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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1335. DG136
1:35 AM GMT on August 18, 2007
Posted By: Stormchaser2007 at 1:35 AM GMT on August 18, 2007.

How?? they only update 50 past the hour....


They are constantly talking about the storm, not just at the tropical update...
1334. surfmom
1:31 AM GMT on August 18, 2007
looks like i'll get waves to surf by/around monday - just not to comfortable watching the boy get strong.
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1333. ChuckieTodd
8:35 PM CDT on August 17, 2007
Posted By: StuccoMan at 8:27 PM CDT on August 17, 2007.
Katrina is the biggest media hyped storm in history.It was not as poerful or big as ivan.If you look at side by side wind swath and sattelite of ivan and katrina.ivan was bigger.Katrina just happen to put NO under water from the soup bowl theory and hit 2 majorly populated areas.Katrina was not that powerful.It made landfall as a cat 3.Andrew was the most impressive storm next to ivan.katrina Not a chance.


WOW. Perhaps I'm confused but didn't Katrina do almos 6 times the damage of Ivan?
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1332. JLPR
1:33 AM GMT on Agosto 18, 2007
Could be starting to have a N component look at the radar yo can see it in the last frames.
but its kinda faint it could be the rain causing an effect.
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1331. Stormchaser2007
9:34 PM EDT on August 17, 2007
How?? they only update 50 past the hour....
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1330. MikeOhio
1:33 AM GMT on August 18, 2007
Posted By: cirrocumulus at 1:31 AM GMT on August 18, 2007.

This blog by Dr. Masters is very informative on the arctic ice and ties in well with the current strenthening hurricane! There are plenty of scientists of different fields looking at the hurricane right now and thinking about the arctic ice.


And no where within this blog does he really mention global warming.

The Arctic Ice could be a cycle or it could not.

Now isn't the time to debate. This isn't a debate club....

Now is the time to watch Dean become a monster.
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1329. atmoaggie
1:34 AM GMT on August 18, 2007
Take look at digital dvorak trend.

dvorak
Member Since: August 16, 2007 Posts: 6 Comments: 12461
1328. KnowYourRole
9:33 PM EDT on August 17, 2007
Posted By: PR51 at 9:30 PM EDT on August 17, 2007.
Where are those who have been writing in this blog that Dean would change its path and would affect directly Puerto Rico? Dean has almost completed his pass through our south and neither a shower nor a gust has been felt in Lajas (South of PR). Thanks GOD, this chapter is closed. Dean passed and there will be no effect in our Enchanted Island. May GOD has mercy with those in Dean projected path..


probably hiding behind the ones who said it would hit Florida.=)
1327. DG136
1:32 AM GMT on August 18, 2007
Stuccoman, are you in the FL panhandle?
1326. bekroweather
1:31 AM GMT on August 18, 2007
My observations/opinions:

* It moves due West (270) the last couple of hours
* Slightly slower
* The convection seems to be consolidating
* The wind field is relatively large
* Getting stronger
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1325. TXWeatherNewb
1:32 AM GMT on August 18, 2007
The simple climb in latitude is indication on some NW motion. It is very slight however, you cannot increase latitude and not be traveling due west.
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1322. Dan187
1:31 AM GMT on August 18, 2007
err sorry, correction
011200 1500N 06520W 6960 02816 9653 +103 +103 133133 136 110 010 00


133 kts in last 10 second period, but max winds of 136 kts
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1321. KEEPEROFTHEGATE (Mod)
1:28 AM GMT on August 18, 2007
it'll be cat 5 by midnight
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1320. WPBHurricane05
9:32 PM EDT on August 17, 2007
I have to go now, but will hopefully be back for the 11pm update.
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1318. KnowYourRole
9:31 PM EDT on August 17, 2007
Posted By: JFLORIDA at 9:26 PM EDT on August 17, 2007.
Ok I think itís about to jog to the NW again.


I have to know what loops the people that think it's moving NW are looking at.
1317. cirrocumulus
1:25 AM GMT on August 18, 2007
This blog by Dr. Masters is very informative on the arctic ice and ties in well with the current strenthening hurricane! There are plenty of scientists of different fields looking at the hurricane right now and thinking about the arctic ice.
Member Since: September 30, 2005 Posts: 0 Comments: 1606
1316. eaglesrock
9:30 PM EDT on August 17, 2007
Dean will be a cat. 5 by morning. It is rapidly intensifying and there is no end in sight.
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1315. PR51
1:20 AM GMT on August 18, 2007
Where are those who have been writing in this blog that Dean would change its path and would affect directly Puerto Rico? Dean has almost completed his pass through our south and neither a shower nor a gust has been felt in Lajas (South of PR). Thanks GOD, this chapter is closed. Dean passed and there will be no effect in our Enchanted Island. May GOD has mercy with those in Dean projected path...
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1314. Relix
1:28 AM GMT on August 18, 2007
JFLORIDA.... NW? its going straight W
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1313. tallahasseecyclone
1:26 AM GMT on August 18, 2007
I don't see why discussions about global warming are really significant at this point. This is the kind of discussion you have when you have nothing to talk about but an Invest that might just become a depression if the stars align just right. Y'all shoulda been getting this out of the way a few days ago :)
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1311. Dan187
1:29 AM GMT on August 18, 2007
saw this message
011200 1500N 06520W 6960 02816 9653 +103 +103 133133 136 110 010 00


thats 133 kts at flight level
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1310. Metallica1990
1:28 AM GMT on August 18, 2007
Posted By: swFLboy at 1:26 AM GMT on August 18, 2007.

Peak wind of 158 just reported fron dropsonde by HH's in Dean


were did you see that?
1308. dean2007
1:22 AM GMT on August 18, 2007
SWflboy I agree with your possible suggestion of Dean becoming a category five hurricane at 11am tomorrow, it actually seems likely more then unlikely. Pretty scary. Maybe this storm would have the size of Katrina and the pressure of WIlma. Scary, I hope thats not right, but a possible scenario.
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1307. MikeOhio
1:27 AM GMT on August 18, 2007
Posted By: cirrocumulus at 1:25 AM GMT on August 18, 2007.

Soon enough even ol' Dr. Gray will be convinced of global warming. He just needs to put his thinking cap on and start studying the multitude of factors besides his chosen few!


I realize you have nothing better to talk about, but quite a few others on this blog/message forum do.
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1305. DeepConvection
1:22 AM GMT on August 18, 2007
Wow, Dean's becoming a monster.
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1303. CajunSubbie
1:27 AM GMT on August 18, 2007
MORE RITA MEMORIES
looks like the GFDL called it on rita as well, with constant right of the consensus.


THE INITIAL MOTION ESTIMATE IS 280/08. RITA HAS ACTUALLY MADE A
LARGE WOBBLE AND SLOWED TO A 285/06 KT MOTION THE PAST 6 HOURS.
HOWEVER...SUCH MOTION CHANGES...WHICH ARE NOT UNUSUAL FOR
EXPLOSIVELY DEEPENING TROPICAL CYCLONES AS THE INNER CORE WIND
FIELD AND CONVECTIVE PATTERN REORGANIZES...ARE CONSIDERED TEMPORARY
AND RITA IS EXPECTED TO SHORTLY RESUME A MORE WESTWARD MOTION. THE
18Z NHC MODEL GUIDANCE IS A LITTLE MORE CONVERGENT THAN PREVIOUS
MODEL RUNS... WITH THE GFS AND GFDL MODELS DOING THEIR USUAL
AFTERNOON EASTWARD SHIFT. THOSE MODELS NOW BRING RITA ACROSS THE
HOUSTON-GALVESTON AREA IN ABOUT 72 HOURS. HOWEVER...THE OTHER
MODELS SEEM TO HAVE STABILIZED THEIR FORECAST TRACKS FARTHER WEST
WITH THE CONSENSUS HAVING SHIFTED A LITTLE MORE TO THE RIGHT. THE
OFFICIAL FORECAST TRACK WAS ALSO SHIFTED TO THE RIGHT...BUT NOT AS
FAR AS THE GFS/GFDL MODELS...SINCE IT NOW APPEARS THAT THE GLOBAL
MODELS HAVE A REASONABLE HANDLE ON WEAKENING THE MID-LEVEL RIDGE

ACROSS TEXAS AND THE GULF COAST BASED 22/00Z UPPER-AIR DATA
INDICATING 40 METER HEIGHT FALLS ACROSS THIS REGION DURING THE PAST
24 HOURS.
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1302. 7544
1:26 AM GMT on August 18, 2007
dont forget wilma stall for along time when she got this strong and dean might too possibly .
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1301. 53rdWeatherRECON
1:28 AM GMT on August 18, 2007
Dean will most likely have the 155 mph winds needed for CAT 5 by 11pm. There is only warmer water and low shear ahead. The eywall replacement cycles will be the only thing to chop him down.
http://www.ssd.noaa.gov/goes/flt/t1/ft-l.jpg
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1300. Stormchaser2007
9:27 PM EDT on August 17, 2007
Posted By: cormit at 9:23 PM EDT on August 17, 2007.
Recon just passing throgh shows max flight level wind of 136 kt and lowest pressure of 935.8 mb.


Where was this?
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1299. VEROBEACHFL1
1:22 AM GMT on August 18, 2007
HELLO ALL, taking a quick break from the ballgame and popping in here------- im still in agreement for the w and sometimes wnw movements for now BUT anytime it will gradually continue NORTHWARD------not a sharp drastic N movement but a definite change in direction and models sometime before 80W...... i been saying this for oh hmm, 3 days now and we will just have to see....some agree, some disagree, ULL is in favor-- somewhat, also the intensity facotor.my "2 cents again".........bye I'll back after the game.............
1298. nolesjeff
1:26 AM GMT on August 18, 2007
Posted By: swFLboy at 1:26 AM GMT on August 18, 2007.

Peak wind of 158 just reported fron dropsonde by HH's in Dean

Where did you get that? link?

also swfl guy
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1297. StuccoMan
8:24 PM CDT on August 17, 2007
Posted By: PensacolaBuoy at 8:21 PM CDT on August 17, 2007.
StuccoMan, I think your Dennis comparison is an excellent one. Compact storm... big damage over relatively small area. I don't fully understand the dynamics of what makes a storm blossom into the Gargantuan storm size that Katrina and Rita were. Heat content of the gulf? I guess we'll see. If it stays small, we're in much better shape. Size really matters when it comes to major hurricanes!


Katrina is the biggest media hyped storm in history.It was not as poerful or big as ivan.If you look at side by side wind swath and sattelite of ivan and katrina.ivan was bigger.Katrina just happen to put NO under water from the soup bowl theory and hit 2 majorly populated areas.Katrina was not that powerful.It made landfall as a cat 3.Andrew was the most impressive storm next to ivan.katrina Not a chance.
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1296. Wishcasterboy
1:18 AM GMT on August 18, 2007
I just checked the stats, and it doesn't look promising. The only slightly good news about Dean is that it has slowed down, and has developed a small eyewall. And even that has downsides. Unfortunately, I can see Dean becoming a category 5 hurricane by tomorrow.
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1295. Relix
1:24 AM GMT on August 18, 2007
Meh... I am going to bed. I wanted some rains and winds here in PR, but so far its been lacking. Boo Dean =P.

Oh and btw... my PC is on 24/7, that is contributing to global warming right? Aaah... whatever =P

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1294. KnowYourRole
9:25 PM EDT on August 17, 2007
Posted By: cormit at 9:23 PM EDT on August 17, 2007.
Recon just passing throgh shows max flight level wind of 136 kt and lowest pressure of 935.8 mb.



where did you get the info. I can't get my page to load.
1293. TXWeatherNewb
1:24 AM GMT on August 18, 2007
Is that mess behind Dean too far south to be of concern??
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1291. nolesjeff
1:25 AM GMT on August 18, 2007
Posted By: cirrocumulus at 1:25 AM GMT on August 18, 2007.

Soon enough even ol' Dr. Gray will be convinced of global warming. He just needs to put his thinking cap on and start studying the multitude of factors besides his chosen few!


LET IT GO!
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1290. WPBHurricane05
9:25 PM EDT on August 17, 2007
Hey storm! What do you think about Dean's intensity? Getting strong.....
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1288. Metallica1990
1:24 AM GMT on August 18, 2007
T# is droping like a rock
1287. cirrocumulus
1:20 AM GMT on August 18, 2007
Soon enough even ol' Dr. Gray will be convinced of global warming. He just needs to put his thinking cap on and start studying the multitude of factors besides his chosen few!
Member Since: September 30, 2005 Posts: 0 Comments: 1606
1285. bappit
1:22 AM GMT on August 18, 2007
I like the global warming posts because they cool off some of the hype about Dean.
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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.