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

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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1933. TXMET
3:40 AM GMT on August 18, 2007
Will the buoy make it? It'll fare better than the folks on Jamaica, I bet.
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1932. BtnTx
10:42 PM CDT on August 17, 2007
Dr Masters never comments? Think he reads this blog?
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1930. weatherwonderer
3:37 AM GMT on August 18, 2007
H2PV excellent, the Earth is a ling organism in its own right. Changes have consequences, its no different then your own life.
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1929. Skyepony (Mod)
3:37 AM GMT on August 18, 2007
Dropsnode in the eyewall...

Dropsonde Observations
Storm Name: DEAN (04L)
Mission Number: 05
Flight ID: AF302
Observation Number: 19
Time: 0300Z
Latitude: 14.8N
Longitude: 65.9W
Surface: 944 mb; Temp: 78F; Dewpt: 78F; SE (130) @ 139 mph
1000mb height: Unavailable
925mb height: 587 ft; Temp: 76F; Dewpt: 76F; SE (140) @ 139 mph
850mb height: 3018 ft; Temp: 70F; Dewpt: 70F; S (175) @ 134 mph
700mb height: 11801 ft; Temp: 60F; Dewpt: 59F; SW (230) @ 74 mph
500mb height: Unavailable
400mb height: Unavailable
300mb height: Unavailable
250mb height: Unavailable
200mb height: Unavailable
EYEWALL 000 SPL 1497N06584W 0302 MBL WND 14618 AEV 00000 DL
M WND 18590 943708 WL150 13615 080 =

944mb winds: SE (130) @ 139 mph
935mb winds: SE (135) @ 129 mph
920mb winds: SSE (150) @ 144 mph
912mb winds: SSE (150) @ 143 mph
904mb winds: SSE (155) @ 136 mph
883mb winds: SSE (160) @ 135 mph
876mb winds: SSE (160) @ 138 mph
865mb winds: SSE (165) @ 136 mph
859mb winds: SSE (165) @ 144 mph
850mb winds: S (175) @ 134 mph
692mb winds: SW (235) @ 69 mph

Member Since: August 10, 2005 Posts: 431 Comments: 44056
1928. littlefish
3:40 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...
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1926. weathersp
11:40 PM EDT on August 17, 2007
Dean's Waves
Member Since: January 14, 2007 Posts: 17 Comments: 4140
1925. Daveg
3:41 AM GMT on August 18, 2007
Posted By: streamtracker at 3:34 AM GMT on August 18, 2007.
Changes in solar input are not correlated with the changes above in the last 45 years at least. Lots of good research published on this in the last few years and several great papers this year.

That's nice and all, but it's not the whole picture...

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.

Prof. Patterson bases his skepticism that man is causing the globe to "run a fever" (as the greenies put it) on his study of storms on the sun, which play havoc with Earth's climate: "Hundreds of studies, using [data from studies of] tree rings in Russia's Kola Peninsula to water levels of the Nile, show exactly the same thing: The sun appears to drive climate change."

But how it does that is crucial. The measured variations of incoming solar energy are not sufficient to explain the rising temperatures observed by evangelist and dissenter alike. "There has to be an amplifier of some sort for the sun to be a primary driver of climate change." The amplifier is a protective solar wind, entering Earth's atmosphere from deep space, enhancing cloud formation which has a cooling effect on the globe. When the sun's "energy output" is greater, Earth warms slightly from direct solar heating, and the stronger solar winds generated during these "high sun" periods block the cosmic rays from deep space. Cloud cover decreases and Earth warms even more. That's what we're seeing (and feeling) now.

When the sun's tantrum subsides, more cosmic rays get through, the cloud cover thickens and the globe cools. Prof. Patterson and a considerable number of his eminent fellows conclude that it's the sun's "output" that has caused the most recent climate change. "Solar scientists," he says, "predict that by 2020 the sun will be starting into its weakest solar cycle of the past two centuries, likely leading to unusually cool conditions on Earth."
Member Since: September 23, 2005 Posts: 0 Comments: 426
1924. Canenut
3:40 AM GMT on August 18, 2007
URNT12 KNHC 180328
A. 18/02:58:10Z
B. 14 deg 53 min N
065 deg 55 min W
C. 700 mb 2547 m
D. 126 kt
E. 148 deg 007 nm
F. 245 deg 117 kt
G. 141 deg 005 nm
H. 935 mb
I. 11 C/ 3049 m
J. 20 C/ 3028 m
K. 10 C/ NA
M. C15
N. 12345/ 7
O. 0.02 / 2 nm
P. AF302 0504A DEAN OB 17
MAX FL WIND 138 KT NE QUAD 01:12:20 Z

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1921. MelbourneTom
3:35 AM GMT on August 18, 2007
Now that Dean has intensified it will be influenced by the upper level stearing currents. No, it is not likely to come to FL but it may be likely to jog north more than the current forcast.

Member Since: June 2, 2007 Posts: 0 Comments: 619
1918. afs
3:33 AM GMT on August 18, 2007
Dave... you want facts?

Here's a whole website full of science created by 1000's of scientists

Link to Intergovernmental Panel on Climate Change website...


Daveg, if you want facts, get them from scientists, not religious leaders and businessmen heavily invested in the industry under fire.

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1916. resinwich
3:29 AM GMT on August 18, 2007
/// We're nowhere near the end of this. Please do NOT let your guard down. People did that right before K, when it was supposedly heading for the florida panhandle, or need I remind you? ///

Yeah, I'm looking at the NHC graphics archive right now. On 8/26, Katrina has just crawled into the Gulf and was forecast to hit toward the middle of the FLA panhandle. 24 hours later, the forecast landfall shifted to near Lake Pontchartrain. By the 29th, New Orleans was under water.
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1914. errantlythought
3:35 AM GMT on August 18, 2007
MIMIC shows the southern movement as a clear wobble, with the storm back to at least a due W movement. Whether that is a return to WNW can only be seen in a few hours.

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1912. thelmores
3:34 AM GMT on August 18, 2007

seems that dean's forward motion (how fast) will play a large role..... seems dean is slowing some, which may end up being a more northerly track. At the current pace, it will be close to catching the ULL....... which perhaps may mean a more NW track.... magic 8-ball would give about as good a guess as me! :)
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1910. H2OMaker
3:36 AM GMT on August 18, 2007
I'm gonna throw out a real smart idea why the ice cap is melting. (AND I'M BEING FACETIOUS)

All the polar orbiting satellites are reflecting too much sunlight onto the snow.

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1909. louisianaboy444
3:37 AM GMT on August 18, 2007
well i'm moving on with my life lol goodnight all and pray for the people in the islands and southern Mexico in the comming days
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1908. TXMET
3:35 AM GMT on August 18, 2007
17 ft wave heights already at the 42059 buoy.
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1907. hurricanex
3:32 AM GMT on August 18, 2007
Hurricane Dean is really symmetric and beautifull we are possibly looking at a cat 5 hurricane. It does not get any stronger than that...........wow awesome.
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1905. bluehaze27
10:32 PM EST on August 17, 2007
hey everyone who is mad at me, I'm sorry. I don't know everything (and I'll readily admit it), however i do know what I see and experience and Global warming is important enough to at least care about. I know this doesn't hold a candle to the immediacy of Dean but that doesn't mean it should be ignored for another day. For now I'll leave it at that and I won't mention it again.
Member Since: March 26, 2007 Posts: 0 Comments: 911
1904. Baybuddy
3:34 AM GMT on August 18, 2007
Okay Guys, Im off to bed. Please, everyone be safe. See yall tomorrow.
Member Since: June 26, 2006 Posts: 0 Comments: 1115
1903. weatherwannabe
3:32 AM GMT on August 18, 2007
Where did all these climate change deniers come from? Is Exxon Mobil paying for blog shills these days? I think Dr. Masters point is accurate. Take some time to think about his point.
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1902. streamtracker
3:33 AM GMT on August 18, 2007
Sun can't be responsible for current trend in either global temperatures or ice sheet cover.

Changes in solar input are not correlated with the changes above in the last 45 years at least. Lots of good research published on this in the last few years and several great papers this year.

This link about solar inputs is to a site run a by a group of several climate science researchers.

When I want to learn about hurricane forecasting I come here, when I want authoritative info on global arming I go there.

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1900. chicagowatcher
3:32 AM GMT on August 18, 2007
local weathercaster describe the weather next week like nothing is happening and then said ooo and dean looks like its most likely headed to mexico in a sad voice lol....people are starting to write off this storm all because the poor thing cant make it up the gulf coast

If it wobbles up to Haiti, it may produce more than enough headlines...
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1899. Skyepony (Mod)
3:34 AM GMT on August 18, 2007

Here's the link, select animation to view the many scary waves forecast to hit islands & land.
Member Since: August 10, 2005 Posts: 431 Comments: 44056
1898. H2OMaker
3:32 AM GMT on August 18, 2007
Or local weather pro's on Fox and ABC (Houston) were both very strident about the fact that the central track at four days out is unimportant, the Cone of Unreliability is.

Also, keep in mind that about 35% of the time, storms like to jump out of the cone and just make their own tracks regardless of how the forecasters and entrail readers guide them.
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3:23 AM GMT on August 18, 2007
Still headed WEST
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1896. BtnTx
10:31 PM CDT on August 17, 2007
Ever notice how Dr Masters never posts a comment on this blog? It wouldn't surprise me if he hardly ever reads. Hope this doesn't get me banned.
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1894. Rick54
10:28 PM CDT on August 17, 2007
rick54 explain.

So far from the models that I have seen it is only the Gulf stream that is likely effected by the salinity changes to the degree that the current is likely to stop. Of course this may change but the primary threat is melting of the Greenland ice cap. If the Gulf stream stops the effect will be to cool the US Northeast across to Europe. BTW the Gulf stream stopped for 5 days or so a few years back if I recall correctly.
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1890. atmoaggie
3:27 AM GMT on August 18, 2007
Posted By: StuccoMan at 3:26 AM GMT on August 18, 2007.

why do people keep comparing katrina to the most powerful storms of all time.For the love of god katrina was a 3 when it hit and was only devastating in wide range due to new orleans in a soup bowl.If you want to compare it to a more noteable hurricane how about andrew or wilma.
Katrina was a 3 and thats that.

Why? RMW (Radius of max winds) made Katrina what it was. The breadth of destruction, and height and breadth of storm surge had everything to do with it. When we run Planteary Boundary Layer (PBL) models to spin up winds to input into a storm surge model, 5 mile RMW changes cause much larger changes in the wind field and storm surge than any 10 knot chanage sustained wind speed. Remember that Camille had a much higher wind speed, but only cuased about the same surge values and over a much smaller area.
Member Since: August 16, 2007 Posts: 6 Comments: 12463
1888. JamaicanGir
10:30 PM EST on August 17, 2007
thanks again MLC

we will try our best to do as Dr. M says and pray it away
1886. louisianaboy444
3:30 AM GMT on August 18, 2007
local weathercaster describe the weather next week like nothing is happening and then said ooo and dean looks like its most likely headed to mexico in a sad voice lol....people are starting to write off this storm all because the poor thing cant make it up the gulf coast
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