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Archives 2020s >> 2021 Forecast Lounge

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cieldumortModerator
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Ida Lounge
      #113963 - Mon Aug 23 2021 02:15 PM


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A broad region of disturbed weather over Central America from the eastern Pacific to the Atlantic side and extending into the southwestern Caribbean is forecast by many model runs to interact with an approaching wave this week and develop. While the approaching wave is not yet Invest tagged, NHC has added it to their TWO and as of this afternoon assigned 40% development probabilities to it within the next 5 days.

While it is possible that this specific wave does not become the nucleus of development itself, it would likely have a hand it in regardless, and development in this part of the Western Atlantic associated with the forming broad area of low pressure looks probable (>50%) within the next seven days or so, and sooner rather than later if this wave does the trick. Thus we are now starting a Forecast Lounge on what could be yet another peak of the season tropical cyclone that would have nowhere to go but land once forming.

The title will be updated with future Invest number/s. It is very possible that more than one Invest will come out of this region over the next week or so, and more than one Lounge may be required.

Just after the 5PM Aug 26 Advisory on NINE was sent out, recon passed through enough of the system to confirm that tropical storm force winds were already occurring at the surface, and NHC issued a special update on now Tropical Storm Ida, the ninth named storm of the 2021 Atlantic Hurricane Season.

Edited by cieldumort (Thu Aug 26 2021 07:15 PM)


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MikeCAdministrator
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Re: SW Caribbean Low Lounge [Re: cieldumort]
      #113967 - Tue Aug 24 2021 08:10 PM

This Caribbean wave Just got tagged as 99L, has a cat 3 o4 4 Corpus Christi hit on the 18Z GFS tuesday afternoon, and CMC and Icon have similar forecasts.

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MikeCAdministrator
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Re: SW Caribbean Low Lounge [Re: MikeC]
      #113968 - Tue Aug 24 2021 09:35 PM

I do want to point out, until the storm actually forms, be careful with the model runs. It is a good inidicator that folks along the western Gulf should watch this one very closely.

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MikeCAdministrator
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Re: SW Caribbean Low Lounge [Re: MikeC]
      #113969 - Wed Aug 25 2021 07:27 AM

6Z GFS has a cat 4 landfall near where Delta made lanfall last year Tuesday morning. (0z was further west toward Sabine Pass)
0Z Euro is similar just east of Sabine pass (near where Laura made landfall last year)
0z UKMET has a Cat 1 approaching South Padre Island when the run ends Monday
0z CMC Monday morning cat 3 landfall Louisiana near where Delta made landfall las year
6z HMON does not develop the system at all

Still no organized system, so take all models with a grain of salt they will probably change multiple times until then.


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cieldumortModerator
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Re: SW Caribbean Low Lounge [Re: MikeC]
      #113970 - Wed Aug 25 2021 09:39 AM



First light shows two areas where consolidation and possible cyclonic flow are taking shape with 99L. The area circled in red appears to have both the best convergence and possible cyclonic surface flow, orange the second best. As of the 8AM TWO, NHC does seem to be tracking the area circled in red, but it is a mixed bag among the models, with some, notably the HMON and HWRF, which notoriously do poorly handling genesis, seemingly hung up over land.

For the models that are picking up on what may be the nucleus of 99L (area in red) spread among their operational runs and individual members mostly develop this into a Tropical Cyclone with those that ramp up more quickly heading into the upper Texas coast all the way out east to NOLA, whereas those that are slower to develop generally favor a southern Mexico to central Texas (around Corpus Christi) landfall.

Until we have certainty on where 99L is, all of this is up in the air. Hopefully several more scatterometer passes and recon come in soon and are digested by the models.


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MikeCAdministrator
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Re: SW Caribbean Low Lounge [Re: cieldumort]
      #113972 - Wed Aug 25 2021 01:57 PM

Spread is again extremely large for the 12Z models, with GFS into Lousiana and UKMet into South/Mid Texas, ensemble graph here highlights it:


12z Euro has a Louisiana landfall Monday evening Cat 3 (961mb) near where Laura made landfall.



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MikeCAdministrator
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Re: SW Caribbean Low Lounge [Re: MikeC]
      #113973 - Wed Aug 25 2021 07:38 PM

18z GFS shifted far right to SE Louisiana based on the init being further north (probably too far north based on satellite), but the system itself on satellite looks like it's on its way to becoming tropical by the morning. 18Z HWRF and HMON have it to hurricane strength before Cuba.

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MikeCAdministrator
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Re: SW Caribbean Low Lounge [Re: MikeC]
      #113974 - Wed Aug 25 2021 08:18 PM

18z HWRF and 18Z HMON both show landfalling category 4 hurricanes in western Louisiana Sunday night or early Monday.

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cieldumortModerator
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Re: Invest 99L Lounge (SW Caribbean Low) [Re: cieldumort]
      #113975 - Thu Aug 26 2021 03:08 AM

Tropical Cyclogenesis may already be underway tonight and it is very possible if not likely advisories on NINE will begin later today.

Some interesting quirks in the models tonight, with also some greater spread.

Based on the surface 'center' outlined in the most recent ASCAT pass from 0304z, HWRF, HMON and GFS all progged 99L's surface 'center' a bit too far to the east for 0300z. This can potentially have an outsized impact on track - and perhaps even intensity - down the road. However, given how robust the apparent developing mid-level circulation is to the north-northeast, the surface swirliness could still jump and align with it, putting the incipient cyclone at even higher latitude - which could open some eyes for Jamaica, Cuba, perhaps even as far east as the eastern Gulf of Mexico, should that occur. Also, in general, the TUTT to 99Ls north that is tracking WSW as it weakens could yet help lift 99L further north early on than models have yet to pick up on (TBD and does bear watching)

ASCAT based rough surface 'center' position as of 03z Aug 26: 14N 78.5W

03z Aug 26 forecast by HWRF, HMON, GFS models' 0z runs:

HWRF: 13.7N 77.5W messy closed circ. (03z too far east and much too organized at the surface)
Landfalls 931mb 114 kt just west of Sabine Pass TX 06Z Tues Aug 31

HMON: 13.75N 77.63W and closed/slightly elongated NNE/SSW (03z too far east and too organized at surface)
Landfalls just a few miles east of Sabine Pass TX 15z Mon Aug 30 979mb/58kt

GFS: 14.12N 76.35W barely closed 'center' on northish portion of NNE/SSW elongated trof (03z much too far east and did not forecast the E-W orienation of subtle surface circ seen in ASCAT)
Landfalling east of Marsh Island LA 0z Mon Aug 30 958mb 80 kt


As always, these early model runs are based on very limited information. Recon missions likely to begin today will add critical details and by the weekend models should have a much better idea of where 99L will go.

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MikeCAdministrator
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Re: Invest 99L Lounge (SW Caribbean Low) [Re: cieldumort]
      #113976 - Thu Aug 26 2021 09:35 AM

6z GFS has it coming into Southeastern Louisiana Sunday afternoon, as a Cat 3, the trend has been weaker and a bit east (Weaker as in cat 3 vs cat 4) Strength will likely be a factor based on how much the ULL currently over florida shears the system and keeps it developing now (Which it's dampening the system at the moment)

6z hwrf has a monday morning landfall near Cypremort Point, LA as a cat 4.

6z hmon has a cat 2 landfall in Southeastern Louisiana Sunday afternoon, moves over New Orleans Sunday night.

Overall trend is a bit east, and slightly weaker than the prior runs.


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MikeCAdministrator
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Re: Invest 99L Lounge (SW Caribbean Low) [Re: MikeC]
      #113984 - Fri Aug 27 2021 01:36 PM

Most models are suggesting a major landfall, example is the simulated IR satellite from teh 12Z HWRF

This shows 938mb storm (Cat 4) at landfall.

Other models are in this general vicinity as well, mostly to the east.


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Re: Invest 99L Lounge (SW Caribbean Low) [Re: MikeC]
      #113986 - Fri Aug 27 2021 03:25 PM

Many intensity models are going into the cat 4 range now, and very high chances for rapid intensification in the Gulf. This can reach cat 5, however there is a small chance of a bit of shear just before landfall that could weaken it slightly. The wide wind field (bands forming over Florida) will likely make a massive wall of water for storm surge particularly at and just to the right of where the Hurricane makes landfall.

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Kraig
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Re: Invest 99L Lounge (SW Caribbean Low) [Re: MikeC]
      #113987 - Fri Aug 27 2021 04:19 PM

Scary to think that Sunday will be the 16th anniversary of Katrina's landfall too!

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cieldumortModerator
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Re: Ida Lounge [Re: cieldumort]
      #113988 - Fri Aug 27 2021 10:55 PM

Something I often like to share in the Lounge is my personal forecast for maximum winds in a given cyclone. I've delayed with Ida for two reasons, but still want to share and I am also eager to read yours, as well.

First, Ida is going to be a monster of a tropical cyclone regardless of where it ranks on the limiting Saffir-Simpson (wind only) Scale.

All too often laypeople see these max wind forecasts and their swaths and conclude xyz storm ain't no big deal where I'm at. Or at my house, etc. This is crazy thinking, but social science and risk communication research into human nature finds we all seem to fall into it at one time or another, which is one of many reasons I personally would like to see us drop the Saffir-Simpson Scale altogether for a much more informative and inclusive scale such as the Masson-Gough Hurricane Scale.

Second, until these extra recon flights over the past 24 hours, there were a few remaining questions as to track, which actually could have thrown max winds more into question, so I just waited it out.

Ida Lifetime Max Wind Odds (Personal forecast).
Cat 1: 2% (This is Ida's current intensity as of this entry)
Cat 2: 8%
Cat 3: 27%
Cat 4: 40%
Cat 5 of 160-175 MPH: 21%
Cat 5 over 175 MPH: 2%

It is worth reiterating in another fashion that Ida very well could become a sizeable tropical cyclone prior to landfall, bringing with her a storm surge fully one or two 'categories higher' than 'normally expected' for a given Saffir-Simpson number. In addition, the ground over much of the forecast track is already saturated from prior rains. With Ida's forward speed expected to slow down, and possibly even come to a crawl at some point, torrential, life-threatening, catastrophic inland flooding may occur across multiple counties, even multiple states, and potentially for multiple days.

On a more inclusive Hurricane Scale, Ida as currently forecast from the NHC at time of landfall could be coming in at something more like "Category 5," even if her winds never make that on the SS Scale.

As far as max winds, something to look for is any potential impingement of her outflow in the western semicircle from interaction with outflow from East Pac Nora 14E located well to Ida's west. This wild card could hold back how strong Ida ultimately gets, but other than that, there isn't a lot else out there that could substantially hold Ida back.


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MikeCAdministrator
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Re: Ida Lounge [Re: cieldumort]
      #113989 - Fri Aug 27 2021 11:28 PM

Looking for the final model fix now that it's over Cuba. Adjustments now are critical for how much New Orleans gets affected, as well as others. The surge is going to be widespread regardless. Ensemble Shifts are what i'm looking at, especially since 18Z ensembles shifted right.

Please note it won't matter much, but with NOLA unable to fully evacuate it would mean much more impact there if the core or eyewall went over vs not.
Other areas in Louisiana are definitely going to be impacted, as well as Mississippi, the degree will depend the exact path.


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Re: Ida Lounge [Re: MikeC]
      #113990 - Sat Aug 28 2021 12:10 AM

0z ICON shifts east/right and slightly stronger near Fourchon /Grande Isle cat 3
0z GFS track pretty much stays the same, but stronger, maybe slightly left.cat 3


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islandtime
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Re: Ida Lounge [Re: MikeC]
      #113995 - Sat Aug 28 2021 08:49 PM

The movement since around 3pm seems to be more NNW. The latest steering current map shows that the high has moved slightly eastward. Any thoughts on how this will affect the forecasting? The apparent movement over the last 4 hours would seem to show a landfall slightly east of New Orleans.

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cieldumortModerator
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Re: Ida Lounge [Re: islandtime]
      #113996 - Sat Aug 28 2021 09:19 PM

Quote:

The movement since around 3pm seems to be more NNW. The latest steering current map shows that the high has moved slightly eastward. Any thoughts on how this will affect the forecasting? The apparent movement over the last 4 hours would seem to show a landfall slightly east of New Orleans.




There had been a more northerly component to Ida's track during the afternoon today. Upon close inspection of all available moisture channels, it appears some of this is steering influence of a subtle mid-level low to Ida's WSW, that is sliding underneath Ida to her southwest, possibly weakening and likely tilting back a little more obviously "negative" as it does. As such, any remaining steering influence from this almost unnoticed feature will likely be to impart a resumption of a more northwesterly track, or even add a temporary wnw push.

Odds still favor an ultimate landfall point west of to roughly over NOLA, rather than east of the city.



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