Models and its characteristics...

[Fego]

I have been told that some models are good forecasting intensity and others forecasting trajectory; some are good when a system is developing and others when is already a storm or hurricane; some are good forecasting in a two or three days basis and others up to a week or more. Then, my question is, where can I get that info about the models?. If doesn't exist, may be somebody, with the knowledge, can help me here. Thanks!

[Recurve]

There have been some excellent explanations in this forum. I don't have a link but you can use the search function. One of the pro mets described each model in detail with its sources and weaknesses.

Here is one such post that I found in my archive:

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Last edited by wxman57 on Tue Sep 20, 2005 2:06 pm; edited 1 time in total

After seeing the various model runs posted online for years, I've decided to do a little write-up on the various models to help those of you with little knowledge of what you're looking at understand them just a little.

Most of the "tropical" models generally posted on this and other forums are pretty worthless for hurricane forecasting. I've compiled a little list of what some of the models are and which ones merit a closer look. If any of you have questions about some other models, I, or any of the other Pro Mets here can try to answer them. And if anyone has some other models or hints/tips about using any of the models, chime on in!

XTRAP -- simple extrapolated track. Assumes the storm just keeps going at the same speed and direction. No physics at all involved. Generally of no use except as a "what if" scenario.

BAMD -- deep layer Beta Advection Model. Good for strong storms in the lower tropics (south of 20N latitude where steering currents remain constant). It doesn't emply much, if any, physics to predict changes in steering currents. Because of that, it shoudl not be used where fronts/trofs highs/lows move on by (north of 20N latitude. Never use it in the Gulf or western Atlantic.

NHC -- The official NHC forecast.

BAMM -- mid layer Beta Advection Model. For weaker to moderate-strength storms in the deep tropics. Same shortcomings as the BAMD model above. Don't use it north fo 20N.

NHCA98E -- Climatology-based "model". Not really a model, just compares the current storm position to previous storms and "guesses" where it might go. Completely useless everywhere.

CLIPER -- CLImatology and PERsistence. No physics, not a real model. It's used by forecasters to determine if their forecasts have any skill at all. If you can't beat climatology and persistence, then you're not a very good forecaster.

LBAR -- Limited BARotropic. Limited alright, limited in its ability to forecast tropical cyclones. Generally ignore it.

UKMET -- Generally not a bad model. It's put out by the United Kingdom met office. It's worth a look at, but tropical cyclones aren't its forte'. It is run twice daily at 12Z (7am CDT) and 00Z (7pm CDT)

GFDL -- Geophysical Fluid Dynamics Laboratory model. This model was designed for hurricanes. It's based upon the latest AVN (American GFS) model. Because of that, though, it may tend to erode ridges too quickly north of stronger cyclones, leading to a right of track bias toward early recurvature. The GFDL did very well with Katrina, better than most other models, in fact. I take a hard look at the GFDL when making a forecast, but it has been all over the place with its forecast for Rita so far.

NOGAPS -- US Navy NOGAPS model. Designed for marine use, mostly. Sometimes does OK with tropical cyclones. Certainly worth a look. Run only twice daily so it's not available as often as other models.

CMC -- Canadian Model. I've never been too fond of this model. It may be good for winter up in Canada, but it's never shown me any expertise with tropical systems. If it gets a storm right, it's just usually pure luck:
http://weatheroffice.ec.gc.ca/model_for ... bal_e.html

NAM/ETA -- The new North American Model (the ETA was renamed recently). One of the worst models out there for the tropics, and just about everything else. Recent "improvements" have really made this model pretty bad for use down south. Ignore it laugh at it, but don't use it to predict the path of a tropical cyclone.

So, of all the models above, the GFDL is one of the better models. But, like I said, it's been all over the place with the Rita track so far and I don't trust it much yet.

I also like to look at the American GFS model for comparison:
http://www.nco.ncep.noaa.gov/pmb/nwprod ... arib.shtml

The GFS model certainly has its shortcomings, but if one knows its strengths/weaknesses, it can be a very good tool. Don't just trust it as-is unless you know what you're doing.

The European model (ECMWF) is a good tool. It's not shown a very good track record with recent storms, however. Until today, it had Rita moving into the BoC or southern Mexico. Here's a link to a site I like to use for the 7-day ECMWF:
http://weather.cod.edu/forecast/loop.ecmwf850t.html

MM5 -- Florida State's MM5 model is definitely worth a look. It's a "home brew" model tweaked by FSU mets. Doesn't have too much of a track record, though:
http://moe.met.fsu.edu/mm5/

Sometimes, the best models are what we call "ensemble" or "consensus" models. Simple "consensus" models just take 2-3 different models and simply average the positions for each time step out to 3-5 days to come up with a "consensus track". Occasionally, this consensus is better than any one model. Some examples of consensus models:

GUNA - GFDL, UKMET, NOGAPS, AVN (GFS)
GUNS - GFDL, UKMET, NOGAPS

More complex "ensemble" models actually analyze a number of models, account for each model's individual weaknesses, combine/average the tracks, then produce a single forecast track. You've probably heard of the Florida Superensemble model. This model has done VERY well with many tropical cyclones. Unfortunately, it's not available to the general public.

Here's a link to a good model page. It has a variety of models, from BAMs to various iterations of the GFDL model, to the GFS model, and some consensus model. Just weed out the "trash" models when looking at it:

http://euler.atmos.colostate.edu/~vigh/guidance/

Click on "Frame 1" of the early model guidance for Rita forecasts.

Oh, and finally, an online friend of mine, Gary Gray, puts out a very good daily analysis of each tropical cyclone. I HIGHLY recommend reading his detailed thoughts on each storm:

http://www.millenniumweather.com/tropical/discuss.html

Last edited by wxman57 on Tue Sep 20, 2005 2:06 pm; edited 1 time in total

[Fego]

Thank you very much Recurve. I'll will create an archive like you did. BTW, that was an excellent research made by Wxman57.

[JtSmarts]

That was an excellent post by wxman57. It should be stickied somewhere.

[Jim Cantore]

I'd been looking for that post Recurve, thanks for posting it.