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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1785. AndyN
3:11 AM GMT on August 18, 2007
It seem sas if the GFDL has finally drank the kool aid and shifted a little south...according to the 1100 discussion even the NHC doesn"t know where Dean is going 3 days from now......
Member Since: December 29, 2005 Posts: 1 Comments: 551
1784. kmanislander
3:11 AM GMT on August 18, 2007
Posted By: moonlightcowboy at 3:10 AM GMT on August 18, 2007.

Have a good sleep, K'man!


I will certainly try.
There may not be much in the days to come
Member Since: August 19, 2006 Posts: 0 Comments: 15725
1783. Daveg
3:10 AM GMT on August 18, 2007
Look at this spread...insane I tell ya...INSANE!

Models
Member Since: September 23, 2005 Posts: 0 Comments: 426
1782. bluehaze27
3:10 AM GMT on August 18, 2007
Yachtdr22, the earth doesn't care about mankind. Only we can care about our own survival and if we aren't careful we may very well find ourselves extinct and than all the deans in the world won't matter.
Member Since: March 26, 2007 Posts: 0 Comments: 813
1781. Skyepony (Mod)
3:10 AM GMT on August 18, 2007
MLB NWS 9:00PM EST
MIGHT HAVE
TO ADD A SMALL POP THERE AS IT LOOKS LIKE THE UPPER LOW IS FORECAST
TO PUSH WEST A LITTLE FASTER...PUTTING SOUTHERN AREAS ON THE MORE
MOIST EAST SIDE TOWARDS SUNRISE.

$$

LASCODY
Member Since: August 10, 2005 Posts: 161 Comments: 37346
1780. moonlightcowboy
3:10 AM GMT on August 18, 2007
Have a good sleep, K'man!
Member Since: July 9, 2006 Posts: 184 Comments: 29594
1779. JamaicanGir
3:09 AM GMT on August 18, 2007
link below are pics of jamaica after gilbert(cat 3) dean is a category 4 heading for Cat 5 it will be real bad if this storm continues on its present forcasted track. we do not have the infrastructure nor the financial capabilities to recover quickly to prevent extended suffering.

http://www.jamaicans.com/gallery/ivan?page=1
1777. mikester
3:07 AM GMT on August 18, 2007
Man sepat still looks impressive even after landfall.
pic
Member Since: April 4, 2005 Posts: 1 Comments: 134
1776. yachtdr22
3:08 AM GMT on August 18, 2007
I think we all can agree that mother nature is pissed off... Super typhoons, hurricanes... polar ice melting.. NONE OF US are out of the woods...
Be safe all
1775. Baybuddy
3:08 AM GMT on August 18, 2007
LOL
Member Since: June 26, 2006 Posts: 0 Comments: 1115
1773. CajunSubbie
3:07 AM GMT on August 18, 2007
Posted By: AndyN at 3:03 AM GMT on August 18, 2007.

When will the forecast discussion be out...Or is something interesting taking place like model interpretations.....I noticed Dean has slowed 1 mph since 5.....slowing will lessen interaction with ull depending on how fast it moves into the NW Gulf......faster dean goes more likely he will interact with ull.....talk among yourselves...


The GFDL is counting on Dean slowing down and interacting with the ULL when it moves into the gulf. right?
Member Since: August 18, 2007 Posts: 0 Comments: 12
1772. kmanislander
3:07 AM GMT on August 18, 2007
I am out for tonight. Will chat some tomorrow
Member Since: August 19, 2006 Posts: 0 Comments: 15725
1770. chicagowatcher
3:07 AM GMT on August 18, 2007
Wow, I really hope Dean doesn't hit Haiti as a cat 5...
Member Since: August 28, 2005 Posts: 0 Comments: 153
1769. wederwatcher555
3:06 AM GMT on August 18, 2007
deans landfall depends largely on the high pressure ridge staying firmly in place for the next 5 days. are the ridge forecasts that far out usually accurate?
1768. Dan187
3:06 AM GMT on August 18, 2007
NHC saying
135 kt near cat 5 landfall in jamaica
140 kt cat 5 landfall in the yucatan
110 kt near cat 4 landfall in Mexico


1765. scla08
3:05 AM GMT on August 18, 2007
I think everyone can pretty much throw out all of the major hurricane models because of the increase in intensity of Dean, a decrease in forward speed, an eye appearing, and I guess what you can call a southern wobble if you wish. I think once the models get a hold of this information and is run, we'll get a better sense of where it will go.
Member Since: July 24, 2006 Posts: 0 Comments: 272
1764. GetReal
3:04 AM GMT on August 18, 2007
Posted By: VegasRain at 3:02 AM GMT on August 18, 2007.

I could not have said it better myself, and wish that I had!
Member Since: July 4, 2005 Posts: 204 Comments: 8806
1763. Baybuddy
3:04 AM GMT on August 18, 2007
Probably hundreds of bloggers come and go on this site. Not one of them has any certainty where this or any storm will end up.
We as a race can neither affix blame for Global Warming or repair damage man may have caused. In the United States, I feel it is more political tool than a legitimate concern.
By the way, Greenland is called Greenland because the ancestors of the Vikings cultivated grapes there! Now it is covered in ICE.
Member Since: June 26, 2006 Posts: 0 Comments: 1115
1761. AndyN
3:03 AM GMT on August 18, 2007
When will the forecast discussion be out...Or is something interesting taking place like model interpretations.....I noticed Dean has slowed 1 mph since 5.....slowing will lessen interaction with ull depending on how fast it moves into the NW Gulf......faster dean goes more likely he will interact with ull.....talk among yourselves...
Member Since: December 29, 2005 Posts: 1 Comments: 551
1760. CajunSubbie
3:03 AM GMT on August 18, 2007
Posted By: louisianaboy444 at 3:01 AM GMT on August 18, 2007.

haha home depot in lafayette is going crazy i really dont think its comming this way but people are all excited now


I'm in lafayette as well, oh well its good for the economy. :)
Member Since: August 18, 2007 Posts: 0 Comments: 12
1759. AnthonyJKenn
3:02 AM GMT on August 18, 2007
On the one hand: The 11 PM advisory simply continues the trend toward the Yucatan and NoMex, with a predicted landfall just south of Brownsville. Louisiana is looking a bit better, pending any last-minute shifts.

On the other hand...Jamaica, the Caymans, and the Yucatan are in BIG, SERIOUS TROUBLE....if Dean continues to blow up like he's doing and passes directly through or just south of Jamaica...we may see Gilbert-to-Wilma magnitude damage...and Yucatan could be much worse.

Actually, this is looking more like Hurricane Mitch in terms of damage and death potential...especially considering all that rain that fell from Erin before then. It could be a absolute disaster for SoTex and the Hill Country..especially if we see a landfall between Brownsville and Port O'Connor that produces the rainfall I expect.

One thing's for sure....Dean will be a baaaaaaad man. There won't be any more like him..at least, none bearing his name.


Anthony

Member Since: September 20, 2005 Posts: 0 Comments: 206
1758. VegasRain
3:02 AM GMT on August 18, 2007
I think it's quite premature to say that Dean will take a southern track because Dean is traveling due West right now. It is likely a temporary wobble, and will begin to take a WNW track within a few hours. The models have been all over the place at the 72 to 120 hour timeframe. They shift North, they shift south, they shift back again. This tells me that the Models are having a difficult time with the Upper Low near Florida, and with the forward speed of Dean. Currently Dean has slowed slightly to about 18mph from the 22mph it was traveling earlier today. At over 18 mph Dean will likely begin to interact with the Upper Low as the Low tracks WSW across the Gulf of Mexico in about 48 hours. This will in all likelyhood bring Dean more Northwest. The NHC is still predicting Dean to make a move over Jamaica and into the Cozemel area.

The bottom line is that Texas is by no means off the hook from Dean. Louisiana isn't either, especially Western Louisiana. Dean could very easily traverse around the Eastern side of the Upper low and track into the northeastern Texas coast. Wait out the model runs, and remember that the model spread is very high right now beyond 72 hours. That means a lot of uncertainty.
Member Since: October 24, 2005 Posts: 12 Comments: 491
1757. bappit
3:01 AM GMT on August 18, 2007
WatchingInHouston: Usually an increase in speed results in an increase in shear weakening the storm, but it does not have to since if the whole column of air is moving at the same speed in the same direction, then the speed of it all is not as important. Then again the chances of that happening is not too great. So slower movement usually leads to better organization and greater intensity. Don't know of a formula relating the two though.
Member Since: May 18, 2006 Posts: 10 Comments: 5953
1756. Daveg
3:01 AM GMT on August 18, 2007
Just a slight digression...I can't resist...

Global warming advocates argue Greenland is in rapid meltdown, and that this threatens to raise sea levels by 20 feet. But according to a 2005 study in the Journal of Glaciology, "the Greenland ice sheet is thinning at the margins and growing inland, with a small overall mass gain." In late 2006, researchers at the Danish Meteorological Institute reported that the past two decades were the coldest for Greenland since the 1910s.

And

The Antarctic ice sheet is melting because of global warming. Yet the Jan. 14, 2002, issue of Nature magazine reported Antarctica as a whole has been dramatically cooling for decades. More recently, scientists reported in the September 2006 issue of the British journal Philosophical Transactions of the Royal Society Series A: Mathematical, Physical, and Engineering Sciences, that satellite measurements of the Antarctic ice sheet showed significant growth between 1992 and 2003. And the U.N. Climate Change panel reported in February 2007 that Antarctica is unlikely to lose any ice mass during the remainder of the century.


Enjoy...always get information from more than one source...it helps...all things in moderation my friends.
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1755. louisianaboy444
3:01 AM GMT on August 18, 2007
haha home depot in lafayette is going crazy i really dont think its comming this way but people are all excited now
Member Since: August 29, 2006 Posts: 22 Comments: 1342
1754. wederwatcher555
3:01 AM GMT on August 18, 2007
the CENTER of the NHC's cone is just a tad under brownsville. This could easily be a U.S. storm and with still 5 days to landfall anything can happen
1752. ChuckieTodd
3:01 AM GMT on August 18, 2007
Posted By: JFLORIDA at 9:52 PM CDT on August 17, 2007.

Dont you guys think its important that the Ice caps are smaller than EVER reported?


It's just as important to me as the last 1000 times it happened.
1749. Melagoo
3:00 AM GMT on August 18, 2007
... they are predicting 160+MPH by Monday ... I think it will be earlier as it did strengthen much quicker then forecast
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1748. littlefish
2:59 AM GMT on August 18, 2007
Yep, just as we've been seeing, Dean is slowing a bit and that ULL to the north aint budging much yet. Will be interesting to see what things look like tomorrow.
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1747. redrobin
2:29 AM GMT on August 18, 2007
Posted By: Daveg at 2:28 AM GMT on August 18, 2007.

One thing I noticed about this blog, is earlier (just today) the models where trending North, and a lot of folks started screaming about how LA was doomed and all that. Now the models have shifted a bit south again, and there is all this screaming about folks in Mexico being doomed.

My point is, can we have some leveled headedness (not a word, but sounds good) about this whole thing? Everyone should watch Dean real close, as the models could easily shift north again. Deep Breaths. :)


I am what you can call a layman in all of this-I have been through several storms, with that in mind I have grown to enjoy this sight. But the above statement is true. I to have noticed every bobble and wobble of Dean as we all have, with that the models have adjusted for a big part of the little movements. BUT when it comes to landfall WELL heck NO ONE KNOWS! To many times the models go to far to the south or to the north. I for one feel TX needs to look out! The overall movement has been west-later wnw then nw-then land fall. But the little wobbles do not add for much and the land fall is to far out. Most of all I live near Houston and have connections to the very military team that was in NO when it all went down. I have to say Between that storm and Rita, I feel that it really doesnt mater where it lands the people there need to be ready as well as the govt should be prepared. TX turned down the help from a certain military branch with Rita and before that the same military branch was told to wait 1 and 1/2 wks with Katrina, which I find odd that, that part has not ever made news.The one week wait was what made the situation worse in N.O.. I pray leasons have been learned and NO HELP will be turned away and we as a Nation remember Katrina and Rita, yet remember DEAN is a new storm with new problems, that can be handled better. Most of all the people effected by this storm (if it lands in US)do not need to be compared to Katrina, they will need the lessons we learned from Katrina. If it goes to N.O. then that very strong city will find away to get through it. Nothing is to much when it comes to people determined to start again. Please keep in mind this is all IMO and I feel very strongly that if I was in the Katrina storm I would get real tired of the "Another Katrina" Heck I was in Allison it makes me laugh when people compare another flood event to it. Simply it was its own storm lets move on! NEXT!
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1746. errantlythought
2:57 AM GMT on August 18, 2007
"things can change really fast"

And they probably will again.

Take note of the fact that twice now the GFDL has picked up on interaction and then dropped it. It's a race, and it still matters. We're nowhere near the end of this. Please do NOT let your guard down. People did that right before K, when it was supposedly heading for the florida panhandle, or need I remind you?
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1745. CHAM0EBIAN
2:52 AM GMT on August 18, 2007
I agree with jflorida...i'm able to process two events at once also...the fact that the arctic water is more than 5 degrees above normal is just as troubling as a cat 5 hurricane...at least we can move out of the hurricane's way...
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1744. ChuckieTodd
9:57 PM CDT on August 17, 2007
Posted By: pseabury at 9:48 PM CDT on August 17, 2007.

Dean is definitely about 22 miles South of the 5PM NHC forecast track. Can see that on both radar and Satellite...


Nice. Thanks for this.
1743. Crisis57
2:58 AM GMT on August 18, 2007
anything on the ULL guys?
1742. sullivanweather
2:57 AM GMT on August 18, 2007
No problem!
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1741. SouthernLady
9:56 PM CDT on August 17, 2007
Thanks for the reality check MLC!!!
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1740. bluehaze27
9:54 PM EST on August 17, 2007
Mikeohio, not to belabor the point (ok yes, to belabor the point) I don't see why people can't handle more than one subject at a time. It's not a slight to those in the path of Dean. I just think everything that can be said about dean has already been said. I feel for those in the path. My family went through Andrew. I just feel I can handle more than one topic at a time, and NOT talking about Dean isn't going to hurt anyones feelings or make Dean any stronger.
Member Since: March 26, 2007 Posts: 0 Comments: 813
1738. louisianaboy444
2:53 AM GMT on August 18, 2007
lol i dont think louisiana will get hit for any of the people wanting it to hit louisiana your hopes were pretty much crushed by the southward movement in the models and i really dont know what they are smoking or what they are seeing but hey if they away from louisiana i'll take it....sorry for all you model lovers out there but i think those things are useless they just get people excited for nothing....look at all the people that were having heartattacks in louisiana earlier lol...things can change really fast
Member Since: August 29, 2006 Posts: 22 Comments: 1342
1737. UnderstandingFL
2:46 AM GMT on August 18, 2007
A Cat 5! That is so sad. I can only imagine what the parents of young children are going through tonight. OMG!!!
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1735. mikester
2:40 AM GMT on August 18, 2007
Looks like africa has some hurricane potential coming along.
pic
Member Since: April 4, 2005 Posts: 1 Comments: 134

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About

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.