Global model runs discussion

[cycloneye]

Dr Jeff Masters discusses about the GFS in a blog at WU.Here is plenty to look at about the GFS phamtom scenarios and I think the doc explains in a good way.

There are no tropical cyclone threat areas in the Atlantic to discuss today, and none of the reliable models for forecasting tropical cyclone genesis is predicting development over the coming five days. However, the 00Z Friday run of the GFS model predicts that a low pressure area will develop over the Western Caribbean by Wednesday, and push northwards into the Gulf of Mexico and become a tropical storm late in the week. The GFS has been fixated on variations of this idea in all of its runs for the past five days--though the timing of when the predicted storm will form has bounced around from 5 - 11 days into the future. Should we be concerned? A 2013 study by a group of scientists led by Florida State's Daniel Halperin found that we have three models that can make decent forecasts of the genesis of new tropical cyclones in the Atlantic: the GFS, European (ECMWF), and UKMET models. The study only evaluated the model skill for forecasts out to four days in the future, and the forecast skill declined markedly for three- and four-day forecasts. In the current scenario, we are talking about forecasts made much further into the future, which are bound to be low-skill. In addition, the study found that the GFS model had a high incidence of false alarms for tropical cyclone genesis forecasts in the Western Caribbean (50%). The other two reliable models for predicting tropical cyclone genesis (European and UKMET) had no hint of a low pressure area developing in the Western Caribbean on Wednesday in their 00Z Friday runs. One additional model to consider: the 00Z Friday run of the NAVGEM model is supporting the GFS's idea of a low pressure area forming in the Western Caribbean by Wednesday. The predecessor to this model, the NOGAPS model, was evaluated in the Florida State study, but performed poorly in making tropical cyclone genesis forecasts. However, when two or more models make the same genesis forecast, the odds of the event actually occurring are increased considerably, the study found.


Figure 1. Friday the 13th, GFS style: The 00Z UTC Friday, June 13, 2014 forecast from the GFS model for nine days into the future shows a powerful tropical storm in the Gulf of Mexico. The purple colors indicate winds of 50 - 60 knots (57 - 69 mph.) But is it a bogus forecast? Very likely.


Figure 2. The 2004–11 GFS forecasts for tropical cyclone genesis, showing Hits (green triangle), False Alarms (red square), and Incorrect Timing (blue circle) event locations. Numbers in parentheses are the numbers of model-predicted events. The model made 46 forecasts that a tropical depression or tropical storm would form in the Caribbean (purple box) during this 8-year period. Fully 50% of these forecasts were False Alarms; 11% of the forecasts verified, but the timing was off by at least a day (IT events); and 39% of the genesis forecasts verified with the right timing. Noteworthy is the model's few False Alarms over the Gulf of Mexico: only 15% of the total. Image credit: Halperin et al., 2013, Weather and Forecasting, "An evaluation of tropical cyclone genesis forecasts from global numerical models."

We know that the GFS model gets in trouble when making predictions of heavy thunderstorm activity via a problem called "convective feedback." Basically, the model sometimes simulates that an unrealistically large area of thunderstorms will develop, destabilize the atmosphere, and cause an area of low pressure to form that will draw in more moisture and create more heavy thunderstorms. This vicious cycle can snowball out of control and generate a bogus low pressure area that can then modify the upper level winds, reduce the wind shear, and allow a tropical depression to form. This problem may be less of an issue in a new version of the GFS model scheduled to be released late this summer; NHC hurricane specialist Eric Blake tweeted on Tuesday a comparison of the old and new 1-week GFS model forecasts for the Western Caribbean made last Tuesday, showing that the upgraded GFS model was not creating nearly as strong of a low pressure system as the old GFS model. Arguing against any development in the Atlantic the remainder of June is the anticipated strengthening in the West-Central Pacific Ocean of the Madden Julian Oscillation (MJO), a pattern of increased thunderstorm activity near the Equator that moves around the globe in 30 - 60 days. An active MJO in that part of the tropics tends to bring large-scale sinking motion to the tropical Atlantic and increased wind shear, which puts a damper on the chances of tropical storm formation in the Atlantic. The MJO is predicted to drift slowly eastwards into the Eastern Pacific by late June, which will tend to keep odds of tropical storm formation lower than average in the Atlantic into late June. All factors considered, I am inclined to give a 10% chance that the GFS model is correct in spinning up a tropical depression late in the week in the Western Caribbean.

http://www.wunderground.com/blog/JeffMa ... #commentop

[weatherwindow]

Thanks for the Masters post, Luis....is it not interesting that several claims have been made on behalf of the GFS over the past few years. They all concerned the correction/mitigation of the feedback issue. Regardless of earlier claims, it has hung around like a bad penny. Apparently, the convective feedback problem is far more intrinsic to the basic modelling than I had been led to believe. Perhaps, the anticipated late summer update, alluded to above, will finally put the problem to rest. However, after following the evolution of the model from the AVN forward, forgive me if I remain skeptical
Grtz from KW, Rich

[HurricaneTracker2031]

My analysis of the computer model situation: http://goo.gl/knqp3Q

If any development would occur, it would be beyond 5 days. Also. the GFS is known to have more false alarms so this is unlikely to happen. What you think?

[HurricaneTracker2031]

An area near Honduras and Nicaragua might be what the computer models are picking up on... Now, it seems that they are right. Development is still shown near 186hr.

My latest analysis of the current situation: http://goo.gl/R5rrnk

The posts in this forum are NOT official forecast and should not be used as such. They are just the opinion of the poster and may or may not be backed by sound meteorological data. They are NOT endorsed by any professional institution or storm2k.org. For official information, please refer to the NHC and NWS products.

[stormlover2013]

Only one model is showing this and it's the gfs, gfs keeps pro longing it and nobody knows where it would go since it's 10 days away and models don't have a good grasp on it.

[beoumont]

Perhaps, the anticipated late summer update, alluded to above, will finally put the problem to rest. However, after following the evolution of the model from the AVN forward, forgive me if I remain skeptical
Grtz from KW, Rich

I recall when the AVN only went out to 84 hours; and since it has been replaced and "upgraded" the reliability for TC genesis, has not really seemed to improve. I will guess that it never will for days four on out.

[Hurricaneman]

The GFS seems to finally be joining the other models with little to no development which means if we see another storm modeled on the GFS we may need the Euro or\and Canadian to join in before believing it, and to that note there doesn't seem to be anything modeled to develop up to July

[Dean4Storms]

What is the disturbed weather and deep convection that the 00Z ECMWF brings up into the eastern Gulf toward the Florida Panhandle starting at the 180 hour? It does not develop this, however it appears to be an area that might need monitoring? Anyone know what is causing it? Tropical Wave?

[KatDaddy]

The tropics are being discussed briefly in this afternoon's Houston-Galveston AFD:

THE 12Z MODELS FROM YESTERDAY AND AGAIN TODAY POINTING TO A POTENT
TROPICAL WAVE MOVING FROM THE CENTRAL CARIBBEAN ON SUNDAY TO THE
YUCATAN ON TUESDAY AND (THEN MODELS DIVERGE) EITHER STALLING PER
GFS IN THE CENTRAL GULF GETTING STRETCHED OUT INTO NRN FL TO BAY
OF CAMPECHE OR PUSHING WEST AND INTO TX ON WEDNESDAY. IF THIS
COMES TO PASS THAT IT REACHES SETX THEN RAIN CHANCES SHOULD
INCREASE DRAMATICALLY.

None of the other GOM AFDs mention anything about.

[KatDaddy]

Perhaps some additional well needed rainfall for the TX Coast if heads this way.

[floridasun78]

i watching area by honduras that area were gfs want form ts past few it not move for past few weeks

[AJC3]

Both the ECM and, to a lesser extent, the GFS are advertising lowering of mid level heights offshore the SE U.S. in the 6-10 day time frame. Of particular interest is the ECM, which is faster/stronger with what takes places at 500 MB. It pinches off a small H50 low and slowly retrogrades it SW into Florida next weekend. Should the global model solutions gravitate toward the ECM, and hold serve, it would not be out of the question to see a baroclincally initiated/enhanced low develop in this general area (offshore the SE U.S.) toward next weekend or very early in the following week.

For grins...21/00Z ECM:

250MB winds (top left), 500MB height/vorticity (top right), 850 MB winds/vorticity (bottom left), SLP/wind/1000-500MB mean RH (bottom right)

Left 4-panel image: 0hr. Right 4-panel image: 240hr.

[NDG]

The Euro most times is bias when it comes to cut off a low in the SE US, is what I have noticed in the past.

[gatorcane]

Following up from AJC3's post above, we have three global models - the ECMWF, the GFS, and CMC that are showing lower heights off the SE US coast in the long-range:

00Z ECMWF, 192 hours:


06Z GFS 192 hours:


00Z CMC 168 hours:

[gatorcane]

12Z ECMWF shows the weak retrograding low offshore the West Coast of Florida heading west at 168 hours:



The 12Z CMC also shows the retrograding low (upper-left hand corner image):

[gatorcane]

Global models still showing the drop in heights off the SE U.S. coast now in the medium range (5 days from now). The GFS shows the lowest heights a bit further north than the ECMWF but same general area:

ECMWF 120 hours:


GFS 120 hours:

[Hurricaneman]

Global models still showing the drop in heights off the SE U.S. coast now in the medium range. The GFS shows the lowest heights a bit further north than the ECMWF but same general area:

ECMWF 120 hours:
http://i58.tinypic.com/141kr3t.jpg

GFS 120 hours:
http://i57.tinypic.com/2zxs7pt.jpg

Actually I think the GFS shows the beginning of height falls around Saturday and while the Euro does it around Sunday so the area near the Carolinas and Northern Bahamas may need to be monitored in the following days with the model support and I wouldn't be surprised if this area gives us a Subtropical or Tropical Depression or Storm as this area of the atlantic has had higher Vertical instability than normal and lower shear

The posts in this forum are NOT official forecast and should not be used as such. They are just the opinion of the poster and may or may not be backed by sound meteorological data. They are NOT endorsed by any professional institution or storm2k.org. For official information, please refer to the NHC and NWS products

[CFLHurricane]

Welp now that Arthur is past Florida, I'm looking forward to the next storm.

Any insight? Anybody?

:crickets:

[Hurricane Alexis]

Welp now that Arthur is past Florida, I'm looking forward to the next storm.

Any insight? Anybody?

:crickets:

Do you only track storms when they're at risk of impacting Florida or are by Florida? Cause Arthur is still out there and is at its peak.

[Alyono]

while the models did not get the TC formation very well... they did pick up on an area of general low pressure several days in advance