ATL: DELTA - Post-Tropical - Discussion

[Keldeo1997]

I think that it will weaken to cat 2, but then get back up to a cat 3 in the southern gulf and then come ashore as a cat 1. We are seeing how easily shear disrupts this system. That tells me that when it gets close to the Gulf shore that the forecasted increased shear will do a number on Delta, and may weaken it down to Cat 1 before it comes ashore....

 https://twitter.com/DerekOrtt/status/1313623255161466881




Derek thinks they will be less shear in the Northern gulf then expected due to the ULAC being further NW then expected.

[GCANE]

Big off-scale IR flashes again.

[wx98]

Hasn't the pressure dropped since the last pass though?

Extrapolated pressure was slightly higher. Haven't seen the drop from the second pass yet.

EDIT: The drop was 963 mbar, up from 961 on the first pass.

[GCANE]

VDM just in. 963mb
Again, no mention of an eye.
The whole thing collapsed.
Its starting all over again with a massive hot tower firing.
See how it looks in the morning.
Good night all.

[3090]

Weaker hurricane ATM could be why it is gaining more latitude? IDK.

[CyclonicFury]

I'm interested to see what kind of structure Delta has after interacting with the Yucatan. Just 6-7 hours ago we were talking about the possibility of a Category 5 landfall near Cancun and it may be a Category 2 instead, fortunately for the Yucatan. I wouldn't be surprised if Delta gets as weak as a Category 1 briefly.

[Steve]

Not only that but the fact that the shear is hitting from the east and it’s moving wnw, it’s not going to destroy or shear off the mid levels. Shear is 30mph out the East, and forward speed this afternoon was 17mph. It’s WNW so maybe effects of slightly more than the 13 point difference. I don’t know physics but that’s fairly obvious.

I have to correct you on this. Shear is shear - it's a vector difference between winds at two different levels [V(upper) - V(lower)], subtracted as a vector, rather than a scalar (number). Typically the V(upper) is either 200mb or 250mb. 500mb is generally used to calculate mid level shear - V(mid) if you wish - however, you can pick any level you want to calculate a shear value.

For instance, if calculated shear is ESE at 30 knots, that doesn't mean that there is 30 knots of ESE upper level wind that can somehow be negated by 15 knots (or x amount) of forward motion toward the WNW. The lower level wind vector used in the shear computation has already been taken into account. Typically, the level for V(lower) 850MB. Assuming that V(lower) is a good proxy for the storm's forward motion (which is an assumption, not necessarily the case), then you can't subtract the forward motion from the shear value - in essence, you would be doing so twice.

The same thing goes for a storm moving directly opposite the shear. If a storm is moving westward at 20 knots and the 200mb wind is calm, that's still 20kt of upper tropospheric shear, relative to the storm. It's important to re-emphasize that shear calculations are only as good as the vector values that go into them, so if either one is off, then the calculated shear will be erroneous as well. I hope this helps you understand the math of shear calculations a bit.

Thanks on that. But we usually see harsher weakening effects when the shear is coming at a sharper angle unless that’s just anecdotal from watching storms come up in the Gulf. We just saw the effects from the other direction on Gamma. I do get the different levels as we see that in the winter sometimes here in the clouds. So is it that the direction of the shear doesn’t matter at all?

[Blinhart]

I just know all the experts were expecting the pinhole eye to fall apart, and have a larger eye form, so this event is happening as expected, albeit a lot earlier than they expected, so it has more time to gain strength, and we have all seen storms get better organized over the Yucatan before, so do not think that this thing won't explode again. Everyone was expecting this to happen.

[TheStormExpert]

Delta is struggling, why am I not surprised!?

[texsn95]

Radar half hour ago.
Not even sure there is an eye any more.
Started with that lead hot tower crashing into the eyewall this afternoon.
This may have gone all the way back to square one.
Big ass 70 mm/hr rain rate hot tower having to rebuild the whole core.
Pinhole madness.
Watching if the VDM confirms.

https://i.imgur.com/grzuUDu.png

Good chance this alters the track

In which direction?

[Aric Dunn]

Remnants of Gammas Circ and vorticity defintely imparting some influence of Delta. possible interms of some low level tugging/shear add that too the easterly mid level shear is giving what we see.

Gamma also appears to still have enough vorticity to impart some more track changes. either in forward motion or unforseen shifts in movement.

[Blinhart]

I don't think it has weakened as much as you guys think, RECON can't measure every single inch of the storm, there isn't a constant wind speed, it fluctuates second to second, foot by foot, the dropsonde could of missed the 140 mph wind by say 500 feet, they would have dropsondes that can measure every foot to get a completely accurate reading. That is why forecasters go by not just dropsondes, but radar, satellite, and many other things that we don't see.

It’s not a Category 4 by any stretch currently. And wind isn’t going to gain 50 mph a half mile away from where Cat 1 winds were recorded. I believe Cat 2 is plausible for current intensity, but not a 145 mph Cat 4.

I didn't say it was a cat 4 right now, but yes I think they can miss stronger winds a half mile away. I'll put it this way I have had it where it is pouring down rain in my back yard and in the front yard it is sunny and dry, so yes there can extreme differences in a short distance.

[Blinhart]

My prediction at this next advisory is that they will go with either 110 or 115 MPH with a prediction of either a Cat 3 or 4 making landfall near Cancun.

[wx98]

I don't think it has weakened as much as you guys think, RECON can't measure every single inch of the storm, there isn't a constant wind speed, it fluctuates second to second, foot by foot, the dropsonde could of missed the 140 mph wind by say 500 feet, they would have dropsondes that can measure every foot to get a completely accurate reading. That is why forecasters go by not just dropsondes, but radar, satellite, and many other things that we don't see.

It’s not a Category 4 by any stretch currently. And wind isn’t going to gain 50 mph a half mile away from where Cat 1 winds were recorded. I believe Cat 2 is plausible for current intensity, but not a 145 mph Cat 4.

I didn't say it was a cat 4 right now, but yes I think they can miss stronger winds a half mile away. I'll put it this way I have had it where it is pouring down rain in my back yard and in the front yard it is sunny and dry, so yes there can extreme differences in a short distance.

A hurricane is a little different than a summertime thunderstorm. But I'm not going to argue.

[ElectricStorm]

I don't think it has weakened as much as you guys think, RECON can't measure every single inch of the storm, there isn't a constant wind speed, it fluctuates second to second, foot by foot, the dropsonde could of missed the 140 mph wind by say 500 feet, they would have dropsondes that can measure every foot to get a completely accurate reading. That is why forecasters go by not just dropsondes, but radar, satellite, and many other things that we don't see.

It’s not a Category 4 by any stretch currently. And wind isn’t going to gain 50 mph a half mile away from where Cat 1 winds were recorded. I believe Cat 2 is plausible for current intensity, but not a 145 mph Cat 4.

I didn't say it was a cat 4 right now, but yes I think they can miss stronger winds a half mile away. I'll put it this way I have had it where it is pouring down rain in my back yard and in the front yard it is sunny and dry, so yes there can extreme differences in a short distance.

I certainly don't think it's a cat 4 right now but I do think it will get back to cat 4, probably once it gets into the gulf

[Blow_Hard]

Radar half hour ago.
Not even sure there is an eye any more.
Started with that lead hot tower crashing into the eyewall this afternoon.
This may have gone all the way back to square one.
Big ass 70 mm/hr rain rate hot tower having to rebuild the whole core.
Pinhole madness.
Watching if the VDM confirms.

https://i.imgur.com/grzuUDu.png

Good chance this alters the track

In which direction?

I'm no Met but my guess would be we could see yet more west shifts to the track.

[ScottNAtlanta]

Looks like Delta was midway through an ERC when it got disrupted . An intense band had wrapped around the southern end right before it got disrupted. That band is building back now. That's the thing with pin hole eyes...they can get really strong but are just as easily disrupted.

[Javlin]

Remnants of Gammas Circ and vorticity defintely imparting some influence of Delta. possible interms of some low level tugging/shear add that too the easterly mid level shear is giving what we see.

Gamma also appears to still have enough vorticity to impart some more track changes. either in forward motion or unforseen shifts in movement.

My first thoughts was a short burst N which we saw on the 5PM but it's been a hair N of W since then which it still looks like a jolt NW could still be at play?odd parameters with this one.

[Aric Dunn]

Remnants of Gammas Circ and vorticity defintely imparting some influence of Delta. possible interms of some low level tugging/shear add that too the easterly mid level shear is giving what we see.

Gamma also appears to still have enough vorticity to impart some more track changes. either in forward motion or unforseen shifts in movement.

My first thoughts was a short burst N which we saw on the 5PM but it's been a hair N of W since then which it still looks like a jolt NW could still be at play?odd parameters with this one.

yeah we could very well see a sudden NNW motion for a brief time.

[ScottNAtlanta]

Here is the last 24 hours...you can see the collapse and it trying to build back