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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734. whirlwind
11:12 PM GMT on August 17, 2007
Johnhopefan...


How about this year breaking the record for the MOST CAT 5 storms???

- I hate it when the Doc and others say in their past blogs that this and that wont develop cause conditions arent like in '05.
Always compare it to '05...
no more maybe..... conditions are diff and STILL we get cat 5's
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733. ezziboo
11:09 PM GMT on August 17, 2007
Longtime lurker; I live in New Iberia, LA. I love this blog and have learned an awful lot from many of you.
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732. weatherspirit
11:11 PM GMT on August 17, 2007
silverstripes,

I know, I've seen almost a due-west/slightly northwest progression with slight wobbles to the south for the past few hours... no telling what he'll do this far out...
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731. animalrsq
7:13 PM EDT on August 17, 2007
http://www.ohsep.louisiana.gov/newsrelated/deandeclaration.htm
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730. JLPR
11:13 PM GMT on Agosto 17, 2007
yeah dean seems to be moving a lil south
its a lil bellow the 15N line
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729. Rick54
6:08 PM CDT on August 17, 2007
All the talk about the models shifting around ....
It is all about the timing of the ULL. If the latest UKMET (which I have not seen yet) shifted back North all it means is that a variable (likely the ULL)at the time of initialization changed in relation to where the model put it on the previous run. As we get more recon as well as get closer to a US or Central American landfall things will become much more clear. Like Dr. Master's said we have a good picture for the next couple of days.
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728. Johnhopefan
11:13 PM GMT on August 17, 2007
Donna,

last night's GFDL model had Dean going to Houston as a Cat 5. If I were you I would definitely follow the storm closely, common sense given even the NHC official path.
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727. HurricaneParty
11:12 PM GMT on August 17, 2007
Governor declares state of emergency

Link to WAFB News Baton Rouge, LA
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726. Metallica1990
11:13 PM GMT on August 17, 2007
Posted By: ClearH2OFla at 11:13 PM GMT on August 17, 2007.

Who is Gabreille and Felix?


the next names
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725. Weather456
11:10 PM GMT on August 17, 2007
For those who miss the update of the Atlnatic wave earlier here it is:

Satellite imagery, 315K potential vorticity charts and 700 mb wind analysis through 1800 UTC indicate that a tropical wave is near 31-32W south of 22N. The last visible loops of the day of the Eastern Atlantic clearly depicts low-mid level cyclonic turning just to the west of the Cape Verde. This wave continues to be envelop in very dry African dust and thus convective active activity remains absent. Another interesting feature is that QuikSCAT shows a second possible circulation within the ITCZ band in the image below.

by Weather456

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724. ClearH2OFla
7:12 PM EDT on August 17, 2007
Who is Gabreille and Felix?
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723. tristanh72
11:12 PM GMT on August 17, 2007
That is very scary for those of us here in Galveston. Dean would have to move through here to get to Houston. If you are not serious, I would really appreciate you not making comments like that.

That was his humble opinion, just not labeled as such.
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721. whirlwind
11:11 PM GMT on August 17, 2007
Looks like this season is not a bust afterall!!!!!

Things are rolling finally...
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720. ClearH2OFla
7:10 PM EDT on August 17, 2007
Hey all have you looked at the Water Vapor loop that ull spinning east of Fla doesnt seem to be moving very rapidly.

As for the CMC i have not a lot of faith in that. If the GFS is showing something maybe.
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719. silverstripes
4:05 PM PDT on August 17, 2007
weatherspirit,

You can not be a southwestcaster. Everyone is trying to make this thing turn north. HAHA. J/K. It looks like it has pretty much been traveling west sometimes a nudge north of west just like the NHC has been saying all along. This is getting laughable with everyone talking about NW and WNW movement. It's been running at 270 to 280 degrees for awhile now. NW is 315 and WNW is almost 300 degrees.
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718. WPBHurricane05
7:10 PM EDT on August 17, 2007
I'm dead serious. She has already requested Federal Emergency funds. Hard to believe, I know.

Link please!
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717. DonnaGalveston
11:10 PM GMT on August 17, 2007
Johnhopefan,

That is very scary for those of us here in Galveston. Dean would have to move through here to get to Houston. If you are not serious, I would really appreciate you not making comments like that.
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716. Metallica1990
11:09 PM GMT on August 17, 2007
Fl30258713

LMAO
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715. Johnhopefan
11:08 PM GMT on August 17, 2007
Forecast:

Dean Houston Cat 5

Gabrielle follows in a Katrina like position

Felix forms further out, heads to east coast.

That is all.
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714. Weather456
11:08 PM GMT on August 17, 2007
Dean is now moving off the 15N line
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713. Masquer08er
11:07 PM GMT on August 17, 2007
I'm dead serious. She has already requested Federal Emergency funds. Hard to believe, I know.

OK Now I understand.
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712. snowboy
11:08 PM GMT on August 17, 2007
ease up barbadosjulie, you're in the clear for time being..
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711. HurricaneParty
11:07 PM GMT on August 17, 2007
Gov Blanco must have looked at the Wunderground GFDL animation... wow, that looks bad for NOLA!

http://www.wunderground.com/tropical/tracking/at200704_v5d.html?extraprod=v5d#a_topad
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710. Fl30258713
11:08 PM GMT on August 17, 2007
Evidence of Pin Hole Eye formation

Evidence of Dean's Pin Hole Eye

This is for Taz ;-)
and anyone else that needs proof.
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709. Weather456
11:06 PM GMT on August 17, 2007
Dean is wobbling...one time its jogs a little north....now its jogging a little south of due west...
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708. littlefish
11:06 PM GMT on August 17, 2007
whirlwind, I think they're developing the wave at 15N 32W. But it has almost NO convection so will have a hard time staying together over the big Atlantic.
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707. H2PV
11:05 PM GMT on August 17, 2007
Posted By: barbadosjulie at 10:59 PM GMT on August 17, 2007.
thanks, the talk here in Barbados is that there is forcasted to be another storm in the coming days that will also affect us. Is this tru?


If it comes soon, then it will hit the "lake of cold rainwater" floating on top that Hurricane Dean just rained down. One hurricane passing puts the kabbosh on the next one for a week or so. There's a cold wake behind storms with the stronger one is, then the deeper and colder the wake. In KATRINA's case that was not true because the Loop Current was hot 250 meters deep, and RITA found no cold pool when it crossed KATRINA's track.
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706. snowboy
11:04 PM GMT on August 17, 2007
StPeteBill, no sign of anything to significantly slow Dean in terms of either forward speed or intensification..
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705. JLPR
11:03 PM GMT on Agosto 17, 2007
Hey guys Will you visit my blog pleasee!!
i set up the areas that could have development in the tropics come to my Blog and tell what you think
oh and i also created a map pointing the areas
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704. LADobeLady
6:05 PM CDT on August 17, 2007
Ya think Gov Blankstare learned her lesson from K?
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703. littlefish
11:01 PM GMT on August 17, 2007
SJ- GFS and UKMET are both punch drunk. They seem to not notice the heat potential Dean ahs underneath it in the water! On another note, the CMC has been drinking way too much cyclone caffeine with 3 systems next week. One a Katrina like birth.
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702. whirlwind
11:04 PM GMT on August 17, 2007
The CMC and GFS are developing someth;ing after Dean.... Same track as dean so far but goes north to FL
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700. HurricaneParty
11:04 PM GMT on August 17, 2007
I'm dead serious. She has already requested Federal Emergency funds. Hard to believe, I know.
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698. Johnhopefan
11:01 PM GMT on August 17, 2007
The most crucial thing for the US is does Dean hit the Yucatan..... if it goes north of the Yacatan, that could mean Cat 5 for Texas. Then it's whether we are talking an upopulated area or a place like Houston!!!!!!!!!

Gilbert, Wilma, all disasters averted thanks to the Yucatan. Eventually one of the storms will make it through the channel with an 880mb type pressure.
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697. silverstripes
4:04 PM PDT on August 17, 2007
Stormjunkie,

Did you d/l some weird Java application last night? Mine has been acting weird too. SOmetimes it's works....sometimes it locks up.
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696. leelee75k
10:57 PM GMT on August 17, 2007
I know all focus should rightly be on Dean, but what is that seemingly huge mass of clouds behind Dean, off of Africa? Is that thing showing signs of development yet?

btw thoughts and prayers to all those in the path of Dean, stay safe.
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695. wederwatcher555
11:03 PM GMT on August 17, 2007
if you extrapolate the hwrf it also has a landfall that is very dangerous (corpus christi)
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694. LADobeLady
6:02 PM CDT on August 17, 2007
Posted By: HurricaneParty at 6:02 PM CDT on August 17, 2007.

The governor of Louisiana has just declared a state of emergency for Hurricane Dean ... just in case!


How shocking, I'm surprised she didn't have to "think" about it for 24 hours.
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693. weatherspirit
11:03 PM GMT on August 17, 2007
looks like in the past three hours, dean has moved more to the southwest... Link
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692. Masquer08er
11:02 PM GMT on August 17, 2007
Are you serious Hurricane Party? Its hard to tell.
Member Since: August 16, 2007 Posts: 0 Comments: 393
691. barbadosjulie
11:02 PM GMT on August 17, 2007
thanks, the talk here in Barbados is that there is forcasted to be another storm in the coming days that will also affect us. Is this tru?

Can someone please answer me, check the models or something, please,
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690. nrtiwlnvragn
11:01 PM GMT on August 17, 2007
18Z GFS has landfall at Belize/Mexican border

Link
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689. Weather456
10:53 PM GMT on August 17, 2007
Look at Dean go

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688. Metallica1990
11:01 PM GMT on August 17, 2007
crisis i think your right the eye is starting to look a little outta shape
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686. StuccoMan
6:01 PM CDT on August 17, 2007
Posted By: DonnaGalveston at 5:59 PM CDT on August 17, 2007.
Here are some live webcams from the area:

http://www.galveston.com/webcams/

As you can see, the water is already rising, and waves are crashing. Roads would probably go under water well in advance of landfall if it comes here.


Good god the storm is in the carribean around 2 corners from you.
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685. bekroweather
10:59 PM GMT on August 17, 2007
Donna in Galveston:

The waves in Galveston currently have nothing to do with Dean. It is like 2000 miles away from Galveston. We just have a little bit of bad weather in SE TX tonight. If it was associated with anything tropical, that would be with the remnant moisture from Erin.
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About JeffMasters

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