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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935. OUFan919
12:00 AM GMT on August 18, 2007
AT LEAST 130mph winds
946mb pressure

Category 4
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934. Crisis57
12:01 AM GMT on August 18, 2007
Posted By: ClearH2OFla at 12:00 AM GMT on August 18, 2007.

Little fish you are right i have been watching it all day not moving to much at all. Dean appears to move moving faster


it moved this mornign then after stopped and hasn't really moved after
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933. calder
12:00 AM GMT on August 18, 2007
dean cat 4
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932. cirrocumulus
12:01 AM GMT on August 18, 2007


One statistic I found fascinating was that of the previous ten wettest Julys on record in Texas, six had major hurricanes hit the Texas Gulf Coast the same year. Texas had one of the wettest Julys ever this year.
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931. hahaguy
11:56 PM GMT on August 17, 2007
dean 130
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930. seflagamma
7:48 PM AST on August 17, 2007
info just in now a Cat 4, got it from TWC.
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929. Tropicnerd13
11:57 PM GMT on August 17, 2007
we have a cat 4 dean
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928. Wundermobay
11:57 PM GMT on August 17, 2007
Dean Cat.4
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927. Crazman
12:01 AM GMT on August 18, 2007
edit reposted from other blogger
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926. drusierDMD
11:56 PM GMT on August 17, 2007
tropic i like it good job
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924. Skyepony (Mod)
11:58 PM GMT on August 17, 2007
That vortex message is 6 hrs old
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922. AnthonyJKenn
11:52 PM GMT on August 17, 2007
Oh..and this just in: The models have all shifted south again: even the doomsday GDFL now has landfall near Galveston-Houston rather than Morgan City/Vermilion Bay.

And as for Stormkat, who always seems to want any storm in the Gulf to hit Louisiana, even when they don't (Rita, Emily, Wilma): You may have lucked out on Katrina's ultimate path, but I'd no more trust you than I would a finger in the wind. Trofs usually don't make it that far south these days to turn a system that rapidly, and the path of least resistance is still more to South Texas and Mexico, not Louisiana. We'll see what happens, but I'll roll with the experts on this one, thank you very much.


Anthony
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921. Metallica1990
12:00 AM GMT on August 18, 2007
Posted By: zingocat at 12:00 AM GMT on August 18, 2007.

Where's the update?


there waiting on the HH
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920. ClearH2OFla
7:56 PM EDT on August 17, 2007
Little fish you are right i have been watching it all day not moving to much at all. Dean appears to move moving faster
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919. KEEPEROFTHEGATE (Mod)
11:24 PM GMT on August 17, 2007
track mark 15,66 C4/H/D
15.2,67
16.1,72 C4/H/D
16.6,75
17.2,77 C5/H/D
17.3,79
18,81 C4/H/D
19,82
21,85
STOP......
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918. Dan187
12:00 AM GMT on August 18, 2007
000
URNT12 KNHC 172356
VORTEX DATA MESSAGE AL042007
A. 17/23:32:00Z
B. 14 deg 52 min N
065 deg 02 min W
C. NA mb 2632 m
D. 119 kt
E. 302 deg 006 nm
F. 048 deg 130 kt
G. 309 deg 010 nm
H. 946 mb
I. 8 C/ 3045 m
J. 18 C/ 3045 m
K. 13 C/ NA
L. CLOSED
M. 16
N. 12345/7
O. 0.02 / 2 nm
P. AF302 0504A DEAN OB 03
MAX FL WIND 130 KT NW QUAD 23:29:00
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916. zingocat
11:59 PM GMT on August 17, 2007
Where's the update?
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915. Fl30258713
11:55 PM GMT on August 17, 2007
Posted By: OUFan919 at 11:53 PM GMT on August 17, 2007.

I have a question:
It looks like there is an upper level low about 1000 miles little NNE of Dean and it is moving at a pretty good clip, possibly faster than Dean. Anybody think that if the ULL entering Florida right now weakens and this low replaces it when Dean is over the Western Caribbean that this will draw Dean farther North??

Look at it here.
http://www.goes.noaa.gov/HURRLOOPS/huirloop.html



Yep, that idea hasbeen discussed several times in the last couple of days.
Still waiting and watching to see how they will interact with each other.
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913. Tazmanian
4:56 PM PDT on August 17, 2007
this is old 05

VORTEX DATA MESSAGE AL042007
A. 17/17:17:00Z
B. 14 deg 46 min N
063 deg 16 min W
C. NA mb 2763 m
D. 110 kt (surface wind)
E. 011 deg 010 nm
F. 107 deg 124 kt
G. 011 deg 011 nm
H. 966 mb
I. 7 C/ 3046 m
J. 19 C/ 3040 m
K. 9 C/ NA
L. CLOSED WALL
M. C17 (eye is 17 miles large)
N. 12345/7
O. 0.02 / 2 nm
P. AF304 0404A DEAN OB 28
MAX FL WIND 124 KT N QUAD 17:13:30 Z

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912. weatherguru
11:58 PM GMT on August 17, 2007
anything could happen i'm going to keep watching til it makes landfall
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911. tallahasseecyclone
11:56 PM GMT on August 17, 2007
Does anyone know what percentage of hurricanes turn north vs south after passing over or near the yucatan?
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910. Crisis57
11:57 PM GMT on August 17, 2007
Posted By: littlefish at 11:56 PM GMT on August 17, 2007.

The GFDL is fine and dandy, but I still don't see that ULL moving much. Am I wrong?


i see it to
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909. Dropsonde
11:53 PM GMT on August 17, 2007
Thanks SJ. Fan of your site BTW, very helpful to me to find all my tropical info after my hard drive crashed a few months ago and I hadn't backed up my bookmarks.

It just struck me how dead on the model was, based on what the HH seem to be finding.
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907. Tropicnerd13
11:56 PM GMT on August 17, 2007
omg lmao on visible sattelite erin looks like a cat 3!
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906. StormJunkie
11:52 PM GMT on August 17, 2007
Also great MIMIC of Dean starting to clear out the eye and intensify.

Posted By: Fl30258713 at 11:47 PM GMT on August 17, 2007.
The UKMET 18Z moved to the track for GFDL 12Z


Not sure where you get that... The 18z Ukmet only goes out 48hrs on the FSU site. Have to wait for WU to update the Ukmet to see what it says...
Member Since: August 17, 2005 Posts: 26 Comments: 16420
905. littlefish
11:55 PM GMT on August 17, 2007
The GFDL is fine and dandy, but I still don't see that ULL moving much. Am I wrong?
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904. Tropicnerd13
11:16 PM GMT on August 17, 2007
hi guys. i just finished making a cone of uncertainty. no, it is not a wishcaster cone, but i feel as though if that ULL goes slow enough, dean will go more north than most of the models are predicting right now. and i am not a wish caster. i just feel that this may be a possible storm track. the black bands represent a day. the thick colorful bands represent the possible storm location and strength. you ought to be able to figure out what the strength means. and please dont jump me for making it. i just feel as though dean will rapidly intensify soon.
d
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903. KYhomeboy
11:52 PM GMT on August 17, 2007
JF... i know what you mean. I am doing the same thing....PRAYING for a nice big northward or westward jog...so that it wont make landfall here like its scheduled too!
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902. Crazman
11:45 PM GMT on August 17, 2007
LMAO Stormkats Hurricane warning office. More like his moms living room...
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901. WPBHurricane05
7:54 PM EDT on August 17, 2007
VORTEX DATA MESSAGE AL042007
A. 17/17:17:00Z
B. 14 deg 46 min N
063 deg 16 min W
C. NA mb 2763 m
D. 110 kt (surface wind)
E. 011 deg 010 nm
F. 107 deg 124 kt
G. 011 deg 011 nm
H. 966 mb
I. 7 C/ 3046 m
J. 19 C/ 3040 m
K. 9 C/ NA
L. CLOSED WALL
M. C17 (eye is 17 miles large)
N. 12345/7
O. 0.02 / 2 nm
P. AF304 0404A DEAN OB 28
MAX FL WIND 124 KT N QUAD 17:13:30 Z
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900. cirrocumulus
11:54 PM GMT on August 17, 2007
Melagoo: And what about Jamaica? They don't look to lucky either!
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899. weatherguru
11:54 PM GMT on August 17, 2007
florida is not out of the woods by any means
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898. cormit
11:52 PM GMT on August 17, 2007
I would imagine the 8pm advisory will reflect sustained winds of 135 mph and pressure of 943 mb.
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897. GaleWeathers
7:53 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.

Somebody else made the same comment about Floridians yesterday. I'm from So Fla and have been following the blog closely for the past few days. I have friends on the gulf in LA, so I do care. I just don't post much, because I'm still learning and wouldn't want to put incorrect info out there.
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896. weatherguru
11:51 PM GMT on August 17, 2007
take a look at the 18z animated model for the gdfl on the tropical page...very scary
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895. OUFan919
11:51 PM GMT on August 17, 2007
I have a question:
It looks like there is an upper level low about 1000 miles little NNE of Dean and it is moving at a pretty good clip, possibly faster than Dean. Anybody think that if the ULL entering Florida right now weakens and this low replaces it when Dean is over the Western Caribbean that this will draw Dean farther North??

Look at it here.
http://www.goes.noaa.gov/HURRLOOPS/huirloop.html
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894. Dropsonde
11:50 PM GMT on August 17, 2007
wetlandsLA: The track is available as a graphic on the weatherunderground tropical page under Dean. The intensity forecast is in text format, not yet on the FSU site, but available here.
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892. Melagoo
11:48 PM GMT 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'....

... has a little more than a tad of arrogance/ignorance :c(
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891. ClearH2OFla
7:48 PM EDT on August 17, 2007
Amystery why do you say that
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890. whirlwind
11:50 PM GMT on August 17, 2007
Charleston TV said... hits Mexico oh well...
guess what.. we are going to pay for those illegals anyway..
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889. ForecasterColby
11:51 PM GMT on August 17, 2007
I'm wondering about Haiti. Look at the size of Dean's bands - he'll be dropping a tremendous, tremendous amount of rain on them as he passes.
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888. cirrocumulus
11:48 PM GMT on August 17, 2007
swFlboy: Any thoughts as to why Erin held together so well? The computer models on the local weather in Amarillo last night at 10 failed to initialize any rain until around 7pm and yet the rain was here at 11am. Makes you wonder what to expect from Hurricanes this year if the models can't even find the rain from Erin!
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887. StormJunkie
11:47 PM GMT on August 17, 2007
Dropsonde, GFDL has been pretty good with intensity, and as far as the swings from NO to mid Tx, that far out I would expect that. The fact that it continues to show the Nward movement in the 3-4 day range is what concerns me. It has been insistent on it. And as many have noted, there was another time the GFDL was the out-lier and held true.

Looking for models, imagery, and much more?
Quick Links
Select the first link in the model section. This is the FSU Experimental model page. For all models except for the GFDL and HWRF, I set the field to 850mb vorticity to view potential genesis or track and size of tropical systems. Select animate then scroll right and page through the model run. The surface maps are also good to look at as the 850mb map will sometimes show features which are not at the surface. The GFS and Ukmet run four times a day; 00z, 06z, 12z, and 18z. The 00z runs usually come out around 2am Est, the 06z around 8am Est, the 12z around 2pm Est, and the 18z around 8pm Est. The CMC, Nogaps and mm5fsu only run at 00z and 12z. The FSU model site can depict the strength of a system which is something you donít get with the line models. There is a great link that shows the mb to ft comparison in the learning section. Also the GFDL and HWRF only work with the field set to Surface Pressure and they only run for active storms. The NWS NCEP model page contains the long range GFS and the NAM as well as several other models. The South Florida Water Management page has a nice spaghetti plot showing most all of the models together. The Weather Underground Tropical section also has some nice spaghetti plots of several of the major models. The GFDL track can usually be found here before it can be seen on the other sites.

Select the first link in the imagery section. This is the Global Hydrology and Climate Data Center. There are several rows of maps. The first column is visible imagery. The second infrared and the third is water vapor. The first row is the W Atl view and the frames update most often and also has the highest max zoom. The next active row down does not have the same zoom level and the images update every 30 minutes. The Carib row uses a different color scale on the IR imagery and shows more whites and reds with weaker convection. Select the map you wish t o view. Below the image that comes up are options that will allow to change size, number of frames, zoom level, quality, etc. Set these parameters the way you choose and then click the area on the map you wish to view. Make sure you select the animate feature if you wish to see a loop. Allow loop to load and enjoy. This site releases images prior to any other site as far as I know.
Member Since: August 17, 2005 Posts: 26 Comments: 16420
886. Neponset
11:50 PM GMT on August 17, 2007
Tidal surge is a major threat during a storm and occures to the right of the eye. It is important to get out of the area of this surge. I am sure there have been studies of the areas effected by these surges, but have not seen any. Does anyone have some info on where this info can be obtained - I am thinking some sort of flood area maps for the worst case scenario for coastal cities.
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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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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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