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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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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484. NormalGuy
9:47 PM GMT on August 17, 2007
thanks StormJunkie, so tonight will be interesting??
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483. VEROBEACHFL1
9:46 PM GMT on August 17, 2007
weather brat---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 wb--
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482. WPBHurricane05
5:47 PM EDT on August 17, 2007
If this thing was headed north of the forecast track, the NHC would say so.
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481. StormJunkie
9:44 PM GMT on August 17, 2007
NormalGuy, I would say the Diurnal cooling can have a larger impact on a developed system in warm waters.
Member Since: August 17, 2005 Posts: 26 Comments: 15671
480. VEROBEACHFL1
9:43 PM GMT on August 17, 2007
lol-- at some of these posts-- OBVIOUSLY every one is not watching EVERY 6 hr post....
---- do you think (for example) the NHC leaves the same track up for 4 or 5 updates?
--of course its gonna be on track because they update and move it for a 6hr period and then it changes the track again.........kabesh!! so it looks like it has been on track for like days....in FACT its gonna change, has changed and will always change.......... from most update to updates,........ i hope we are clear on this......
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479. weatherboyfsu
9:45 PM GMT on August 17, 2007
Yeah...... I understand what your saying but for the NHC to post that, they obvisiously see something prudent on their model analysis........
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478. ClearH2OFla
5:42 PM EDT on August 17, 2007
Looking at this link. It looks like the Atl swirlie for lack of a better term is moving east and the bahama swirlie is moving west but slowly and the space between them is getting bigger then it was this AM any thoughts here is the link Link
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477. TXKiwi
9:43 PM GMT on August 17, 2007
Donna / Metallica

An evac is unlikely before Monday. You have another 24-36 hours to beat the rush.

IF you have a nice place to go and call it an end of summer holiday, then go now and call it a holiday.

If an evac would be a major inconvenience then I would wait another 24 hours and ask the question again....

Its a game of cat and mouse... wait to long you get caught, go too soon it's a waste. There is no right answer as to how soon to beat the rush.

I'm going to Louisiana in about 4 hours, so I'll tell you how bad traffic is on I10 if you ask me late tonight
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476. weatherspirit
9:42 PM GMT on August 17, 2007
Donna,

I would wait until at least three days out. That way, you'll know what the forecast potentially is... right now, there are too many variables in Dean's overall path... but the time to prepare is now...
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475. SouthCentralTex
9:43 PM GMT on August 17, 2007
I am leaning towards leaving, but does anyone know how early I'd need to leave to "beat the rush"?

Getting off the island should be your main focus. If a Cat 5 was to hit Galveston, there would be no place to go. I'd say given the traffic problems with getting off of the island that first thing Monday would be a good bet if the track becomes more consistent with a Galveston landfall.
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474. Metallica1990
9:44 PM GMT on August 17, 2007
i honestly beleive there is no beating the rush you leave when they tell you to but you could try and find a route that no one would use most times people use the interstates and major highway find a road that will take you from the coast that no one really uses then get out when they tell you to
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472. JAC737
9:44 PM GMT on August 17, 2007
I believe the mandatory evacuation of Galveston Island during Rita did not start until the storm entered the Gulf. We are still 2 days away. This storm could go anywhere. Just get prepared. You can always drink your bottled water and make tuna casserole come the fall.
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471. canewatch
9:40 PM GMT on August 17, 2007
I've been watching the ULL on the visible moisture sat. loop. It appears that the ULL moved west about 100 miles for Deans move west of 150 miles. Given a ratio of 3 to 2, and assuming the low holds together, the ULL should be just south of the Texas coast when Dean nears the straight between Yucatan and Cuba. This will effectively stop a turn to the right and send it into Mexico. The only way it will follow the GDFL is for the ULL to weaken considerably in the next two days. If that happens, Katie bar the door.
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470. NormalGuy
9:43 PM GMT on August 17, 2007
Okay on the radio here in Northern Mississippi, they just said that the office of emergency management will consider issuing evac orders starting late saturday or sunday. They are going with the better safe than sorry logic...Donna take heed ma'am, leave early if you have somewhere to go. think of it as getting away for a few days. and relax, and by the way pay your homeowners before you leave town...LOL
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469. DonnaGalveston
9:43 PM GMT on August 17, 2007
Thank you all for answering my questions. I will be back a bit later for some updates on the storm. I really look to this blog to say the things the weathercasters on tv can not say. I am heading out to gas up the car and to get a few groceries in case we end up evacuating tomorrow or Sunday.

Today at work I got an email an the whole Galveston portion of our company is currently running in "Hurricane Mode" until further notice.
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468. weatherbrat
9:35 PM GMT on August 17, 2007
Verobeach ~

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. Is this going to continue to be Dean's trend?

That ULL looks weak and elongated, moving slowly west. I do not believe it is going to be a major player in keeping Dean to the west. I believe that a more northerly track, as the GDFL model shows, will indeed happen. But, please, that is just my opinion from what I am see and researching.

We will all have to wait and see. Even Dr. M said that the next 1-2 days is pretty predicable, but what will come after that?

My thoughts and prayers go out to the people in Jamiaca.
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467. littlefish
9:39 PM GMT on August 17, 2007
I know the CMC is crazy about giving birth to hurricanes but have you seen the very Katrina like genesis and path it gives to a system after Dean? Yeesh...
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466. SlimPBC
9:44 PM GMT on August 17, 2007
The eye is back. Looks like it might be here to stay for a while.
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465. whirlwind
9:43 PM GMT on August 17, 2007
When Rita hit you guys... some of you were stuck in traffic and outta gas.... half day in traffic I think it was.

As soon as it hit Yuck pan or near.... get outt town
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464. getalife
9:42 PM GMT on August 17, 2007
Posted By: DonnaGalveston at 9:41 PM GMT on August 17, 2007.

I am leaning towards leaving, but does anyone know how early I'd need to leave to "beat the rush"?


Donna, I would wait until at least Monday myself, but of course by then everyone may be on their way and it would be a Rita situation all over again. I would say Sunday to beat the rush.
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463. weatherboyfsu
9:41 PM GMT on August 17, 2007
From my own experience, if a hurricane is heading in your general direction and you have the luxury of leaving early, then leave early.....If you have someone to go stay with that is 50 miles or more inland, then go stay with them.....why wait if you dont have to......thats less people on the roads.......if you live on the and are planning on living if it comes your way then leave early and then if goes a different direction, then, come back......I know, I know that everyone doesnt have that option but for those who do.......go for it..........
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462. wetlandsLA
9:41 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
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461. Metallica1990
9:41 PM GMT on August 17, 2007
Posted By: DonnaGalveston at 9:41 PM GMT on August 17, 2007.

I am leaning towards leaving, but does anyone know how early I'd need to leave to "beat the rush"?


Thats a tough one for me to tell anyone else have thoughts on this
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460. amd
9:39 PM GMT on August 17, 2007
this northern component of movement only occurs during phases of strengthening.

The NHC has been amazingly accurate in terms of their forecasts the past couple of days, and seem to have this storm pegged. IMO
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459. bayoubrotha
9:42 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.
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458. littlefish
9:42 PM GMT on August 17, 2007
Thanx Nash...
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457. wederwatcher555
9:41 PM GMT on August 17, 2007
the gfdl and hwrf have this hitting major population centers. the ukmet is flipping back and forth and the gfs is consistent with a very south hit. there is no real consensus.
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456. whirlwind
9:40 PM GMT on August 17, 2007
And the roof?


Roof...where...did someone call me.... LMAO...sorry IKE if your watching.. had to
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455. getalife
9:40 PM GMT on August 17, 2007
No I didn't miss it. But there is no scientific data telling me this is going north. But hey, maybe if everyone keeps talking about it a north turn will happen, lol.
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454. VEROBEACHFL1
9:39 PM GMT on August 17, 2007
--any takers on DEAN crossing the 20 BEFORe it gets to 80w?
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453. TXKiwi
9:39 PM GMT on August 17, 2007
Donna's main question was if it hit Galveston should I hide in a closet.

If you live close to the water (anywhere in Galveston is close) and a Hurricane ("even" a Cat 3, let alone 4 or 5) was coming to your town...

it's a no brainer...
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452. JAC737
9:37 PM GMT on August 17, 2007
I live in Galveston County. When Rita was coming, we spent 18 hours in the car going toward Dallas. We gave up. It took only 45 minutes to get home. We evacuated the next day and the highways were deserted. We made great time toward Corpus. We also had a better idea of where the storm was headed. Our original plan would have evacuated us INTO the path of the storm!!! Better Safe than sorry in Galveston.
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451. wetlandsLA
9:38 PM GMT on August 17, 2007
yes rob it is a head of forcast but..lok at the end point to that forcast
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450. Melagoo
9:41 PM GMT on August 17, 2007
Animated SEPAT

Link
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449. sccoastarea
5:37 PM EDT on August 17, 2007
For the person that asked for a link to the news on St Lucia here it isLink

3 people have died in this storm now.
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448. DonnaGalveston
9:40 PM GMT on August 17, 2007
I am leaning towards leaving, but does anyone know how early I'd need to leave to "beat the rush"?
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447. whirlwind
9:38 PM GMT on August 17, 2007
Calm down peeps... its too early... prepare yeah but no panicing...
Im just charging my camera batteries....memory cards..check....another historic storm we are about to go through....


ULL looks slow..... more north Dean will come
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446. SWFLdrob
9:38 PM GMT on August 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.
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445. paulfrmpasschristian
3:38 PM CST on August 17, 2007
I park underneath my house, and got water to my ceiling..That was a direct hit though, I can see the Bay of St Louis(MS) from my house
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444. UnderstandingFL
9:25 PM GMT on August 17, 2007
I have no idea about reading the satellite images, but to those of you that do, can someone please see if what is to the east of Florida in this picture has a chance of developing, or will it affect Dean. I am glad that my State will not meet this hurricane (hopefully). I hope not, but I've been wondering...

http://www.ssd.noaa.gov/goes/east/tatl/loop-avn.html

There's something further east of Dean. I don't even want to look at that now.
443. weatherboyfsu
9:39 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.

Getalife.......did you miss this?
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442. nash28
9:37 PM GMT on August 17, 2007
Whoever said 18z is out needs to realize 18z isn't finished running yet. Don't even bother with the BAM family of runs. Look at the GFDL, GFS ensemble, UKMET, NOGAPS and the Euro.
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441. VEROBEACHFL1
9:38 PM GMT on August 17, 2007
--- i have no thoughts on that "other" mess off africa yet for me--- maybe tonight tho :)
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440. Soloco2
9:30 PM GMT on August 17, 2007
Donna........been thru a few..go, girl!!
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439. miken62
9:26 PM GMT on August 17, 2007
why do people have to keep posting Sat pics ...
I think 99% of the people here know how to look at Sat pics just thru Wunderground alone never the thousands of other sites..
I think it's a waste of space and time ..
PS

Just a thought
Member Since: January 14, 2003 Posts: 0 Comments: 213
438. getalife
9:37 PM GMT on August 17, 2007
There is no indication it's "going north". Why do I keep reading that??
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437. nrtiwlnvragn
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.


I would have to disagree with that. After going through the eyewall of Andrew, I will never stay for a Cat 4 or 5. Most evacuations are for storm surge, which I would evactuate for if I lived in an area with storm surge.
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436. NormalGuy
9:36 PM GMT on August 17, 2007
Okay, quick question, I know that during forming storms the Diurnal max and min, are big factors. On existing powerful hurricanes do they have the same affect? My question being last night it didn't strength too much but tonight with an existing eye will this thing blow up more than already there??? Anyone please? Trying to learn here..
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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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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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