ATL: DELTA - Post-Tropical - Discussion

[ElectricStorm]

If I'm not mistaken, the Western Yucatan is pretty flat, combine that with the fact that the storm's moving a pretty quick pace, I don't think the Yucatan is going to affect it that much. The core will likely be larger so it's not like it will be another pinhole where it can collapse easily. Also, I take back what I said earlier about this weakening like Patricia, I don't think it weakened as much as we thought it did and it could easily get back up or maybe even stronger than it was before. It's still officially a cat 4

[edu2703]

Now that the tiny 4nm wide eye has collapsed and gone. It should be able to reconstruct with a larger stable eyewall from now on.

The question is: Will Delta have enough time to build a solid eyewall before landfall or will only happen when it enters the Gulf.

[NDG]

Delta has definitely has weakened this evening, based on the second pass so far.

[GCANE]

Speachless.
Many times I see gravity waves in the cirrus but never a mesoscale shockwave like this.
Insane!!!!

[edu2703]

Recon pick up only 63 kts SFMR winds on the NE quadrant. Not even hurricane intensity.

[MGC]

Shear working its magic on Delta.....lets hope the inner core can't recover.....MGC

[wx98]

Oof, that pass supports an 80-85 mph Cat 1. Pressure rising a little more.

[SconnieCane]

Shear working its magic on Delta.....lets hope the inner core can't recover.....MGC

Why does shear always show up when it's not supposed to (per the models within the last 24 hours) and isn't there when it was forecast to be? I bet you there's a lot less shear as Delta approaches the US Gulf Coast than was forecast as of yesterday (although SSTs will still put a cap on intensity at that point).

[edu2703]

It seems that Delta weakened as fast as it strengthened and it all happened on the same day.

[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 to 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.

[EquusStorm]

[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.

[AJC3]

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.

[aspen]

Recon pick up only 63 kts SFMR winds on the NE quadrant. Not even hurricane intensity.

Usually, the NE quadrant is the strongest, but for Delta it has been the NW quadrant.

[GCANE]

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.

[ConvergenceZone]

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....

[bella_may]

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

[GCANE]

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

Good point

[Hammy]

Oof, that pass supports an 80-85 mph Cat 1. Pressure rising a little more.

NOAA tends to under measure the winds, though I'm not sure why this is.

[Kazmit]

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