ATL: ZETA - Post-Tropical - Discussion

[Steve]

Here's a really cool 50 second timelaspe view of the eye approaching and crossing over some part of New Orleans and then the backside. You can see how orange things got (stole my avatar picture from storm2k met Dylan). Calm lasted around 10-15 minutes before the backside kicked it.

https://www.kplctv.com/2020/10/29/watch ... over-nola/

[underthwx]

Here's a really cool 50 second timelaspe view of the eye approaching and crossing over some part of New Orleans and then the backside. You can see how orange things got (stole my avatar picture from storm2k met Dylan). Calm lasted around 10-15 minutes before the backside kicked it.
W
https://www.kplctv.com/2020/10/29/watch ... over-nola/

That is quite an amazing video of Zeta....thanks for sharing that Steve....I hope that you, and everyone affected by Zeta are safe, and doing well today!

[Kazmit]

Here's a really cool 50 second timelaspe view of the eye approaching and crossing over some part of New Orleans and then the backside. You can see how orange things got (stole my avatar picture from storm2k met Dylan). Calm lasted around 10-15 minutes before the backside kicked it.

https://www.kplctv.com/2020/10/29/watch ... over-nola/

That's awesome with the clouds speeding up in the eyewall and then slowing and abruptly changing direction in the eye.

[Ryxn]

Alas, the storm has gone post-tropical. Good riddance.

[Steve]

Here's a really cool 50 second timelaspe view of the eye approaching and crossing over some part of New Orleans and then the backside. You can see how orange things got (stole my avatar picture from storm2k met Dylan). Calm lasted around 10-15 minutes before the backside kicked it.
W
https://www.kplctv.com/2020/10/29/watch ... over-nola/

That is quite an amazing video of Zeta....thanks for sharing that Steve....I hope that you, and everyone affected by Zeta are safe, and doing well today!

Thanks wx. I had to come into work today, but otherwise, we made out great. I haven't talked to my daughter yet today to see if she and her mom got power on yet. But it's cool out today, so that shouldn't be a problem outside of creature comfort stuff.

[CrazyC83]

I'll do a full best track tomorrow, but here are my thoughts on the peak intensity of Zeta.

* Surface observations were quite significant. There were unofficial reports of sustained winds over 100 mph in southern Lafourche Parish and a gust to 136 mph. The strongest winds would have been over Grand Isle and into Plaquemines Parish where there were no observations. Even in southern Mississippi, sustained winds were well into hurricane territory. (New Orleans, where the eye went through, had relatively modest winds in comparison - likely a low-end category 1 or a strong tropical storm impact. That was because of the fast motion moving the strongest winds east.) All that data suggests winds of at least 90 kt.

* The highest flight-level winds were 119 kt, which would ordinarily support winds of 107 kt at the surface using a 90% reduction factor. Using an 80% reduction factor to account for the nearby trough interaction, however, would result in winds of 95 kt at the surface.

* The highest SFMR reading was 106 kt, but it was flagged and in very shallow water with shoaling issues. I would disregard all SFMR readings near landfall, or at least weigh them a lot less.

* The highest radar velocities were around 126 kt at 10,000 feet around the time of landfall. Using the same caveats as the flight-level winds would translate to winds of 101 kt at the surface.

* The minimum pressure at landfall I estimate was 967 mb, based on a combination of dropsondes (often misplaced, one would translate to 964 mb while the lowest eye drop was 970 mb), inland pressure observations (971 mb in New Orleans) and extrapolated pressures (about 967 mb). Based on that, using the KZC that would translate to about 95 kt when considering the fast motion I believe.

* The satellite signature was fast improving at landfall. From what I could see it was a T5.5 which would equate to 102 kt.

* Conclusion: I believe the landfall intensity was 95 kt, which was the operational intensity. It was difficult to decide between 95 kt and 100 kt. However, I'm not fully convinced that 100 kt would be accurate since the radar may have been transient. The 106 kt SFMR reading could be a deciding point except it was literally at the edge of the marsh. A case could be made for a category 3 landfall, but it is not convincing enough for me.

Thanks for summarizing all of this information, Crazy!

Just a question, what literature supports the 80% reduction figure that you have listed here for systems that interact with upper level troughs? I'm familiar with Franklin, Black, & Valde (2003) which document the 90% reduction in 700 mb FL wind for standard warm core systems. I'd have to imagine that there is a significantly smaller sample size for these kinds of systems, and thus there is probably more uncertainty in that reduction factor as a result.

I went back to the TCR with Hurricane Wilma in 2005 (ahead of Florida landfall) and applied the similarities as that was a fast moving storm ahead of a trough. The flight level winds for Wilma pre-FL landfall actually supported category 4 using normal reduction values.

[ColdMiser123]

I'll do a full best track tomorrow, but here are my thoughts on the peak intensity of Zeta.

* Surface observations were quite significant. There were unofficial reports of sustained winds over 100 mph in southern Lafourche Parish and a gust to 136 mph. The strongest winds would have been over Grand Isle and into Plaquemines Parish where there were no observations. Even in southern Mississippi, sustained winds were well into hurricane territory. (New Orleans, where the eye went through, had relatively modest winds in comparison - likely a low-end category 1 or a strong tropical storm impact. That was because of the fast motion moving the strongest winds east.) All that data suggests winds of at least 90 kt.

* The highest flight-level winds were 119 kt, which would ordinarily support winds of 107 kt at the surface using a 90% reduction factor. Using an 80% reduction factor to account for the nearby trough interaction, however, would result in winds of 95 kt at the surface.

* The highest SFMR reading was 106 kt, but it was flagged and in very shallow water with shoaling issues. I would disregard all SFMR readings near landfall, or at least weigh them a lot less.

* The highest radar velocities were around 126 kt at 10,000 feet around the time of landfall. Using the same caveats as the flight-level winds would translate to winds of 101 kt at the surface.

* The minimum pressure at landfall I estimate was 967 mb, based on a combination of dropsondes (often misplaced, one would translate to 964 mb while the lowest eye drop was 970 mb), inland pressure observations (971 mb in New Orleans) and extrapolated pressures (about 967 mb). Based on that, using the KZC that would translate to about 95 kt when considering the fast motion I believe.

* The satellite signature was fast improving at landfall. From what I could see it was a T5.5 which would equate to 102 kt.

* Conclusion: I believe the landfall intensity was 95 kt, which was the operational intensity. It was difficult to decide between 95 kt and 100 kt. However, I'm not fully convinced that 100 kt would be accurate since the radar may have been transient. The 106 kt SFMR reading could be a deciding point except it was literally at the edge of the marsh. A case could be made for a category 3 landfall, but it is not convincing enough for me.

Thanks for summarizing all of this information, Crazy!

Just a question, what literature supports the 80% reduction figure that you have listed here for systems that interact with upper level troughs? I'm familiar with Franklin, Black, & Valde (2003) which document the 90% reduction in 700 mb FL wind for standard warm core systems. I'd have to imagine that there is a significantly smaller sample size for these kinds of systems, and thus there is probably more uncertainty in that reduction factor as a result.

I went back to the TCR with Hurricane Wilma in 2005 (ahead of Florida landfall) and applied the similarities as that was a fast moving storm ahead of a trough. The flight level winds for Wilma pre-FL landfall actually supported category 4 using normal reduction values.

Interesting, thanks. I do see that the NHC used an 0.80 ratio for the 700 mb wind for Wilma, and the justification they used for this lower conversion factor was that the 850-200 mb shear was around 25 kt. Despite how fast Zeta was moving, shear was actually only moderate yesterday. This same layer of shear was forecast on the GFS around 18z yesterday to be ~10-15 kt, so maybe a 0.85 conversion would be a better estimate as opposed to 0.9?

[jlauderdal]

Heavy rains and wind going in lake toxaway,nc..300,000 without power in Atlanta and we are downstream from that

Power is out lake toxaway, nc

Be extra cautious if you go out. There are reports of trees and power lines down all across Transylvania county.

Went to cashiers and highlands...river and falls were raging..saw one tree down, power is back...70 and mostly sunny...took only 3 hours for the system to move through

[Steve]

Power is out lake toxaway, nc

Be extra cautious if you go out. There are reports of trees and power lines down all across Transylvania county.

Went to cashiers and highlands...river and falls were raging..saw one tree down, power is back...70 and mostly sunny...took only 3 hours for the system to move through

Nice. Rainbow Falls was my best new discovery 2 weeks ago up there. That and Sky Top Orchards near Hendersonville. You’re like the 3rd person besides us I talked to who was up there within the last 2 weeks.

[CrazyC83]

Thanks for summarizing all of this information, Crazy!

Just a question, what literature supports the 80% reduction figure that you have listed here for systems that interact with upper level troughs? I'm familiar with Franklin, Black, & Valde (2003) which document the 90% reduction in 700 mb FL wind for standard warm core systems. I'd have to imagine that there is a significantly smaller sample size for these kinds of systems, and thus there is probably more uncertainty in that reduction factor as a result.

I went back to the TCR with Hurricane Wilma in 2005 (ahead of Florida landfall) and applied the similarities as that was a fast moving storm ahead of a trough. The flight level winds for Wilma pre-FL landfall actually supported category 4 using normal reduction values.

Interesting, thanks. I do see that the NHC used an 0.80 ratio for the 700 mb wind for Wilma, and the justification they used for this lower conversion factor was that the 850-200 mb shear was around 25 kt. Despite how fast Zeta was moving, shear was actually only moderate yesterday. This same layer of shear was forecast on the GFS around 18z yesterday to be ~10-15 kt, so maybe a 0.85 conversion would be a better estimate as opposed to 0.9?

That might be what they investigate as well.

[Javlin]

Back on line on genny though lots of limbs down watched the storm from the front porch with a Jameison just awesome winds gusting I figure 80/90mph .I lost about 30/40% of the shingles on the S/side of the house have a hole in the roof of the shop an a huge tree landed on my shed,neighbors shed and a car he had in his back yard.The area is basically without power unless you are close to a hospital or something of that nature.I have to say this was a cool storm how I luved sitting on the N porch watching it blow and the tranformers lit the shy up such a Nice turquoise color!!

[jlauderdal]

Be extra cautious if you go out. There are reports of trees and power lines down all across Transylvania county.

Went to cashiers and highlands...river and falls were raging..saw one tree down, power is back...70 and mostly sunny...took only 3 hours for the system to move through

Nice. Rainbow Falls was my best new discovery 2 weeks ago up there. That and Sky Top Orchards near Hendersonville. You’re like the 3rd person besides us I talked to who was up there within the last 2 weeks.

Its a good place to come for fall colors and in this case a bonus chase was included..by the time we returned, the power was back and the sun was out...very different than the Florida systems..off to atanta tomorrow, will report on any damage I see there then back to sofla , get through the election and then this Caribbean system lurking

[Keldeo1997]

 https://twitter.com/DerekOrtt/status/1321645364735283201




Could of been far worse

[Ubuntwo]

https://twitter.com/DerekOrtt/status/1321645364735283201

Could of been far worse

The core *did* survive the Yucatan as a very convectively shallow ring. That's why it took off so quickly, with the first new convection wrapping into an eye.

[SconnieCane]

https://twitter.com/DerekOrtt/status/1321645364735283201

Could of been far worse

My thoughts exactly. The delay in intensification caused by the recovery time after being over the Yucatan coupled with the fact that the waters in the NGOM, while not "cold" by any stretch, were just not as abnormally warm for October as they were in 2018. Just like with Michael, the trough interaction was timed absolutely perfectly to strengthen the TC rather than shear it.

[CrazyC83]

The posts in this forum are NOT official forecasts and should not be used as such. They are just the opinion of the poster and may or may not be backed by sound meteorological data. They are NOT endorsed by any professional institution or STORM2K. For official information, please refer to products from the NHC and NWS.

Here is what I would have for the best track for Zeta:

AL282020, ZETA, 31,
20201023, 0000, , LO, 17.9N, 81.2W, 25, 1007,
20201023, 0600, , LO, 18.2N, 81.3W, 25, 1007,
20201023, 1200, , LO, 18.6N, 81.5W, 25, 1007,
20201023, 1800, , LO, 18.9N, 81.8W, 25, 1007,
20201024, 0000, , LO, 18.9N, 82.1W, 25, 1007,
20201024, 0600, , LO, 18.7N, 82.3W, 25, 1006,
20201024, 1200, , TD, 18.5N, 82.6W, 30, 1006,
20201024, 1800, , TD, 18.3N, 83.0W, 30, 1005,
20201025, 0000, , TS, 18.1N, 83.2W, 35, 1005,
20201025, 0600, , TS, 17.9N, 83.4W, 40, 1004,
20201025, 1200, , TS, 17.8N, 83.6W, 45, 1003,
20201025, 1800, , TS, 18.0N, 83.8W, 50, 1001,
20201026, 0000, , TS, 18.2N, 84.0W, 55, 996,
20201026, 0600, , HU, 18.5N, 84.2W, 65, 992,
20201026, 1200, , HU, 18.9N, 84.8W, 65, 989,
20201026, 1800, , HU, 19.4N, 85.7W, 70, 983,
20201027, 0000, , HU, 19.9N, 86.6W, 70, 980,
20201027, 0330, L, HU, 20.3N, 87.4W, 75, 976,
20201027, 0600, , HU, 20.6N, 87.9W, 65, 983,
20201027, 1200, , TS, 21.3N, 89.0W, 60, 989,
20201027, 1800, , TS, 22.2N, 90.0W, 60, 991,
20201028, 0000, , HU, 23.2N, 90.8W, 65, 990,
20201028, 0600, , HU, 24.4N, 91.5W, 70, 985,
20201028, 1200, , HU, 26.0N, 91.7W, 80, 976,
20201028, 1800, , HU, 28.0N, 91.1W, 90, 972,
20201028, 2130, L, HU, 29.3N, 90.3W, 95, 967,
20201029, 0000, , HU, 30.2N, 89.6W, 80, 972,
20201029, 0600, , TS, 32.6N, 87.4W, 55, 985,
20201029, 1200, , TS, 35.1N, 83.2W, 45, 989,
20201029, 1800, , EX, 37.5N, 78.2W, 45, 991,
20201030, 0000, , EX, 38.1N, 71.5W, 45, 990,


A few thoughts:

* Genesis is unchanged, with minor adjustments pre-Yucatan landfall.

* The landfall in the Yucatan I estimate was at 75 kt, which is slightly above operational. That is based on the surface data suggesting a pressure around 976 mb, which is lower than the last Recon estimate of 980 mb at 00Z.

* I considered keeping it a hurricane all the way across the Yucatan, however, there was enough weakening that I brought it down to a tropical storm briefly - but only to 60 kt. The first full Recon flight after it emerged found a hurricane, although there was some improvement in the satellite signature (which supports a slightly lower intensity as it emerged) even though an inner core remained solidly intact across the Yucatan.

* As mentioned in another post, I agreed with the operational peak intensity at Louisiana landfall of 95 kt (with a pressure of 967 mb), although an argument for 100 kt could be made. I did adjust the landfall point slightly eastward based on radar observations.

[Steve]

https://twitter.com/DerekOrtt/status/1321645364735283201

Could of been far worse

Love me some Derek, but he went in pretty hardcore that it wasn’t intensifying - which it wasn’t - a few hours off the Yucatán. Hurricane models were closing in on 30 hours, and the depictions clearly showed intensification back into a hurricane (except CMC) was going to happen. I’m just noting it, because it doesn’t cost him any points with me. Even Aric was telling people to look for eastern adjustments around then, and after the pros and GCANE, he’s one of the best. We all miss things, but it was cool to see the models finally get another storm right in a year they have been suspect in every situation.

[Nimbus]

A lot of Storm2k folks in recovery mode this year after the storms, Philadelphia reported wind gusts in the low 30's as Zeta blew through so I guess we are officially extratrop now.

Snow in Texas and 96L possibly staying in the Atlantic so we might not be done.

[Shell Mound]

 https://twitter.com/iCyclone/status/1322313419240935424



 https://twitter.com/iCyclone/status/1322322921197576192



 https://twitter.com/iCyclone/status/1322384376202731520



 https://twitter.com/iCyclone/status/1322058011146420224



 https://twitter.com/iCyclone/status/1322328500343361539