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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1985. Skyepony (Mod)
3:48 AM GMT on August 18, 2007
Atleast Sepat ran over Tawain pretty quick.
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1983. Daveg
3:55 AM GMT on August 18, 2007
Wow..look at Dean just ride 15N....
Link
Member Since: September 23, 2005 Posts: 0 Comments: 426
1980. StuccoMan
10:53 PM CDT on August 17, 2007
ULL hasn't moved all day and it looks like dean is going to get very close to it here by tomorrow morning if it doesn't move.
This is going to be a very weird outcome and one thing is for sure.The GFDL might go down in history as one very reliable model or one that jumped the gun.! outcome is going to come out of this either way.I have a feeling this storm is gonna do the unexpected real soon.
1979. afs
3:51 AM GMT on August 18, 2007
Masquer08er:

This weather blog is written by a scientist with Doctorate in Meteorology.
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1978. 786
3:51 AM GMT on August 18, 2007
I understand that the States is always more important and why not?? I mean everyone there is all the more special. I am in Cayman about to get a cat 5 hurricane over me. Ivan was worse for us then any U.S hurricane in history. Have some humility please. There are 50,000 people here and we are about to lose our livelihoods and all you guys can think about is the States. Realise there is more in this world then the United States
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1977. bappit
3:54 AM GMT on August 18, 2007
Looks like dry air is wrapping around Dean on this loop.
Member Since: May 18, 2006 Posts: 10 Comments: 6061
1973. nola70119
3:52 AM GMT on August 18, 2007
Too close to call....
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1970. atmoaggie
3:52 AM GMT on August 18, 2007
AtmoAggie,
M.S. Agri. from SFASU - I have no problem reading scientific journals, articles, and drawing conclusions whether or not funding influenced the results. Or if it was good hard science.
Good.
Personally, I became a pro at chicken poo's influence on creek's and rivers algea counts.
Cool! Seriously, I expect that would aid any oxygen depletion events nicely.
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1969. H2PV
3:50 AM GMT on August 18, 2007
Posted By: Daveg at 3:41 AM GMT on August 18, 2007
A small snippet from a Popular Science article..
What the global-warming fanatics won't cede is the fact that the Earth's climate has never been stable. "The only constant," argues Prof. Patterson, "is change; it changes continually and at times quite rapidly. Many times in the past temperatures were far higher than today, and occasionally temperatures were colder." As recently as six thousand years ago it was on average just under 2 degrees warmer than now. Ten thousand years ago ... temperatures rose as much as 4 degrees in a decade 100 times faster than the past century's warming that has so upset environmentalists.


That never happened. In 1998 the temperatures spike to a peak. 87% of all species of corals in the world bleached and 40% of all those subsequently died off. 2002 and 2005 were rival years for coral bleaching.

The reason those corals lived until 1998 to die is because they didn't get exterminated by heat-death at any earlier period in Earth history. Mass die-offs in corals are easy to spot in coral fossil records. There are no coral fossil records which verify the bogus claims that "Populist Scyanzz" claims.

There was no HOTTER temperatures for 50,000,000 years at least. If you claim there was then you bring the coral records with you to prove it.
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1968. AndyN
3:47 AM GMT on August 18, 2007
I love it when my local weatherman spews the NHC track like it is gospel.....the NHC even said in 1100 discussion they don't really have a clue what is gonna happen 3-4 days from now....Like someone said earlier..Katrina was going to Pensacola, then Mobile then next thing I knew I was in New Orleans for 10 days on a deployment in support of homeland security response....
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1967. errantlythought
3:46 AM GMT on August 18, 2007
MrNiceville at 3:47 AM GMT on August 18, 2007.
Hey gang - just got in off the road.

What's up - looks like the tracks are all adjusting w and or s a bit...


It's been all over the place today. GFDL is shifting back and forth between us and texas, and other models are going everywhere from yucatan to brownsville, etc. Dean recently took a small(1min)southern wobble, but by MIMIC it looks like he's back on track WNW.

I still cant figure out what the heck the ULL is doing
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1965. Metallica1990
3:49 AM GMT on August 18, 2007
thank you katadman :)
1963. CuriuosGa
3:41 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.
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1961. littlefish
3:48 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
1960. NeO73
3:45 AM GMT on August 18, 2007
remember Charlie.....Link
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1959. katadman
3:38 AM GMT on August 18, 2007
Posted By: Metallica1990 at 3:19 AM GMT on August 18, 2007.

Posted By: BigToe at 3:18 AM GMT on August 18, 2007.

OK Metallica1900..... You NAILED it.

even though i think that was sarcasm thanks



No sarcasm here. I only wish I could be as accurate. Congrats!
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1957. greg531
3:42 AM GMT on August 18, 2007
Where is the August 1915 Cat 4 Galveston in the Archives map? Loods like it's track is the same as the GFDL model.....
Guess we see which is better in this storm...
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1956. Masquer08er
3:40 AM GMT on August 18, 2007
Daveg, if you want facts, get them from scientists, not religious leaders and businessmen heavily invested in the industry under fire.

or, weather blogs ;-)
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1955. MrNiceville
3:46 AM GMT on August 18, 2007
Hey gang - just got in off the road.

What's up - looks like the tracks are all adjusting w and or s a bit...
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1952. streamtracker
3:46 AM GMT on August 18, 2007
Dave I think I'll stick to peer-reviewed articles from my info.

By the way the Patterson is not a physical scientist, he's trained as a historian.
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1951. HIEXPRESS
3:41 AM GMT on August 18, 2007
Posted By: Skyepony...the many scary waves...

Their's [NAH] don't look big enough.
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1950. ForecasterColby
3:45 AM GMT on August 18, 2007
Dean is a male name. They alternate, and Erin was the E storm, so..yeah.
1949. weathersp
11:45 PM EDT on August 17, 2007
42059 is 103 miles from the eye right now..
Member Since: January 14, 2007 Posts: 17 Comments: 4140
1948. TXMET
3:44 AM GMT on August 18, 2007
Regarding the ULL, it seems to be staying put, that's the main thing. Where it is, it may not be close enough to redirect Dean NW.
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1947. Metallica1990
3:45 AM GMT on August 18, 2007
man dean is starting to look like he weakening slightly
1946. H2OMaker
3:44 AM GMT on August 18, 2007
AtmoAggie,

M.S. Agri. from SFASU - I have no problem reading scientific journals, articles, and drawing conclusions whether or not funding influenced the results. Or if it was good hard science. Personally, I became a pro at chicken poo's influence on creek's and rivers algea counts.
Member Since: Posts: Comments:
1944. guygee
3:43 AM GMT on August 18, 2007
Posted By: Weather456 at 11:19 PM GMT on August 17, 2007.
"Is Dean a boy or girl? I'm curious"

Dean is my wife's name, or so my real wife tells me.
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1941. errantlythought
3:42 AM GMT on August 18, 2007
Posted By: littlefish at 3:41 AM GMT on August 18, 2007.
That N ULL is weakening quite a bit, looks like Dean's high is winning out and maybe the west trak is proving correct. But if he slows, things get harder to predict...


I've been watching the ULL all day, and it seems to have been strengthening. Why do you belive it is weakening? Just wondering if I've missed something.
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1940. Daveg
3:42 AM GMT on August 18, 2007
Anyway, my point in my posts is that man-made global warming isn't happening, but global warming IS caused by a variety of factors. Does that mean we shouldn't take care of the planet and pollute less? Absolutely not. It's our home, we need to take care of it.

Now...back to Dean...I'm all worn out on the climate change stuff. =)
Member Since: September 23, 2005 Posts: 0 Comments: 426
1939. 28feetabovesealevel
3:42 AM GMT on August 18, 2007
BTNTX

I'm sure Dr. Masters gave up on this blog a long time ago.....
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1937. Stormy2day
11:41 PM EDT on August 17, 2007
anything happening in that spin off the east coast of florida.
27/79ish?
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About

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.