ATL: ERIN - Tropical Storm - Discussion

[aspen]

Is there a chance that it gets so far south that it runs into the shredder, stays too weak that it misses the weakness and gets into the gulf?

Highly unlikely at the moment. Even the HAFS-A model, which shows a marginal TS or TD all the way to 60W, still has it slide just north of the islands. Erin will likely be steered north to some degree even in these weak scenarios. A weaker short- to mid-term Erin raises the odds of an East Coast or Bahamas impact at the most.

[wxman57]

Significant south and west track shift in NHC's 15z advisory. A good bit closer to the islands. They mention some trusted models taking Erin even closer to the islands. I think they'll shift the track more to the south and west at 21z

[aspen]

Odd that the NHC held at 40 kt for 11am despite the 12z BT dropping to 35 kt.

[Blown Away]

Significant south and west track shift in NHC's 15z advisory. A good bit closer to the islands. They mention some trusted models taking Erin even closer to the islands. I think they'll shift the track more to the south and west at 21z

How far W and S would Erin need to go to result in a solution towards Bahamas/SFL?

[AutoPenalti]

Significant south and west track shift in NHC's 15z advisory. A good bit closer to the islands. They mention some trusted models taking Erin even closer to the islands. I think they'll shift the track more to the south and west at 21z

How far W and S would Erin need to go to result in a solution towards Bahamas/SFL?

Even if it does, Models seem to be consistent on a weakness appearing just north of the Islands.

[cycloneye]

For our members in the northern Leewards BVI, USVI and where I am in Puerto Rico, we have to be very vigilant to the advisories from NHC and also, begin to prepare in case a tropical storm warning or hurricane warning is issued.

[wxman57]

Significant south and west track shift in NHC's 15z advisory. A good bit closer to the islands. They mention some trusted models taking Erin even closer to the islands. I think they'll shift the track more to the south and west at 21z

How far W and S would Erin need to go to result in a solution towards Bahamas/SFL?

There is nothing to keep it from turning northward once it passes the NE Caribbean. I do not see any threat to Florida.

[wxman57]

For our members in the northern Leewards BVI, USVI and where I am in Puerto Rico, we have to be very vigilant to the advisories from NHC and also, begin to prepare in case a tropical storm warning or hurricane warning is issued.

Luis, our newest forecaster is from San Juan. She got her masters at Colorado State and has worked with Klotzbach on the season outlooks. She started in April and is doing very well.

[LarryWx]

Tuesday will be a important day to see how far down in latitude, the circulation goes.

The good news in the short-term for the US is that Erin climbed slightly from 17.4N to 17.6N (275 degree heading) since the previous advisory vs a prog to stay at 17.4N (270 degree heading). Could be a good sign regarding keeping the latitude instead of losing much. We’ll see!

Followup to above: Per the 5AM advisory, Erin dropped back down slightly from 17.6N to 17.4N with a 265 degree heading. The new track has a low point of 17.0N tomorrow instead of 17.1N. The 17.0N will be a key latitudinal benchmark to compare to tomorrow.

Followup to followup:
The 11AM position dropped from 5AM’s 17.4N to 17.2N. Also, the new track dips down to 16.5N tomorrow vs the prior advisory’s 17.0N:

FORECAST POSITIONS AND MAX WINDS

INIT 12/1500Z 17.2N 36.3W 40 KT 45 MPH
12H 13/0000Z 16.8N 39.1W 40 KT 45 MPH
24H 13/1200Z 16.5N 42.3W 40 KT 45 MPH

[USTropics]

Finally got my office all set up at the new place and some time to really check out Erin and the models this morning! First thing that jumps out on satellite imagery, Erin has a vigorous circulation but is convectively limited. This can be best seen in water vapor RGB composites (and some other features I will point out):





Erin's circulation (green) is easy to spot here, and it’s also very evident convection is not able to build with much height/deepen. A healthy tropical cyclone will have deep white/fringe blue, but here we get this mixture of red in the high cloud (an indication that convection is not able to sustain vertically). There are three main negative factors that I am seeing:

1) the surrounding SSTs and OHC environment is not conducive for deep moisture generation. Water temps are close to 78F, and OHC is 0. This is essentially the minimal surface temperature that can support a system, and it really caps the available latent heat for producing deep convection.

Sea Surface Temperatures with current position:


OHC values with previous track:


2) I want to also note the environment out in front is taking A LOT of work to moisten. I’ve outlined the SAL line riding out in front (orange) in the WV RGB image above, but you can also clearly see it here in the CIMSS product:




3) Additionally, there is a mid level circulation (pink, future track in dashed pink) that has formed within the monsoonal trough, and this will begin to pivot along Erin’s flank today and then head northwest tomorrow (where models show the vorticity being stretched out and the moisture sacrificed to the SAL gods). Over the next two days though, this feature will interact with Erin's moisture envelope/profile and negatively strip some of the convective potential away.

700mb (mid-level) vorticity product showing second mid-level vort to the east of Erin:


So that is kind of what is going on currently, now I’ll transition to what the models are forecasting and note some trends. I’ll start with what the models have been showing the past 4-6 runs, and how they have been verifying. The trend so far has been for shifts to the south in the operational models, which we can analyze with the last 4 runs of the ECMWF (light blue previous runs -> dark blue current run), with verified positions marked in X from Brian Tang's page:


Here are the last 6 runs of the GFS and CMC:




Some things to note in terms of potential land interaction, and I'll start with the islands/Caribbean here first. The models are showing another WSW motion around ~45W, and we can see in the 06z ECMWF height contours how the orientation of this ridge will lend to that motion. If Erin dips down to 16N, chances of at least some impacts to the islands greatly increases imo.



Thereafter, Erin’s speed and strength will be important factors in how far west she gets. It’s important to note that we only have ~24 hours of data so far on Erin, but in the graphic below can clearly see almost all the models have been too slow and too far north with Erin:



As Erin continues to deal with those negative conditions over the next several days, the question becomes when will Erin have the environment to produce deep convection and really strengthen? The longer that process takes to occur (and the shallower Erin remains), the more influence the low-level steering/trade winds has and the more ‘flex’ the ridge can have on driving Erin at faster forward speed.

Current steering layer for a weak tropical cyclone:


Moving on to potential impacts in the United States, I want to just focus on the main steering elements here (as models have a difficult time nailing these details down at such large lead times right now). Much of what I outlined above has compounding effects on the long-term track of Erin. This is the end of the 06z ECMWF run, and I’ve roughly outlined the ridge in red and have put a purple dash where the weakness/’recurve alley’ will be forming:

[syfr]

^^^ Great presentation of info, so that even an electrical engineer can understand it! ^^^

Thank you.

[Nimbus]

I would trust the model runs more if Erin wouldn't keep streaking southwest.
She is picking up moisture for a CDO at 17N now.
Needs to start heading due west pretty soon or the model initialization will be worthless.

[Ian2401]

Looks like Erin is right at 17N now, maybe heading a little bit more W than earlier - although it's hard to tell as some convection has covered the previously exposed center. Looks like it's matching up well with the 11am NHC forecast, which currently has it hitting 16.8N by 00z tonight. That'll be the next benchmark to watch.

[Sciencerocks]

[cycloneye]

Good data about CONUS landfalls.

 https://x.com/FerragamoWx/status/1955330103183016293

[SconnieCane]

Good data about CONUS landfalls.

 https://x.com/FerragamoWx/status/1955330103183016293

I don't know if this tells us that much at this juncture, since it's still far enough east that within 150 miles of its current position will include a lot of tropical cyclones that recurved along 40 or 45W, which we know won't be the case here.

[cycloneye]

18z Best Track:

AL, 05, 2025081218, , BEST, 0, 171N, 374W, 40, 1006, TS

[MarioProtVI]

Finally got my office all set up at the new place and some time to really check out Erin and the models this morning! First thing that jumps out on satellite imagery, Erin has a vigorous circulation but is convectively limited. This can be best seen in water vapor RGB composites (and some other features I will point out):

https://i.imgur.com/LNTDfwd.gif

https://i.imgur.com/XcZjPhz.png

Erin's circulation (green) is easy to spot here, and it’s also very evident convection is not able to build with much height/deepen. A healthy tropical cyclone will have deep white/fringe blue, but here we get this mixture of red in the high cloud (an indication that convection is not able to sustain vertically). There are three main negative factors that I am seeing:

1) the surrounding SSTs and OHC environment is not conducive for deep moisture generation. Water temps are close to 78F, and OHC is 0. This is essentially the minimal surface temperature that can support a system, and it really caps the available latent heat for producing deep convection.

Sea Surface Temperatures with current position:
https://i.imgur.com/biwdFUL.png

OHC values with previous track:
https://i.imgur.com/9w5tysq.png

2) I want to also note the environment out in front is taking A LOT of work to moisten. I’ve outlined the SAL line riding out in front (orange) in the WV RGB image above, but you can also clearly see it here in the CIMSS product:

https://i.imgur.com/443Zk2b.jpeg


3) Additionally, there is a mid level circulation (pink, future track in dashed pink) that has formed within the monsoonal trough, and this will begin to pivot along Erin’s flank today and then head northwest tomorrow (where models show the vorticity being stretched out and the moisture sacrificed to the SAL gods). Over the next two days though, this feature will interact with Erin's moisture envelope/profile and negatively strip some of the convective potential away.

700mb (mid-level) vorticity product showing second mid-level vort to the east of Erin:
https://i.imgur.com/U2eGR9j.png

So that is kind of what is going on currently, now I’ll transition to what the models are forecasting and note some trends. I’ll start with what the models have been showing the past 4-6 runs, and how they have been verifying. The trend so far has been for shifts to the south in the operational models, which we can analyze with the last 4 runs of the ECMWF (light blue previous runs -> dark blue current run), with verified positions marked in X from Brian Tang's page:
https://i.imgur.com/v00KReL.png

Here are the last 6 runs of the GFS and CMC:
https://i.imgur.com/bPp0FNQ.png

https://i.imgur.com/9AwVxYC.png

Some things to note in terms of potential land interaction, and I'll start with the islands/Caribbean here first. The models are showing another WSW motion around ~45W, and we can see in the 06z ECMWF height contours how the orientation of this ridge will lend to that motion. If Erin dips down to 16N, chances of at least some impacts to the islands greatly increases imo.

https://i.imgur.com/iRB7TQS.png

Thereafter, Erin’s speed and strength will be important factors in how far west she gets. It’s important to note that we only have ~24 hours of data so far on Erin, but in the graphic below can clearly see almost all the models have been too slow and too far north with Erin:

https://i.imgur.com/sIgvkVN.png

As Erin continues to deal with those negative conditions over the next several days, the question becomes when will Erin have the environment to produce deep convection and really strengthen? The longer that process takes to occur (and the shallower Erin remains), the more influence the low-level steering/trade winds has and the more ‘flex’ the ridge can have on driving Erin at faster forward speed.

Current steering layer for a weak tropical cyclone:
https://i.imgur.com/X2J0nxS.png

Moving on to potential impacts in the United States, I want to just focus on the main steering elements here (as models have a difficult time nailing these details down at such large lead times right now). Much of what I outlined above has compounding effects on the long-term track of Erin. This is the end of the 06z ECMWF run, and I’ve roughly outlined the ridge in red and have put a purple dash where the weakness/’recurve alley’ will be forming:
https://i.imgur.com/2Az4EO5.png

Always a pleasure seeing your detailed analysis on here


Meanwhile there’s definitely agitated cirrus in Erin’s circulation, meaning DMAX should give a big boost to it tonight.

[cycloneye]

5 PM. Still some islands are in the southern end of cone but there was a slight shift to the north.

[msbee]

Finally got my office all set up at the new place and some time to really check out Erin and the models this morning! First thing that jumps out on satellite imagery, Erin has a vigorous circulation but is convectively limited. This can be best seen in water vapor RGB composites (and some other features I will point out):

https://i.imgur.com/LNTDfwd.gif

https://i.imgur.com/XcZjPhz.png

Erin's circulation (green) is easy to spot here, and it’s also very evident convection is not able to build with much height/deepen. A healthy tropical cyclone will have deep white/fringe blue, but here we get this mixture of red in the high cloud (an indication that convection is not able to sustain vertically). There are three main negative factors that I am seeing:

1) the surrounding SSTs and OHC environment is not conducive for deep moisture generation. Water temps are close to 78F, and OHC is 0. This is essentially the minimal surface temperature that can support a system, and it really caps the available latent heat for producing deep convection.

Sea Surface Temperatures with current position:
https://i.imgur.com/biwdFUL.png

OHC values with previous track:
https://i.imgur.com/9w5tysq.png

2) I want to also note the environment out in front is taking A LOT of work to moisten. I’ve outlined the SAL line riding out in front (orange) in the WV RGB image above, but you can also clearly see it here in the CIMSS product:

https://i.imgur.com/443Zk2b.jpeg


3) Additionally, there is a mid level circulation (pink, future track in dashed pink) that has formed within the monsoonal trough, and this will begin to pivot along Erin’s flank today and then head northwest tomorrow (where models show the vorticity being stretched out and the moisture sacrificed to the SAL gods). Over the next two days though, this feature will interact with Erin's moisture envelope/profile and negatively strip some of the convective potential away.

700mb (mid-level) vorticity product showing second mid-level vort to the east of Erin:
https://i.imgur.com/U2eGR9j.png

So that is kind of what is going on currently, now I’ll transition to what the models are forecasting and note some trends. I’ll start with what the models have been showing the past 4-6 runs, and how they have been verifying. The trend so far has been for shifts to the south in the operational models, which we can analyze with the last 4 runs of the ECMWF (light blue previous runs -> dark blue current run), with verified positions marked in X from Brian Tang's page:
https://i.imgur.com/v00KReL.png

Here are the last 6 runs of the GFS and CMC:
https://i.imgur.com/bPp0FNQ.png

https://i.imgur.com/9AwVxYC.png

Some things to note in terms of potential land interaction, and I'll start with the islands/Caribbean here first. The models are showing another WSW motion around ~45W, and we can see in the 06z ECMWF height contours how the orientation of this ridge will lend to that motion. If Erin dips down to 16N, chances of at least some impacts to the islands greatly increases imo.

https://i.imgur.com/iRB7TQS.png

Thereafter, Erin’s speed and strength will be important factors in how far west she gets. It’s important to note that we only have ~24 hours of data so far on Erin, but in the graphic below can clearly see almost all the models have been too slow and too far north with Erin:

https://i.imgur.com/sIgvkVN.png

As Erin continues to deal with those negative conditions over the next several days, the question becomes when will Erin have the environment to produce deep convection and really strengthen? The longer that process takes to occur (and the shallower Erin remains), the more influence the low-level steering/trade winds has and the more ‘flex’ the ridge can have on driving Erin at faster forward speed.

Current steering layer for a weak tropical cyclone:
https://i.imgur.com/X2J0nxS.png

Moving on to potential impacts in the United States, I want to just focus on the main steering elements here (as models have a difficult time nailing these details down at such large lead times right now). Much of what I outlined above has compounding effects on the long-term track of Erin. This is the end of the 06z ECMWF run, and I’ve roughly outlined the ridge in red and have put a purple dash where the weakness/’recurve alley’ will be forming:
https://i.imgur.com/2Az4EO5.png

Excellent analysis. Thank you for sharing. Watching very closely from the Northeast Caribbean