ATL: DELTA - Post-Tropical - Discussion

[tiger_deF]

Going to make a bold prediction and say that I think it will surpass it's previous peak in terms of maximum intensity and get near category 5 status. Those in the forecast cone feel free to totally disregard this prediction, but multiple times this season the moment people here start writing off the storm, ESPECIALLY in the Gulf, the storm always surprises. Only thing standing in the way of Delta is structural mechanics and cooler SST's, shear is looking to be very low, TPW is potent, upper level dynamics look ideal to grow and ventilate the storm effectively, and for goodness sakes it's 2020.

[ColdMiser123]

I'm sorry, but where do you see shear??? No one is mentioning any shear anywhere. Everyone is saying the shear is suppose to be almost nothing until right when it starts turning N/NNE, and then they don't know if the upper air wind might actually help it vent and gain some strength.

Mid level shear will be <10 kt for the next 24-30 hours, and only increases to >15 kt a few hours before landfall. Not too much preventing this from intensifying currently, and how strong it gets now will be key for how strong it remains with landfall Friday afternoon-evening.

Well we better hope that shear and mid-level shear increases before landfall as SW Louisiana doesn’t need yet another major hurricane threat just over a month after the last!

I'm not convinced that this level of mid-level shear alone would be enough to significantly disrupt a storm like this before landfall, given that the shear is ramping up right before landfall. Mid-level shear increased to around 20 kt just before landfall with Laura, and there was little change from peak intensity just before landfall.

However, the main difference here is the cooler sea surface temperatures. That should almost certainly lead to some kind of weakening. The big question is how much weakening, and that will depend on how quickly Delta is moving across the cooler water just offshore.

A stronger vortex will also tend to be more resistant to stronger upper level shear relative to a more shallow vortex, so exact intensity matters here as well.

[edu2703]

The last thing Lake Charles need right now is a hurricane. Even a weak Cat 1 would cause many problems for people still recovering from Laura.

 https://twitter.com/doceotors/status/1313945130240442370

[EquusStorm]

Starting to look pretty classic, just waiting on the core to fully recover. Much more stacked with the upper level anticyclone today

[Stormgodess]

I'm sorry, but where do you see shear??? No one is mentioning any shear anywhere. Everyone is saying the shear is suppose to be almost nothing until right when it starts turning N/NNE, and then they don't know if the upper air wind might actually help it vent and gain some strength.

Mid level shear will be <10 kt for the next 24-30 hours, and only increases to >15 kt a few hours before landfall. Not too much preventing this from intensifying currently, and how strong it gets now will be key for how strong it remains with landfall Friday afternoon-evening.

Agreed, and please do not downplay this one people. A storm of this size at category 2 is going to produce a large storm surge. Plus, it is hitting an already devastated area of LA/TX.

Our local Meteorologist made some interesting points about the Winds that Baton Rouge could face under the current forecast. Exceeding what they faced for Katrina, Rita, Isaac... And there was damage then... And comparing it to Andrew when there was significant damage.

Its about 28 mins into this video. The rest of the video also has some great wind speed models.

https://www.facebook.com/stevecaparotta ... 7859882532

[FixySLN]

I'm of the mind the track changes. A gradual shift west isn't 2020 enough. Isn't it also a fairly strange track for a system entering the gulf in October? I don't doubt the guidance of the NHC...it's what they do. It's just been a very strange year and the Gulf has had it's own agenda since June. Waiting for Delta to slow down, see something it likes...I dunno. Doesn't feel right.

I'm no met...don't chase me with pitchforks. Listen to your local government and the NHC. I'm just expressing an opinion.

[psyclone]

This forum (and the weather world in general) would be far better off focusing a tad less on peak wind intensity/category and much better to focus on wind radii. Size matters enormously for sea sloshing and that is even more important in an enclosed sea basin like the gulf which is loaded with corners and shallow shelves...all of which lend themselves to surge enhancement. Water sloshes most efficiently in the corners of the bathtub. In my amateur opinion that is the "field of play" to focus on rather than the saffir simpson scale "scoreboard" which is not of as much value. Delta's windfield is likely to increase somewhat as it approaches the northern gulf. even if peak intensity decreases or fails to meet expectations...surge potential may not decrease...or paradoxically, it may actually increase somewhat if we exchange somewhat lower max intensity for a larger windfield.

[psyclone]

I'm of the mind the track changes. A gradual shift west isn't 2020 enough. Isn't it also a fairly strange track for a system entering the gulf in October? I don't doubt the guidance of the NHC...it's what they do. It's just been a very strange year and the Gulf has had it's own agenda since June. Waiting for Delta to slow down, see something it likes...I dunno. Doesn't feel right.

I'm no met...don't chase me with pitchforks. Listen to your local government and the NHC. I'm just expressing an opinion.

You have a hurricane bucking climo. it happens. It's an August track in October. In 2004 Charley played October in August.

[SconnieCane]

even if peak intensity decreases or fails to meet expectations...surge potential may not decrease...or paradoxically, it may actually increase somewhat if we exchange somewhat lower max intensity for a larger windfield.

Exactly what we saw with Katrina and Ike, and outside the Gulf, Sandy, but from a weather-geek perspective extreme wind intensity is more interesting.



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[supercane4867]

Looks like the Yucatan knocked it down more than expected, 75 kts now, which may mean it is a category lower when it comes ashore in Louisiana. May end up not as bad as initially expected, but it depends on how much the core has been disrupted by the land interaction and whatever it was that caused the core to fall apart just before landfall, and whether or not it can reorganise quickly. I remember Georges in 1998 failed to gain much intensity over the Gulf after it came off Cuba but the Yucatan is flatter than Cuba. Time will tell. Looking like it will still come ashore as a hurricane so should still be taken seriously.

Actually quite the contrary. The effects of interaction with Yucatan is less than expected for a landfalling hurricane. Had it came ashore with a pinhole eye as what it once appeared to be, the small inner core would completely vanish over Yucatan resulting in a much looser structure. Recent microwave suggests this is obviously not the case due to the fact that it struggled with wind shear in the Caribbean. Land interaction only helped its re-organization process if anything.

Interesting. If land interaction assisted its re-organisation, why the drop in intensity by two categories, when it was forecast to stay at least mid range category two during it land crossing? Gilbert didn't weaken below cat 2 when crossing the Yucatan and that had an overland track that was further away from water, although that was cat five at landfall.

Because the landfall intensity was forecasted to be 135kt but it only made landfall at 110kt due to shear and emerged over water with 75kt winds which isn’t that much weakening consider it was already struggling before landfall.

[cheezyWXguy]

Starting to see the twin hot towers rotating around the center on opposite sides. Probably a sign this has bottomed out on weakening and should resume strengthening soon

[Visioen]

1 thing I know for sure: this storm's favorite color is pink

[tolakram]

Visible loop
https://whirlwind.aos.wisc.edu/~wxp/goes16/grb/meso_vis_sqrt/meso1_60.html

Unlike prior to landfall I don't see mid level cloud tops heading toward the center so my amateur observation is that the mid level shear is gone. You can also tell exactly where the center is as it rotates.

[ElectricStorm]

The NHC is less bullish on peak and landfall intensity in the newest advisory. I'm still sticking with my Cat 4 peak/Cat 3 landfall prediction. There is always a chance of a weaker landfall, considering EWRC will likely be in play at some point. But I'm pretty confident it will get back to Cat 4... At least for now

[edu2703]

 https://twitter.com/JackSillin/status/1313964769754460160

[gfsperpendicular]

[Hurricane Mike]

Video Update on Delta
https://www.youtube.com/watch?v=TkoMpUgblok

[al78]

Actually quite the contrary. The effects of interaction with Yucatan is less than expected for a landfalling hurricane. Had it came ashore with a pinhole eye as what it once appeared to be, the small inner core would completely vanish over Yucatan resulting in a much looser structure. Recent microwave suggests this is obviously not the case due to the fact that it struggled with wind shear in the Caribbean. Land interaction only helped its re-organization process if anything.

Interesting. If land interaction assisted its re-organisation, why the drop in intensity by two categories, when it was forecast to stay at least mid range category two during it land crossing? Gilbert didn't weaken below cat 2 when crossing the Yucatan and that had an overland track that was further away from water, although that was cat five at landfall.

Because the landfall intensity was forecasted to be 135kt but it only made landfall at 110kt due to shear and emerged over water with 75kt winds which isn’t that much weakening consider it was already struggling before landfall.

Thanks, it makes sense now.

[LarryWx]

I hope to post more on this later. There are some analogs that I've seen that worry me about the chance that Delta landfalls as a major:

Opal of 1995, Carmen of 1974, Hilda of 1964, and especially the 1886 cat 3 that slammed near where this is headed. All of these years were like 2020, weak to moderate La Nina.

1. Opal: also in early Oct came off Yucatan. It went from a TS to a 916 mb cat 4 in the N Gulf within only 48 hours

2. Carmen of 1974: came off Yucatan as only a TS. Went from TS to cat 4 H within only 48 hours just S of LA.

3. Hilda of 1964: in early October in the C GOM south of LA went from a TS to a cat 4 941 mb H (150 mph winds) within only a 36 hour period.

4. 1886 LA H: about the same time in Oct became a cat 3 only within 100 miles offshore LA and made landfall in W LA with ~120 mph winds. Lowest pressure was 955 mb possibly onshore.

I'll be looking for more analogs.

[Fancy1001]

Does anyone else think that Delta reached category 5 during the first half of that 3 hours that recon wasn't in the storm yesterday before it fell apart.