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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535. miken62
10:04 PM GMT on August 17, 2007
if GFDL is correct ....bye bye NOLA
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534. Biloxigal
10:04 PM GMT on August 17, 2007
Ok - take it from someone that's been though several hurricanes - even with that said - Katrina taught me several additional lessons:
1. If it's large and coming for you - get out!!! There's no reason to stay! Also - plan to be away for several weeks.
2. If you stay (we stayed for Katina - CRAZY!), go to a WELL built building. TAKE YOUR WATER AND FOOD WITH YOU! Enough for several weeks.
3. Even if you don't live near water - you can just live near a ditch or anything that holds water - you can flood. You don't have to be in a flood area! Don't expect any food or water to be left when you return home.
4. Be sure to take a can opener with you!
5. Don't expect the government to help if you've lost all your food and water. If it hadn't been for relatives in B'ham bringing food and water - who's knows.
6. Generators aren't any good if you have nothing to generate.
Best I can say - get out (and take your pictures and anything you can't replace!)
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533. GotSand
10:02 PM GMT on August 17, 2007
Food for thought: Since I live in Navarre Beach Florida (Panhandle) I know what happens when hurricanes enter the GOM and hit any one of the five states. All Five States Are Affected. In a rudimentary fashion, I will attempt to lay out the process. In this case, lets assume the storm does in fact hit Texas or Louisiana. Here's the scenario (a proven scenario)

All oil rigs in the Gulf will be evacuated 48-72 hours prior to the storm. (how many are there again?)How many will be out of commission and for how long.

Damage to the refineries has always been significant in Texas and Louisiana not to mention the Chevron refinery that just burned up.

Fact: The majority of the panhandle states receive fuel via Barge.

Fact: We will receive no gas for up to three weeks.

Fact: If another storm follows within three weeks of the initial storm and threatens your area, you may have no gas to evacuate. Highly possible in this case given whats behind DEAN.

Fact: Jack Daniels will not run your vehicle?

Bottom line: the effect of the storm will reach out and touch a large junk of the GOM states.
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532. weathersp
5:58 PM EDT on August 17, 2007
Ok I made a map explaining MY views on things..

Blue= Track Dean may take
Red= People in these areas should watch dean closely.
Hot Pink= People in theses area's should be making preparations to leave or have at least 3 days of supplies.

Dean= See Key above
Member Since: January 14, 2007 Posts: 17 Comments: 4140
531. Wundermobay
10:04 PM GMT on August 17, 2007
We are expected to start feeling the effects of Dean ,Tommorrow evening
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530. sngalla
5:56 PM EDT on August 17, 2007
Max Mayfield on channel 10 just said for the last 3 years that the GFDL model has been the most accurate. The ULL not moving as predicted is one reason for this being the most outlier of the models.
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529. jj292
9:59 PM GMT on August 17, 2007
Every model is predicting something different with the ULL.

Nothing we can really do but wait and watch.
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9:55 PM GMT on August 17, 2007
track mark
16.1,72 C4/H/D
17.2,77 C5/H/D
18,81 C4/H/D
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527. steelmagnolia44
10:03 PM GMT on August 17, 2007
I've been reading the various blogs over the past several days. One thing I have always heard forecasters say is don't go by the center line in the forecast cone......that the storm will be on one side or the other of that center line as it continues on its path.

If that is true, then the models predicting a more northerly track toward major population centers like Houston are not really "off", and are within or near the NHC 5 day cone at this point.

Is that correct? Please comment!

I enjoy reading everyone's opinions and wish none of us had to deal with Dean!


Member Since: August 24, 2005 Posts: 0 Comments: 45
526. Crisis57
10:02 PM GMT on August 17, 2007
EYE is visable now and wow Dean looks impressive
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524. miken62
10:00 PM GMT on August 17, 2007
Donna ....too many opinions ...do what you think is best........
the end
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523. finnadat
9:56 PM GMT on August 17, 2007
The rita evacuation trainwreck happened b/c people in the woodlands were going up to dallas or austin while nobody who lives north of I10 should leave. so those in low areas or within 15 miles of the coast can.

That said, nobody will have a clue for another 48 hours and if it does hit south of Galveston/Houston we'll still get some significant bands, but if it is south of corpus or east of beaumont houston will be fine.
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522. Wundermobay
9:59 PM GMT on August 17, 2007
Hurricane Watch now in effect for the Island.
Everyone is on edge of their seats,Many supermarkets
are almost empty.It is very hard to find canned goods .
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519. weatherboyfsu
9:56 PM GMT on August 17, 2007

If you were my mother, I would come get you but your not.......so if you have somewhere you could go stay, family, etc., then get on down the road and have some fun....Whats the worst thing that could happen if you leave early? the storm turns another way.......whoopy doo hooray hooray...as my dad would say...........besides its always a good thing visiting family, friends, etc............
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518. whirlwind
9:58 PM GMT on August 17, 2007
How about the archive of how Dean looked as he matured?? Animation from TS or wave to where he is now? Any links?
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516. Wundermobay
9:56 PM GMT on August 17, 2007
Hello everyone
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515. Meteorologist1969
9:54 PM GMT on August 17, 2007
I know the meteorological issues with making this comment, but from a casual perspective for some of you, notice that whether Dean heads south or north of Jamaica may in turn hint at whether the GFDL (North of Jamaica) proves correct or the other models (South of Jamaica) prove accurate. Could be an early indication of where Dean will go.

I agree that Dean is headed west, not NW.
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514. WPBHurricane05
5:58 PM EDT on August 17, 2007
Donna, if your in the 3 day cone than you might want to evacuate.
Member Since: July 31, 2006 Posts: 56 Comments: 8112
513. TXKiwi
9:57 PM GMT on August 17, 2007
Thanks whirlwind
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512. stormybil
9:50 PM GMT on August 17, 2007
wow the size of dean is even getting bigger this is going to take up alot of realestate
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511. whirlwind
9:54 PM GMT on August 17, 2007
GREAT link Kiwi...!!
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510. StormJunkie
9:53 PM GMT on August 17, 2007
My bad Donna...I was not thinking...If Dean is headed towards the Island you need to be off of it. Forget all those questions I asked. Those are for folks 15+ miles inland. So sorry, I need to be more careful. This jave thing has me frustrated.
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509. wetlandsLA
9:54 PM GMT on August 17, 2007
thank you sammo
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508. Metallica1990
9:54 PM GMT on August 17, 2007
the eye looks like its clearing and growing
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507. sammo
9:50 PM GMT on August 17, 2007
Posted By: wetlandsLA at 9:44 PM GMT on August 17, 2007.
1800 z stands for ZULU the time the military uses it is the sam time as GMT....In other words if you live on the east coast ZULU time is 4 hrs ahead of you

someone back me up on this..Please

Yes....this is correct
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506. MaxTempest
9:53 PM GMT on August 17, 2007
Is there a website that saves all of the satellite frames so you can view as a continuous loop starting days ago?
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505. WPBHurricane05
5:52 PM EDT on August 17, 2007
Why give up Vero? Its a debate, no matter how hard you try I'm not going to agree with you and your not going to agree with me. This is just a blog, and we are stating our own opinions.
Member Since: July 31, 2006 Posts: 56 Comments: 8112
504. Pedibrainpa
9:53 PM GMT on August 17, 2007
Donna...leave!!! My husband lived in Galveston when Alicia (cat 3) hit...they boarded up and left. I left for Rita with my kids, pets, etc., an hour before the mandatory evac time started and made it to Dallas in 4 hours. If you wait til mandatory evacs you will be sitting in traffic. Remember that Galveston is a sand bar...the only part of the island "spared" in 1900 was the northcentral east end...where all the old houses/bishops palace/UTMB, etc are.

Leaving and having nothing happen to your home is good...not leaving and being stuck (or worse) is not...Cat 4 or 5 heading here and I am leaving Pearland. Please be safe!

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503. edhanna
9:52 PM GMT on August 17, 2007
Posted By: TXKiwi at 9:51 PM GMT on August 17, 2007.

Earlier today someone posted a link for a loop of (I think) the NHC tracks showing the change in track from forecast to forecast...

It didn't show Dean, but how the forecast was moving each time

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502. TXKiwi
9:53 PM GMT on August 17, 2007
this is the loop... slow it down and watch it... really interesting

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501. miken62
9:50 PM GMT on August 17, 2007
The best thing for this system would be for it to head southwest into the less populated southern Yucatan toward the Tulum area where there is very little population...otherwise Cancun and Cozumel can't handle another big hit ...Wilma did tremendous damage a few years ago which I saw first hand just a few months after; and damage was still unbelievable.
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499. ioweitall2charley
9:50 PM GMT on August 17, 2007
Hey guys...I always follow this blog and enjoy the resource and yes even the bickering...Having lived through Charley and Wilma I can honestly say that all scientific computations aside no one can be certain of landfall this far out...neither Charley nor Wilma were forcast for our area and yes I understand steering currents etc...but I am keeping an eye on Dean...even if he doesnt have one LOL
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497. StormJunkie
9:52 PM GMT on August 17, 2007
New spike of deep convection near the eye wall. Looks like one of those "pilliars" that was in that NOAA video?
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496. DocBen
9:51 PM GMT on August 17, 2007
Cat 5 before leaving the Caribbean.
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495. JLPR
9:43 PM GMT on Agosto 17, 2007
Posted By: getalife at 9:38 PM GMT on August 17, 2007.

There is no indication it's "going north". Why do I keep reading that??

I know. People darn near rooting for this thing to hit the N Gulf coast...or to be right. Dean has been moving along the 15N line, nearly directly west for a little bit now and seems to jump a very bit more north during his strengthing phases IMO.

all i care is PR and a little wooble north can decide between TS winds or just gusts here in PR
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494. Melagoo
9:50 PM GMT on August 17, 2007
Dean is not moving north. It has been heading west 280 for the last three days.

The NHC has been right on track.

... then Jamaica is in for a very rough ride!

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493. StormJunkie
9:49 PM GMT on August 17, 2007
Should be NG, it is getting to some very warm waters.

Got to finish resolving my java issues...man this has been a cruddy day.

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492. Masquer08er
9:47 PM GMT on August 17, 2007
If you want to book a hotel somewhere, you can always cancel. That is alot easier to do than finding one at the last minute.
Member Since: August 16, 2007 Posts: 0 Comments: 397
491. retaining1
9:33 PM GMT on August 17, 2007

I stayed at my house in Beaumont, Texas for Hurricane Rita in 2005. It was scary due to the tornadoes passing by the house every 10 minutes or so. Anyone who thinks you can't hear a tornado coming when you are in the eyewall is dead wrong! We heard them about 30-seconds away, then watched the roof breathing in and out and listened for some crashing noises outdoors. If the house didn't shake, then whatever crashed probably didn't hit the house. You look between lightning flashes to see where the trees fell. It can be a really intense experience, I was scared to death but enjoyed every minute of it. If Dean hits Houston, I'm planning to stay again.

If you evacuate from Galveston, please remember that the National Guard will set up on the county lines and on the I-45 bridge. If you evacuated from Galveston and aren't part of the recovery effort... you can't get back in. You could be kept out of Galveston for 2-3 weeks or more. It happened to a lot of my friends from Port Arthur & Nederland, Tx. The national guard will set up at all major highways at county lines and along major access roads. If you evacuated... you STAY OUT until they say civilians can return. That is, unless you know of any back roads you can take to get around the national guard checkpoints.
If you DO leave, see if you can get someone official sounding (from Entergy, the Telephone Company, the Gas Company, some tree service or something) to write you a letter stating your name and vehicle license plate #, and that you are part of the recovery effort. Most national guardsmen have only 15-seconds to decide if you are full of B.S. or if you are truly part of the recovery effort. That's not enough time to make a phone call. If it looks official, they may let you back in to Galveston. If not, wait 4-hours and try again at the same checkpoint when a different group is on duty.
P.S.: It also helps if you have a magnetic tag or sign for your car door that says (bogus name.. "tree service", or "electrical" or "construction" or "plumbing"). Then, they may not even question you on returning home.

Don't stay in harm's way, but leaving definitely has the risk that you will be kept out until the official "return" order is given... which may be 2-3 weeks or longer.
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9:50 PM GMT on August 17, 2007
--i give up--im outta here---be back later........... :)
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489. Metallica1990
9:48 PM GMT on August 17, 2007
Posted By: VEROBEACHFL1 at 9:48 PM GMT on August 17, 2007.

If someone would print out both the 11:00 a.m. and 5:00 p.m. tracks and put them over the top of each other, they would see NHC's slight shift to the north.
---thank you--

so what! are you trying to prove something if the track has shifted then big deal both tracks had this thing hitting jamaica and thhe yucatan WOW BIG SHIFT
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488. TXKiwi
9:48 PM GMT on August 17, 2007
Earlier today someone posted a link for a loop of (I think) the NHC tracks showing the change in track from forecast to forecast...

It didn't show Dean, but how the forecast was moving each time
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487. snotly
9:47 PM GMT on August 17, 2007
symetric eye and buzzsaw appearance im going out on a limb and saying 145-150 mph winds by 8 am Sat with pressure 925 mb
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486. rwdobson
9:48 PM GMT on August 17, 2007
the key word is "slight" shift to the north.
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485. ClearH2OFla
5:48 PM EDT on August 17, 2007
Vero its ok calm down im on board with you LOL
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Cat 6 lead authors: WU cofounder Dr. Jeff Masters (right), who flew w/NOAA Hurricane Hunters 1986-1990, & WU meteorologist Bob Henson, @bhensonweather

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