Global model runs discussion

[LarryWx]

Today's 12Z Euro still shows no support for model U as it has basically nada for the W. Caribbean. It had only one very weak low on one run. Otherwise, it has had nada.

[gatorcane]

Today's 12Z Euro still shows no support for model U as it has basically nada for the W. Caribbean. It had only one very weak low on one run. Otherwise, it has had nada.

12Z Euro shows an EPAC system again, starting to get some consistency from the Euro on something in the EPAC while the GFS thinks it develops in the SW Caribbean:

[Hammy]

12z Euro is showing the Pacific system either making it's way into the Caribbean or aiding in another low forming, as it now shows vorticity and a weak low in the Caribbean. The Atlantic system, while weaker, is still showing up in some form, meaning it's still not out of the question for development (given the model developed Edouard on a single run at the ten day mark, then failed to develop it again until about 2-3 days prior.)

[gatorcane]

12z Euro is showing the Pacific system either making it's way into the Caribbean or aiding in another low forming, as it now shows vorticity and a weak low in the Caribbean. The Atlantic system, while weaker, is still showing up in some form, meaning it's still not out of the question for development (given the model developed Edouard on a single run at the ten day mark, then failed to develop it again until about 2-3 days prior.)

Interesting indeed, 240 hours below:

[LarryWx]

No offense meant to other posters, but I'm personally still considering the Euro's support for Model U as being virtually zero as the timing/surface low route is way different and the Euro never has anything more than a very weak low in the NW Caribbean.

[blp]

Euro moves the EPAC system over C.America as it has done on several runs but difference now is that a portion of it reaches the NW Carribean. So the difference between it and the GFS are still quite large in the short term but the end result favors something on the Atlantic in the mid to long range.

[SFLcane]

Steve Gregory... Great read http://www.wunderground.com/blog/SteveGregory/comment.html?entrynum=247

The tropical environment continues to be generally hostile to tropical cyclone formation, but a gradual decrease in wind shear and a somewhat more favorable overall flow pattern MAY begin to take shape, particularly in the western CARIB, next week.

The GFS is famously far too aggressive in developing tropical cyclones in the western CARIB both at the start and end of the hurricane season – and has been ‘forecasting’ a tropical formation in the western CARIB between Days 13-15 seemingly during every other model run for over the last couple weeks. HOWEVER, over the past few days, much greater continuity in these forecasts has appeared, with several other global models also (very roughly) picking up on this trend as well.

Though the probabilities of a cyclone formation have increased – with a formation increasingly likely in about 7-10 days in the western CARIB – conditions do not appear favorable for a cyclone to form during the next 5-days. This trend is also in rough agreement with several other global models.

[Hammy]

No offense meant to other posters, but I'm personally still considering the Euro's support for Model U as being virtually zero as the timing/surface low route is way different and the Euro never has anything more than a very weak low in the NW Caribbean.

I've personally stopped checking MU at all now except to get an idea of the long range temperatures here.

[SFLcane]

FIM..

[blp]

No offense meant to other posters, but I'm personally still considering the Euro's support for Model U as being virtually zero as the timing/surface low route is way different and the Euro never has anything more than a very weak low in the NW Caribbean.

There is no offense. We are all stating our opinions which is what is awesome about this site. The Euro and GFS are developing different lows no question. The end result is what I am looking at and both models do agree that a large trough over the E. Coast is going to drag tropical moisture into the NW Caribbean the question is how strong and the timing on whether or not it will get picked up completely or left behind as another ridge builds in. It is hard to argue against the EPAC origin the Euro shows with how favorable it is right now.

[Dean4Storms]

The 12z ECM is basically onto the GFS depiction with a Low in the Western Carib. Sea and a Trough in the central US. It is just delayed back in time more than the GFS. GFS could be too fast or the ECM to slow.

ECM ENS @ 240hrs
http://www.tropicaltidbits.com/analysis ... atl_11.png

ECM OP...@ 240hrs

http://www.tropicaltidbits.com/analysis ... atl_11.png

12z GFS at 240hrs
http://www.tropicaltidbits.com/analysis ... atl_37.png

[gatorcane]

This is a nice addition to Levi's site:

"New! ECMWF and EPS basic WMO products are now available at 0.5° resolution."

http://www.tropicaltidbits.com/analysis/models/

[asd123]

Nice, but missing a lot of parameters such as 2m temp, wind, precip, 850 mb temp wind, so on...

[crownweather]

Nice, but missing a lot of parameters such as 2m temp, wind, precip, 850 mb temp wind, so on...

Those parameters, I believe, are at a higher resolution (0.125 degrees) and costs A LOT of money to obtain.

[gatorcane]

Though the NAM is not a good tropical model, it has started showing something forming in the SW Caribbean the past few runs. Here is how the 18Z NAM run ends at 84 hours where the low is stationary:

[gatorcane]

18Z GFS yet again showing genesis with a 1005 MB low at 96 hours:

[LarryWx]

Steve Gregory... Great read http://www.wunderground.com/blog/SteveGregory/comment.html?entrynum=247

The tropical environment continues to be generally hostile to tropical cyclone formation, but a gradual decrease in wind shear and a somewhat more favorable overall flow pattern MAY begin to take shape, particularly in the western CARIB, next week.

The GFS is famously far too aggressive in developing tropical cyclones in the western CARIB both at the start and end of the hurricane season – and has been ‘forecasting’ a tropical formation in the western CARIB between Days 13-15 seemingly during every other model run for over the last couple weeks. HOWEVER, over the past few days, much greater continuity in these forecasts has appeared, with several other global models also (very roughly) picking up on this trend as well.

Though the probabilities of a cyclone formation have increased – with a formation increasingly likely in about 7-10 days in the western CARIB – conditions do not appear favorable for a cyclone to form during the next 5-days. This trend is also in rough agreement with several other global models.

I feel that Steve Gregory's writeup is very good and makes perfect sense. However, with all due respect to Mr. Gregory, I don't at all agree with him that the GFS "has been ‘forecasting’ a tropical formation in the western CARIB between Days 13-15 seemingly during every other model run for over the last couple weeks". Note that I bolded his reference to days 13-15. If one were to look back at the documentation of the GFS runs on the last few pages of this thread, he/she would realize that the GFS has been very consistent with development in the W. Caribbean near 10/10 since at least that one run Luis showed from 9/26, nine days ago. Granted, on that run, genesis was, indeed, on day 14 (10/10). However, it has consistently gotten closer than day 14 ever since then. So, genesis hasn't been on days 13-14 in over a week. By the runs of one week ago (9/28), genesis had already moved up to days 11-12. Now it is all of the way up to ~days 3-5. I think it is very important to correct this for the record because it shows that the GFS' timeframe has not at all been slipping since this genesis date of 10/10 first appeared. In showing a genesis that isn't slipping, it shows that it is a totally different situation vs. that May/June horrible debacle and should give the GFS some more credibility than if it were to have continued slipping.

[gatorcane]

By 120 hours the 18Z GFS shows the low starting to move slowly NNW...like previous runs.

[blp]

18z Navgem has this starting up at 36hr moves it inland over Honduras 66hr and keeps heading WNW over the coast until it goes inland again over Belize. It does keep it strong 1002mb despite all the land interaction, which is a change from the 12z which killed it over land.

[Dean4Storms]

We'll know more on this by mid week, by then either the GFS back peddles to match more in line with ECM or drops it altogether if it is wrong. Have to say that climatologically speaking it is possible and the overall pattern fits.