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Major Hurricane Delta

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17 minutes ago, Moderately Unstable said:

As we have already seen, with this storm directly in fact, what happens tonight has very little to do with what happens in 2 days. The nhc weakens the storm near landfall for sound meteorological reasons: the water is cold near the coast, shear increases near the coast, and perhaps dry air tries to entrain the circulation near the coast. If ALL THREE of those things hit at maximal extent, it doesn't take a PhD to recognize significant weakening would occur. Storms can rapidly intensify, AND as we saw, rapidly weaken. Ergo, don't fall into the forecasting trap of seeing something happening now and assume that it must be true later too! *If the storm is stronger at landfall, it will be due to a high rate of forward speed and having limited time for these objectively bad for the storm things to impact it*. Cold water weakens hurricanes. So does shear. So does dry air. *There is no physical mechanism near the coast that is expected to be favorable for hurricane maintenance and strength*. The degree of unfavorability and landfall intensity will come down to shear and any dry air entrainment. We know the water is marginal. If no shear or light shear is present, it will exceed the forecast intensity at landfall. If shear is moderate, or the inner circulation entrains dry air, the storm will weaken about to the degree the nhc is noting.

Yesterday, we had warm ssts and modest shear and bam, cat 4 drops to cat 2 on a dime. That was in a supposedly pristine environment. Right now we are continuing to see steady strengthening. That's what we can say objectively. Not how that affects landfall. If the storm were 12 hours from landfall and strengthening, different story.

 

MU/CD

well the shear weakened the storm considerably so the environment was not pristine..

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15 minutes ago, Moderately Unstable said:

As we have already seen, with this storm directly in fact, what happens tonight has very little to do with what happens in 2 days. The nhc weakens the storm near landfall for sound meteorological reasons: the water is cold near the coast, shear increases near the coast, and perhaps dry air tries to entrain the circulation near the coast. If ALL THREE of those things hit at maximal extent, it doesn't take a PhD to recognize significant weakening would occur. Storms can rapidly intensify, AND as we saw, rapidly weaken. Ergo, don't fall into the forecasting trap of seeing something happening now and assume that it must be true later too! *If the storm is stronger at landfall, it will be due to a high rate of forward speed and having limited time for these objectively bad for the storm things to impact it*. Cold water weakens hurricanes. So does shear. So does dry air. *There is no physical mechanism near the coast that is expected to be favorable for hurricane maintenance and strength*. The degree of unfavorability and landfall intensity will come down to shear and any dry air entrainment. We know the water is marginal. If no shear or light shear is present, it will exceed the forecast intensity at landfall. If shear is moderate, or the inner circulation entrains dry air, the storm will weaken about to the degree the nhc is noting.

Yesterday, we had warm ssts and modest shear and bam, cat 4 drops to cat 2 on a dime. That was in a supposedly pristine environment. Right now we are continuing to see steady strengthening. That's what we can say objectively. Not how that affects landfall. If the storm were 12 hours from landfall and strengthening, different story.

 

MU/CD

I have a degree in meteorology. I understand man. I'm talking about it getting stronger the next day or so in the more favorable conditions. If you end up with a stronger storm in the short term, you will likely have it landfall stronger. Yes it has plenty working against it as it nears landfall but a well formed core of a strong hurricane just won't instantly degrade. Yes there will be weakening but with a larger circulation developing as were already seeing. That won't break down as fast as Delta did prior to landfall in Yucatan when the circulation was much smaller. It all depends on what happens while the environment is ripe for intensification 

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6 minutes ago, StormchaserChuck! said:

ERC.

I don’t think it’s an ERC since the eyewall never really has been stable yet. I think it’s more due to the fact that there isn’t a super strong eyewall so the wind max isn’t as concentrated.

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9 minutes ago, StormChaser4Life said:

I have a degree in meteorology. I understand man. I'm talking about it getting stronger the next day or so in the more favorable conditions. If you end up with a stronger storm in the short term, you will likely have it landfall stronger. Yes it has plenty working against it as it nears landfall but a well formed core of a strong hurricane just won't instantly degrade. Yes there will be weakening but with a larger circulation developing as were already seeing. That won't break down as fast as Delta did prior to landfall in Yucatan when the circulation was much smaller. It all depends on what happens while the environment is ripe for intensification 

I do as well. I agree with your principle--you are right, all things equal, you have a stronger initial intensity, your final intensity for a given time B is higher. But all things are not equal. We had a well formed core of a strong hurricane wilt away under moderate shear when a quasi linear convective band dessicrated the pinhole eye. Working in favor of slower lowering of intensity is a projected increase in the diameter of the eye, and larger size of the storm, which should lend a degree of stability and buffer it against some of these deleterious things. I don't disagree with your supposition that the storm gets stronger in the next 24-36 hours. Everyone agrees there. This is more a question of, let's say we have a 130mph cat 4 (being very generous here)...that is still going to weaken substantially in the 8 hours it has to traverse the suboptimal conditions. 100-110 landfall is reasonable with a 130 mph storm, and again that would be stronger than it is projected to get. We have so many analogues and examples to go off of to further that point. It isn't like the conditions are going to deteriorate with 3 hours to go before landfall. We are talking 6-12 hours. That's a lot of time for change for a hurricane. 

12 minutes ago, nycwinter said:

well the shear weakened the storm considerably so the environment was not pristine..

You're right. I should have said forecasted to be pristine. But, that is somewhat the point I was getting at. Gangbusters ssts and moist air but some shear and goodbye organized eye. 

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Pressure has risen from 974mb -976mb in the last 2 hrs. 

Don't know what's going on, but it's not strengthening.

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5 minutes ago, Moderately Unstable said:

I do as well. I agree with your principle--you are right, all things equal, you have a stronger initial intensity, your final intensity for a given time B is higher. But all things are not equal. We had a well formed core of a strong hurricane wilt away under moderate shear when a quasi linear convective band dessicrated the pinhole eye. Working in favor of slower lowering of intensity is a projected increase in the diameter of the eye, and larger size of the storm, which should lend a degree of stability and buffer it against some of these deleterious things. I don't disagree with your supposition that the storm gets stronger in the next 24-36 hours. Everyone agrees there. This is more a question of, let's say we have a 130mph cat 4 (being very generous here)...that is still going to weaken substantially in the 8 hours it has to traverse the suboptimal conditions. 100-110 landfall is reasonable with a 130 mph storm, and again that would be stronger than it is projected to get. We have so many analogues and examples to go off of to further that point. It isn't like the conditions are going to deteriorate with 3 hours to go before landfall. We are talking 6-12 hours. That's a lot of time for change for a hurricane. 

You're right. I should have said forecasted to be pristine. But, that is somewhat the point I was getting at. Gangbusters ssts and moist air but some shear and goodbye organized eye. 

Not saying you're wrong because that's a distinct and likely possibility. All comes down to what it does tomorrow. Just was saying it's a possibility, what I said. Very odd hurricane. It has maintained very impressive convection but has lacked to really get a strong defined core likely because of the shear. 

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11 minutes ago, Amped said:

Pressure has risen from 974mb -976mb in the last 2 hrs. 

Don't know what's going on, but it's not strengthening.

It is. It's just not RIing, which seems to be a trend on this thread (either the storm must ri or weaken). The windspeeds on the last pass through the eyewall are up a touch again. What you're seeing there with the 2 mb differences does not actually play a major role in terms of estimating minimum pressure. 2mb can be because your dropsonde (or plane) didn't perfectly hit the exact center of the storm. The trend overall with the pressures is they're approximately holding steady with winds perhaps up 5 knots. We've seen storms increase wind speeds before without dropping pressure. It isn't currently strengthening but it isn't weakening either. Typical non RI hurricane intensification can go like that. You inch up, then steady, then up more, then steady. Less rocket, more stairs. 

Edit: 2mb is statistically bordering on non significant, but 10 mb would be. Hence, if you see a big swing, assuming it gets duplicated, that's real. 

MU

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20 minutes ago, the ghost of leroy said:

lol is the raw adt still 7.3 yall?

Actually mister ghost, and supreme sock puppet overlord, it's now a whopping 9.9! Whew man, batten down the hatches mates we're all doomed ahhhhhhh *runs in a circle while entire computer terminal burns in the background*!!!!!!!!! 200 mph winds incoming! Also in advance Happy Halloween! I'm sure you must be thrilled as we approach the peak time of year to scare children! 

This is fun!

Edit: this is sarcasm. 

MU

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Moderately Unstable, you are superb in your contributions to this board with very reasoned explanations.  I had an earth science degree with a smattering of met courses decades ago and am deeply appreciative for your input here.  Keep up the good work.  From what happened to Delta yesterday I think we're into nowcasting.

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Delta's southern outflow arm is streaming into the Pacific Gulf of Tehuantepec [as if pulled]; using the NHC/NESDIS GOES16 Geocolor image, which is too big to insert here [tried various ways?].

The northern outflow doesn't seem as defined or vigorous, may account for the slower development?

Delta has also been making a more westerly course than progged, this worries me here in Coastal Bend Texas; the extra westering may scootch the ultimate track over too far for us.

Do I need to give the boat the full 'batten down' in the slip, schedule a haulout? Decisions decisions ...

 

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I thought Delta would look better by now.  Earlier this evening, it appeared it was about to enter a phase in which convection would start pinwheeling around the center, but it has not happened.  It has gone back to the firehose look, with only one point of initiation on the west side.  The last recon found the pressure still stuck in the 970s and the surface wind (SFMR) at only 70 kt.

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BULLETIN
Hurricane Delta Advisory Number  15
NWS National Hurricane Center Miami FL       AL262020
400 AM CDT Thu Oct 08 2020

...DELTA MOVING NORTHWESTWARD OVER THE GULF OF MEXICO...
...HURRICANE CONDITIONS AND LIFE-THREATENING STORM SURGE EXPECTED
TO BEGIN ALONG PORTIONS OF THE NORTHERN GULF COAST ON FRIDAY...


SUMMARY OF 400 AM CDT...0900 UTC...INFORMATION
----------------------------------------------
LOCATION...23.4N 91.8W
ABOUT 450 MI...725 KM SSE OF CAMERON LOUISIANA
MAXIMUM SUSTAINED WINDS...100 MPH...155 KM/H
PRESENT MOVEMENT...NW OR 305 DEGREES AT 15 MPH...24 KM/H
MINIMUM CENTRAL PRESSURE...973 MB...28.74 INCHES

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Hurricane Delta Discussion Number  15
NWS National Hurricane Center Miami FL       AL262020
400 AM CDT Thu Oct 08 2020

Satellite images indicate that Delta remains a well organized
hurricane with a central dense overcast feature and curved bands
beyond that.  There is still no indication of an eye, however, in
geostationary satellite images. The Air Force Hurricane Hunters
were in Delta a few hours ago and toward the end of that mission,
they reported maximum flight-level winds of 102 kt and SFMR winds of
77 kt.  Based on a blend of this data, the initial intensity was
increased to 85 kt at 0600 UTC.  Since the cyclone appears to be
generally steady in strength since that time, the wind speed is held
at that value.  Both the NOAA and Air Force Hurricane Hunters will
be investigating Delta later today, and that data will help us
assess its strength and structure.

The track forecast reasoning is unchanged.  Delta is currently 
moving northwestward at 13 kt on the southwestern periphery of an 
Atlantic subtropical ridge.  The western portion of the ridge is 
expected to weaken later today as a trough moves eastward across 
the south-central United States. This change in the steering 
pattern should cause Delta to turn northward by late tonight and 
north-northeastward by Friday night.  This motion should take the 
core of the hurricane to the Louisiana coast in a little more than 
36 hours (sometime Friday afternoon or evening).  After landfall, a 
turn to the northeast is forecast as a larger trough approaches 
Delta from the west. The models are in very good agreement, and the 
NHC track forecast is just an update of the previous one.

Delta is expected to continue gradually strengthening during the 
next 24 hours while it remains over warm deep waters and in an 
environment of low wind shear and a high amount of moisture.  Based 
on these favorable environmental conditions and the trend in the 
models, Delta is forecast to regain major hurricane status by 
tonight.  Just prior to making landfall, the cyclone is forecast to 
level off in strength or weaken slightly as it moves over the cooler 
shelf waters and into somewhat less favorable atmospheric 
conditions.  Rapid weakening is forecast after Delta moves inland.  
The intensity models are in fairly good agreement, and the NHC 
intensity forecast lies near the middle of the guidance envelope. It 
should be noted that the NHC 1-2 day intensity forecasts are subject 
to errors of around 1 Saffir-Simpson category.

The aircraft and fairly recent scatterometer data indicate that
Delta is gradually growing in size. This trend is expected to
continue as Delta approaches the Louisiana coast. The NHC wind
radii forecast follows a consensus of the global and hurricane
regional models.

Key Messages:

1. Delta is expected to grow in size as it approaches the northern
Gulf Coast, where life-threatening storm surge and dangerous
hurricane-force winds are likely beginning Friday, particularly for
portions of the Louisiana coast.  Storm Surge and Hurricane Warnings
are in effect, and residents in these areas should follow advice
given by local officials and rush preparedness actions to
completion.

2. Significant flash, urban, small stream and minor to isolated 
moderate river flooding is likely Friday and Saturday from portions 
of the central Gulf Coast into portions of the Lower Mississippi 
Valley. As Delta moves farther inland, heavy rainfall is expected in 
the Ohio Valley and Mid-Atlantic this weekend. 


FORECAST POSITIONS AND MAX WINDS

INIT  08/0900Z 23.4N  91.8W   85 KT 100 MPH
 12H  08/1800Z 24.6N  93.0W   95 KT 110 MPH
 24H  09/0600Z 26.4N  93.7W  100 KT 115 MPH
 36H  09/1800Z 28.8N  93.4W   90 KT 105 MPH
 48H  10/0600Z 31.3N  92.4W   55 KT  65 MPH...INLAND
 60H  10/1800Z 33.3N  90.9W   30 KT  35 MPH...INLAND
 72H  11/0600Z 34.6N  89.0W   20 KT  25 MPH...POST-TROP/REMNT LOW
 96H  12/0600Z...DISSIPATED

$$
Forecaster Cangialosi

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5 hours ago, STxVortex said:

 

Delta's southern outflow arm is streaming into the Pacific Gulf of Tehuantepec [as if pulled]; using the NHC/NESDIS GOES16 Geocolor image, which is too big to insert here [tried various ways?].

The northern outflow doesn't seem as defined or vigorous, may account for the slower development?

Delta has also been making a more westerly course than progged, this worries me here in Coastal Bend Texas; the extra westering may scootch the ultimate track over too far for us.

Do I need to give the boat the full 'batten down' in the slip, schedule a haulout? Decisions decisions ...

 

Made a screen shot of Delta's tail. Wishing you luck in dealing with this storm. 1154454489_Delta1.png.74b5ab0a31ef7e36987ed519b1755d09.png

 

 

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Delta has about 24 hours left to strengthen. Current storm structure with expanding wind field does make RI likely IMHO. Will likely be a weakening Cat 2 on landfall which should limit the potential for major structural damage. Also, some of the surge will be areas affected by Laura, so a saving grace there is some of the more vulnerable structures are already gone. 

That being said, the large wind field will still bring significant impacts. Also, still plenty of debris around the Lake Charles area, with many tarps on roofs. 

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8 hours ago, Moderately Unstable said:

It is. It's just not RIing, which seems to be a trend on this thread (either the storm must ri or weaken). The windspeeds on the last pass through the eyewall are up a touch again. What you're seeing there with the 2 mb differences does not actually play a major role in terms of estimating minimum pressure. 2mb can be because your dropsonde (or plane) didn't perfectly hit the exact center of the storm. The trend overall with the pressures is they're approximately holding steady with winds perhaps up 5 knots. We've seen storms increase wind speeds before without dropping pressure. It isn't currently strengthening but it isn't weakening either. Typical non RI hurricane intensification can go like that. You inch up, then steady, then up more, then steady. Less rocket, more stairs. 

Edit: 2mb is statistically bordering on non significant, but 10 mb would be. Hence, if you see a big swing, assuming it gets duplicated, that's real. 

MU

Where's CD?

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Haven't posted much in this thread, but have been saying all along that folks expecting a big second peak intensity in the GOM may be disappointed. Betting on something as extreme as a cat 4 for a system that has been structurally unstable and quickly expanding in size, during a season with an observed propensity to limit intensity as least excuse imaginable seemed like a risky proposition to me. That said, no issue at all with a very destructive surge potential due to the expanding size.

DELTA will likely intensify at a fairly methodical pace to a secondary peak of high cat 2/low cat 3, before striking the coast as either a low end cat 2 or even high end cat 1.

Regardless, wind will not be the main story, unlike Laura.

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14 minutes ago, 40/70 Benchmark said:

Haven't posted much in this thread, but have been saying all along that folks expecting a big second peak intensity in the GOM may be disappointed. Betting on something as extreme as a cat 4 for a system that has been structurally unstable and expanding in size quickly, during a season with an observed propensity to limit intensity as least excuse imaginable seemed like a risky proposition to me. That said, no issue at all with a very destructive surge potential due to the expanding size.

Almost none of the 12z intensity guidance makes it a major again. Pressure may drop some before it weakens a bit before landfall, but storm is expanding in size so you will still have a significant surge impacts as you said plus broad area of wind impacts. On radar this will almost certainly have the "half cane" look often associated with north Gulf landfalls. Models have been shown dry air eroding the south side prior to landfall.

Btw, for radars we will have to rely on Houston long range and then Fort Polk as LCH radar is still out. 

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Best upper tropospheric support to get the most out of the heat content will be this afternoon. That is when I expect significant intensification to begin. Modeling also suggests this, though the magnitude of the 6z ECMWF was a little surprising. I don't expect that degree of RI. But I do think Delta will make a run at Cat 4 even if it may max out as an upper Cat 3. It's going to be a large hurricane regardless.

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RE: 6z ECMWF; I think it is overdoing it little but it is worth picking up on why. Delta has yet to pass through the best upper divergence and lowest shear it will have in its existence. That begins this afternoon and continues to just before landfall when SSW mid-level flow begins infringing on the core with dry air. That and cooler SSTs should have it weakening significantly into landfall. Whether it is a Cat 3 or a 2 at landfall is a bit trivial as weakening storms do not always mix down winds as effectively as strengthening storms at the same category. The big story will still be the surge Delta builds up this evening and pushes into the coast with a larger circulation.

 

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