Which model do you trust? And, Arctic sea ice reaches a record minimum

By: Dr. Jeff Masters , 7:33 PM GMT on August 17, 2007

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Hurricane Dean, now a major Category 3 hurricane with 125 mph winds, continues to intensify and grow larger in size. Dean pounded Martinique and St. Lucia this morning, and claimed its first victim when a 62-year old man died on St. Lucia while trying to save his cow from raging flood waters.

Dean's eye is now visible on long range radar out of Puerto Rico. Buoy 42059 is in Dean's path, and should be interesting to watch.

We're fairly confident of the 1-2 day forecast, which has Dean headed west to west-northwest over the Central Caribbean, very close to Jamaica and the Cayman Islands, then into the Western Caribbean. After that, things become murkier. The latest 12Z runs of the NOGAPS, UKMET, GFS, and HWRF computer models all show Dean hitting the Yucatan Peninsula, and continuing on into the Gulf of Mexico towards a second landfall near or south of the Texas border. The HWRF run is slower, and does not take Dean to the coast at the end of its forecast period. The big outlier is the GFDL model, which now takes Dean northwest into central Louisiana. Which model is correct? The problem is that each model has a different solution for the behavior of an upper-level low pressure system expected to be over the Gulf of Mexico early next week. Which model should we trust?

In 2006, the official NHC forecast performed better than any of the individual computer forecast models. However, several "consensus" forecasts made using an average of the "big four" computer models (GFDL, GFS, UKMET, and NOGAPS), slightly outperformed the official forecast at some time periods (Figure 1). The Florida State Super-Ensemble (FSSE), for example, combines the "big four" models on the basis of past performance in an attempt to correct for biases in those models. (The FSSE is owned by a private company, which makes it available to NHC but not the general public). The Florida State Super Ensemble slightly out-performed the official NHC forecast at most forecast times.

The "big four" models are plotted on wunderground.com's computer model page for Dean, (along with the inferior BAMM model, which is plotted since it is always available quickly, and has done well at longer range forecasts in the past). We do not get tracking points for the ECMWF or HWRF models at this point, so you'll have to go the raw plots to see those forecasts. Note that three of the "big four" models performed well in 2006, with the GFDL and GFS performing the best. The UKMET had a very poor showing in the Atlantic in 2006. However, the UKMET was the best-performing model in the Eastern Pacific in 2006, along with the GFDL and BAMM models.

The European Center's model (ECMWF) outperformed the "big four" consensus models for 72, 96, and 120 hours forecasts in the Atlantic. However, the ECMWF model was generally not available in time to be used by forecasters. Efforts are being made to make the ECMWF available in a more timely fashion for the 2007 season, which would be a big help. We also have the new HWRF (Hurricane Weather Research Forecast) model this year. In tests done on a number of hurricanes for past years, the HWRF performed about as well as the GFDL (Figure 2).



Figure 1. Track forecast skill in 2006 of the official forecast and the various models, compared to a "zero skill" forecast using NHC's CLIPER5 model. The CLIPER model (short for CLImatology and PERsistence) is a model that makes a forecast based on historical paths hurricane have taken, along with the fact that hurricanes tend to keep moving in the direction they are going (i.e., their current motion persists). Note that many models had a negative skill for their 120 hour (5 day) forecast. The official NHC forecast had about 10% skill at 5 days. Image credit: NHC.

Figure 2. Track errors for 48-hour forecasts from the 2006 version of the GFDL model (black) and the new HWRF model (red). The HWRF model performed better on some hurricane than the GFDL, and worse on others. Overall, the two models had about the same performance on the cases tested. Image credit: Naomi Surgi, NOAA Environmental Modeling Center.

In conclusion, the official NHC forecast outperforms all the individual models, particularly at long ranges. Looking at the individual model plots can be helpful to determine the uncertainty in the forecast, but it's tough to beat the NHC. In the case of Dean, where one model is an outlier from the rest, it is usually better to believe the consensus of the other models.

If you want to look at plots of the individual models, I've written a description of the various models and where to find these plots on our tropical weather page.

Arctic sea ice shrinks to record low
The National Snow and Ice Data Center announced today that Arctic sea ice has just surpassed the previous single-day (absolute minimum) record for the lowest extent ever measured by satellite. Satellite measurements began in 1979. Sea ice extent has fallen below the 2005 record low absolute minimum and is still melting. Sea ice extent is currently tracking at 5.26 million square kilometers (2.02 million square miles), just below the 2005 record absolute minimum of 5.32 million square kilometers (2.05 million square miles). This new record was set a full five weeks before the usual late September minima in ice extent, so truly unprecedented melting is occurring in the Arctic. The most recent images from the North Pole webcam show plenty of melt water and rainy conditions near the Pole.


Figure 2. Current extent of the polar sea ice, compared to the normal for this time in August (pink line). Image credit: National Snow and Ice Data Center.

I'll have an update Saturday morning.
Jeff Masters

Hurricane Dean near the island Puerto Rico (Hector777)
the ciclonic surge hard mind in Salinas,Puerto Rico mines the Community Las Ochenta in the south of Puerto Rico
Hurricane Dean near the island Puerto Rico

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3235. StormJunkie
2:01 PM GMT on August 18, 2007
Yeah paul, but it is still mid Tx and the N out-lier. Not to mention, the 06z run yesterday did the same thing and then went back N of that at 12z...

Sorry, my bad...The 06z run is S Tx...My fault!!
Member Since: August 17, 2005 Posts: 26 Comments: 16866
3234. CJ5
9:00 AM CDT on August 18, 2007
SJ, I just looked at the latest GFDL and it appears it moved thier landfall forcast further W. Yesterday it was east TX now its the border. Is this the latest or have they went back to E Tx?
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3233. nrtiwlnvragn
2:00 PM GMT on August 18, 2007
Wecouldoit

Thanks for that URL, I replaced my existing Favorites for the SFWMD with that one. Much more information.
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3232. paulfrmpasschristian
8:01 AM CST on August 18, 2007
not likely at this point bootsie..just keep your eye one it though
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3231. TXMET
1:59 PM GMT on August 18, 2007
Tang, I saw the same thing, but for what it's worth, all the models now have it going S of Corpus Christi. We'll see, though, it's still a long way out.
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3230. StormJunkie
1:57 PM GMT on August 18, 2007
Good point atmo! I now remember the NWS telling me that in Chas when I visited. That is what I love about this place, sometimes I have to hear it multiple times before I can get it to stick...lol

Charleston NWS launches balloons at 7 and 7 est. Which is one hour before 00 and 12 z
Member Since: August 17, 2005 Posts: 26 Comments: 16866
3229. fire831rescue
1:57 PM GMT on August 18, 2007
Posted By: Bootsie1 at 1:57 PM GMT on August 18, 2007.
Could this monster hit Mississippi?


Let's hope not. But we can't rule everything out. Just be sure you are prepared with all of your emergency supplies and have an evac plan just in case.
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3228. Bootsie1
8:57 AM CDT on August 18, 2007
Could this monster hit Mississippi?
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3227. JRRP
1:41 PM GMT on Agosto 18, 2007
I REPEAT: DEAN LOOK LIKE IT GOING TO HAITI
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3226. cchsweatherman
1:42 PM GMT on August 18, 2007
Good morning all. Last night, I have to be honest with you all, was the first time I really understood the magnitude of this storm and how many lives this will either significantly change or even destroy and I could not help but to cry thinking of the possible outcome of a monster storm like this to the vulnerable Caribbean islands. No matter what happens, someplace is never going to be the same after this hurricane gets through with them. I prayed for anyone in the storm's path last night. This is no longer a time for wishcasting as you all would like to call it, but a call to duty for your assistance to whomever gets struck with the heart of this storm.

I know this is a blog concerning tropical weather, particularly now Hurricane Dea, so I have some comments on that topic as well. Looking at the latest WV loop, it appears as if the ULL is migrating SW towards the western tip of Cuba and the Yucatan Peninsula. Someone correct me if they feel I am wrong, but that is what I am seeing right now. If that is the case, the Yucatan and quite possibly Texas could be shielded from any direct hit from Hurricane Dean. I have never in my life seen a storm that while Hurricane Hunters were out that was rapidly strengthening in every pass. This is a very powerful hurricane and certainly one of the largest in Caribbean history.

Well, I will talk to you later.
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3225. CJ5
8:57 AM CDT on August 18, 2007
Posted By: StormJunkie at 8:56 AM CDT on August 18, 2007.
The likely hood that Dean will go N is very slim.

So CJ, you are ruling out the GFDL?

You could not pay me to bet against the GFDL.


That is a tough call SJ on the GFDL. I personal think that there is not much out there that will bring it N. I think after 80w we may get a WNW movement but nothing major. I could be wrong but my tracks have held so far....
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3224. atmoaggie
1:58 PM GMT on August 18, 2007
SJ, I went looking for radiosonde data and it isn't NOAA, but many of the international airports that launch radiosondes at only 0z and 12z (Including some in the Caribbean).

Back later...
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3223. putintang3
1:52 PM GMT on August 18, 2007
Well I don't know about all of ya'll, but yesterday I was feeling pretty good that Dean would not effect the Central Gulf coast. But this morning after looking at the NW movement,
it looks to me that it will miss the next tracking point to the north of it. I now have a sick feeling in my stomach. My husband is on a barg in the gulf. He says he will be staying on the barg. I want him to come home, I don't care how much money we lose, they can take the darn vechicles, they can have it all. As long as he comes home.
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3222. TXMET
1:55 PM GMT on August 18, 2007
two things.

first, the ULL is still there, and looks about the same to me as last night, though I have not seen a plot of its pressure over time. Second, it is moving very very slowly west. So slowly in fact, that I think Dean will pass it.
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3221. paulfrmpasschristian
7:55 AM CST on August 18, 2007
GFDL has moved South hasn't it
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3220. KEEPEROFTHEGATE (Mod)
1:57 PM GMT on August 18, 2007
yes cj5 unforunatly
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3219. paulfrmpasschristian
7:56 AM CST on August 18, 2007
PR radar


Link
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3218. jamnkats
1:51 PM GMT on August 18, 2007
Posted By: Kaea at 1:31 PM GMT on August 18, 2007.
What am I doing wrong? Tried to ask if Roatan was OK, did Dean pass by it, almost 30 mins ago, comment never appeared - help? Please if anyone knows if Roatan got hit (or will) or help me figure out how to post here?


I can't see how it came close. Roatan is off the Honduras coast. No?
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3217. Bootsie1
8:56 AM CDT on August 18, 2007
Could this monster hit Mississippi?
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3216. CJ5
8:56 AM CDT on August 18, 2007
Posted By: KEEPEROFTHEGATE at 8:55 AM CDT on August 18, 2007.
... to form as dean makes landfall into texas


You still thinking a TX landafll?
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3215. dean2007
1:42 PM GMT on August 18, 2007
All I'm saying is that Dean has the possibility of obtaining 200mph winds. Its only a possibility. I don't think it will, but Camille is such a storm where the cloud patterns, with the outflow and the central dense overcast are pretty similar. A scary thought, but it looks like Dean is moving more north now. Maybe the westward motion has stopped, this would help out Jamiaca, but not the Gulf Coast.
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3214. KEEPEROFTHEGATE (Mod)
1:56 PM GMT on August 18, 2007
soon maybe after 11 am update nhc
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3213. StormJunkie
1:54 PM GMT on August 18, 2007
The likely hood that Dean will go N is very slim.

So CJ, you are ruling out the GFDL?

You could not pay me to bet against the GFDL

When I say N I mean mid Tx over to La....As opposed to the Brownsville S scenarios that many of the models have insisted on.
Member Since: August 17, 2005 Posts: 26 Comments: 16866
3212. VegasRain
1:50 PM GMT on August 18, 2007
Posted By: Tampalookout54 at 1:46 PM GMT on August 18, 2007.

Guys,
I was hoping one of you can let me know if this seems true. It looks like Dean is having an effect on the ULL, because in the last few frames of the water loop it appears that the ULL has picked up considerable speed. What do you huys think?


It's the anti-cyclone to the north of Dean that is moving forward in tandem with Dean that is pushing the ULL towards the West. It will probably move just ahead of Dean, and depending on how fast Dean goes through the Caribbean it could start to have effects on Dean by Monday (shear/more northwest movement).
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3211. KEEPEROFTHEGATE (Mod)
1:51 PM GMT on August 18, 2007
looks like something is to come from 11,35 may become invest soon models showed earlier that another hurricane to form as dean makes landfall into texas
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3210. BiloxiGirl
1:55 PM GMT on August 18, 2007
When will Dr. M update again?
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3209. StormJunkie
1:45 PM GMT on August 18, 2007
refinery land would really suck.

Amen Comt, not that this would be good for anyone, but that would real bad for everyone.
Member Since: August 17, 2005 Posts: 26 Comments: 16866
3208. watchingnva
1:52 PM GMT on August 18, 2007
if anyone on here is in PR right now...im gonna be curious how this major feeder band coming through soon is going to be like...
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3207. Kaea
7:52 AM MDT on August 18, 2007
Thank you, Miken - I appreciate the answer. I'll keep on looking at satellite but seems to have passed Roatan by. Good for them, still praying for Jamaica and mainland US....Thanks again.
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3206. i12BNEi
1:51 PM GMT on August 18, 2007
Can someone post a link to the models of the next "expected" system please?
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3205. weatherwonderer
1:48 PM GMT on August 18, 2007
The long range radar out of Puerto Rico is showing the NW movement as well.
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3204. weathergeek5
1:47 PM GMT on August 18, 2007
Posted By: fire831rescue at 1:45 PM GMT on August 18, 2007.
The more I look at the track, so far it APPEARS it's jogging a little more north than predicted. I'm just afraid of what will happen if it gets into the gulf. BTW, what does PR mean on this blog? Just wondering.


Puerto Rico
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3203. AllyBama
1:45 PM GMT on August 18, 2007
well, considering the probabilities of Dean, I would suggest that people invest a few bucks into gas cans and get them filled this weekend..the price per gallon is sure to go back up and with the model runs indicating another GOM storm in a few weeks, the price will not drop much - if at all...JMHO
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3202. CJ5
8:45 AM CDT on August 18, 2007
Posted By: comtrader at 8:44 AM CDT on August 18, 2007.
sj
i am NOT a met (i do computational finance and know a bit of physics so the models make some sense to me)so take my musings with many grains of salt.


Your musing are right on. The ULL you are watching on that map is the only thing, other than a slight intensity draw, that will bring Dean N. That model has not changed much for many days and jives with the other models. The likely hood that Dean will go N is very slim.
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3201. calder
1:47 PM GMT on August 18, 2007
puerto rico
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3200. atmoaggie
1:44 PM GMT on August 18, 2007
Truly no one on the Gulf Coast is out of the woods, the models always flop around in the 3-5 day range. Also, for some reason the 06z and 18z runs seem to often show "the other possibility"

I have a theory about that. Some of the NOAA facilities and airports only launch radiosondes (upper air obs) for the 0z and 12z times and those get assimilated into the general circulation models to nudge the first guesses of the initial conditions closer to any real in situ obs. I wonder if anyone has done a comparative skill study on the 0z, 6z, 12z, and 18z runs.
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3199. Tampalookout54
1:40 PM GMT on August 18, 2007
Guys,
I was hoping one of you can let me know if this seems true. It looks like Dean is having an effect on the ULL, because in the last few frames of the water loop it appears that the ULL has picked up considerable speed. What do you huys think?
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3198. fire831rescue
1:43 PM GMT on August 18, 2007
The more I look at the track, so far it APPEARS it's jogging a little more north than predicted. I'm just afraid of what will happen if it gets into the gulf. BTW, what does PR mean on this blog? Just wondering.
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3197. StormJunkie
1:43 PM GMT on August 18, 2007
Thanks Ally and SEFL :-)

And SEFL, if one is approaching me then I likely will be concentrating more on my plan and counting on the other great folks here to keep me informed.
Member Since: August 17, 2005 Posts: 26 Comments: 16866
3196. comtrader
1:32 PM GMT on August 18, 2007
sj
i am NOT a met (i do computational finance and know a bit of physics so the models make some sense to me)so take my musings with many grains of salt.
if you look at the model runs (the GFS link is under the tropical / hurricane tab) and go to the upper air graphics and look at the maps under the column of the 500mb vort you can see the ull progress across the gulf. you can see the counter clockwise air flow around the low. if you look out around 48 hours or so, you can see dean in the picture. at this point the ull will be near the coast of texas and the counter clockwise flow will be north towards nola. dean will be nearing the yucatan channel. in the next few frames the high builds in behind the low cutting off the northern flow and keeps dean from heading up into the gulf. if the ull were to progress more slowly thru the gulf or loop farther south it would have more of a chance to 'catch' dean. in the worst case (for east tx/la dean would get pulled north and would end up hitting the gulf east of the entrance of the ull. from the models this seems pretty unlikely. more likely is that dean gets near enough to follow the low up into the houston area. this would be the worst case from a lives lost/us economy standpoint. a cat 5 running thru refinery land would really suck.
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3195. BiloxiGirl
1:44 PM GMT on August 18, 2007
When will new model graphics be posted on sfwmd.gov site?
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3194. JPV
1:40 PM GMT on August 18, 2007
Posted By: MissBennet

*Sigh of relief!* Just woke up and I see that the GFDL came in to consensus with the other models. So happy for NGOM but so sad for Mex and Tex. =(


I wouldn't relax just yet. Especially not due to nearly useless 5 day forecasts.
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3193. miken62
1:37 PM GMT on August 18, 2007
The island of Roatan should be fine ...that island is very far southoff the coast of Honduras
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3191. StormJunkie
1:39 PM GMT on August 18, 2007
NOWCAST, you are correct. Dean is well N of the forecast points and looks to remain N of them.

Truly no one on the Gulf Coast is out of the woods, the models always flop around in the 3-5 day range. Also, for some reason the 06z and 18z runs seem to often show "the other possibility"
Member Since: August 17, 2005 Posts: 26 Comments: 16866
3190. CJ5
8:40 AM CDT on August 18, 2007
Looks like a W track is the concesus, as it has been nearly since TD4. There is nothing in the cards that is going to "swing" Dean N.
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3189. AllyBama
1:38 PM GMT on August 18, 2007
Good morning all....

SJ..I value your opinion, so what is your thoughts or is it too early to tell?
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3188. MissBennet
1:29 PM GMT on August 18, 2007
*Sigh of relief!* Just woke up and I see that the GFDL came in to consensus with the other models. So happy for NGOM but so sad for Mex and Tex. =(

Really sad for Jamaica right now though!
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3187. FLPanhandle
1:36 PM GMT on August 18, 2007
Last three updates on PR radar show NW movement. We will have to see what next satellite update shows.
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3186. SEFL
1:35 PM GMT on August 18, 2007
Stormjunkie

"SEFL...

You would prefer to spend 6 months constantly worrying about the next possible hurricane?

Thank goodness it is no longer then 6months! I think I would loose it. Although I completely understand that my addiction for the tropics is not for everyone!

I am glad there are people like you who have the interest and are willing to share information. It is because of that that I can make my decisions about what I am going to do and when I am going to do it and then let go and not be concerned when I don't have to be. It is a fact that it is more dangerous crossing a busy street, but sometimes you need to get to the other side!! :)
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3185. IMA
1:39 PM GMT on August 18, 2007
I've found a great resource regarding taking an inventory of your home. This is good for anyone to have, not just those in hurricane-prone areas. There's good info here: Link and here: Link and then a free download from them here: Link
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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.