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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1385. WatchingInHouston
1:23 AM GMT on August 18, 2007
StormJunkie - ForecasterColby... or anybody intimately familiar with the models - Do you have any specifics as to how TCHP contributes to intensification?

I created this loop: TCHP LOOP

It shows a considerable depreciation in TCHP values over the past two weeks through the Western Caribbean/Yucatan Strait. With all other variables being equal - any guesstimates (I won't hold you to a hard figure!!) on the difference in potential intensification between the peak on the 13th and what we're seeing now?

Thanks in advance.
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1384. Metallica1990
1:42 AM GMT on August 18, 2007
wow 145 mph 936mb

this storm is exploding

drop of 10 mb in an hour and a half

a 10 mph increase in an hour and a half
1383. edhanna
1:43 AM GMT on August 18, 2007
145mph winds!
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1381. bappit
1:40 AM GMT on August 18, 2007
Carlos Guerra
columnist
San Antonio Express-News
cguerra@express-news.net

Your post is nonsensical. Most of the deaths from Katrina occurred hours after the storm had passed due to failed flood walls. Nothing like the Lake Borgne/Lake Ponchartrain basin exists near Brownsville for accumulating the storm surge. Neither is there the concentration of population living below sea level. Katrina-like? No way man.

As bad as Dean looks, panic and overreaction can also be dangerous.
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1379. louisianaweatherguy
1:41 AM GMT on August 18, 2007
Bob Breck from New Orleans Fo8 Weahter says...

If Dean gets above 17.0N when it gets to Jamaica, we may have to worry about Dean affecting the Louisiana Coastline...
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1376. PR51
1:37 AM GMT on August 18, 2007
Relix, be relax. Go to sleep, because you will not see even a drop of water from this storm. I told you yesterday that this storm would not mean anything for us. But some alarmists tend to indicate that there would be torrential rains and gusty winds. ?Do you know what did Dean leave us? a hot night, just that.
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1372. weatherwonderer
1:28 AM GMT on August 18, 2007
Faethe, exactly no aurgument here. I didn't say strong hurricanes are a result of anything. That is for the specialist to decide. If you read my post correctly, it didn't even say that people are responsible. That is the debate part of it.

Dean will is a monster, the only thing keeping it from going West is the ULL. Current thinking (and models) is that will only have minimal impact on its course, however, The NHC was leaning on experience by stating the GFDL model was showing the "classic" path that many of these canes have taken. Since this not a perfect science, experience plays a role in what makes these guy good at what they do. So they left the door open for that possibility.
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1371. quakeman55
1:41 AM GMT on August 18, 2007
Pressure now down to 936 mb!
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1370. leftyy420
1:40 AM GMT on August 18, 2007
URNT12 KNHC 180136
VORTEX DATA MESSAGE AL042007
A. 18/01:15:40Z
B. 14 deg 51 min N
065 deg 29 min W
C. NA mb 2579 m
D. 111 kt
E. 044 deg 011 nm
F. 136 deg 138 kt
G. 044 deg 011 nm
H. 936 mb
I. 10 C/ 3056 m
J. 20 C/ 3047 m
K. 008 C/ NA
L. CLOSED
M. 15
N. 12345/7
O. 0.02 / 2 nm
P. AF302 0504A DEAN OB 09
MAX FL WIND 138 KT NE QUAD 01:12:20 Z
Member Since: Posts: Comments:
1369. Dan187
1:39 AM GMT on August 18, 2007
000
URNT12 KNHC 180136
VORTEX DATA MESSAGE AL042007
A. 18/01:15:40Z
B. 14 deg 51 min N
065 deg 29 min W
C. NA mb 2579 m
D. 111 kt
E. 044 deg 011 nm
F. 136 deg 138 kt
G. 044 deg 011 nm
H. 936 mb
I. 10 C/ 3056 m
J. 20 C/ 3047 m
K. 008 C/ NA
L. CLOSED
M. 15
N. 12345/7
O. 0.02 / 2 nm
P. AF302 0504A DEAN OB 09
MAX FL WIND 138 KT NE QUAD 01:12:20 Z

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1368. Crazman
1:41 AM GMT on August 18, 2007
936 MB holy moly.
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1367. bluehaze27
1:38 AM GMT on August 18, 2007
Hello all, while everyone is focused on Dean (and rightfully so) there is another storm about to form around 30 longitude
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1366. hurricane23
9:40 PM EDT on August 17, 2007
000
WTNT64 KNHC 180135
TCUAT4
HURRICANE DEAN TROPICAL CYCLONE UPDATE
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL042007
930 PM AST FRI AUG 17 2007


DATA FROM THE AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT CURRENTLY
INVESTIGATING HURRICANE DEAN INDICATE THAT MAXIMUM SUSTAINED WINDS
HAVE INCREASED TO 145 MPH...CATEGORY FOUR ON THE SAFFIR-SIMPSON
HURRICANE SCALE.

$$
FORECASTER KNABB
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1365. StuccoMan
8:40 PM CDT on August 17, 2007
Posted By: DG136 at 8:39 PM CDT on August 17, 2007.
Posted By: StuccoMan at 1:37 AM GMT on August 18, 2007.
yeah i live in gulf breeze.

You do business with Color Wheel Paints dont you...


do business with alot of paint company's.
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1364. atmoaggie
1:40 AM GMT on August 18, 2007
Did you not read my post.Katrina hit a gambling town...

Funny. That WAS sarcasm, right?
Member Since: August 16, 2007 Posts: 6 Comments: 12463
1363. KnowYourRole
9:39 PM EDT on August 17, 2007
Posted By: cormit at 9:38 PM EDT on August 17, 2007.
reconaissance coming from www.tropicalatlantic.com.


thanks cormit.
1362. 7544
1:39 AM GMT on August 18, 2007
i dont think the dean has catch up with ull yet can it still happen .
the ull isnt moving yet
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1361. FatPenguin
1:37 AM GMT on August 18, 2007
Posted By: MikeOhio at 1:35 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.

++++++++++++++++++++++++++++++++++++++

Agreed. There will be plenty of time to review and discuss when the season is over.

Focus should be on this storm, and this season.

FYI, I think Dr. Masters mentioned the Arctic news because it will likely be a front page story in September.
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1360. BeenThereinMiami
1:36 AM GMT on August 18, 2007
Hi Gang, Check out the NDBC buoy readings just to the west of Dean at 15.01 N 67.5 W. Should be interesting to watch as Dean moves closer.

Link
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1359. hurricane23
9:40 PM EDT on August 17, 2007
Here are a few radar pics from the puerto rico radar of now very powerful hurricane dean.

Hurricane dean with NHC forcast track.

dean

Close-up eye pic.

dean
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1358. bappit
1:31 AM GMT on August 18, 2007
Dr. Master's mentioned this buoy. Feel for the buoy, do not be this buoy. Looks like Dean will pass very close to it. Dean is still over 100 miles away.
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1357. leftyy420
1:39 AM GMT on August 18, 2007
HURRICANE DEAN TROPICAL CYCLONE UPDATE
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL042007
930 PM AST FRI AUG 17 2007


DATA FROM THE AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT CURRENTLY
INVESTIGATING HURRICANE DEAN INDICATE THAT MAXIMUM SUSTAINED WINDS
HAVE INCREASED TO 145 MPH...CATEGORY FOUR ON THE SAFFIR-SIMPSON
HURRICANE SCALE.
Member Since: Posts: Comments:
1356. fldude99
1:38 AM GMT on August 18, 2007
Posted By: StuccoMan at 1:37 AM GMT on August 18, 2007.
Posted By: DG136 at 8:34 PM CDT on August 17, 2007.
Stuccoman, are you in the FL panhandle?


yeah i live in gulf breeze.I was 6 miles from the center of dennis when it cam ashore.3 miles from the coast.Storm was powerful but brief..Not much surge.Seems like smaller compact cyclones have a much smaller surge.Ivan put Tiger point under 8 feet of water.Put okaloosa Island under 6 feet of water and that was over 140 miles from where the center came ashore.


One reason for that is that you were on the west side of the eye of Dennis.
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1355. DonnaGalveston
1:38 AM GMT on August 18, 2007
Hi everyone, back to check on the progress of the storm. Is there any indication out there that Galveston may be ok?
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1354. Fl30258713
1:23 AM GMT on August 18, 2007
There was a global cooling between the 1930's to 1970's due to pollution that caused new changes in air quality standards for Industry in our country. Just fyi.

I do agree this topic of GW is or should be totally separate from this blog.

I understand Dr Master's posted the information on ice levels, but this is a tropical weather blog.

GW has to much politics mixed in with it and many strong opinions for all obvious reasons.

Good topic to discuss, but I'm not interested in it here or now.
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1352. guerra2100
8:13 PM CDT on August 17, 2007
Ideology and faith-based science aside, if Dean makes landfall at or south of the Texas-Mexico border -- and it is as intense as it appears to be building to -- don't be surprised to see another Katrina-level disaster, but it will be in two countries.

The Lower Rio Grande has developed dramatically in the last decade. Not only has the population exploded but so too has the amount of impermeable ground cover that has paved this region.

The population and impermeable cover level is roughly double on the Mexican side.

In other words, massive rainfall will result in unprecedented flooding in the United States' own Third World.

There is really only one northern evacuation route out of the lower valley because the second major northern highway out of the region is at such low elevation that it is likely to flood early on.

So don't forget that this newspaper man and old storm hand has offered a heads up.

Carlos Guerra
columnist
San Antonio Express-News
cguerra@express-news.net
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1351. DG136
1:37 AM GMT on August 18, 2007
Posted By: StuccoMan at 1:37 AM GMT on August 18, 2007.
yeah i live in gulf breeze.


You do business with Color Wheel Paints dont you...
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1350. moonlightcowboy
1:33 AM GMT on August 18, 2007
I take it all back, and say that I just don't know. I'm gonna stick with my earlier thoughts after looking at the lastest sfc map! Looking at the sats too much. But, it sure does look like it's trying to go west! That high is reaching far west and that little area may just still be enough to pull it northwards. Too tricky, plus add the unpredictability of these things, shoot, it's still early.

Hey, I like the GFDL, outlier and all; but, it's reading something the rest of us can't see. I still think it's going to readjust its track southwards somewhat.

...stupid guess, playa del carmen to galveston!
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1349. Stormchaser2007
9:37 PM EDT on August 17, 2007
Posted By: nolesjeff at 9:37 PM EDT on August 17, 2007.
Posted By: Stormchaser2007 at 1:35 AM GMT on August 18, 2007.

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

No, they have been giving updates about every 10 minutes, afterall THEY ARE THE HURRICANE AUTHORITY!!


In the 3 years i've been blogging here i've never seen a more promising record breaking storm ( Exceptions For Rita, Katrina, Wilma ECT).
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1348. StuccoMan
8:35 PM CDT on August 17, 2007
Posted By: ChuckieTodd at 8:36 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?


Did you not read my post.Katrina hit a gambling town hence much more populated and ruptured the levees that flooded new orleans.
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1347. bekroweather
1:37 AM GMT on August 18, 2007
I see the potential N trend in the last frame that some people are talking about. For the time being its just one frame - so not that trustworthy, but could mean something down the way.
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1346. Masquer08er
1:36 AM GMT on August 18, 2007
Link

PR Radar
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1345. cormit
1:35 AM GMT on August 18, 2007
reconaissance coming from www.tropicalatlantic.com.
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1344. atmoaggie
1:36 AM GMT on August 18, 2007
WOW. Perhaps I'm confused but didn't Katrina do almos 6 times the damage of Ivan?

That would be population, fragility/vulnerability of the infrastructure, and most important, RMW (radius of max winds). RMW had a major role in the miles and miles of devistation and the height and breadth of the storm surge.
Member Since: August 16, 2007 Posts: 6 Comments: 12463
1343. HiWay
1:33 AM GMT on August 18, 2007
A large factor in my opinion is that it has yet to reach the hottest of waters. IF it takes that more northerly turn and makes it way through the heart of the gulf, esp if it decides to follow the hotter tracks of water in the GOM. (I never see people mention the fact that they follow the better food (hot water) to a degree, despite everything else if you compare SST's and tracks). I think if that occurs we will have many records broken and see the storm not only grow in strength at a record amount, but tap the still un-stirred waters of the GOM and balloon to an enourmous size of TS winds and a much broader hurricane force swath. Sounds very pessimistic, but I think a lot of people seem to get a funny vibe about "The Dean."
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1342. Quint
1:37 AM GMT on August 18, 2007
Someone earlier mentioned Allen 1980 and Gilbert 1988 as possible tracks for Dean. Take a look at Beulah 1967. People in Florida should not let their guard down until the storm passes Jamaica or even 80w. If you don't believe me see Cleo 1964, Inez 1966. That said, I do believe the model consensus track, especially with the storm moving this fast. Isn't it true that fast moving stoms are less likely to make large directional changes?
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1341. MikeOhio
1:36 AM GMT on August 18, 2007
WOW. Perhaps I'm confused but didn't Katrina do almos 6 times the damage of Ivan?


No you aren't confused, but I think the point is that Ivan was stronger as was Andrew.

Katrina didn't even directly hit where the most damage was done (New Orleans)...
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1339. StuccoMan
8:34 PM CDT on August 17, 2007
Posted By: DG136 at 8:34 PM CDT on August 17, 2007.
Stuccoman, are you in the FL panhandle?


yeah i live in gulf breeze.I was 6 miles from the center of dennis when it cam ashore.3 miles from the coast.Storm was powerful but brief..Not much surge.Seems like smaller compact cyclones have a much smaller surge.Ivan put Tiger point under 8 feet of water.Put okaloosa Island under 6 feet of water and that was over 140 miles from where the center came ashore.
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1338. bekroweather
1:35 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


And the center of the storm is to the south of the forecasted track points.
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1337. nolesjeff
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....

No, they have been giving updates about every 10 minutes, afterall THEY ARE THE HURRICANE AUTHORITY!!
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1336. Relix
1:35 AM GMT on August 18, 2007
I think I am gonna go sleep, I was waiting for a rain event, but nothing. Meh
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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...
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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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