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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3285. extreme236
2:24 PM GMT on August 18, 2007
what i noticed with the wave at 35w is that the gfs developed it in the itcz convection part of the storm, and thats where QS picked up some cyclonic turning as well
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3284. Drakoen
2:24 PM GMT on August 18, 2007
Posted By: ClearH2OFla at 2:23 PM GMT on August 18, 2007.

Hey Drak so it appears we are out the woods on this one. My thoughts and prayers with those in his path however. My question now turns to the two apparent areas following Dean. Any thoughts on those


coordinates please...
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3283. cchsweatherman
2:22 PM GMT on August 18, 2007
I would not place FL out of the woods because we do not know what this ULL will do. Has anyone beside me seen this ULL migrating SW towards the Florida Straits and the Yucatan Channel? This could be huge factor in the future path of Hurricane Dean.
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3282. lowerbamagirl
2:24 PM GMT on August 18, 2007
Good Morning All: Has the disturbance right off Africa been labled an invest. It seems no one is really giving that one a second thought. I remember this blog with 96L (for about five days)! LOL. Anyway, just wondering about it. If anyone has a link, please post. Thanks.
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3281. ScoobaSteve
9:23 AM CDT on August 18, 2007
I feel truly sick and worried for the people of the Cayman Islands, one of my favorite places in the world.

There's not much elevation on the island(Grand Cayman) at all except on one end. Where do those 30,000 people go to be safe?
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3280. ClearH2OFla
10:22 AM EDT on August 18, 2007
Hey Drak so it appears we are out the woods on this one. My thoughts and prayers with those in his path however. My question now turns to the two apparent areas following Dean. Any thoughts on those
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3279. comtrader
2:20 PM GMT on August 18, 2007
cch,
if you look at the latest run of the NAM it has the center of circulation of the ULL about 300 miles south of the same GFS solution 24 hours out....
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3278. IMA
2:14 PM GMT on August 18, 2007
a654321r & PrgalI'm so happy for y'all!! I live in TX and am a couple hundred miles from the coast. I have to worry about flooding -- Erin almost got me -- but not the winds (other than tornadic) like y'all would've had to worry about. :)
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3277. nola70119
2:19 PM GMT on August 18, 2007
GFDL has said North of Jamaica, but so did the left-turning GFS yesterday....but the more north of Jamaica the more the chance of a slight NW move later in the gulf.
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3276. weatherwonderer
2:19 PM GMT on August 18, 2007
I guess Dean will do as it does. The straight edge is merely an extrapolation. :)
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3275. fire831rescue
2:16 PM GMT on August 18, 2007
Posted By: LALady at 2:14 PM GMT on August 18, 2007.
bootie - I have been lurking for a few days now. I do not believe SE Louisiana or Mississippi or in any danger. I realize that we should stay alert but I believe that the NHC is pretty close to the actual track...they have been fairly accurate even this far out (maybe with a 100 mile margin of error). I would have a hard time believing that Dean would hit the LA/MS area at this time.


Don't put LA/MS out of the woods just yet. Many events are factored into where this storm is headed. A change in any one of them could cause it to turn. And even if we don't get the full brunt, I know MS couldn't even take a small hit. Still too many people in FEMA tin cans right now. Imagine all the people homeless again after only two years.
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3274. CajunSubbie
2:20 PM GMT on August 18, 2007
last ir frame continues WNW/NW movement, radar also continues this motion.. its going to miss its next forcast track by a good bit.
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3273. Relix
2:19 PM GMT on August 18, 2007
Wow... what masquer says is right. There's a huge, nasty band going to hit the south.
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3272. Drakoen
2:18 PM GMT on August 18, 2007
Morning everyone. I see Dean is looking impressive.
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3271. SEFL
2:15 PM GMT on August 18, 2007
"I have been in the computer field for 15 or so years and the models used to predict storm paths are only as good as the programmers (some more so called experts)."

Exactly why, just like the stock market, there are lots of PEOPLE to analyze the computer generated information. The NHC is not just one person emailing computer output to TV stations. :)
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3270. raindancer
2:19 PM GMT on August 18, 2007
I realize everyone is jumpy about the WNW trend now - BUT if you look at the scatter plot of the models - they ALL predict the shift to the WNW and they almost all predict either a direct or very near direct hit on Jamaica. It looks to me as though Dean is "right on predicted course" with the models.
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3269. nola70119
2:15 PM GMT on August 18, 2007
The more N it passes Jamaica the more the rest of the Gulf comes into play. The 2am HNC forecaster said the w an n Gulf are all the same probability for TS winds right now, that the guidance past monday is sketchy.
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3268. StormJunkie
2:17 PM GMT on August 18, 2007
I know CJ! Dean is a mystery for know as far as Mex and the Conus go.

SW told me yesterday that he was looking to 2 pints to help give his guidance. Jamaica and the Yucatan...I think those are good points to watch as well.
Member Since: August 17, 2005 Posts: 26 Comments: 16874
3267. JPV
2:15 PM GMT on August 18, 2007
Posted By: weatherwonderer

Right now using a straight edge, it appears that Dean will hit Jamaica dead on.


Is the hurricane aware that it's supposed to follow the path of your straight edge?
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3266. Relix
2:13 PM GMT on August 18, 2007
Report from Puerto Rico: Winds are right now at a consistent 17MPH, very impressive considering I live in the north coast. Some gusts readings are around 29MPH with a few over 30. A few rains every two hours or so.

A uncle of mine is currently receiving tropical storm force winds in Cabo Rojo.
Member Since: August 3, 2006 Posts: 0 Comments: 2741
3265. quipment
2:13 PM GMT on August 18, 2007
The track Dean has taken the last four hrs. would bring the storm north of Jamaica. Is this what the gfdl has been saying?
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3264. Masquer08er
2:10 PM GMT on August 18, 2007
Looks like a nasty band is about to move onto Puerto Rico.
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3263. weatherwonderer
2:14 PM GMT on August 18, 2007
We don't need models we now know where Dean is going. Its going to Cozumel. The Mexican gov, should not allow Cantore near Cozumel! :)
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3262. russh46
2:14 PM GMT on August 18, 2007
Cantore is going to the wrong country imho
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3261. cantstopthinking
2:14 PM GMT on August 18, 2007
LOL, people are so funny, go ahead and listen to the so called experts. Predicting weather is about as accurate as predicting the stock market, were you can also find many so called experts. I have been in the computer field for 15 or so years and the models used to predict storm paths are only as good as the programmers (some more so called experts). There are no experts in life just well educated guessers!! My novice advice says be prepared for the worse, stock up on supplies and keep in contact with family. Keep a close eye on exact storm positions not someone’s prediction.
Most of all be safe!!!
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3260. Prgal
2:13 PM GMT on August 18, 2007
Posted By: a654321r at 2:12 PM GMT on August 18, 2007.

Well we in puerto rico have really (understatment !!) dodged a bullet. I can not imagine what it would have been like if we had gotten a direct hit. Flooding would have been incredible, and all of the buildings would be mostly with out windows unless they had good storm shutters. I am next to the san juan bay, 9th floor, no rain and winds around 20 - 25.


I agree totally! I think that the wind gusts are higher than 25 where I live but its not that bad.
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3259. LALady
2:04 PM GMT on August 18, 2007
bootie - I have been lurking for a few days now. I do not believe SE Louisiana or Mississippi or in any danger. I realize that we should stay alert but I believe that the NHC is pretty close to the actual track...they have been fairly accurate even this far out (maybe with a 100 mile margin of error). I would have a hard time believing that Dean would hit the LA/MS area at this time.
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3258. strangesights
2:07 PM GMT on August 18, 2007
Is the high just south of the Florida panhandle expected to remain there over the next several days?
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3257. SEFL
2:13 PM GMT on August 18, 2007
FWIW, Cantore is going to Cozumel.
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3256. weatherwonderer
2:12 PM GMT on August 18, 2007
Right now using a straight edge, it appears that Dean will hit Jamaica dead on.
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3255. CJ5
9:08 AM CDT on August 18, 2007
Posted By: StormJunkie at 9:07 AM CDT on August 18, 2007.
you are correct CJ, that is the latest. But it is the 06z and so I am discounting it until I see the 12z run. Remember Katrina and the way the GFDL flipped and flopped prior to locking it in?

Not to mention, when has the 5 day cone ever not shifted a fair amount at least once...Now, I know that is really no solid logic or anything, but I just can not get it out of my head. N to mention that Dean is now N of all forecast points...


All valid points, SJ. Thats why I have not changed my cone yet. If I was being stubborn I would shift my thoughts to Brownsville and S but I just am not willing to do that yet..lol

The only think I am wonder is if the GFDL is betting on the ULL or something else. If it betting on the ULL it is going against any of the analysis I can find.
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3254. a654321r
2:07 PM GMT on August 18, 2007
Well we in puerto rico have really (understatment !!) dodged a bullet. I can not imagine what it would have been like if we had gotten a direct hit. Flooding would have been incredible, and all of the buildings would be mostly with out windows unless they had good storm shutters. I am next to the san juan bay, 9th floor, no rain and winds around 20 - 25.
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3253. Prgal
2:07 PM GMT on August 18, 2007
Good morning everyone. Watchingnva, I live in Puerto Rico and its been quiet where I live. Just a few showers and its windy but its nothing compared to what Dean really is. I live in the northern side so I am not sure how is the weather in the south.
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3252. putintang3
2:05 PM GMT on August 18, 2007
I am sorry for my last post, I am just really freak out about the whole thing, I think I need to get off the internet. I am getting very paranoid. I just don't trust anything anybody says, and certainly not anything a government official says. I mean jees I am from Louisiana, they all nothing but a bunch of money hungry idoits, only concerned about their own position.
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3251. OUFan919
2:09 PM GMT on August 18, 2007
That is a big wobble to the WNW, around 295 degrees I think. Wonder if this will keep up or not.
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3250. bajelayman2
2:09 PM GMT on August 18, 2007
Is it too early to ask if any models have forecast track guidance re the wave at 11N?
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3249. weathers4me
2:08 PM GMT on August 18, 2007
Dean moving NW last few hours.




http://mkwc.ifa.hawaii.edu/satellite/satanim.cgi?chnl=ui4&domain=cta&size=large&period=720&incr=60& rr=900&satplat=goes12&overlay=off
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3248. HurricaneJoe
2:10 PM GMT on August 18, 2007
42059 - buoy

Temperature: 80.4°F
Dewpoint: 77.7°F
Wind: S at 47 mph
gusting to 58
Pressure: 995.2 mb
Wave Height: 16 ft
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3247. guygee
2:09 PM GMT on August 18, 2007
I looks to me that Dean has taken a heading slightly north of the official NHC track over the period from 0815Z to 1245Z. Please click on the thumbnail below to see my graphical track approximation, and keep in mind my interpretation of the location of the exact center of Dean may have some error one way or the other.

Free Image Hosting at www.ImageShack.us
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3246. Bootsie1
9:03 AM CDT on August 18, 2007
I don't want to panic but after Katrina, I don't want to be caught off guard again. Our weather man said something about a low coming over FL and if that stalled then it will turn North and could head for us. Do any of you know of a Low that is coming over FL? If so do you think it will stall over the Gulf?
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3245. NOWCAST
2:05 PM GMT on August 18, 2007
Storm Junkie, do you think the convection off florida is already signs of ULL interaction with Dean? This may be the reason for the NNW?
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3244. bajelayman2
2:06 PM GMT on August 18, 2007
Keeper, re 11N:

I agree, this is now starting to REALLY pull together and even though Navy has not labelled an Invest maybe we can expect so soon.

Here we go again....
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3243. cchsweatherman
2:06 PM GMT on August 18, 2007
Hye louisianaweatherguy, have you noticed what I have noticed in concern to the ULL? It appears to have gone SW and heading for the Yucatan Channel. Any thoughts?
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3242. Eyewall911
2:07 PM GMT on August 18, 2007
None og the models have this nw movement. none
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3241. paulfrmpasschristian
8:07 AM CST on August 18, 2007
3240. StormJunkie
2:03 PM GMT on August 18, 2007
you are correct CJ, that is the latest. But it is the 06z and so I am discounting it until I see the 12z run. Remember Katrina and the way the GFDL flipped and flopped prior to locking it in?

Not to mention, when has the 5 day cone ever not shifted a fair amount at least once...Now, I know that is really no solid logic or anything, but I just can not get it out of my head. N to mention that Dean is now N of all forecast points...
Member Since: August 17, 2005 Posts: 26 Comments: 16874
3239. louisianaweatherguy
2:02 PM GMT on August 18, 2007
two things:

- Dean has slowed and has made more than a wobble to the WNW... we'll how long this lasts... the longer it lasts, bad news for Texas and possibly W Louisiana...

- Other thing... look at the High above Dean and the interaction with the ULL to its west... You can see the flow switch from east to west to southeast to northwest... **Looking like Dean's trying to sneaky around the edge of the HIGH...

HERE'S WHAT TO WATCH.... how quickly will this ULL move off and allow the HIGH to build in?
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3238. CJ5
9:02 AM CDT on August 18, 2007
Posted By: KEEPEROFTHEGATE at 8:58 AM CDT on August 18, 2007.
yes cj5 unforunatly


Of course, TX is pretty big lol. I have not taken Galveston and S out of my cone but I am inclined to think the Brownsville will be more likely if it doesn't go into MX. Like may others, I am still hanging my hat on a slight WNW curve but the more I study and the further W he moves it seems more and more unlikely.
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3237. jerrygFLA
2:04 PM GMT on August 18, 2007
Great image of the storm. Looks like the Northern movement is confirmed on the last few frames.

http://mkwc.ifa.hawaii.edu/satellite/satanim.cgi?chnl=ui4&domain=cta&size=large&period=720&incr=30& rr=900&satplat=goes12&overlay=off
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3236. highndry1
2:03 PM GMT on August 18, 2007


pun intended?
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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: 16874

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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.

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