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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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: 16970
2584. MrNiceville
7:24 AM GMT on August 18, 2007
SJ - any opinion on the relative closing rate between the ULL and Dean?
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2583. GPTGUY
2:22 AM CDT on August 18, 2007
SOTC..That's not the real Stormtop....this ST0RMT0P is using a 0 instead of an O...go back to Dr. Masters archive blog from last year or two years ago and you will be able to tell...stormtop is now stormkat he was on here thu night saying Dean is a LA/MS/AL storm
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2582. StormJunkie
7:22 AM GMT on August 18, 2007
Thanks JG, and Story ☺

That said, I am really only paying back what the Dr, and so many other folks in this blog have helped me learn
Member Since: August 17, 2005 Posts: 26 Comments: 16970
2581. Starwoman
9:19 AM CEST on August 18, 2007
Posted By: FLCrackerGirl at 2:13 AM EST on August 18, 2007.

StormJunkie!! (waves from out in lurker's corner)
SJ You Really Should Be Appaluded for Your Efforts & Dedication to The Blog. Kudos on An Outstanding Job Covering the Info & Link Requests. Your Observations & Commentaries Are Right on Point Also. Keep Up The Good Work.
FRAN

i second that


I third that lol

Another "thank you" ( we're queing here *s*), I really appriciate your posts.

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2579. JamaicanGir
2:18 AM EST on August 18, 2007
caymangone
will do as long as power remains and given that CWJA does not take down ADSL sats
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2578. StormJunkie
7:18 AM GMT on August 18, 2007
Posted By: FLCrackerGirl at 7:13 AM GMT on August 18, 2007

FRAN!!! ☺ ☺ Morning to you, thanks, and great to see you!!!

What you doin up this time of the am~)
Member Since: August 17, 2005 Posts: 26 Comments: 16970
2576. StoryOfTheCane
7:18 AM GMT on August 18, 2007
it happens, it gets like a zoo in here and its hard to deal with everyone comin after ya at once
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2575. caymangone
7:15 AM GMT on August 18, 2007
Thanks will be watching your posts for info
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2574. StormJunkie
7:14 AM GMT on August 18, 2007
That looks more reasonable given the data SOTC!

marina owner, I get your point, and I have been there. Hugo. Charleston portion. Senior in HS. That said, my point was mostly that they are both bad. Especially if it is a 145mph that went to 130mph during an EWRC because the surge is going to come like it was a 145mph. I would not think that surge changes much during an EWRC. Kind of the Katrina effect, it brought a Cat 5 surge with it even though it was weakening.
Member Since: August 17, 2005 Posts: 26 Comments: 16970
2573. StoryOfTheCane
7:17 AM GMT on August 18, 2007
Posted By: FLCrackerGirl at 2:13 AM EST on August 18, 2007.

StormJunkie!! (waves from out in lurker's corner)
SJ You Really Should Be Appaluded for Your Efforts & Dedication to The Blog. Kudos on An Outstanding Job Covering the Info & Link Requests. Your Observations & Commentaries Are Right on Point Also. Keep Up The Good Work.
FRAN

i second that


I third that lol
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2572. LSU
7:17 AM GMT on August 18, 2007
I came off harsh too, long day.
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2571. JamaicanGir
2:15 AM EST on August 18, 2007
Posted By: FLCrackerGirl at 2:13 AM EST on August 18, 2007.

StormJunkie!! (waves from out in lurker's corner)
SJ You Really Should Be Appaluded for Your Efforts & Dedication to The Blog. Kudos on An Outstanding Job Covering the Info & Link Requests. Your Observations & Commentaries Are Right on Point Also. Keep Up The Good Work.
FRAN


i second that
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2570. StoryOfTheCane
7:16 AM GMT on August 18, 2007
sorry for the harshness LSU, only meant to say arrogant, I was out of line.
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2569. louisianaweatherguy
7:13 AM GMT on August 18, 2007
WOW... now the latest model runs are consistent with JUST to the SOUTH of Brownsville, TX, but with GFDL so far to the north still, I would go with Just to the NORTH of Brownsville if I had to guess using these model runs...

I have a feeling tommorrow's model runs will be a little different....
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2568. mikester
7:15 AM GMT on August 18, 2007
IN this pic i wounder if we have another hurricane/typhoon building off the coast of mexico???
pic
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2567. LSU
7:14 AM GMT on August 18, 2007
Okay, that makes much more sense.

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2566. VEROBEACHFL1
7:13 AM GMT on August 18, 2007
----i agree with the first one till80w---or i should say---the top one.............
2565. PRmarinaowner
7:11 AM GMT on August 18, 2007
Its not too bad right now in Fajardo (NE corner of PR) Maybe 22-24 kn or so and no rain (dry) all night. Anyone in St. Croix? Wonder how they're doing?
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2564. FLCrackerGirl
3:09 AM EDT on August 18, 2007
StormJunkie!! (waves from out in lurker's corner)
SJ You Really Should Be Appaluded for Your Efforts & Dedication to The Blog. Kudos on An Outstanding Job Covering the Info & Link Requests. Your Observations & Commentaries Are Right on Point Also. Keep Up The Good Work.
FRAN
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2562. sullivanweather
7:07 AM GMT on August 18, 2007
I think most of the folks in here that believe the storm will turn north are in some how jaded by Ivan, Katrina, Rita and Dennis.

I'm still seeing a Gilbert/Emily type track. I just can't see how this storm will turn north into a 590+/500mb high. That just doesn't make sense.

GFS 96hr. 500mb forecast
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2561. Crisis57
7:13 AM GMT on August 18, 2007
Dean
2560. StoryOfTheCane
7:13 AM GMT on August 18, 2007
Here, I took a little more time on this one..

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2559. StormJunkie
7:11 AM GMT on August 18, 2007
Let's hope so Houstonian, but I would not bet against the GFDL from what I have seen.
Member Since: August 17, 2005 Posts: 26 Comments: 16970
2558. JamaicanGir
2:11 AM EST on August 18, 2007
caymangone

it is really quiet here now
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2557. stormybil
7:08 AM GMT on August 18, 2007
my loops are jumping i cant tell hehe
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2556. VEROBEACHFL1
7:10 AM GMT on August 18, 2007
your not alone storyofthecane----- im with ya-----WNW coming------- IMO--thats all........
2555. Crisis57
7:08 AM GMT on August 18, 2007
You can see here that the nasty side of this storm is on the SE side of the eye
Dean
2554. mikester
7:09 AM GMT on August 18, 2007
Now dean is starting to look really mean.
pic
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2553. Hellsniper223
7:10 AM GMT on August 18, 2007
Thats not StormTop

It's St0rmt0p
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2552. PRmarinaowner
7:04 AM GMT on August 18, 2007
145 mph would be 24% more powerful than a 130 mph hurricane. I guess one's perspective would depend on whether or not one was IN the hurricane or not. LOL
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2551. caymangone
7:06 AM GMT on August 18, 2007
Evening Jamaican Girl - dead calm in Cayman at the mo - how is it in Jamaica?
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2548. StormJunkie
7:07 AM GMT on August 18, 2007
SOTC, I think the issue, and my question would be, how could you leave half of Tx and all of Mex out and yet have the whole Big Bend in the cone? Again, that could be right, but there is not much if any data to support a Big Bend or even panhandle hit right now. That could change though...but unlikely imho.
Member Since: August 17, 2005 Posts: 26 Comments: 16970
2546. StoryOfTheCane
7:06 AM GMT on August 18, 2007
ty stormy, I dont throw things out from left field, i think people forget that these are just predictions and nothing more..
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2545. mikester
7:06 AM GMT on August 18, 2007
Here is nice picture of dean in the bottom right side of the screen.
Link
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2544. JamaicanGir
2:03 AM EST on August 18, 2007
ivan was not a direct hit and it was on the southern side of the island and for me it took 3 weeks for our power to be returned and i live in a tourist resort town that would have been restored as a priority, don't want anything near a cat3
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2543. LSU
7:04 AM GMT on August 18, 2007
OHHHHH I get it, you live in Louisiana so anybody who even brings up the possibility of it heading that way must get attacked..that must be it huh

No, that's actually not it at all. It was more along the lines of your track being several thousand miles off the NHC/Model tracks, and your posting the 18z GDFL as "category 5 hitting LA", when that model shifted to the west long ago. So no, I wouldn't even call your guess "educated".
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2542. stormybil
7:03 AM GMT on August 18, 2007
me too story last year you were great with your predictions or was it this year its late now
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2538. Hu
6:58 AM GMT on August 18, 2007
First of all, global warming is causing the ice caps to melt. What else is new. Most people don't even care. How sad! A lot of people will be killed by Dean. Again, who cares if YOU are not affected. Again, how sad! Human greed will be the downfall of this earth. Again, how sad! What happened to the 60's and 70's when people really cared? Those days are gone. How sad!
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2537. StormJunkie
7:03 AM GMT on August 18, 2007
KRL, you can also find that link here.

Also, it will be interesting to see the MIMIC once it updates.
Member Since: August 17, 2005 Posts: 26 Comments: 16970
2536. StoryOfTheCane
7:03 AM GMT on August 18, 2007
Posted By: LSU at 7:02 AM GMT on August 18, 2007.
????? What kind of remark is that? Its just my educated guess, quit being an arrogant prick...

I'm not being arrogant at all. I'm being sensible. Putting a track through central Florida, even the edge of a track, is simply not sensible. Unfortunately, some people read these comments and take them seriously, which is why you shouldn't post the things you do.


The red lines were just the outer extremities. The gold line is where I put the storm going, the red lines are just room for error.
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2535. mikester
7:03 AM GMT on August 18, 2007
Dean's eye appears to be stable. I don't see any eye reformation you guys are talking about. He finally has a nice eye.
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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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