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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435. hahaguy
9:37 PM GMT on August 17, 2007
ckearh20 can u post the link for that cmc model
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433. WPBHurricane05
5:37 PM EDT on August 17, 2007
Do not focus on every model run, or wobble. Use the models only as a guide.
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432. SWFLdrob
9:37 PM GMT on August 17, 2007
was looking at some old forecast advisories for Dean from the NHC.

the 5 a.m. advistory on wednesday looked like this

FORECAST POSITIONS AND MAX WINDS

INITIAL 15/0900Z 12.2N 44.2W 45 KT
12HR VT 15/1800Z 12.4N 46.6W 50 KT
24HR VT 16/0600Z 12.8N 50.1W 55 KT
36HR VT 16/1800Z 13.2N 53.7W 60 KT
48HR VT 17/0600Z 13.8N 57.1W 70 KT
72HR VT 18/0600Z 15.0N 63.0W 80 KT
96HR VT 19/0600Z 16.0N 68.5W 90 KT
120HR VT 20/0600Z 17.5N 74.0W 100 KT

guess that means Dean is ahead of schedule and south of that line?
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431. HurricaneDean2007
5:37 PM EDT on August 17, 2007
If Corpus gets the major hurricane, San Antonio would be SLAMBAST'd.
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430. rwdobson
9:36 PM GMT on August 17, 2007
"I don't think storm surge would be an issue as we are over 8 feet off the ground and our home is mostly concrete"

in katrina, people in mississippi were swept out of their 3rd floor apartments by the storm surge. the sruge could easily be 20 feet high.
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429. wetlandsLA
9:37 PM GMT on August 17, 2007
I ment AST + 4 hrs
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428. ClearH2OFla
5:34 PM EDT on August 17, 2007
Vero i think we are ok here. I do agree with you though that before this is all over we will have more of northern component. any thoughts on the two sys showning on the cmc behind dean.
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427. Johnhopefan
9:35 PM GMT on August 17, 2007
Last night GFDL had 155knt (190mph?) Dean going right into Houston. If that happens that would be 1000 times worse then Katrina.
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426. wederwatcher555
9:35 PM GMT on August 17, 2007
and its not just the gfdl. the new hwrf has dean aiming for corpus christi which is still south but not like the gfs
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425. wetlandsLA
9:35 PM GMT on August 17, 2007
18z = ast = 4 hrs = 18 GMT
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424. WPBHurricane05
5:34 PM EDT on August 17, 2007
Only evacuate if you are told to do so. We don't need another Rita evacuation when people evacuated who didn't need to.
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423. DonnaGalveston
9:31 PM GMT on August 17, 2007
I live right on the water, but I don't think storm surge would be an issue as we are over 8 feet off the ground and our home is mostly concrete. My neighbor told me that he heard it was coming right for us with winds over 150 mph. How can that be true? I am going to watch this here all weekend unless we evacuate early. I noticed lines at the gas station already. I passed several trucks with plywood in the back, and some towing boats away from the water. I am just afraid of leaving to early. We left for Rita when we could have just stayed home and have been safe. We have thought about waiting and leaving just before landfall because friends here said the roads were deserted around here right before Rita hit well to our north and east.
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422. Tazmanian
9:33 PM GMT on August 17, 2007
i have a vary bad feeling about this storm
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421. StormJunkie
9:35 PM GMT on August 17, 2007
oops, my bad on the double post
Member Since: August 17, 2005 Posts: 26 Comments: 15644
419. StormJunkie
9:32 PM GMT on August 17, 2007
Easy with the pics y'all, the blog is busy...

We have 6 images in 50 comments...And 50 comments are flying by like every 15 minutes or so...

Just want the blog to be useful even for those with a slower connection. No offense, I like the pics myself. But I know not everyone is on cable...
Member Since: August 17, 2005 Posts: 26 Comments: 15644
418. rwdobson
9:35 PM GMT on August 17, 2007
just click on someone's name to get to their blog.
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416. weatherboyfsu
9:30 PM GMT on August 17, 2007
Lefty420 and Stormjunkie......I will email you if things warrant a trip to stormchase......

This time of year when we get a storm like this, its hard for me to concentrate on my work........For whats it worth, a hurricane is a natural entity and it has beauty but it also needs respect. It is also one of the few things that man cannot control. I live in a very favorable area for hurricanes and I will not move. I live about 90 miles inland for a reason.
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415. VEROBEACHFL1
9:35 PM GMT on August 17, 2007
"basically" my azz.......... keep checking those 6hr updates......... your gonna get surprised each time........

--"people keep calling this a wobble...maybee it is but enough of these "WOBBLES" will cause the whole track to be off...the latest frame shows another "WOBBLE""

and people have been saying for the last 3 days "look, it's going north of the forecast! it's gonna turn north!"...and it has not. it's still basically on the same track the NHC was predicting 3 days ago.
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414. JadeInAntigua
8:55 PM GMT on August 17, 2007
Wow, we are really getting some serious rainfall and wind now... thought for sure the worst of it was this morning, but it just keeps going and going...
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412. VEROBEACHFL1
9:34 PM GMT on August 17, 2007
---well, at least there is a few of you who can see that the NHC did change their track to a slightly nortern track--- from the 11am. to the 5pm
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411. rwdobson
9:33 PM GMT on August 17, 2007
"people keep calling this a wobble...maybee it is but enough of these "WOBBLES" will cause the whole track to be off...the latest frame shows another "WOBBLE""

and people have been saying for the last 3 days "look, it's going north of the forecast! it's gonna turn north!"...and it has not. it's still basically on the same track the NHC was predicting 3 days ago.
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410. sngalla
5:32 PM EDT on August 17, 2007
Norcross just pointed out that the GFDL is historically accurate and that gives us pause.
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409. OUFan919
9:34 PM GMT on August 17, 2007
SouthDadeFish: Don't forget about Ivan!!
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408. wederwatcher555
9:32 PM GMT on August 17, 2007
what 18z runs? are they even out yet?
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407. WPBHurricane05
5:32 PM EDT on August 17, 2007
5 PM track Link

11 AM track Link

Looks the same, except for the location of Dean.
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405. GainesvilleGator
9:25 PM GMT on August 17, 2007
DonnaGalveston, I would listen to your local officials. As Dean comes closer, I expect TV coverage to be around the clock.
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404. Metallica1990
9:32 PM GMT on August 17, 2007
Posted By: WPBHurricane05 at 9:31 PM GMT on August 17, 2007.

Only evacuate if you are told to do so.


but drawing up a plan now definatly wouldnt hurt
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402. StormJunkie
9:29 PM GMT on August 17, 2007
There is a lot that goes in to that choice DG, and welcome aboard!

What type of house is it?
How close to water front/surge are you?
Flood prone area?
Trees around the house?
Do you have enough supplies?
Can you deal with two to three weeks no electricity?
What condition is the house in?
And the roof?
Answering all of those questions and then making the choice that you are "somewhat safe" based on those questions and quite a few others is up to you. There is always some risk if you stay behind.
Member Since: August 17, 2005 Posts: 26 Comments: 15644
400. Johnhopefan
9:28 PM GMT on August 17, 2007
Lets face it, all the play by play about Yucatan, this wobble or that wobble, this model or that model....... there is only one thing on everyone's mind really..... Cat 5 Dean & HOUSTON!!!!!!!!!!!!!

Cat 5 Dean Houston is a lot different then Cat 3 Dean South Texas, Mexico or Louisiana.
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399. WPBHurricane05
5:30 PM EDT on August 17, 2007
Only evacuate if you are told to do so.
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398. OZarkfrompcola
4:29 PM CDT on August 17, 2007
781 MB before going into the gulf....watch out BIG EASY....WHERE'S STORMTOP...written in SANDSTONE.....OZ
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397. wetlandsLA
9:28 PM GMT on August 17, 2007
hey guys

It has been a while.

I have to agree w/NHC....the track looks good and the 18z models have shifted back left from the 12z models and the GDFL is a large outlyer.

Just my thoughts

I would have said Huston This morning but now....I agree with NHC
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396. rwdobson
9:30 PM GMT on August 17, 2007
Donna, you need to ask local emergency officials about that. There are probably maps showing evacuation zones etc. The big issue would be storm surge. People in Katrina were literally washed out of their houses by the surge.
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395. Drakoen
9:30 PM GMT on August 17, 2007
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394. SouthDadeFish
9:25 PM GMT on August 17, 2007
Dean in looking great. Once that eye completely clears out i think we might see some rapid intensification unfortunately.... I hope this one can spare Jamaica.... It looks like right now they may get a cat 5 strike.... that would be unbelieveable. Well Dean sure does have that classic hurricane look goin. Maybe next year we will all be comparing Carribean storms to Gilbert, Allen, AND Dean.
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393. Metallica1990
9:29 PM GMT on August 17, 2007
Posted By: DonnaGalveston at 9:29 PM GMT on August 17, 2007.

What would Dean do in Galveston if he hit here? Would we be safe if we just boarded up and hid in the closet? I've never been through a hurricane.


Depends on 2 things

1 how strong it is
2 your location

if your close to the water and this thing is a monster you should start thinking about evacuating
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392. TXKiwi
9:29 PM GMT on August 17, 2007
Donna

No. You will not be safe if (and its a big if) Dean hit Galveston.

With respect, only an idiot would answer "yes" to the question "am I safe if I hide in a closet".
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391. DontPass
9:29 PM GMT on August 17, 2007
Does anyone know the extent of damage on St. Lucia, or a link with updated information on when the St Lucia airports will reopen? Thanks!
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390. ShesACaneiac
5:29 PM EDT on August 17, 2007
Hi, all. Donna, this would not be a great first hurricane. Even I would bail on this one.
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389. retaining1
9:15 PM GMT on August 17, 2007
I've seen a LOT of generators on trailers today in Houston. Several were pulling into one refinery, while others are going to local businesses. People are starting to get ready just in case.

On another note... I'd rather rely on the ants and squirrels in nature for common sense rather than those squirrels who will be planning the next evacuation disaster from Houston.

I have heard several people comment during the last 2-weeks here in Houston that there are no birds around. It's true. You still see seagulls and waterfowl, but there are almost no birds. Today, I looked at the sky and there were absolutely none. It's been that way here lately and people have noticed.
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387. weatherboyfsu
9:28 PM GMT on August 17, 2007
Hang in there.......INCOZUMEL>........

WE are definitely praying for you but someone is going to take a punch..... unless the ole mighty can produce some 25 knots wind shear......
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386. Crisis57
9:28 PM GMT on August 17, 2007
Monster
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385. WPBHurricane05
5:27 PM EDT on August 17, 2007
For the short term Dean is right on track. At 5pm they moved the track west since Dean is moving west. It hasn't moved north or south between 11am and 5pm.
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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.