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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835. Weather456
11:41 PM GMT on August 17, 2007
I think Dean maybe a cat 4....look at the AVN floater loop
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834. WPBHurricane05
7:42 PM EDT on August 17, 2007
I guess since FL is out of the woods, all the Floridians dont care anymore....this blog is no where near as active right now when a Cat 3-4-5 is heading toward Fl.

I live in Florida and I do care. I've been on here since about 4:30pm.
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833. o311
7:38 PM EDT on August 17, 2007
if dean is about to hit your town, put your important documents in a plastic container and then put the container in the dishwasher because it is pretty much watertight. My wife heard that in a hurricane meeting she had today at her hospital.
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831. sngalla
7:41 PM EDT on August 17, 2007
South Florida here.
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830. IKE
6:39 PM CDT on August 17, 2007
18Z GFDL takes Dean SW of Houston by 50-100 miles. All other models have a Yucatan to Mexico landfall.

Looking at an IR satellite on Dean...it's moving due west to slightly south of due west.

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829. katadman
11:33 PM GMT on August 17, 2007

I live in Helotes but have been working in the NOLA area for the past two years. Fortunately, I am able to get baack to the Republic with some frequency. I was talking to my wife and grown daughter last night and this morning about the heavy downpours. All of the highland lakes were already flowing over the spillways, as well as Canyon Lake and Lake Medina. Since you live in the hill country, you know all too well the dangers of flash flooding. Be careful attempting any low-water crossings. Don't take chances. - Scott
Member Since: September 7, 2006 Posts: 0 Comments: 1083
828. Dropsonde
11:40 PM GMT on August 17, 2007
18Z GFDL forecast (text format). (FTP site that the data comes from) It's calling for a CAT 5 landfall in Central TX:

HOUR: .0 LONG: -63.61 LAT: 14.80 MIN PRESS (hPa): 962.39 MAX SURF WIND (KNOTS):110.01
HOUR: 6.0 LONG: -65.27 LAT: 15.05 MIN PRESS (hPa): 949.73 MAX SURF WIND (KNOTS):115.93
HOUR: 12.0 LONG: -66.96 LAT: 15.38 MIN PRESS (hPa): 942.60 MAX SURF WIND (KNOTS):128.70
HOUR: 18.0 LONG: -68.62 LAT: 15.80 MIN PRESS (hPa): 946.88 MAX SURF WIND (KNOTS):112.51
HOUR: 24.0 LONG: -70.23 LAT: 16.28 MIN PRESS (hPa): 942.08 MAX SURF WIND (KNOTS):126.14
HOUR: 30.0 LONG: -71.80 LAT: 16.82 MIN PRESS (hPa): 940.52 MAX SURF WIND (KNOTS):128.94
HOUR: 36.0 LONG: -73.70 LAT: 17.45 MIN PRESS (hPa): 941.38 MAX SURF WIND (KNOTS):124.67
HOUR: 42.0 LONG: -75.54 LAT: 18.05 MIN PRESS (hPa): 938.73 MAX SURF WIND (KNOTS):127.27
HOUR: 48.0 LONG: -77.37 LAT: 18.69 MIN PRESS (hPa): 940.59 MAX SURF WIND (KNOTS):125.77
HOUR: 54.0 LONG: -79.27 LAT: 19.27 MIN PRESS (hPa): 937.30 MAX SURF WIND (KNOTS):123.99
HOUR: 60.0 LONG: -81.09 LAT: 19.79 MIN PRESS (hPa): 926.35 MAX SURF WIND (KNOTS):141.40
HOUR: 66.0 LONG: -82.93 LAT: 20.46 MIN PRESS (hPa): 916.26 MAX SURF WIND (KNOTS):147.26
HOUR: 72.0 LONG: -84.72 LAT: 21.22 MIN PRESS (hPa): 913.01 MAX SURF WIND (KNOTS):151.88
HOUR: 78.0 LONG: -86.34 LAT: 21.93 MIN PRESS (hPa): 908.22 MAX SURF WIND (KNOTS):150.08
HOUR: 84.0 LONG: -87.92 LAT: 22.70 MIN PRESS (hPa): 907.73 MAX SURF WIND (KNOTS):152.92
HOUR: 90.0 LONG: -89.49 LAT: 23.65 MIN PRESS (hPa): 910.11 MAX SURF WIND (KNOTS):152.13
HOUR: 96.0 LONG: -90.95 LAT: 24.71 MIN PRESS (hPa): 910.49 MAX SURF WIND (KNOTS):147.08
HOUR:102.0 LONG: -92.38 LAT: 26.02 MIN PRESS (hPa): 912.77 MAX SURF WIND (KNOTS):141.88
HOUR:108.0 LONG: -93.99 LAT: 27.31 MIN PRESS (hPa): 909.43 MAX SURF WIND (KNOTS):150.27
HOUR:114.0 LONG: -95.55 LAT: 28.59 MIN PRESS (hPa): 913.01 MAX SURF WIND (KNOTS):137.47
HOUR:120.0 LONG: -96.96 LAT: 29.76 MIN PRESS (hPa): 938.88 MAX SURF WIND (KNOTS): 65.29
HOUR:126.0 LONG: -98.00 LAT: 30.85 MIN PRESS (hPa): 957.53 MAX SURF WIND (KNOTS): 45.49
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827. sporteguy03
11:39 PM GMT on August 17, 2007
Posted By: Amystery at 11:39 PM GMT on August 17, 2007.
I guess since FL is out of the woods, all the Floridians dont care anymore....this blog is no where near as active right now when a Cat 3-4-5 is heading toward Fl.

I'm in FLorida and I very much do care I have friends in LA. I also care where it goes it could severely impact gas here, heck when Katrina hit there were lines hoarding the gas here so yes we still very much care in FL, thank you very much!
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826. wederwatcher555
11:40 PM GMT on August 17, 2007
if the gfdl is on crack the gfs is on more crack. it has dean going in a straight line west and the moving south
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825. wetlandsLA
11:40 PM GMT on August 17, 2007
look at the links on the wu tropical page
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824. NASA101
11:38 PM GMT on August 17, 2007
No the models have not shifted south..
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823. swlaaggie
5:37 PM CST on August 17, 2007
Posted By: Amystery at 5:36 PM CST on August 17, 2007.

new GFDL goes back to Houston, rest of models trending S......looks like a Mexico Cane ala Gilbert, Emily etc

Frickin maddening. Good Lord, in 24 hours the GFDL has taken it from Houston to just west of NOLA and back to west of Houston. The average of these swings would be very bad for us in SW La.
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822. cormit
11:40 PM GMT on August 17, 2007
Recon just passing thru showed wind speed of 150 mph (10% factor removed gives us 135 mph) and pressure of 952.5 mb.
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821. ClearH2OFla
7:40 PM EDT on August 17, 2007
I live on the west coast of Florida and I am here. Until the ULL does its thing im not letting my guard down.
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820. JLPR
11:38 PM GMT on Agosto 17, 2007
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819. wederwatcher555
11:40 PM GMT on August 17, 2007
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818. wederwatcher555
11:38 PM GMT on August 17, 2007
no...it is a bullseye on galveston
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817. extreme236
11:35 PM GMT on August 17, 2007
it could hit jamaica with more than 145mph stormkat
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816. Metallica1990
11:39 PM GMT on August 17, 2007
typhoon nancy holds the record for longest period of being a catagory 5 5 and a half days
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815. SWFLdrob
11:38 PM GMT on August 17, 2007
anyone got a link to that new GFDL? can't seem to find the 18z. thx
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813. StuccoMan
6:38 PM CDT on August 17, 2007
can someone post the link to the 18z because the 18z i have puts it in middle Louisiana
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812. Baybuddy
11:38 PM GMT on August 17, 2007
Godspeed Donna.
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811. NASA101
11:37 PM GMT on August 17, 2007
Please be correct in your statements....the new 18Z GFDL in NOT a bullseye on Galveston- Houston, some 100 miles WEST! Look at the graph again PLEASE!!
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810. Baybuddy
11:37 PM GMT on August 17, 2007
How many miles to Texas Mexico border?
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808. DonnaGalveston
11:33 PM GMT on August 17, 2007

Thank you for that advice. My husband is actually in the process right now of going through our files and putting important documents into a small fire/waterproof container we can carry with us. He is also going to make a video of the outside of our home, and inside each room of our home incase we need to file an insurance claim. I am glad you mentioned the safety deposit box at the bank; I didn't even consider that. We have a "Hurricane Checklist" which was handed at the beginning of the hurricane season, and we are trying to follow that.
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807. nola70119
11:36 PM GMT on August 17, 2007
I was Houston, New Orleans, and now Galveston......whats next, Pensacola?
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806. ForecasterColby
11:34 PM GMT on August 17, 2007
Generally, yes, storms don't stay at peak intensity for long. Dean might well be an exception, given the low shear, ULL outflow channel, and insane TCHP in the Caribbean. The only thing limiting Dean's strength until he reaches the Yucatan is internal processes.
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804. wederwatcher555
11:36 PM GMT on August 17, 2007
new gfdl with a bullseye on galveston and then houston. still consistent with dean missing the yucatan
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803. NASA101
11:34 PM GMT on August 17, 2007
18Z GFDL moved about 100 west of Houston! So today GFDl has been fluctuating between west of Houston and East of Houston (New Orleans)!! Hmmm, interesting!!
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802. WPBHurricane05
7:34 PM EDT on August 17, 2007
New Hurricane Hunter graphic from WU

I love this site!
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801. Metallica1990
11:34 PM GMT on August 17, 2007

to answer your question about how long cat 5s can last
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800. Daveg
11:34 PM GMT on August 17, 2007
Crossing 15N 65W right exactly where the NHC said it would. So far the NHC track is a good one, but we've got a long way to go.
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798. littlefish
11:33 PM GMT on August 17, 2007
IMA- after Katrina, the earlier the better in trying to organize for a mass evacuation if you ask me. If youy only get 2 days to plan and you are not extremely organized, it'd be tough to evacuate high population areas (remember the Houston mess with people running out of gas, etc on the freeways?). Better to be saf As the saying goes... but ya it seems early.
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797. JLPR
11:33 PM GMT on Agosto 17, 2007
Luiz Munoz International Airport
Lat: 18.43 N Lon: 66 W Elev: 9 ft
Last Update on Aug 17, 6:56 pm AST

Partly Cloudy and Breezy

(28C) Humidity: 79 %
Wind Speed: E 21 G 25 MPH
Barometer: 29.91"
Dewpoint: 75F (24C)
Heat Index: 89F (32C)
Visibility: 10.00 mi.
More Local Wx: 2 Day History:

Soon i should get some TS gusts
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796. ForecasterColby
11:30 PM GMT on August 17, 2007
Let me emphasize again - Dean's eye is not pinhole. A pinhole is a stable eye that's only ~5-6 miles in diameter (Wilma's got as small as 2). Dean's eye, per the 5PM, is 15nm wide.
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795. tampahurricane
11:31 PM GMT on August 17, 2007
the only way it would turn north is if the ULL erodes at the high which could happen.
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794. bekroweather
11:31 PM GMT on August 17, 2007
18Z GFDL solution moved to a landfall north of Corpus Cristi, close to Matagorda in 4.5 days.
793. iahishome
11:27 PM GMT on August 17, 2007
It's good if Dean peaks too early right?

It's very rare that storms stay cat 5 for days right?

Scary Dean
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792. CosmicEvents
11:24 PM GMT on August 17, 2007
Posted By: DonnaGalveston at 11:24 PM GMT on August 17, 2007.

Our neighborhood home owners association has scheduled an emergency meeting on Sunday afternoon to discuss Dean.
Hi Donna......My sister lived in Galveston for 10 years...nice place.
I would strongly advise that you listen to your local emergency management, and watch the storm track closely yourself, using NHC and this site....to make your evacuation decision. Don't rely on your homeowner's association meeting in 2 days in considering when and where to evacuate. If it was me I'd be packing, waiting and watching. Best of luck to you and yours.
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791. StuccoMan
6:31 PM CDT on August 17, 2007
Posted By: gatagus07 at 6:30 PM CDT on August 17, 2007.
Just as I thought....even the GFDL is joining the crowd.....Mexico/Texas border is your landfall

Thats a pretty reckless comment considering the 18z puts it further east.

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790. sngalla
7:32 PM EDT on August 17, 2007
The GFDL has gone back to the left. Link
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789. presslord
7:31 PM EDT on August 17, 2007
amen Neponset...I live on Johns Island...evaced to Manning....90 mins north...bad move....it was still awful
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788. wederwatcher555
11:33 PM GMT on August 17, 2007
new gfdl looks like its back to galveston
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787. IMA
11:24 PM GMT on August 17, 2007
Well, we're northwest of San Antonio, in the Hill Country, and we had to evacuate our house last night. We did not flood, thank God; however, we lost yards and yards of bank & the bridge we share with about 6 other homes, the only way we have in and out, was destroyed. We are packing up all keepsakes this weekend and will get them to San Antonio, just in case.

That said, there's a difference between being smart/prepared & being an alarmist. I can not freakin' believe that the gov. of LA already declared a state of emergency. As someone else said, it could scare someone to death. Conversely, if Dean comes nowhere close, it could very well lead to complacency with the next one. It's just irresponsible and obviously just a way for her to be able to say, "...but I TOLD you!" if it does hit. Disgusting.
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786. icepilot
5:29 PM CST on August 17, 2007
unfortunatly Hurricanes are considered small, locallized weather patterns/events in world weather.

but not really to me- grin - I live in Fl
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785. Baybuddy
11:27 PM GMT on August 17, 2007
Donna always err on the side of caution. If you are full of nervous energy, you can get all of your important documents and prepare them to travel. I feel tupperware works well. Also, if you have any valuables in a safe deposit at a bank close to the coast, I would pull it.
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