHC odds up to 80%, I figured it's time for a thread. 

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Tropical Weather Outlook
NWS National Hurricane Center Miami FL
800 AM EDT Mon Jul 8 2019

For the North Atlantic...Caribbean Sea and the Gulf of Mexico:

1. A trough of low pressure located over central Georgia is forecast to
move southward toward the northeastern Gulf of Mexico, where a broad
area of low pressure is expected to form in a couple of days.  Some
gradual development is possible thereafter and a tropical depression
is likely to form by the end of the week while the low meanders near
the northern Gulf Coast.  Regardless of development, this system has
the potential to produce heavy rainfall along portions of the
northern and eastern U.S. Gulf Coast later this week.  For more
information about the rainfall threat, please see products issued by
your local weather forecast office and the NOAA Weather Prediction
Center.  Interests along the northern Gulf Coast and the Florida
peninsula should monitor the progress of this system.
* Formation chance through 48 hours...low...10 percent.
* Formation chance through 5 days...high...80 percent.

Forecaster Stewart

 

The overview above is a good summary. For the last few days we've been tracking a trough of low pressure tracking over the eastern CONUS toward the Gulf of Mexico. This has been expected to interact with a boundary over the Gulf, initiating tropical genesis. The signal for development has gotten stronger in the last few days, and all the major guidance has projected development in some form. You can see the vorticity signature pretty well at 850mb. 

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Looking at the environment in the Gulf, conditions are generally favorable for development. First let's look at SSTs and TCHP. Things are warm in the Gulf as they usually are, but this season has led to significant positive anomalies with regard to SSTs. TCHP on the other hand, is a bit lower, but still enough for development and intensification. Note the warm eddy that lies in the path of the potential system should it take a more westward track. 

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With regard to moisture, unlike much of the Atlantic basin, the Gulf does not have a particularly dry environment. It is important to note that the GFS, which has been less robust with intensification, does have some dry air lurking to the north of the system toward the end of the forecast period. How much entrainment occurs is critical to the development of convection. 

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Shear is another thing to consider, and while there is currently low shear in the Gulf, there are some indications looking at the GFS soundings that later in the forecast period some northerly shear could act to limit organization. That said, shear does not look particularly strong during the period. For some prior GFS runs, there was increased shear interacting with the system in the eastern Gulf because of an east coast trough, but that signal has faded almost completely in recent runs. 

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Intensity forecasting is hard. It is particularly difficult with something as broad as this and relatively little time over water. One potential limitation I see particularly on the GFS is the size of the system making it difficult to organize in time. The Euro hasn't had that issue, showing steady intensification once the mid level vort is able to develop a surface low. As a result, we see a stronger system on the Euro and most recently the legacy (old) GFS. 

It's important to note that we saw something similar with 91L, with proximity to land and shear keeping development from happening until it was too late. This was even as the Euro was most bullish with development.

The bottom line is that things remain up in the air both in track and intensity, so folks all along the Gulf should keep a close eye on this one. 

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something that needs to be discussed:

The MS river is still in flood , at New Orleans it's 16 feet, at Baton Rouge still at major flood stage around 42 feet

This is the first time in recent memory the river has been this high during Hurricane Season, usually its 8 feet or less

the levee will overtop New Orleans at 20 feet 

 

Hell Is High Water
When will the Mississippi River come for New Orleans?

....One of the most unnerving aspects of this year’s record high water is that it now coincides with the start of hurricane season. The Army Corps’ river levees are built with the assumption that tropical storms would coincide with a river only 8 feet high—less than half its present height. Hurricane Katrina pushed a surge of 13 feet up the river. Hurricane Isaac made the river run backward, with a surge of 8 feet up to Baton Rouge. A storm surge of that size right now would cause the Mississippi to overtop the levees in New Orleans, a catastrophe in its own right that would weaken the barriers below, threatening worse.

https://slate.com/business/2019/06/new-orleans-mississippi-river-high-water-climate-change.html

 

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Steve Caparotta, Ph.D.

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@SteveWAFB
 38m38 minutes ago
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(6/) So what we know is that significant storm surge is possible on the MS River when it's relatively low (typical of the summer), but surge potential is unclear in its elevated state. A stage of ~16 feet now vs 2'-3' w/ previous storms means there is much more downhill momentum
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Steve Caparotta, Ph.D.

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@SteveWAFB
 37m37 minutes ago
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(7/) Earlier in the summer I asked several people if this scenario had been modeled and there wasn't a clear answer. There were some indications the Corps was looking into it a month or so ago, but if they did, that data has not been released to my knowledge.

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Could be another Anita like  development in 1983 if it stays over water  long enough.

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12z Euro bringing a somewhat slowly moving and strengthening Cat 1/2 hurricane ashore between Houston and Lake Charles early Saturday morning. Really hope this doesn't shift west into more populated areas in Houston as by this run, brings Houston tropical storm conditions. Slow movement dropping very heavy rain close to the coast and in the Lake Charles areas with slightly lesser amounts inland.

0c3a39c6ff4eac8f8fd0ae9105d1ba9b.png

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Could be another Anita like  development in 1983 if it stays over water  long enough.

I am sure you meant Alicia since you mentioned 1983. In bringing back both blasts from the past, I may as well touch briefly on both. Anita in 1977 formed out of your prototypical tropical wave à la W.Africa/MDR/ITCZ corridor. It just gained latitude and crossed S.FL due to an upper trough/cutoff over that SE CONUS. As the cutoff lifted out and a strengthening ridge took over, the disturbance/wave axis closed off under an extremely favorable upper ridge in the E-Central GOM. The TC rapidly intensified to a Category 5, but the building ridge protected Texas and drove Anita on a WSW track into Mexico. OTOH, though also notable for its rapid intensification, Alicia developed out of a similar scenario that we are seeing unfold with our current invest 92L: A continental airmass stationary boundary with an attached MCS/mid level vort. The problems any system like this faces is proximity to land and developmental time over water. The keys to watch unfold will be 1) how broad is the surface vort max upon cyclogenesis, 2) how low in latitude that vortex forms and, lastly, 3) how strong does the ridge build in behind the Great Lakes/New England upper trough. GFS ens camp has remained broader and closer to land and therefore weaker. ECMWF has been further south and faster to develop a more defined vortex at onset of TC genesis out over water. If Euro scenario infolds IRL, then that would increase chance to have an Alicia like cyclone, though still not expected. A blend of both ensembles based on the past few days, if unchanged, would probably meet the criteria for a TC with enough time over water and enough upper support to reach a strong tropical storm to Category 1 intensity. Though running out of time to intensify further to something similar to Alicia. This of course *IF* the surface vortex that forms is not too broad.
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RE: "NHC already releasing key messages".

Oddly, earlier today the NHC had a topline link on the main page that read: 'Key Message for potential Yucatan System' at around 1400hCDT. That link actually went to the 'GOM system' message, and then soon disappeared [don't know how long it appeared, at least 10-15 minutes].

So, is something brewing in down around the Yucatan that the NHC isn't quite sure enough about yet, or was that line just a mistyped glitch? Haven't seen any reference to a tropical wave or whatever near the Yucatan in the NHC 'tropical wx discussions'.

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9 minutes ago, STxVortex said:

RE: "NHC already releasing key messages".

Oddly, earlier today the NHC had a topline link on the main page that read: 'Key Message for potential Yucatan System' at around 1400hCDT. That link actually went to the 'GOM system' message, and then soon disappeared [don't know how long it appeared, at least 10-15 minutes].

So, is something brewing in down around the Yucatan that the NHC isn't quite sure enough about yet, or was that line just a mistyped glitch? Haven't seen any reference to a tropical wave or whatever near the Yucatan in the NHC 'tropical wx discussions'.

Definitely a mistyped glitch.

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1 hour ago, Windspeed said:

I am sure you meant Alicia since you mentioned 1983. In bringing back both blasts from the past, I may as well touch briefly on both. Anita in 1977 formed out of your prototypical tropical wave ala W.Africa/MDR/ITCZ corridor. It just gained latitude and crossed S.FL due to an upper trough/cutoff over that SE CONUS. As the cutoff lifted out and a strengthening ridge took over, the disturbance/wave axis closed off under an extremely favorable upper ridge in the E-Central GOM. The TC rapidly intensified to a Category 5, but the building ridge protected Texas and drove Anita on a WSW track into Mexico. OTOH, though also notable for its rapid intensification, Alicia developed out of a similar scenario that we are seeing unfold with our current invest 92L: A continental airmass stationary boundary with an attached MCS/mid level vort. The problems any system like this faces is proximity to land and developmental time over water. The keys to watch unfold will be 1) how broad is the surface vort max upon cyclogenesis, 2) how low in latitude that vortex forms and, lastly, 3) how strong does the ridge build in behind the Great Lakes/New England upper trough. GFS ens camp has remained broader and closer to land and therefore weaker. ECMWF has been further south and faster to develop a more defined vortex at onset of TC genesis out over water. If Euro scenario infolds IRL, then that would increase chance to have an Alicia like cyclone, though still not expected. A blend of both ensembles based on the past few days, if unchanged, would probably meet the criteria for a TC with enough time over water and enough upper support to reach a strong tropical storm to Category 1 intensity. Though running out of time to intensify further to something similar to Alicia. This of course *IF* the surface vortex that forms is not too broad.

Yea, i meant Alicia

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1 hour ago, MattPetrulli said:

Definitely a mistyped glitch.

For clarity, I should have mentioned that the 'Key Message' for the GOM system was also present with the one described above, which to me appeared to be more than just a mistyped glitch, and the Yucatan is ~1Kmi away [I checked both several times and they each went to the GOM message, at that time]. At any rate a curiosity, since one rarely sees errors on the NHC.

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Levi and @Windspeed summarize it wonderfully. There's still a great deal of uncertainty that remains, and it's underlined by the split between the GFS and Euro. We've seen time and again other models being forced to catch up to the Euro in the tropical forecasting, but every setup is different and with recent upgrades to both operational models this is the first higher stakes test during hurricane season. 

On one hand, we've seen how large and disorganized systems fail to take advantage of favorable environments. One only needs to look back at 91L. This scenario is certainly possible here if the mid and lower level vorts cannot align early on.

However, the biggest factor for significant intensification of a tropical system is the organization of the inner core. If you're able to get that, it becomes a lot easier for intensification to take place and for it to last longer. The Euro very clearly shows what can happen if there's a faster organization of the center. 

Both the 500mb and 850mb vorts are pushing toward the coast. This is where the battle will be won. Watch for the strength and alignment of the two and the firing convection for hints of what direction things are going. 

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GFS with a pretty significant shift toward the Euro tonight with regard to intensity. 92L gets a good bit more vertically stacked and as a result you have a 993mb low heading toward the TX/LA border before a TX landfall. Interestingly, the low weakens after peaking in intensity at 108, but again, quite a shift with how quickly it organizes.

Another thing that’s new is the rainfall. Big jump in accumulated precip as the low meanders in Texas. LA bears the brunt of the precip bullseye. 

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GFS with a pretty significant shift toward the Euro tonight with regard to intensity. 92L gets a good bit more vertically stacked and as a result you have a 993mb low heading toward the TX/LA border before a TX landfall. Interestingly, the low weakens after peaking in intensity at 108, but again, quite a shift with how quickly it organizes. Another thing that’s new is the rainfall. Big jump in accumulated precip as the low meanders in Texas. LA bears the brunt of the precip bullseye.
Higher CAPE values and strong low-level convergence off the Gulf into a NW tracking surface low. All the GFS op needed was a stronger surface vortex further off the coast versus the very weak disturbance that had been prevalent in previous runs. Regardless of eventual landfall intensity there would be significant impacts to already stressed tributaries that [mention=142]janetjanet998[/mention] alluded to earlier.
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00z UKIE scoots along the S LA coast from hours 72 (near New Orleans) to 96 (south of Lake Charles, LA) before finally going all the way inland into W LA at 120... and then slowly moves north into S AR at 144.  This would be a nightmare flooding-wise across the region (SE TX/LA/AR)

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Tropical Weather Outlook
NWS National Hurricane Center Miami FL
200 AM EDT Tue Jul 9 2019

For the North Atlantic...Caribbean Sea and the Gulf of Mexico:

A trough of low pressure located over southwestern Georgia is
producing disorganized showers.  This disturbance is expected to
move southward or southwestward during the next day or so, and a
broad area of low pressure is forecast to form over the northeastern
Gulf of Mexico on Wednesday.  Once the disturbance is over water,
environmental conditions are expected to be conducive for
development and a tropical depression is likely to form by the end
of the week while the system moves westward across the northern Gulf
of Mexico.  Regardless of whether or not a tropical cyclone
develops, this system has the potential to produce heavy rainfall
along portions of the northern and eastern U.S. Gulf Coast later
this week.  For more information about the rainfall threat, please
see products issued by your local weather forecast office and the
NOAA Weather Prediction Center. Interests along the Gulf Coast from
the Upper Texas coast to the western Florida peninsula should
monitor the progress of this system.
* Formation chance through 48 hours...medium...40 percent.
* Formation chance through 5 days...high...80 percent.

$$
Forecaster Cangialosi

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Up to 50% 48hrs on the NHC 7:00 am CDT update.

I'm not the best at reading models so can someone tell me what happened on the 6Z GFS?

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17 minutes ago, NavarreDon said:

Up to 50% 48hrs on the NHC 7:00 am CDT update.

I'm not the best at reading models so can someone tell me what happened on the 6Z GFS?

Just like some of the other GFS runs, it stays strung out and disorganized. 92L isn’t able to take advantage of a favorable environment. It has been inconsistent and at this point, it looks out of step with the other guidance which developed 92L more during the 0z suite of runs.

Solution can’t be tossed, but I think it’s an outlier right now. We’re going to learn a lot today, I think, as the 500 and 850mb areas of vorticity push offshore.

I’ll be watching the convective trends today. Does that convention organize a bit? Does it push further south? Does the convention remain intense? Things I hope to get answers to today.

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Levi Cowan @TropicalTidbits

 
 
 
 

Surface obs this morning indicate a surface trough extension along the Florida panhandle. This is a feature the GFS picked up on but the ECMWF missed. Watching today for whether this feature or something closer to Tampa becomes dominant - a very important detail for 92L's future

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Quite the step from the 12z guidance for sure...definitely heading in more of an alarming direction...especially for LA. 12z GFS spitting out as much as 20"+ in some areas and given the synoptic look that isn't unreasonable. The posts in here regarding the river levels make this situation even more eye opening. Not only does there seem to be a push towards a stronger storm, but there seems to be fairly decent agreement in track...even with this though a slight adjustment will have big ramifications. 

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