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

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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8:06 AM GMT on August 18, 2007
------i think he just started to hit WNW right at the 67W where i said it should---but it might just be a jog----lets wait about an hour.........
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2634. sflhurricane
8:03 AM GMT on August 18, 2007
According to the National Weather Service in Miami, the ULL should be moving west towards the Gulf... "The upper level low will continue to move west tonight and through
South Florida on Saturday...and into the Gulf of Mexico Saturday

However, from looking at this extended-lengh loop of the ULL, one can see the ULL moving towards the west to start but now moving more SW towards the straights and western Cuba.. Could that ultimately affect the final fate of Dean? Here
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8:04 AM GMT on August 18, 2007
WNW very soon now---- cmon DEAN dont make a liar outta me LOL................ you KNOW your going there!
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2632. stormybil
8:01 AM GMT on August 18, 2007
in fll too got the storms here early i posted that the uul is real too but as vero and i been saying its a strong ull that was suppose to be gone by now . even the mets said it was weak and will not effect dean but you can see how its pulling the stuff north from the cuba area and thats where dean is heading if that ull stays tight we can see a big change tomorow in the forcast .
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2631. MauiHawk
7:59 AM GMT on August 18, 2007
You will notice the ULL moving VERY SLOWLY towards the west as forecasted but its now moving basically SSW. Also you will notice Dean catching up to the ULL...And about the ULL, wasn't it supposed to dissipate and get replaced by a huge High that would bridge from the Southeast to the Mid-Atlantic, because IMO that ULL is not dissipating

I'm no expert-- but instead of focusing on the center of the ULL, look at the eastern edge of its influence. It appears to me to be retreating westward nearly as fast as Dean is moving. My amatuer guess is that we are looking at ridging building in behind the ULL, and building in faster than the low is moving. Could that not be an indicator of its impending demise?
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2630. GPTGUY
3:00 AM CDT on August 18, 2007
Does anyone know if there are any troughs coming down when Dean is in the NW Caribbean...or will the high stay strong enough to keep Dean west?..with all the unseasonably cool weather up north in the 60's any weakness like a trough or front that comes down could erode the high and draw Dean more northerly...is that a possiblity? or not?
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8:00 AM GMT on August 18, 2007
depends how fast and what direction that ULL will go---its supposed to go on a westward
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2628. sflhurricane
7:58 AM GMT on August 18, 2007
Stormybil... I dont know much about ULLs but in that sat. loop, doesnt it look like that ULL is intensifying (instead of dissipating as the NHC said it would)... Look at the convection firing up... I live in Ft. Lauderdale (right under the ULL as we speak) and we just had a thunderstorm about an hour ago
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2627. houstongator
2:58 AM CDT on August 18, 2007
A good Decoder.

I was in the Rita mess also, Two dogs, one hamster, one 5 year old girl, and one wife. 400 miles of gas in the tank after we filled up in what I think was the last gas in eastern Texas. Instead of staying on I-10 near Beaumont (where the entire state of texas was apparently headed) - we went through downtown and it was a ghost town. We probably cut off 4 or 5 hours from just that 25 minute cut through. So we ended up only taking 39 hours getting to Alabama and sleeping only one night in a truck stop --- ahh, good times.

Go away, Dean.
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7:59 AM GMT on August 18, 2007
yup stormy!
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7:58 AM GMT on August 18, 2007
if its gonna get sucked in of course it would shear....
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2624. stormybil
7:54 AM GMT on August 18, 2007
saw that sf look how the ull is pulling everything north . thas wild if dean goes a little more north that ull will pull him over cuba right .
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2623. sflhurricane
7:55 AM GMT on August 18, 2007
If Dean were to feel the affects of the ULL, what would take place?

1)Would Dean just get sheared but still travel to the West?
2)Would Dean get sheared and travel towards the ULL?
3)Am I way off?

Answers please... Thanks
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7:52 AM GMT on August 18, 2007
--well like he said-- DEAN is moving 2x faster than that ULL...........so its a tough call BUT anytime--if not now--- by 67, 68 or 69 W we SHOULD start seeing a WNW movement in DEAN................ and wobble like crazy until at least 80W or before it...IMO-----not enough hours yet to go from there...........this is all IMO and MN also...
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2621. sflhurricane
7:51 AM GMT on August 18, 2007
Check this out

That link shows a long, extended loop of the ULL near the Bahamas. You will notice the ULL moving VERY SLOWLY towards the west as forecasted but its now moving basically SSW. Also you will notice Dean catching up to the ULL...And about the ULL, wasn't it supposed to dissipate and get replaced by a huge High that would bridge from the Southeast to the Mid-Atlantic, because IMO that ULL is not dissipating
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2620. FLCrackerGirl
3:46 AM EDT on August 18, 2007
Night SJ.
Really Nice To See Level-Headed Discussions & Courtesy Prevailing. Thanks Everyone.
You'all Have A A Good One.
Fran Out.
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2619. StormJunkie
7:48 AM GMT on August 18, 2007
sb, it shows well on the GHCC site as well.

Quick Links

Select the first link in the imagery section. This is the Global Hydrology and Climate Data Center. There are several rows of maps. The first column is visible imagery. The second infrared and the third is water vapor. The first row is the W Atl view and the frames update most often and also has the highest max zoom. The next active row down does not have the same zoom level and the images update every 30 minutes. The Carib row uses a different color scale on the IR imagery and shows more whites and reds with weaker convection. Select the map you wish t o view. Below the image that comes up are options that will allow to change size, number of frames, zoom level, quality, etc. There is also a box that on SOME maps will allow you to turn on lat/lon lines. Set these parameters the way you choose and then click the area on the map you wish to view. Make sure you select the animate feature if you wish to see a loop. Allow loop to load and enjoy. This site releases images prior to any other site as far as I know.

We will have to see if it continues though or if it is a jog...

Ok, night all. See everyone with the next model runs around 8am est.

kata, I think that is what is keeping everyone, even the models and the pros guessing right now.
Member Since: August 17, 2005 Posts: 26 Comments: 17143
2618. JamaicanGir
2:51 AM EST on August 18, 2007
thanks SJ
i am also heading to bed long day ahead

good night all
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2617. mikester
7:51 AM GMT on August 18, 2007
Well if this distrubance off of africa can get itself together we might have another hurricane on our hands.
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2616. katadman
7:47 AM GMT on August 18, 2007
Posted By: MrNiceville at 7:25 AM GMT on August 18, 2007.

SJ - any opinion on the relative closing rate between the ULL and Dean?

I guess this is the same question I posed (albeit rather clumsily) several hours ago but never saw a response. Anyone?
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2615. KRL
7:47 AM GMT on August 18, 2007

Current Atlantic Water Vapor Loop Link
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2614. StormJunkie
7:45 AM GMT on August 18, 2007
JG, that is one area I still lack. There use to be a great site that offered decoded real time recon, but it is not active anymore.

This is the best I can do, and I have not figured out how to use it yet, so I can not explain it yet...

Recon Data

That said, I need to head back to bed. See y'all in the morning.

Get your ducks in a row JG and my thoughts will be with y'all
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2613. stormybil
7:44 AM GMT on August 18, 2007
heres a new jog for you slow it down and follow the 15 line

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2612. redrobin
7:46 AM GMT on August 18, 2007

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2611. Pnscola
7:39 AM GMT on August 18, 2007
Well, it's 2:40am here in Pensacola, I see some of you are still up. I am SO depressed that Dean is now 150mph. It's going to devastate those in its path. My friend in Houston says she won't evacuate due to the MESS created when Rita approached. So sad. Can someone explain what ULL stands for? Is it Upper Level Low? Headed to bed but will check for the answer tomorrow. Thanks to everyone who tries to keep us informed.

One more question- when these intensify to Cat 4 or 5, can Dean can make his own environment and override "ULL" and other inhibitors that would normally affect lesser category storms? After being through Dennis and Ivan here in Pensacola, I seem to remember that phrase- make their own environment?

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2610. houstongator
2:45 AM CDT on August 18, 2007
I am new at this, but does this show the effect of the ULL? It also shows it as still digging south, I think. Again - new at this.
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2609. JamaicanGir
2:40 AM EST on August 18, 2007
is the HH still out flying and anyone has the lasstest info
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2608. StormJunkie
7:39 AM GMT on August 18, 2007
Could be MN, and that is likely what the GFDL is picking up on as that would induce a more northern component no?
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2607. StormJunkie
7:37 AM GMT on August 18, 2007
Thanks again Fran ☺

And you are so right, there are many hear that are very helpful! Although I have tracked for over 20 years, I have learned more here in the last 3 then I had in the last 18+

As for the insomnia, sorry to hear that. Can be very frustrating. I have nights with the same issues. The worst are when you have commitments the next morning...Arghh!
Member Since: August 17, 2005 Posts: 26 Comments: 17143
7:36 AM GMT on August 18, 2007
--this is all IMO-------WNW till about 80W.....will not know the rest until at LEAST 36 hrs.........
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2605. FLCrackerGirl
3:27 AM EDT on August 18, 2007
SJ, Modesty Aside, The Kudos are Well Deserved & It's Folks Like You & Skyepony, StormW, & So Many Others Who Contribute Unselfishly with Your Time & Area of Expertise that Really Makes This a Community.

(oh, insomnia & big storm watching more fascinating than the tube..lol)
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2604. ChristopherH
7:32 AM GMT on August 18, 2007
how far north is your gut telling you?

My gut tells me New York should start preparing. (JOKE).

Honestly, I don't really know, and certainly gut feelings don't count for nearly as much as scientific data, etc., used by the models, and the NHC ... I just have a feeling we will see the track shift North. How much, not sure. But I wouldn't rule out LA at all.
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2603. fliptill
7:32 AM GMT on August 18, 2007
if the high doesnt set in over florida as quickly as thought what happens then?
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2602. MrNiceville
7:32 AM GMT on August 18, 2007
I need to go back in archive loops, but in the current loop, Dean is moving roughly twice as fast as the ULL. My concern is that the ULL can be seen to be effecting the weather south of Cuba, so it's no great stretch to extrapolate an effect on Dean in 36 - 48 hours time... IMO
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7:31 AM GMT on August 18, 2007
STOrmy---i think DEAN is slowing due to the change in the WNW direction-------- it should start goping that way by now and the next few hours..........wait and see.........i had some coffe so i guess im here for the 5am. and again ---IMO
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2600. MrNiceville
7:31 AM GMT on August 18, 2007
SB - ever so slightly
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2599. StormJunkie
7:25 AM GMT on August 18, 2007
No MN, I have really been just taking in everyone s opinions on that, and most of those opinions are low confidence right now...Guess it is just a wait and see. Although it looks to be moving fairly slow as it pushes across the S tip of Fla in front of Dean?
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7:30 AM GMT on August 18, 2007
yes mrniceville---nail on the head!!
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2597. stormybil
7:29 AM GMT on August 18, 2007
is dean slowing down now
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2596. fliptill
7:29 AM GMT on August 18, 2007
more to come?
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2595. MrNiceville
7:29 AM GMT on August 18, 2007
Need to wait 48 hours and see if Dean ignores the ULL to it's NW or follows the weakness...
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2594. caymangone
7:21 AM GMT on August 18, 2007
gnight all stay stay safe jam
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2593. fliptill
7:29 AM GMT on August 18, 2007
how far north is your gut telling you?
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7:28 AM GMT on August 18, 2007
WNW movement of DEAN to come very very soon...............IMO
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2591. StoryOfTheCane
7:27 AM GMT on August 18, 2007
there are a couple areas worth monitoring, remember this is fireball season..

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2590. ChristopherH
7:15 AM GMT on August 18, 2007
Do gut feelings count? Louisiana?

I don't know if gut feelings count, or not, but I have that same feeling .. I don't know why. We will see. I have this very strong feeling the track will shift North.
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2589. mikester
7:27 AM GMT on August 18, 2007
Not really forming right now. We will have to wait and see if it does. Right now no nothing is forming behind dean as of right now.
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2588. fliptill
7:26 AM GMT on August 18, 2007
someone told me there is another wave forming behind dean off africa is there any truth to this?
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2587. StoryOfTheCane
7:23 AM GMT on August 18, 2007
lol StormTop is great, definitely livens up those nights with nothin goin on. are the days still brutal on here? I dont even bother gettin on during the day, i just wait til night when everything calms down a bit.
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2586. JamaicanGir
2:24 AM EST on August 18, 2007
SJ, doing a great job i am learning every day and you always try to answer all questions of the newbies

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2585. StormJunkie
7:24 AM GMT on August 18, 2007
Wow, SJ don't blush often...lol

Seriously Thanks y'all, but again, only passing along what this site and these folks have brought to me while observing the wonder we call mother nature :~)
Member Since: August 17, 2005 Posts: 26 Comments: 17143

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Dr. Masters co-founded wunderground in 1995. He flew with the NOAA Hurricane Hunters from 1986-1990. Co-blogging with him: Bob Henson, @bhensonweather

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