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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2035. nola70119
4:04 AM GMT on August 18, 2007
Canenut, got it. Just over the Yucatan into the Gulf toward Mex/Us border......
Member Since: June 16, 2006 Posts: 0 Comments: 1560
2034. mikester
3:34 AM GMT on August 18, 2007

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2033. AllyBama
4:05 AM GMT on August 18, 2007
Suwanee...Katrina moved a lot of stationary oil rigs..lol
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2032. TheCaneWhisperer
4:03 AM GMT on August 18, 2007
Hard to imagine a monster like this can pick a needle out of a haystack! Didn't know you were from the cayman's KY. Thoughts are with you as well. I have family in S Jamacia, they are in the process of evac.
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2030. bappit
4:04 AM GMT on August 18, 2007
The big flare up in convection to the SE of Dean looks kind of like a dry line. Dry air pulled in from the west meets moist air from the southeast.
Member Since: May 18, 2006 Posts: 10 Comments: 5951
2028. C2News
12:04 AM EDT on August 18, 2007
So, where is Dean headed? Is he expected to track northwestward?
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2027. VegasRain
4:04 AM GMT on August 18, 2007
Concentric Eyewalls on San Juan Radar??
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2020. Daveg
4:03 AM GMT on August 18, 2007
Posted By: i12BNEi at 4:03 AM GMT on August 18, 2007.
strange to see it ride the 15 like that for so long.Asleep at the wheel?


For the folks in Jamaica, I sure how so. Stay asleep Dean!
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2019. bappit
4:00 AM GMT on August 18, 2007
The cloud tops have warmed. The outflow clouds in the dry slot are evaporating and the CDO is smaller. Looks like weakening to me.
Member Since: May 18, 2006 Posts: 10 Comments: 5951
2018. Canenut
4:04 AM GMT on August 18, 2007
NOLA70119,
Link

North by about 2 degrees thru 90 hours
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2017. Suwanee
4:03 AM GMT on August 18, 2007
Does anyone have a link to oil rig locations in the GoM (fixed ones since I'm assuming they'll be able to move the mobile ones). Thanks.
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2016. AndyN
4:00 AM GMT on August 18, 2007
Check out the ULL and the movement or lack thereof. Awesome view of Dean and the everpresent eye. Link
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2015. H2PV
4:01 AM GMT on August 18, 2007
Posted By: treehuggingsister at 3:47 AM GMT on August 18, 2007.
...Hurricanes were here before people, but Dean might have been a tropical storm still instead of a near category 5 major hurricane.


Oh, please. I can't take it any more. As Scotty from Star Trek said "...and if my Grandma had wheels, she'd be a wagon."

Exactly. What an irresponsible bit of whoo-wah that statement was. Your knee jerk reasoning for LAST year's COMPLETE lack of adrenaline weather rushes was...what? GW time out? The cool thing about science used to be that ALL the facts made the science, not the other way around.

Talk about Dean. Talk about what info the the technology and science we have available at this moment show you. That's FACT. Not conjecture, not supposition, not DOGMA, not Kool-Aid. It's QUANTIFIABLE FACT.

(Even the 'inconvenient' ones that maybe don't go with your parade.)


Last year had no lack of adrenaline weather. The beat was stead, one MAJOR hurricane every 13 to 14 days, summer, winter, spring and fall from Katrina, August 2005 to Bondo, Christmas 2006. It never let up. Only a fool would look at one part of the globe and ignore the rest.

Since January 2007 there was the longest perior of no major hurricanes in recorded history since modern flight and satellite records. Still, the beat goes on with one major hurricane every 15 days since January 1st, New Years Day.

You refused to look outside your southern-eastern interest US area, and declared there was nothing interesting in 2006, THEN you add "The cool thing about science used to be that ALL the facts made the science, not the other way around."

What about these facts???

35 MAJOR Hurricanes category 3, 4 or 5 SINCE Katrina. August 27th 2005 through December 31st 2006.
Average one every 13 days. 11 super-hurricanes Category-5

GLOBAL means GLOBAL. Global Warming Action moves around but it doesn't move to outer-space. If it's not in your backyard, it's in somebody else's and you can see it just by looking for it. It's very much too large to hide.

http://en.wikipedia.org/wiki/2006_Atlantic_hurricane_season
* 2.8 Hurricane Gordon Cat-3
* 2.9 Hurricane Helene Cat-3

http://en.wikipedia.org/wiki/2006_Pacific_hurricane_season
Storms
* 2.3 Hurricane Bud Cat-3
* 2.5 Hurricane Daniel Cat-4
* 2.10 Hurricane Ioke Cat-4
* 2.11 Hurricane Ileana Cat-3
* 2.12 Hurricane John Cat-4
* 2.14 Hurricane Lane Cat-3

http://en.wikipedia.org/wiki/2006_Pacific_typhoon_season
Storms
* 1.1 Typhoon Chanchu (Caloy) May 8 Cat-4
* 1.3 Typhoon Ewiniar (Ester) June 30 Cat-4
* 1.8 Typhoon Saomai (Juan) August 5 Cat-5
* 1.13 Typhoon Shanshan (Luis) Cat-4
* 1.14 Typhoon Yagi Cat-5
* 1.15 Typhoon Xangsane (Milenyo) Cat-4

http://en.wikipedia.org/wiki/2006_North_Indian_cyclone_season
Season summary
* 1.2 Very Severe Cyclonic Storm Mala (02B) April 24 Cat-3

http://en.wikipedia.org/wiki/2005-06_Southern_Hemisphere_tropical_cyc...
eason Storms
o 2.1.5 Very Intense Tropical Cyclone Carina February 23
Catagory-4
* 2.2 Southeast Indian Ocean/Western Australia
o 2.2.2 Severe Tropical Cyclone Bertie-Alvin November 21
Cat-4
o 2.2.4 Severe Tropical Cyclone Clare January 7 Cat-3
o 2.2.5 Severe Tropical Cyclone Daryl January 21 Cat-3
o 2.2.7 Severe Tropical Cyclone Floyd March 22 Cat-4
o 2.2.8 Severe Tropical Cyclone Glenda March 24 Cat-5
* 2.4 Coral Sea/Eastern Australia
o 2.4.3 Severe Tropical Cyclone Larry March 16 Cat-5
o 2.4.4 Severe Tropical Cyclone Monica April 17 Cat-6
* Severe Tropical Cyclone Wati Cat-3

http://en.wikipedia.org/wiki/2006-07_Southern_Hemisphere_tropical_cyc...
* 2.1.3 Tropical Cyclone Bondo

2005 Cyclones after Katrina =================

http://en.wikipedia.org/wiki/2005_Atlantic_hurricane_season
* Katrina Cat-5 August 24
* Maria Cat-3
* Rita Cat-5
* Wilma Cat-5
* Beta Cat-3

http://en.wikipedia.org/wiki/2005_Pacific_hurricane_season
* Jova Cat-3
* Kenneth Cat-4

13 Cat-3s, 10 Cat-4s, 12 Cat-5s = 35

Katrina August 24, 2005 Cat-5
Hurricane Rita Cat-5
Hurricane Wilma Cat-5
Severe Tropical Cyclone Glenda March 24 Cat-5
Severe Tropical Cyclone Larry March 16 Cat-5
Severe Tropical Cyclone Monica April 17 Cat-6
Super Typhoon Saomai (Juan) August 5, 2005 Cat-5
Super Typhoon/Hurricane Ioke Cat-5
Super Typhoon Yagi Cat-5
Super Typhoon Cimaron Cat-5
Super Typhoon Durian Cat-5
Super-Cyclone Bondo Cat-5

Hurricane Kenneth Cat-4
Hurricane Daniel Cat-4
Super Typhoon Chanchu (Caloy) May 8 Cat-4
Super Typhoon Ewiniar (Ester) June 30 Cat-4
Very Intense Tropical Cyclone Carina February 23 Catagory-4
Severe Tropical Cyclone Bertie-Alvin November 21 Cat-4
Severe Tropical Cyclone Floyd March 22 Cat-4
Typhoon Shanshan Cat-4
Typhoon Xangsane (Milenyo) Cat-4
Typhoon Chebi Cat-4

Hurricane John Cat-3
Hurricane Maria Cat-3
Hurricane Beta Cat-3
Hurricane Jova Cat-3
Hurricane Bud Cat-3
Hurricane Ileana Cat-3
Severe Tropical Cyclone Clare January 7 Cat-3
Severe Tropical Cyclone Daryl January 21 Cat-3
Severe Tropical Cyclone Wati Cat-3
Very Severe Cyclonic Storm Mala (02B) April 24 Cat-3
Hurricane Gordon Cat-3
Hurricane Lane Cat-3
Hurricane Helene Cat-3
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2014. i12BNEi
4:02 AM GMT on August 18, 2007
strange to see it ride the 15 like that for so long.Asleep at the wheel?
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2013. KYhomeboy
4:01 AM GMT on August 18, 2007
Cane it would be nice to see Dean's eye continue to travel due west along 15 degrees...this would lessen the chances of landfall or passing extremely close to us. But for now...its eye is set on us...quite literally. Looks like Ivan II to me...but we're preparing for the worst and hoping for the best.
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2012. VegasRain
3:57 AM GMT on August 18, 2007
San Juan Radar seems to show that Dean has concentric eyewalls, there is a definite gap in the radar echos about 20 miles or so from the center. Dean might be getting ready for an Eyewall Replacement Cycle. But I am not for sure about that....
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2008. guygee
3:45 AM GMT on August 18, 2007
Posted By: JFLORIDA at 3:44 AM GMT on August 18, 2007.
Dr Masters never comments? Think he reads this blog?

"I dont think anyone could read ALL of this - but he does comment on a lot of stuff and answer sometimes in the next days blog."

I am reasonably sure he checks up on the blog comments, either by skimming or using the filers. He seems to almost always address his comments towards some current issues on this blog, while also driving home some of the very important news that gets mostly ignored in the mass media (i.e. record low arctic ice coverage). Dr. M. is an honest and earnest scientist, despite his obvious political opinions that sometimes show through (e.g. the Proenza case). Give him a break, he got his tenure in the Flordy State University System (no small achievement for an actual American-born citizen).
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2007. atmoaggie
4:01 AM GMT on August 18, 2007
Can you imagine going up and down for a total of 46 feet every 10 seconds in a boat? No thanks, I'll stay on terra firma.

Wave height
Member Since: August 16, 2007 Posts: 6 Comments: 12461
2006. Daveg
4:00 AM GMT on August 18, 2007
If Dean will just hold this course a bit longer, we might get lucky and Jamaica will be spared. Fingers crossed.
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2004. TheCaneWhisperer
3:56 AM GMT on August 18, 2007
Jamacia and the Caymans! NHC has the 3 day track nailed. ULL is starting to pull off to the SW, anticyclone still intact. I see no deviation from the 3 day track. My thoughts are with you K-Man and Caymanite, I know you guys have been through a lot the past 3 years.
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2003. treehuggingsister
3:59 AM GMT on August 18, 2007
In 1998 the temperatures spike to a peak.

Um, no, they don't.

"Red faces at NASA over climate-change blunder
In the United States, the calendar year 1998 ranked as the hottest of them all until someone checked the math.

After a Toronto skeptic tipped NASA this month to one flaw in its climate calculations, the U.S. agency ordered a full data review.

Days later, it put out a revised list of all-time hottest years. The Dust Bowl year of 1934 now ranks as hottest ever in the U.S. not 1998."

Coral might be bleaching as you say, but it wasn't because of the heat in '98. And that's NASA redoing their own data. But dang if I didn't see a thing about it, you know, in big bold letters on the front page. That would have been...inconvenient.
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2002. nola70119
3:58 AM GMT on August 18, 2007
Link to GFS?
Member Since: June 16, 2006 Posts: 0 Comments: 1560
2001. sucar1720
3:53 AM GMT on August 18, 2007
Hi! I'm new here and very interested in tropical storms,I can see I will learn a lot here! I have one question that is probably off topic and that is, What has kept the core of the earth molten for so long ? Will it eventually cool down? Just wondering. Now Back to Dean
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2000. Rick54
10:50 PM CDT on August 17, 2007
rick54, I believe the last time the currents stopped was during the late 1700's during the Revolutionary war.

Sorry I can't find a better reference right now it's kind of late to go digging to find a journal article but they are out there...

The Gulf Stream completely shut down off Britain in 2004, confirming a prediction of global warming.

Scientists have uncovered more evidence for a dramatic weakening in the vast ocean current that gives Britain its relatively balmy climate by dragging warm water northwards from the tropics. The slowdown, which climate modellers have predicted will follow global warming, has been confirmed by the most detailed study yet of ocean flow in the Atlantic.

Most alarmingly, the data reveal that a part of the current, which is usually 60 times more powerful than the Amazon river, came to a temporary halt during November 2004.


http://schneibster.gnn.tv/headlines/11965/Gulf_Stream_Stopped_for_Days_butthere_snoglobalwarming
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1999. Himicane
10:32 PM CDT on August 17, 2007
I understand the concern with the timing of non Dean related topics such as ice sheet melting. Looking at a probable Cat 5 storm which will hit the US and/or it's neighbors is a much more immediate threat than the long term effects of a thinning ice sheet - whatever the cause.

If he wishes to stray from the immediate threat, it's his prerogative...and it's my prerogative to look for a blog which doesn't stray from the immediate threat.

Now on to the ULL interaction.
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1995. runningfromthestorms
3:57 AM GMT on August 18, 2007
786 - we will be thinking of all of you in the path of this storm and you will all be in our prayers and we will be there for you after the storm passes. God bless.
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1994. katadman
3:53 AM GMT on August 18, 2007
Posted By: CuriuosGa at 3:49 AM GMT on August 18, 2007.

As a new member to this blog I have learned that hurricane forecasting is much more reliable in the past. I have much to learn on this subject so research is on the order.
As for the global warming, the climate is getting warmer. Is this warming trend mearly a temporary wobble in the climate trend or the climates true course? We have proof of a tropical climate and proof of an ice age. Think i will have a glass of wine and pontificate.



Perfect! Mind if I join you?
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1991. VegasRain
3:51 AM GMT on August 18, 2007
Posted By: clwstmchasr at 3:44 AM GMT on August 18, 2007.

Looking at the water vapor the ULL is now really on the move crossing FL. Maybe the GFS is right. Let's wait and see. New GFS model run coming out now.


I don't think the ULL is moving at all. It seems to be moving ever so slowly towards the Southwest, but the center of the low has pretty much remained stationary near West Palm Beach.
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1989. Metallica1990
3:56 AM GMT on August 18, 2007
Link

in this loop the eye looks awesome
1987. errantlythought
3:54 AM GMT on August 18, 2007
Posted By: littlefish at 3:49 AM GMT on August 18, 2007.
errant, look at this address and look at last frame. The 700 mbar level shows a weakening N ULL.

http://cimss.ssec.wisc.edu/tropic/real-time/atlantic/winds/wg8vor3.html


Thanks little. That is interesting. I had been looking at the 500mb level, however, and noticed it is consistant. I realize that may not, however, make much of a difference. What is the difference in interaction factor, if you know?
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1985. Skyepony (Mod)
3:48 AM GMT on August 18, 2007
Atleast Sepat ran over Tawain pretty quick.
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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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