ATL: Ex-INVEST 91L - Models

[SFLcane]

[TomballEd]

First 91L SHIPS. The medium steering model used before NHC issues a forecast track extrapolated beyond xx time would suggest a very close call for the NE Caribbean. I forgot the name of the improved BAMM model. Just uses GFS forecast wind for track, not super sophisticated but not necessarily wrong.

* GFS version *
* ATLANTIC 2025 SHIPS INTENSITY FORECAST *
* IR SAT DATA AVAILABLE, OHC CLIMO USED *
* INVEST AL912025 09/04/25 12 UTC *

TIME (HR) 0 6 12 18 24 36 48 60 72 84 96 108 120 132 144 156 168
V (KT) NO LAND 20 21 22 23 25 32 43 51 63 70 78 81 82 83 84 87 90
V (KT) LAND 20 21 22 23 25 32 43 51 63 70 78 81 82 83 84 87 90
V (KT) LGEM 20 21 21 23 24 28 32 36 42 48 54 58 58 58 58 60 63
Storm Type TROP TROP TROP TROP TROP TROP TROP TROP TROP TROP TROP TROP TROP TROP TROP TROP TROP

SHEAR (KT) 5 6 3 3 5 3 4 6 6 7 9 8 11 7 9 8 9
SHEAR ADJ (KT) 0 -2 -1 0 0 0 1 2 0 -1 1 3 5 5 0 1 3
SHEAR DIR 57 67 106 188 255 158 214 119 139 166 248 239 258 245 274 286 263
SST (C) 27.7 27.6 27.7 27.8 27.8 27.8 27.8 28.3 28.2 28.4 28.3 28.5 28.3 28.5 28.8 28.7 28.9
POT. INT. (KT) 132 130 131 132 132 133 133 140 139 142 141 145 142 144 149 147 150
200 MB T (C) -53.8 -53.6 -53.7 -54.0 -54.0 -54.1 -54.0 -54.0 -53.9 -54.0 -54.2 -54.0 -54.2 -53.8 -53.9 -53.6 -53.6
200 MB VXT (C) -0.2 -0.2 -0.3 -0.2 -0.2 -0.2 -0.1 -0.1 -0.2 -0.2 -0.2 0.0 0.0 0.0 0.0 0.1 0.2
TH_E DEV (C) 5 5 5 5 5 4 5 6 6 8 7 8 8 9 9 10 9
700-500 MB RH 65 66 68 70 68 73 69 64 60 60 60 61 58 58 58 59 58
MODEL VTX (KT) 9 9 9 9 9 11 14 12 14 14 16 15 15 14 14 13 13
850 MB ENV VOR 37 44 45 42 38 39 48 27 21 16 8 2 -14 -23 -33 -32 -18
200 MB DIV -21 -28 -19 -11 -8 58 56 51 -24 -8 25 5 1 25 20 15 11
700-850 TADV 0 0 -1 -1 -2 -2 -4 -1 0 3 3 2 -2 -2 4 0 -3
LAND (KM) 1751 1787 1768 1734 1716 1706 1642 1515 1383 1263 1132 1073 925 764 654 505 341
LAT (DEG N) 12.1 12.2 12.2 12.1 12.1 12.3 12.6 12.8 13.0 13.2 13.5 14.2 15.2 xx.x xx.x xx.x xx.x
LONG(DEG W) 33.5 34.3 34.8 35.5 36.1 37.5 39.0 40.6 42.4 44.3 46.6 48.8 51.1 xxx.x xxx.x xxx.x xxx.x
STM SPEED (KT) 8 6 6 6 6 7 8 8 9 10 11 12 12 11 10 9 11
HEAT CONTENT 20 20 20 21 21 23 24 23 25 29 35 38 46 50 51 54 55

[kevin]

First 91L SHIPS. The medium steering model used before NHC issues a forecast track extrapolated beyond xx time would suggest a very close call for the NE Caribbean. I forgot the name of the improved BAMM model. Just uses GFS forecast wind for track, not super sophisticated but not necessarily wrong.

* GFS version *
* ATLANTIC 2025 SHIPS INTENSITY FORECAST *
* IR SAT DATA AVAILABLE, OHC CLIMO USED *
* INVEST AL912025 09/04/25 12 UTC *

TIME (HR) 0 6 12 18 24 36 48 60 72 84 96 108 120 132 144 156 168
V (KT) NO LAND 20 21 22 23 25 32 43 51 63 70 78 81 82 83 84 87 90
V (KT) LAND 20 21 22 23 25 32 43 51 63 70 78 81 82 83 84 87 90
V (KT) LGEM 20 21 21 23 24 28 32 36 42 48 54 58 58 58 58 60 63
Storm Type TROP TROP TROP TROP TROP TROP TROP TROP TROP TROP TROP TROP TROP TROP TROP TROP TROP

SHEAR (KT) 5 6 3 3 5 3 4 6 6 7 9 8 11 7 9 8 9
SHEAR ADJ (KT) 0 -2 -1 0 0 0 1 2 0 -1 1 3 5 5 0 1 3
SHEAR DIR 57 67 106 188 255 158 214 119 139 166 248 239 258 245 274 286 263
SST (C) 27.7 27.6 27.7 27.8 27.8 27.8 27.8 28.3 28.2 28.4 28.3 28.5 28.3 28.5 28.8 28.7 28.9
POT. INT. (KT) 132 130 131 132 132 133 133 140 139 142 141 145 142 144 149 147 150
200 MB T (C) -53.8 -53.6 -53.7 -54.0 -54.0 -54.1 -54.0 -54.0 -53.9 -54.0 -54.2 -54.0 -54.2 -53.8 -53.9 -53.6 -53.6
200 MB VXT (C) -0.2 -0.2 -0.3 -0.2 -0.2 -0.2 -0.1 -0.1 -0.2 -0.2 -0.2 0.0 0.0 0.0 0.0 0.1 0.2
TH_E DEV (C) 5 5 5 5 5 4 5 6 6 8 7 8 8 9 9 10 9
700-500 MB RH 65 66 68 70 68 73 69 64 60 60 60 61 58 58 58 59 58
MODEL VTX (KT) 9 9 9 9 9 11 14 12 14 14 16 15 15 14 14 13 13
850 MB ENV VOR 37 44 45 42 38 39 48 27 21 16 8 2 -14 -23 -33 -32 -18
200 MB DIV -21 -28 -19 -11 -8 58 56 51 -24 -8 25 5 1 25 20 15 11
700-850 TADV 0 0 -1 -1 -2 -2 -4 -1 0 3 3 2 -2 -2 4 0 -3
LAND (KM) 1751 1787 1768 1734 1716 1706 1642 1515 1383 1263 1132 1073 925 764 654 505 341
LAT (DEG N) 12.1 12.2 12.2 12.1 12.1 12.3 12.6 12.8 13.0 13.2 13.5 14.2 15.2 xx.x xx.x xx.x xx.x
LONG(DEG W) 33.5 34.3 34.8 35.5 36.1 37.5 39.0 40.6 42.4 44.3 46.6 48.8 51.1 xxx.x xxx.x xxx.x xxx.x
STM SPEED (KT) 8 6 6 6 6 7 8 8 9 10 11 12 12 11 10 9 11
HEAT CONTENT 20 20 20 21 21 23 24 23 25 29 35 38 46 50 51 54 55

Hmm very low shear and even when it picks up a little bit to 6 - 11 kt later in the run it's mostly in the general direction of the movement of 91L. Pretty much as good as you're gonna get in terms of open Atlantic shear.

[Teban54]

Old info, but with the most recent full runs of the two biggest global models like this... It's gonna be quite a ride if they play out. Fortunately, they're 300+ hours out.

(Both models already had the storm on a northward motion past this time, but still.)

[ronjon]

Think most of the global models are too slow. Two weeks to make it to the Bahamas longitude? The GFS is faster than the Euro though.

[MEANINGLESS_NUMBERS]

Operationals see E Carib and CONUS but ensembles favor recurve/Bermuda:

[Hypercane_Kyle]

The delayed development is definitely throwing the models for a loop. I would not be surprised if this one ends up in the Caribbean.

[TomballEd]

Fox Weather apparently develops probs from a consensus of US and Euro ensembles and Google. Highest probs from the Fox consensus model points towards the NE Caribbean.

 https://x.com/bryannorcrosstv/status/1963596128080859145

[BobHarlem]

Most 6z GFS ensembles still recurve it past the islands. However a few don't which is the biggest change on the 6z set. Something to watch, but I'm not overly concerned much yet (despite the operationals) for the US anyway -- Bermuda is different as is the Caribbean (see Euro ensembles). Only a few GFS ensembles show the leewards.

One thing on the euro and especially the google deep mind ensembles, it's a lot weaker. The google ones basically kill it off in the Caribbean.



6z Euro ensembles are much more a threat to the Caribbean

[jlauderdal]

The delayed development is definitely throwing the models for a loop. I would not be surprised if this one ends up in the Caribbean.

Google AI wasn't thrown for a loop; it liked that track from the start. Will have to watch the ensembles and see if we start getting members taking the westerly route

[kevin]

Using Dvorak to get reasonable wind estimates for the pressure, the 0z Euro run would result in about 30 - 35 ACE from 91L in the next 360 hours. And it's still a MH at +360 hrs.

[BobHarlem]

The delayed development is definitely throwing the models for a loop. I would not be surprised if this one ends up in the Caribbean.

Google AI wasn't thrown for a loop; it liked that track from the start. Will have to watch the ensembles and see if we start getting members taking the westerly route

Deep mind also poofs it in the Caribbean.

[TomballEd]

I assume the GFS has had improvements since then, but it used to be common for the model to break down the ridging to quickly. Ike was a an interesting example of this. I can't get the animation loaded, but right up to the end, Ike was always W of the NHC forecast, which is heavily influences by the GFS, its ensembles, and hurricane models using GFS initial and boundary conditions. Just one example. As I said, maybe this has been fixed in the 17 years since.

[SFLcane]

The delayed development is definitely throwing the models for a loop. I would not be surprised if this one ends up in the Caribbean.

Google AI wasn't thrown for a loop; it liked that track from the start. Will have to watch the ensembles and see if we start getting members taking the westerly route

Deep mind also poofs it in the Caribbean.

Just too small for the model to resolve at the moment.

[TomballEd]

The delayed development is definitely throwing the models for a loop. I would not be surprised if this one ends up in the Caribbean.

Google AI wasn't thrown for a loop; it liked that track from the start. Will have to watch the ensembles and see if we start getting members taking the westerly route

Deep mind also poofs it in the Caribbean.

The Graveyard becomes less deadly the deeper into Autumn the season goes, as the low over N. South America slowly weakens. A closed circulation would resist the loss of surface convergence caused by the accelerating trades. 10 days out, when the system would be entering the Caribbean, if it entered the Caribbean, shear peaks below 20 knots. Not favorable for strengthening but not enough to quickly shear apart a closed low especially since ensemble PW is near normal at that time across the Caribbean.

[SFLcane]

Just some specuation on my part but I had not noticed this but the long range eps does have some members bending west a la the gfs. Those westward members might smooth out in time just north of the caribbean

[LarryWx]

Just some specuation on my part but I had not noticed this but the long range eps does have some members bending west ala gfs. Those westward members might smooth out in time just north of the caribbean

https://i.postimg.cc/4Nh9XntD/nnn.jpg

This EPS and other runs still strongly favor either a safe recurve from Conus or it staying weak or dissipating for those that stay further south and go into or near the Caribbean. So, there’s still a long ways to go before this would possibly be considered a significant threat to the Conus. Also, the threat is currently still higher for the NE Caribbean due to those members that stay further S. I’m assuming you largely agree with all of this. If not, please tell me where you disagree.

But even so, Erin did come in 200 miles/3 degrees of longitude further W than forecasted by the NHC and models 4 days earlier.

[TomballEd]

This seems about right. Convection is waning now, we'll see how much it comes back tonight. Enough convection might close the low.

 https://x.com/DCAreaWx/status/1963623784885232101

[kevin]

12z ICON run. The wind speed has been added and is based on the Dvorak relation of the modelled pressure. Remains an invest or borderline TD for the next 2 - 3 days and then develops into a TS. Further south than 00z ICON by about 2 degrees at the end of the run. About halfway between 06z GFS (which is more north) and 00z Euro (which is more south).

Time (hr) / Pressure (mb) / Wind speed (kt)
Peak intensity = 952 mb / 110 kt (+174hr)
Total ACE = 12.0
00 / 1013 / -
06 / 1010 / -
12 / 1012 / -
18 / 1009 / 30
24 / 1011 / -
30 / 1009 / 30
36 / 1011 / -
42 / 1009 / 30
48 / 1010 / -
54 / 1008 / 30 - TD
60 / 1009 / 30
66 / 1006 / 35 - TS
72 / 1007 / 35
78 / 1002 / 40
84 / 1001 / 45
90 / 995 / 55
96 / 993 / 55
102 / 988 / 65 - C1
108 / 986 / 65
114 / 981 / 75
120 / 986 / 65
126 / 983 / 70
132 / 978 / 80
138 / 977 / 80
144 / 968 / 90 - C2
150 / 963 / 100 - C3
156 / 965 / 95
162 / 953 / 110
168 / 957 / 105
174 / 952 / 110
180 / 960 / 100

[Teban54]

12z ICON run. The wind speed has been added and is based on the Dvorak relation of the modelled pressure. Remains an invest or borderline TD for the next 2 - 3 days and then develops into a TS. Further south than 00z ICON by about 2 degrees at the end of the run. About halfway between 06z GFS (which is more north) and 00z Euro (which is more south).
[...]
https://i.imgur.com/wO0jjOt.gif

The trailing TS that 12z ICON shows behind the MH 91L is pure gold (even though, of course, it has happened before). It will most likely be gone in future runs, however.