ATL: IRMA - Models

[birddogsc]

While Floyd was at a much higher latitude across the top of the islands on its track, the last few days of the Euro look Floyd-ish to me.

[sma10]

That's actually the spread of the ensembles and not the storm stretching out. NAVGEM out to 160 hours (in spurts). Looks like a landfall around Palm Beach County. Coming in at 950 so strong Cat 3 there. I don't know if I buy the run, but it makes enough sense.
https://www.tropicaltidbits.com/analysi ... 0&ypos=200

Now we've got the JMA, CMC, and NAV trying to kill me. Nice lol

It's good to be in the crosshairs this far out

Problem is you're in the crosshairs of the clueless models, so strangely enough there may be some bizarre, reverse ju-ju going on. Lol

[Blown Away]

6-7 days both GFS/Euro have at Cat 4/5 in SE Bahamas just missing SFL, probably TS/Hurricane gusts, and into Carolinas... The FL/Carolinas westward squeeze play playing out... Man starting to become a real concern..

[stormreader]

Two notes and then I’m off for the night.

1. Euro and GFS are nearly identical at hour 144 with trough and ridge placement/orientation. This is a big deal because that’s not far out and getting within range where we will see much smaller changes. The fact they’re so close now at this range tells me the pattern is being resolved gradually and chances for an East Coast hit are very high, imo.
2. Most likely track is, IMO, Floyd as the synoptic setup at days 5-6 favors a storm that comes close to FL but then gets lifted north into the weakness. Florida will be very close but I believe they’ll be spared a landfall. NC may not be as fortunate.

It would be easy to say this was a Floyd setup if this was a five day forecast. But this is 8-9 days out. This storm will no doubt come very close to Fl. If you think it will be moving radically north in the Fl coastal waters, then you are counting on a trough-ridge relationship that simply might not be there in 8-9 days. The odds are much in favor of the ridge, and an actual Fl impact, or, unusual as it might seem to many, a trek south of Fl and into the GOM.

[T'Bonz]

Yuck. Another NC hit. Lucky this is too far out to count.

[stormreader]

Again like I mentioned once this wsw motion started.. I knew the models would start to swing more westerly.. now just watch if this drops even a little south of forecast it will cause a slow down resulting in the ridge building and more westerly. the Florida straights and gulf are still not out of the woods.

Thank you! I don't feel so alone. Still putting the Carolina's in my "Irma window" for now, but I always thought that the depth and lasting power of the trough were suspect. I believe that when this forecast is refined and altered, it will be in favor of the ridge, and my consideration of a trek through the Fl Straits and into the GOM will not seem so outlandish.

[Digital-TC-Chaser]

[Aric Dunn]

As much of a scientist as I am... I hate looking at the data and having "feelings" .......... after having a review of current synoptics. Once this bottoms out with the wsw to sw motion I just dont see the ridge cutting off and allowing such a sharp turn..

A very distinct possibility is we get this wsw to sw motion ( with some wobbles as it deepens) then as the ridge slides/weakens IRMA does not just turn it travels more westerly and gradually turns ( how they almost always do) coming through the NE islands and anywhere from PR To DR and then becasue of the longer track the trough lifts out ridging builds in and the flow becomes more zonal. at which time IRMA is in the SE bahamas heading W to wnw for the florida straights.. without anything left to turn it right away.

[Blown Away]

Whats playing out is models are dipping down to @16.3N in the short term before turning, which is delaying the arrival to the trough near the CONUS and causing W shifts... Mets have hinted at this scenario...

[stormreader]

As much of a scientist as I am... I hate looking at the data and having "feelings" .......... after having a review of current synoptics. Once this bottoms out with the wsw to sw motion I just dont see the ridge cutting off and allowing such a sharp turn..

A very distinct possibility is we get this wsw to sw motion ( with some wobbles as it deepens) then as the ridge slides/weakens IRMA does not just turn it travels more westerly and gradually turns ( how they almost always do) coming through the NE islands and anywhere from PR To DR and then becasue of the longer track the trough lifts out ridging builds in and the flow becomes more zonal. at which time IRMA is in the SE bahamas heading W to wnw for the florida straights.. without anything left to turn it right away.

Yes sir. A very real possibility which I have considered for a couple of days now. Climo and storm strength have played a part in my thinking, too. Keeping the window open for Carolinas and then south to north coast of Cuba, but, I have to tell you that the southern part of my thinking is gaining in influence.

[stormreader]

Whats playing out is models are dipping down to @16.3N in the short term before turning, which is delaying the arrival to the trough near the CONUS and causing W shifts... Mets have hinted at this scenario...

Problem: Any further delays might cause Irma to actually miss the trough. It's a very transitory feature anyway, in early Sept, it will be lifting out in a heartbeat, delay the storm's arrival, and it might simply miss it altogether, and take a southern trek over S Fl, or even through the Fl Straits and straight into the GOM. Not saying this will happen, but I said a couple of days ago that a track out to sea seemed almost impossible. Much more likely for NW into the Carolinas, WNW continued into Fl(looking more likely now), or a trek further south through the Straits and into the GOM, which might not seem so far-fetched.

[sma10]

As much of a scientist as I am... I hate looking at the data and having "feelings" .......... after having a review of current synoptics. Once this bottoms out with the wsw to sw motion I just dont see the ridge cutting off and allowing such a sharp turn..

A very distinct possibility is we get this wsw to sw motion ( with some wobbles as it deepens) then as the ridge slides/weakens IRMA does not just turn it travels more westerly and gradually turns ( how they almost always do) coming through the NE islands and anywhere from PR To DR and then becasue of the longer track the trough lifts out ridging builds in and the flow becomes more zonal. at which time IRMA is in the SE bahamas heading W to wnw for the florida straights.. without anything left to turn it right away.

I mentioned a couple days ago that the GFS' post-SW dip had a red flag, in that it was "po-going" Irma's track from WSW to WNW almost instantaneously. It just didn't make sense, and we can see that there is now a smoothing of the track where she moves due westerly for a time, thus resulting in an overall SW shift of track.

Re: PR/DR, I happen to agree with you. I have the sense that somehow this system will get engaged in Hispaniola. Over many years I have seen systems modeled to "just barely skirt" the DR north coast, resulting in a very dangerous situation for the US. But it seems, without fail, that if a system gets close enough the circulation gets pulled in. I guess we'll find out in a few days, but something to watch for.

[Aric Dunn]

As much of a scientist as I am... I hate looking at the data and having "feelings" .......... after having a review of current synoptics. Once this bottoms out with the wsw to sw motion I just dont see the ridge cutting off and allowing such a sharp turn..

A very distinct possibility is we get this wsw to sw motion ( with some wobbles as it deepens) then as the ridge slides/weakens IRMA does not just turn it travels more westerly and gradually turns ( how they almost always do) coming through the NE islands and anywhere from PR To DR and then becasue of the longer track the trough lifts out ridging builds in and the flow becomes more zonal. at which time IRMA is in the SE bahamas heading W to wnw for the florida straights.. without anything left to turn it right away.

I mentioned a couple days ago that the GFS' post-SW dip had a red flag, in that it was "po-going" Irma's track from WSW to WNW almost instantaneously. It just didn't make sense, and we can see that there is now a smoothing of the track where she moves due westerly for a time, thus resulting in an overall SW shift of track.

Re: PR/DR, I happen to agree with you. I have the sense that somehow this system will get engaged in Hispaniola. Over many years I have seen systems modeled to "just barely skirt" the DR north coast, resulting in a very dangerous situation for the US. But it seems, without fail, that if a system gets close enough the circulation gets pulled in. I guess we'll find out in a few days, but something to watch for.

well, the dynamics of land interaction especially with Hispaniola has well been documented, it is by no means certain... angle of approach is a big player...

hurricane Goerges passed nearly over the center of the highest peaks and the low level center just sort of molded around it. all the while Hurricane Jean went south to the north got completely disrupt and reformed..

then there is hurricane debby in 2000 that approached at a similar angle that IRMA might and it literally like a tether ball got snagged and actually the low level center rotated around the mountains while the mid level kept moving as usual and there was no shear ...

it's not exactly known.. but always needs to be watched...

with IRMA I don't think it's going to get close enough to have any major issues with DR.. well at least at the moment.

[Airboy]

How many days ahead do models normaly handle devolepment of ridges with high accurancy?

[Aric Dunn]

How many days ahead do models normaly handle devolepment of ridges with high accurancy?

That is not an answerable question..

[AutoPenalti]

How many days ahead do models normaly handle devolepment of ridges with high accurancy?

Without Gulfstream data, it's pretty obscure.

[chaser1]

What is alarming, is an apparent recognition by all 0Z global models affirming greater W. Atlantic height rises then previously forcast, and a rapidly retreating deep E. CONUS short-wave. Right now, I'm far less concerned about any models particular 7 day forecast solution than i am about the models continuing to advertise this synoptic pattern which seemingly increases ridging over the Conus AND the West Atlantic. With that pattern in place a lot may ride on nearer term motion and the slightest deviation to Irma's forward speed and track. Those variables may have significant implications on where Irma may well end up. I'm pretty convinced there's a serious threat to the N. Leewards and Virgin Islands. For now, I'll leave the various models to play landfall roulette with this hot potato but I'll tell you this much.... with strong high pressure in the mid levels showing signs of quickly filling in the wake of a fast retreating E. CONUS short wave I believe the 500 mb pattern will ultimately bridge. Therefore, at some point I believe the net result will cause Irma to reach the Gulf of Mexico. Who she visits along the way or thereafter will be the devils' details to sort out.

[Digital-TC-Chaser]

http://www.ndbc.noaa.gov/?lat=20.185718 ... =&op=&ls=n

[USTropics]

How many days ahead do models normaly handle devolepment of ridges with high accurancy?

Below are some links that allow you to ascertain how well a model forecast has verified as a function of forecast hour and cycle (it shows the most recent run in blue and then cycles through the previous runs for the same forecast hour in red):

ECMWF 00z/12z- http://www.wpc.ncep.noaa.gov/html/ecmwf0012loop500.html
GFS 00z/12z - http://www.wpc.ncep.noaa.gov/html/gfs0012loop500.html
GFS 06z/18z - http://www.wpc.ncep.noaa.gov/html/gfs0618loop500.html
UKMET 00z/12z - http://www.wpc.ncep.noaa.gov/html/ukmet0012loop500.html
NAM 00z/12z - http://www.wpc.ncep.noaa.gov/html/nam0012loop500.html

[USTropics]

Anomaly correlation coefficient (AC score) can help as well (this is for a 5 day forecast; above a 0.9 is considered a good 5-day forecast score):