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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285. SquirrelRJ
8:56 PM GMT on August 17, 2007
Wilma at 882mb is the record low in the atlantic.
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283. Xion
8:54 PM GMT on August 17, 2007
This looks to be an exciting storm. Sorry for those that feel differently....

Dean WILL break record books.....

Maybe take over #1 spot over Wilma for lowest pressure?

Imagine if Dean reaches 180-200 mph??

forget Katrina....


Unfortunately they can't have a plane in their 24/7, so they might miss the lowest pressure.

Just like they did with Wilma which must have bottomed out at least a little below 882 mb.
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282. Unlabled
8:55 PM GMT on August 17, 2007
errr make that west
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281. ecflawthr
8:54 PM GMT on August 17, 2007
rita is a good example. they evacuated houston and she went north
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280. SquirrelRJ
8:54 PM GMT on August 17, 2007
Ill take a bet it doesn't hit FL.
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279. HurricaneDean2007
4:55 PM EDT on August 17, 2007
I am starting to doubt that Dean will even hit the Yucatan at all.Probably will pass between Yucatan and Cuba.
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278. Unlabled
8:52 PM GMT on August 17, 2007
I really think that we will know where this is going between 80N-85N
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276. gsueagle07
8:54 PM GMT on August 17, 2007
Hmmmm I thought Gilbert had the lowest measured pressure in the Atlantic...Wilma????
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275. leftyy420
8:54 PM GMT on August 17, 2007
weatherboyfsu

us landfall u still looking to chase. i am debating going to the gulf coast but might if i can find a partner
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274. TX
8:45 PM GMT on August 17, 2007
some are in the discussion to blast others who are freaked out...the discussion is alive only because of concerned/freaked out people. fear is a precursor for motivation and that is what keeps some people going while for others it drags them down, and those who it drags down arent the ones who are adding anything worthwhile to the discussion...ill keep my worries, continue to lose sleep, monitor tell-tale signs all-around, and maintain my insatiable appetite for weather-related discussion. Those who agree will continue to dismiss polarized and erroneous dissenters of a mass consensus who are rationaly ignorant towards opined science-skeptics. i too am skeptical, but not here to discourage people and their postings. For the depth and breadth of all you contributors surpasses anything ive ever been a part of on a consistent and altruistic basis.
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273. missippinumismatist
8:46 PM GMT on August 17, 2007
I'm not an expert, but I've watched enough of these things turn N as they pass Cuba that I will stock up tonight. I'm in South MS and I have a BAD feeling about this. Some swore RITA would hit the middle of TX until it knocked on LA's front door.
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272. Xion
8:53 PM GMT on August 17, 2007
Dean could break records.
Just hope he breaks a very important record.
Strongest storm ever that killed nobody.
Be safe people,Dean looks like a mean beast.


Too late. He already killed one person. :(

But maybe he will beat Wilma (probably after an eyewall replacement) without hurting anybody in the process, just like Wilma did out there. :)
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271. StormJunkie
8:49 PM GMT on August 17, 2007
Afternoon all!

Still working my dang java issue, but am very close to having it resolved soon!!!

I do see Dean is growing to be a monster. Have missed so much today though...Arghh!

See y'all in an hour or so

Easily find preparedness info, forecast models, and imagery. These are the many links that are posted here time and time again.

Quick Links
Member Since: August 17, 2005 Posts: 26 Comments: 16874
270. whirlwind
8:48 PM GMT on August 17, 2007
This looks to be an exciting storm. Sorry for those that feel differently....

Dean WILL break record books.....

Maybe take over #1 spot over Wilma for lowest pressure?

Imagine if Dean reaches 180-200 mph??

forget Katrina....

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269. weatherboyfsu
8:50 PM GMT on August 17, 2007
and all interests in the Caribbean
Sea and the Gulf of Mexico should closely monitor the progress of
Dean.



I believe someone already said that earlier today.......Hmmmmmmmmmm............. Who was that????????????? lol..........

Anybody giving any Million to One bets on it not hitting florida?
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268. gsueagle07
8:50 PM GMT on August 17, 2007
Sounding more and more like a Yucatan and Mexico storm....and I believe tomorrow you will see the GFDL come back in line with all the other ones......
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267. PalmBeachWeatherBoy
8:51 PM GMT on August 17, 2007
what a suprise another track shift, damn jamaica is in for trouble
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266. StuccoMan
3:42 PM CDT on August 17, 2007
LOL these blogs continue to amaze me.Here is some good information.I have been tracking storms on the computer for almost 10 years and watching the models on allot of them.My past experience is If you are in the models track 6-7 days out.Than you are almost 100 percent guaranteed to not get this storm.I would be shocked if this storm hit Houston or Galveston and that is just straight up.

All these people making claims that Florida and NO is 100 percent clear need your head examined.People look at where this storm is at.
It is just now crossing into the Caribbean.It has 5 days to get to the Yucatan.Allot of weather patterns can greatly change and shoot this storm up the middle of the Gulf.The NHC does not give ceartian forecast past 5 days for a reason.there 3 day forecast are usually dead on and Texas is well beyond a 6-7 day landfall.
Lets not be ignorant and say you know where this storm is going because no one knows for sure.Way to many clusters and disagreements in the models right now and NHC said yesterday the forecast was more ceartian than today.So much can change in 48 hrs and dean wont even be halfway thou the Caribbean.
Texas wishcasters need to relax and just pay more attention to the 3- 4 day outlook and not the 6-7
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265. thewebisode
8:49 PM GMT on August 17, 2007
Well I'm not focusing on Florida anymore. You guys can wish all you want. That's just silly. And yes, I know Florida is a GOM state, but you know what I meant!!

Well, it's not so much a wish really, I mean even the NHC has Key West in the cone, and this is from an older track. With the trend of the storm riding the northern track of the forecast, it is most likely more of Florida will be included in the NHC cone sometime this weekend if not before.
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264. MTJax
8:52 PM GMT on August 17, 2007
This image from the NECP should give a clear indication of the areas it could go. There are no certain paths 5 days out. The possible paths are in the image

Latest NCEP/Tropical Prediction Center (TPC) Forecast Positions
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263. atmoaggie
8:52 PM GMT on August 17, 2007
check message, guygee
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262. C2News
4:51 PM EDT on August 17, 2007
Posted By: snowboy at 4:51 PM EDT on August 17, 2007.
REPEATING THE 500 PM AST POSITION...15.0 N...64.5 W. MOVEMENT
TOWARD...WEST NEAR 21 MPH. MAXIMUM SUSTAINED WINDS...125 MPH.
MINIMUM CENTRAL PRESSURE...961 MB.


So, that was the position close to an hour ago...
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260. Keys99
8:49 PM GMT on August 17, 2007
The NWS Key West site 4pm forcast discussion gives some insight as to what they think the ULL will do. just thie forcast though
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259. Metallica1990
8:50 PM GMT on August 17, 2007
Posted By: diabeticstorm at 8:49 PM GMT on August 17, 2007.

Well I'm not focusing on Florida anymore. You guys can wish all you want. That's just silly. And yes, I know Florida is a GOM state, but you know what I meant!!


Dont focus on anything in the US yet its still too early to tell
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258. snowboy
8:50 PM GMT on August 17, 2007
REPEATING THE 500 PM AST POSITION...15.0 N...64.5 W. MOVEMENT
TOWARD...WEST NEAR 21 MPH. MAXIMUM SUSTAINED WINDS...125 MPH.
MINIMUM CENTRAL PRESSURE...961 MB.
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257. sporteguy03
8:47 PM GMT on August 17, 2007
The
steering pattern continues to be controlled by the high pressure
system to the north of the hurricane and the mid to upper-level low
over the southwestern Atlantic and Florida.

Now they said it ULL controlling steering with High.
Member Since: July 7, 2005 Posts: 0 Comments: 5417
256. weatherboyfsu
8:46 PM GMT on August 17, 2007
One more time!!!!!!!


The bottom line is that Dean is expected to be a dangerous hurricane
through the next several days...and all interests in the Caribbean
Sea and the Gulf of Mexico should closely monitor the progress of
Dean.


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255. diabeticstorm
8:46 PM GMT on August 17, 2007
Well I'm not focusing on Florida anymore. You guys can wish all you want. That's just silly. And yes, I know Florida is a GOM state, but you know what I meant!!
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254. Relix
8:47 PM GMT on August 17, 2007
Yup, I know they will be doing that at 8PM, they want to make sure of certain things I guess. And WTF... NHC says 15, but... are they reading the southernmost part of the eye of something? I don't know, I see it at around 15.2-15.3. Whatever... they are the ones with the experts.
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253. CFL
8:49 PM GMT on August 17, 2007
new trackLink
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252. DeepintheHearta
8:46 PM GMT on August 17, 2007
weatherboy,

the GFDL's accuracy beats the #2 and #3 most accurate models by a grand total of 15 miles. there is little reason to suspect that it is significantly more accurate than the other solutions, virtually all of which plot an entirely different solution for the effects of the ULL. this doesn't mean GFDL is wrong, of course, but it is obviously an outlier at this point and should be treated as such. I guess we'll know more in 10 minutes.
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251. sammo
8:48 PM GMT on August 17, 2007
I think it's interesting to note that Dean will graze (may already be in) Hebert box #1 - as a cat3, of course. Will be interesting to see where it goes...
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250. cormit
8:45 PM GMT on August 17, 2007
stsimons, Agreed. I just didn't know if there was a website that showed this information. The storm that is on this site is an old storm. It was working last year. Any help??
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249. C2News
4:48 PM EDT on August 17, 2007
5 day Track on NHC website is still from 1 pm...
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248. welshcayman
8:44 PM GMT on August 17, 2007
Posted By: JFLORIDA at 8:42 PM GMT on August 17, 2007.

8am 14.4N 61.7W
11am 14.6N 62.6W
2pm 14.8N 63.6W

Then 15N 64.W? welsh?


Latest report from the NHC states the position as;

AT 500 PM AST...2100Z...THE CENTER OF HURRICANE DEAN WAS LOCATED
NEAR LATITUDE 15.0 NORTH...LONGITUDE 64.5 WEST

Therefore the movement in the past 3 hours is almost identical to the movement all day. Again, the current movement of the system is almost exactly what the NHC said it would be.
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246. A4Guy
8:28 PM GMT on August 17, 2007
I cannot believe they did not update the track!!!!!!!!!!!
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245. Xion
8:45 PM GMT on August 17, 2007
Does anybody know the exact time (AST of course) the Hurricane Hunters will depart and/or reach the storm tonight?
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244. weatherboyfsu
8:46 PM GMT on August 17, 2007

data from the Air Force hurricane hunter plane earlier today
indicated that Dean reached 110 knots. Next plane is expected to
reach Dean around 00 UTC tonight. Satellite images continue to show
an eye feature...numerous cyclonically curved convective bands
which are still affecting a large portion of the Lesser Antilles.
The outflow is well established in all quadrants. Although the
possibility of some fluctuations in intensity due to eyewall
replacement cycles could occur at any time...the shear is forecast
to remain low and the ocean temperature increases westward. This
would call for an overall upward intensity trend. This is
supported by the SHIPS....GFDL and hwrf intensity guidance.

Dean is moving toward the west or 280 degrees at 18 knots. The
steering pattern continues to be controlled by the high pressure
system to the north of the hurricane and the mid to upper-level low
over the southwestern Atlantic and Florida. This low is forecast
to weaken and move westward and be replaced by a ridge. This
pattern would maintain Dean over the Caribbean on a general
westward track across northern Yucatan and the western Gulf of
Mexico. The GFDL shows a more northwesterly track across extreme
western Cuba and the central Gulf of Mexico. While this solution is
outside the overall model guidance envelope...it can not be rule
out completely since this model has an excellent forecast track
history. The official track forecast is an update of the previous
one and follows the model consensus.

The bottom line is that Dean is expected to be a dangerous hurricane
through the next several days...and all interests in the Caribbean
Sea and the Gulf of Mexico should closely monitor the progress of
Dean.


Forecast positions and Max winds

initial 17/2100z 15.0n 64.5w 110 kt
12hr VT 18/0600z 15.5n 67.4w 115 kt
24hr VT 18/1800z 16.4n 70.8w 120 kt
36hr VT 19/0600z 17.3n 74.0w 125 kt
48hr VT 19/1800z 18.0n 77.0w 130 kt
72hr VT 20/1800z 20.0n 84.0w 130 kt
96hr VT 21/1800z 22.0n 90.0w 100 kt...inland
120hr VT 22/1800z 24.5n 96.0w 105 kt

$$
forecaster Avila

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242. WPBHurricane05
4:44 PM EDT on August 17, 2007
No one is out of the woods until this storm dissipates, even than were sometimes not out of the woods:


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241. CURIOUSWEATHERGRL
8:42 PM GMT on August 17, 2007
I had to leave for a while...so I don't if my question was ever answered... what has to happen for the storm to turn more north towards LA/MS. Has the ULL moved at all?
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240. PalmBeachWeatherBoy
8:44 PM GMT on August 17, 2007
by when should the track be clearer? cause so far nobody is sure
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239. floridafisherman
8:40 PM GMT on August 17, 2007
rick, often the local weather people see things that the NHC doesnt. when charlie was making landfall, the NHC was predicting a tampa landfall up until 45 min before actual landfall in pt charlotte. our local weather guys caught that almost 4 hrs ahead of the NHC.

if they see something in that ULL that might effect deans path, then im watching it too.
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238. fldude999
8:43 PM GMT on August 17, 2007
Posted By: PalmHarbor at 8:42 PM GMT on August 17, 2007.

Posted By: diabeticstorm at 8:20 PM GMT on August 17, 2007.
Florida is completely out of the woods now. Let's focus on the states in the Gulf.


The entire west coast and panhandle of FL IS in the gulf..if the ULL picks it up..my money is on the FL panhandle or Mobile, AL
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237. mostormspotter
3:41 PM CDT on August 17, 2007
Why are people freaking out about this? I understand and agree that preparation well ahead of time is always advisable when thinking about hurricanes, and I also know full well that hurricanes, like weather in general, are nonlinear dynamical systems and are thus inherently unpredictable. (I grew up in S. Florida and had Andrew destroy my house).


I think that after 2005, folks started to realize that these storms can have effects on the entire nation. Living in Missouri, I am dreading the spike in gas prices, yet hioing to catch some major rain off of Dean. That said I would not be upset at all if it fizzled, but it is clear that such an event will not happen.
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236. nola70119
8:41 PM GMT on August 17, 2007
Destin, you are right, by Florida I meant South FL.....what I was trying to say is that right now there is no reason for anyone to think that the storm is headed to Jax or Tampa Bay. There are NO models that give any indication of that...
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235. JLPR
8:43 PM GMT on Agosto 17, 2007
i would say its at 15.0 15.1
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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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