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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885. Metallica1990
11:51 PM GMT on August 17, 2007
Posted By: Xion at 11:51 PM GMT on August 17, 2007.

ADT jumped .2 again! Eek!

This storm is deepening, and rapidly.

The only thing that will inevitably weaken it is an eyewall replacement cycle.


even after that it will strengthen again
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883. Weather456
11:49 PM GMT on August 17, 2007
Posted By: JRRP at 11:48 PM GMT on August 17, 2007.

I HAVE A QUESTION
WHO IS THE NEXT INVEST?
OR WHAT NUMBER WILL BE?


Most likely...Central Atlantic wave

next invest is 92L
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882. Xion
11:49 PM GMT on August 17, 2007
ADT jumped .2 again! Eek!

This storm is deepening, and rapidly.

The only thing that will inevitably weaken it is an eyewall replacement cycle.
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881. weathermanwannabe
7:47 PM EDT on August 17, 2007
Got home from work, finished dinner, and wow..Dean's eyewall is looking pretty sinister...Thank God that the earlier NW movement was just a jog and that it continues on a westward track at present..These few degrees make all the difference for PR and Hispanola.....
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880. wetlandsLA
11:48 PM GMT on August 17, 2007
where are you all geting the 18z runs of the gfdl from?
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879. zingocat
11:45 PM GMT on August 17, 2007
I been gone today, but been lurking some. I read a few post. Thanks for the update StormKat. Donna in Texas, take pictures of everything!! Video is good, but an adjuster does not have the formats for different cameras and pictures are easy to upload to insurance companies. Use zip lock bags to put papers in to store or carry. And last, keep your insurance declarations page with you. The whole policy is even better! Last, do not panic, this thing is a long ways off. Do as the people on this blog advises. Watch your local TV stations and stay close for updates.
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878. DonnaGalveston
11:48 PM GMT on August 17, 2007
Thank you IKE, that is somewhat reassuring.
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876. presslord
7:48 PM EDT on August 17, 2007
it is unimaginably horrible
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875. Metallica1990
11:47 PM GMT on August 17, 2007
they must be holding off the 8 PM advisory till they get the info from the hurricane hunters
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874. Daveg
11:46 PM GMT on August 17, 2007
Of course, it's also a good possibility it could head mainly N to WNW and go right into the Northern Mexico coastline.

I'll stick with my original thought still, and go with anyone from Northern Mexico to Houston should be keeping a REAL close eye on this bad boy.

And then everyone else should at least keep paying attention.

For now I think we might need to start praying for the good folks in Jamaica.
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872. JLPR
11:46 PM GMT on Agosto 17, 2007
123knots = 141mph
damn scary
strong winds there
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871. nrtiwlnvragn
11:43 PM GMT on August 17, 2007
Gulfstream jet mission tomorrow 8:00 PM - Looks like the models really need it!

Also, bouy drop mission Sunday 8:00 AM center near 20N 84W
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870. JRRP
11:41 PM GMT on Agosto 17, 2007
I HAVE A QUESTION
WHO IS THE NEXT INVEST?
OR WHAT NUMBER WILL BE?
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869. IKE
6:45 PM CDT on August 17, 2007
Posted By: DonnaGalveston at 6:45 PM CDT on August 17, 2007.
This is really scaring me.


Donna...all of the reliable models, excluding the GFDL aim Dean into Mexico...well south of you. The model consensus says you should be okay. The GFDL is a reliable model, but even it is trending further south + Dean is moving due west to slightly south of due west.
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867. wederwatcher555
11:46 PM GMT on August 17, 2007
ill take your word for it kat
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866. whirlwind
11:44 PM GMT on August 17, 2007
Thanks StormKat.... thats what I said also 3 days ago. Except I said FL first as cat 3 then Texas cat 5.


I expect Dean to be somewhere near 170-180mph when it hits the Gulf Coast, as some private weather agencies predict.

Buy stocks in contruction people....roofing too...BUT I got plenty of work here..dont call me.. thanks..
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865. MaxTempest
11:47 PM GMT on August 17, 2007
high res of the development of Dean from the past four days

select "all frames" from the drop-down.
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864. Fl30258713
11:47 PM GMT on August 17, 2007
The UKMET 18Z moved to the track for GFDL 12Z
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863. Metallica1990
11:45 PM GMT on August 17, 2007
Posted By: DonnaGalveston at 11:45 PM GMT on August 17, 2007.

This is really scaring me.


Dont be scared just be prepared :)
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861. Weather456
11:44 PM GMT on August 17, 2007
Fri Aug 17 2007
2250 GMT
Latitude 16.0 N
Longitude 66.9 W
No turbulence
Currently flying in and out of clouds
Flight altitude 10007 feet (3050 meters)
Flight level winds 50 degrees at 45 knots (51 mph)
Temperature 8 C Dewpoint 5 C
Surface winds 50 at 35 knots (40 mph)
Remarks: AF302 0504A DEAN OB 01
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860. wederwatcher555
11:45 PM GMT on August 17, 2007
the gfs wasnt an outlier before but now it is extremely far south. it has company with the nogaps. they are taking dean in a straight line west. no turn whatsoever
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859. Dropsonde
11:45 PM GMT on August 17, 2007
WOW at the recon data. The GFDL was initialized at 2 p.m. and its 6 hour intensity forecast looks to have nailed Dean!
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857. katadman
11:41 PM GMT on August 17, 2007
Posted By: wederwatcher555 at 11:40 PM GMT on August 17, 2007.

no...it is a bullseye on galveston
Posted By: wederwatcher555 at 11:40 PM GMT on August 17, 2007.

Link


Study your map weder. That is SW of Galveston/Houston. Take it from a native.
Member Since: September 7, 2006 Posts: 0 Comments: 1081
856. presslord
7:43 PM EDT on August 17, 2007
one of our local (Charleston) TV weather wags said tonight..."...with any luck, Dean will 'just' hit Mexico...and not cause any problem for 'people'....
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855. Tazmanian
4:43 PM PDT on August 17, 2007
this says the found 123kt winds

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854. IKE
6:45 PM CDT on August 17, 2007
Posted By: Amystery at 6:44 PM CDT on August 17, 2007.
Basically, dont let your guard down, but looks more and more like a Jamica, Yucatan, and then Mexico problem.


No other model(reliable) indicate Texas landfall


True.
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853. OUFan919
11:42 PM GMT on August 17, 2007
Do I see an ULL north of Dean in the Central Atlantic moving west and catching up to Dean??
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852. DonnaGalveston
11:43 PM GMT on August 17, 2007
This is really scaring me.
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851. bekroweather
11:41 PM GMT on August 17, 2007
Almost all models moved south in the 18Z.
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850. quakeman55
11:41 PM GMT on August 17, 2007
Check out this long range radar out of San Juan. Shows a clear picture of Dean's closed eye and its movement.
Member Since: March 31, 2002 Posts: 1 Comments: 1276
849. AnthonyJKenn
11:24 PM GMT on August 17, 2007
Good old Kitty Blanks....how quick on the trigger to react. LOL

Probably a bit premature for a SoE right now, since any impact on Louisiana even if the nightmare scenario of the GDFL does take shape would not be until around Monday of Tuesday at the most...but I guess that after Katrina, you just can't be more careful, I guess.

I'm having the same problem loading Java as some of you are...any update on the latest model runs would be greatly appreciated.

And...why would the GFS be considered any more of an outlier than the GDFL?? Looking at the models I've seen, most of them are still bunched in Yucatan and SoTex (Brownsville/South Padre Island) or NMex, with one reacing out for
Corpus Christi/Port O'Connor). I see only two models that go as far up as Louisiana: the GDFL and one going straight to Galveston Bay.

Maybe the GFS may not be the best on prediction as some others here may say, but most of the consensus just hasn't budged from the original NHC forcasted path (albeit with a slight nudge north). In fact, the NHC path is actually slightly NORTH of the model consensus, probably only in deference to the lone soldier of the GDFL.

Things may change in a couple of days, and everyone along the Gulf Coast shoul prepare as if it may head their way (and I'd say that everyone from NOLA west to Mexico should pay special attention....but until I see the northerly shift real soon for my own eyes, I'm gonna trust the experts of the NHC and Dr. Masters for who they are, and stick with my hunch that this will be a mostly SouthCenTex/SoTex/Mexico event. A bad, bad event wherever this storm hits, but not one for upper Texas or Louisiana to suffer...nearly as much.

If I'm wrong, and this monster does come my way, then I will gladly eat my crow...in Destin, Florida with my niece.


Anthony

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848. Skyepony (Mod)
11:43 PM GMT on August 17, 2007
Recon is flying again:)

23:29:00
14.98N 65.17W
2,844 m
-flight winds From 48 (NE) at 126 kts (144.9 mph)
gust 130 kts (~ 149.5 mph)
surface winds 93 kts
rainrate 63 mm/hr
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847. Melagoo
11:44 PM GMT on August 17, 2007
I think the predictions are fairly widespread do to the fact that DEAN is still quite far away
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846. Metallica1990
11:43 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.

Im a south floridian and I careive been on since i woke up this afternoon lol :)
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845. WPBHurricane05
7:44 PM EDT on August 17, 2007
Recon found 123 knots according to this!! Link
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844. cirrocumulus
11:37 PM GMT on August 17, 2007
icepilot: Not in Weather for Dummies! An MIT scientist/meteorologist explains how indeed hurricanes are air conditioners! Check it out and you will learn something interesting!
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842. hurricane91
7:42 PM EDT on August 17, 2007
i live in swfl and im on here to
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841. MisipiGrl
11:42 PM GMT on August 17, 2007
"dishwasher because it is pretty much watertight. "

After Katrina, my dishwasher had over a foot of rancid salt water in it. I'm lucky, though. I actually HAD a dishwasher left. Those to my South never found theirs.
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840. ForecasterColby
11:42 PM GMT on August 17, 2007
152.92kt on that GFDL. Good god. That's...*grabs calculator*...176mph.
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839. JLPR
11:42 PM GMT on Agosto 17, 2007
wow this thing is big damn TS winds all the way up here
__________________________________________

Tonight...Cloudy. Numerous showers and scattered thunderstorms until early morning...then showers and scattered thunderstorms late in the night. Windy. Some thunderstorms may produce gusty winds and heavy rainfall. Lows 78 lower elevations ranging to 66 higher elevations. East winds 20 to 30 mph with gusts to around 50 mph. Chance of rain 90 percent.
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838. WPBHurricane05
7:42 PM EDT on August 17, 2007
I think Dean maybe a cat 4....look at the AVN floater loop

Yeah, looks like Dean will become a dangerous hurricane.
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837. cormit
11:42 PM GMT on August 17, 2007
Pressure of 942.9 mb just recorded at 7:31:30 PM Eastern Time. Winds of 150 mph at flight level (135 mph at surface level). This hsould be reflected on the 8pm advisory.
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836. Daveg
11:41 PM GMT on August 17, 2007
While it can't be ruled out...I seriously doubt LA will take a hit this time around, but I am sweating it out for Corpus or Houston. Looks like a more likely target in that range.
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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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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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