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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1234. SWFLdrob
1:10 AM GMT on August 18, 2007
alexandra steele is a walking skeleton...almost as scary as Dean at this point.

Dean needs shear and cold water...Steele needs a double cheeseburger...neither are likely.
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1233. MikeOhio
1:10 AM GMT on August 18, 2007
The first time a hurricane was seen by a satellite was during the 1960s. That's it. And the only hurricanes it saw were ones that affected the United States directly.


Well I was thinking ship reports and the like, but you're right, without actually seeing the storms we never truly knew until just recently in our time as a species on this planet.

I'm not saying one thing is right or the other, but I am saying that we have a very very small sample over a very LARGE timespan. It is illogical to jump to conclusions.
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1232. TheCaneWhisperer
1:14 AM GMT on August 18, 2007
Doughnuts anyone? Man, Dean is taking off.
1231. extreme236
1:13 AM GMT on August 18, 2007
wow, dean's eye is becoming very symetrical, earlier it was a bit sloppy
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1230. floridafisherman
1:09 AM GMT on August 18, 2007
stucco, it hit barbados BEFORE it underwent this rapid strengthening. barbados would be like grenada in 2005 if dean hit it at this strength.
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1229. weatherwonderer
1:08 AM GMT on August 18, 2007
Faethe tell that to Dr. Masters, I'm not being political, it has simply been made a political issue. What it is, is what it is... I,m just defending his position, nothing more. I agree to stop though, it is not the primary issue of this blog.





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1228. Metallica1990
1:13 AM GMT on August 18, 2007
Posted By: Xion at 1:12 AM GMT on August 18, 2007.

CI# /Pressure/ Vmax
5.7 / 958.0mb/107.2kt

Up .1 again.


just asking but were do you find that info can i have a link
1226. tharsheblow
1:05 AM GMT on August 18, 2007
One thing I believe I observed in contrasting the current Tropical Cyclone Heat potential in the Gulf and comparing it with what it was around the time of Katrina is it appears the warm eddy has shifted closer to the coast of LA. I would think thusly if a storm happened to make a beeline for the LA coast at a sufficient clip it might not weaken as much prior to landfall. A scary thought, I might be off base.
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1225. cormit
1:12 AM GMT on August 18, 2007
The recon is going back through, so far up to 111 knots at 15.04N, 65.15W...will know more in 10 minutes when it completes its pass.
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1224. WildHorseDesertTx
8:12 PM CDT on August 17, 2007
My comment about global warming was sarcasm..... sorry! LOL
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1223. 53rdWeatherRECON
1:13 AM GMT on August 18, 2007
http://www.ssd.noaa.gov/goes/flt/t1/rb-l.jpg
THIS IS GOING TO BREAK WILMA'S RECORDS.
The pressure measured in Wilma, 882 mb, is currently the lowest recorded pressure for a tropical cyclone the Atlantic Basin, as well as the lowest pressure for any cyclone measured in the Western Hemisphere. At its peak intensity, the eye of Wilma was about 3 miles (5 km) in diameter, the smallest known eye of an Atlantic hurricane.[1]
In a 30 hour period, the pressure dropped from 982 mbar to the record-low of 882 mbar, while the winds increased to 185 mph (300 km/h).
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1221. littlefish
1:11 AM GMT on August 18, 2007
Skye- looks to me like the ULL is what will get squished if it doesn't move soon. Of course, that may give it a chance to interact with Dean maybe. If it is still around to any extent in a few days.
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1220. tampahurricane
1:10 AM GMT on August 18, 2007
the track is going to shift more to the north in the morning.
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1219. Xion
1:11 AM GMT on August 18, 2007
CI# /Pressure/ Vmax
5.7 / 958.0mb/107.2kt


Up .1 again.

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1217. KnowYourRole
9:10 PM EDT on August 17, 2007
Posted By: SaBenDa at 9:07 PM EDT on August 17, 2007.
Using my graphics, a ruler, via the PR radar..Dead on W...


you don't need a ruler to see that=)
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1216. Metallica1990
1:10 AM GMT on August 18, 2007
can we not talk about global warming this is about dean
1215. CrazyTech
1:10 AM GMT on August 18, 2007
I know it's early, but a Cat. 5 right up towards Houston is a very scary thought right now. The GDFL isn't perfect, but that's not something I like to see.
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1214. StuccoMan
8:10 PM CDT on August 17, 2007
This is a small compact storm like dennis was.Do not believe the hype.Look how close it got to barbados and LOL
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1213. thelmores
1:06 AM GMT on August 18, 2007
If I hear one more thing about global warming, I think my head may explode!
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1211. extreme236
1:09 AM GMT on August 18, 2007
navy has dean with 120kt winds
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1209. WildHorseDesertTx
8:07 PM CDT on August 17, 2007
Re: KEEPEROFTHEGATE

I anybody else going to be happy when school starts back up?

oooooopsss, I mean Dean sure does look bad, and I am sure it is only because of Global Warming (tm)
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1208. Relix
1:08 AM GMT on August 18, 2007
Meeeh, so far only a quick event of rain. Gusts are around 20MPH, nothing too impressive here in PR. I don't know the south... I heard the winds are near 40MPH down there. But here... it hasn't been anything "great" so far (I wanted rains and at least a nice showing of winds).
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1207. SaBenDa
1:07 AM GMT on August 18, 2007
Using my graphics, a ruler, via the PR radar..Dead on W...
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1206. atmoaggie
12:59 AM GMT on August 18, 2007
++++++++++++++++++++++++++++++++++++++++
What does warmer water do to developing storms? Weaken or strengthen?

What happened to an 800-year-old coral reef in the Carib back in 2005? Unprecedented warm waters killed it.

There are many, many factors in creating a major hurricane, but common sense dictates that we might get more major storms if there's more warm water.


Did you read the link? Global warming also increases shear and I think most everyone here knows what that does, I need not insult anyone and ask if that results in a stronger or weaker storm. Chris Landsea and Pat Fitzpatrick (another PhD hurricane meteorologist in support) both studied under Bill Gray. These two have written books refuting the CNNscience/AlGore-type reports.
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1205. Tazmanian
6:06 PM PDT on August 17, 2007
all i am saying is



WOOOOOOOOOW EEEEEEEEEEEEK WOOOOOOOOOOW EEEEEEEEEEK WOOOOOOOOOW EEEEEEEEEEEEK WOOOOOOOOOW EEEEEEEEEEEK WOOOOOOW
Member Since: May 21, 2006 Posts: 5089 Comments: 114055
1204. Xion
1:07 AM GMT on August 18, 2007
Has anyone seen the latest GFDL? It calls for a cat. 5 super-hurricane with 195 mph winds bearing down on Houston. We hope this doesn't happen, but I think it's a possibility. How would this happen? First, the ULL needs to shift into a position where Dean can support that northwesterly track. Then, he would have to avoid all land and move over the areas of high TCHP and 90 degree SSTs. If that happens, then watch out Gulf Coast. You may be in for a Tip-like storm.

You mean 175 mph. The NHC never puts it above that until post-analysis. :p
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1203. txhuntgal
1:07 AM GMT on August 18, 2007
"Folks here in Houston are indeed becoming a bit tense -- the network of electronic signs along the major Houston freeways are flashing a message stating that a major hurricane is entering the Gulf and advises us to keep our gas tanks filled! With the Rita evacuation fiasco still fresh in our memories, many of my friends say they will NOT evacuate, no matter what the city officials say."

TexasWeatherNut, that is good to hear from my end. I am in Huntsville and still have nightmares of Rita and the contraflow nightmare! We are still the first designated exit from the contraflow. Will be gassing up tomorrow as well as getting water, batteries, canned food. I don't plan on waiting til the last moment.

To the hobbyists here, I have enjoyed reading the chatter and will continue to do so....excellent thoughts and forecasts here. I am trying not to be overly concerned about Dean as anything can happen. Look at Rita, predicted to come straight at Galveston/Houston and then made just enough of a turn to avoid a dead on strike.

Keep up the good work!
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1202. howarjo1943
1:00 AM GMT on August 18, 2007
The global warming moonies are back. I told a friend earlier "Algore is practically salivating right now over Dean and the heat wave across the east the last couple of weeks." Big Al's gonna ride this heat wave all the way to the white house. Yeagghhhhhh!!
Seriously, who do you trust, Landsea and William Gray who are experts in climatology and the tropics or a politician hiring scientists to further his agenda. Folks, all of the weather we are experiencing now has occurred in the past. Relax.
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1201. bappit
12:54 AM GMT on August 18, 2007
Cheyanne, the Rita "evacuation" was a fiasco indeed. Fortunately, the odds are against Dean maintaining a level 4 or 5 intensity all the way to landfall, especially that far north (further to travel). Remember Allen? It weakened significantly before landing at Brownsville. Even if it were an intense hurricane, severe damage would occur mostly near the right eye wall. Conditions would have to be just so for it to destroy your house in Baytown--not that it could not happen, but other events are probably more likely to destroy your house.

I was amazed at the Rita panic. People bolted before a warning was ever issued!
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1200. tampahurricane
1:05 AM GMT on August 18, 2007
also if the storm keeps up a fast forward speed it would go more north.
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1198. MikeOhio
1:04 AM GMT on August 18, 2007
For all we know, this amount of Cat 5s recently are part of a cycle. It could be global warming, it could be that we, as humans, have only been accurately measuring Hurricanes for what 70 years? A bit more than that?

Anyway, it's absolutely USELESS (not to mention classless) to debate it right now as there is nothing anyone can do except prepare and hope and pray that those in the areas that will be affected come through it alive.

I don't know where Dean will end up, I can only hope that it doesn't affect too many people. It appears that Jamaica will get hit and hit hard.
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1197. coffeecrusader
1:06 AM GMT on August 18, 2007
The wave in the Eastern Atlantic is looking pretty impressive tonight. It will probably be the next one to watch.
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1196. JPV
1:06 AM GMT on August 18, 2007
Posted By: KnowYourRole

I would listen to your local emergency management folks before listening to anyone on this blog. Just my two cents.


Yeah, they did so well during Katrina.
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1195. NOWCAST
1:05 AM GMT on August 18, 2007
lol to think back in the 70's they were talking about global cooling... It's a cycle.
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1193. whipster
7:06 PM CST on August 17, 2007
Hugging the 15 is what I see
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1192. philliesrock
9:02 PM EDT on August 17, 2007
Has anyone seen the latest GFDL? It calls for a cat. 5 super-hurricane with 195 mph winds bearing down on Houston. We hope this doesn't happen, but I think it's a possibility. How would this happen? First, the ULL needs to shift into a position where Dean can support that northwesterly track. Then, he would have to avoid all land and move over the areas of high TCHP and 90 degree SSTs. If that happens, then watch out Gulf Coast. You may be in for a Tip-like storm.
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1191. KEEPEROFTHEGATE (Mod)
12:57 AM GMT on August 18, 2007
and h2pv the ice will all but be gone at the n pole very soon sooner than anyone will expect the edvince is there we are just dening its presence albert eiesten once said there is only 2 infinate things in exsistance the universe and human stupity
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1189. moonlightcowboy
1:03 AM GMT on August 18, 2007
foofi, I don't think that's gonna happen, really! Dean is moving west, the trough is further west, it'll follow behind it with the steering currents. The high is building, moving east to join up with the Atl high. It stays southwards. This is not even a Texas storm IMH ignorant O. Nothing to bring it north now.

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1188. SWFLdrob
1:04 AM GMT on August 18, 2007
dean eye on san juan radar


Link
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1187. jetpixx
1:04 AM GMT on August 18, 2007
Well, people are finally getting what they wanted...a massive, destructive hurricane. I am glad that Florida appears to be dodging this one, as I like my air conditioning and cold beer. Good luck to our friends down in Haiti, especially, as well as Jamaica and the Caymans...not that it means much, but I am pulling for you! That thing is a buzzsaw.
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1186. KnowYourRole
9:03 PM EDT on August 17, 2007
Posted By: weatherguru at 8:59 PM EDT on August 17, 2007.
last couple of frames has him making a jog to the NW


what loops are you looking at? I see nothing moving NW.
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1185. Metallica1990
1:04 AM GMT on August 18, 2007
Posted By: paulfrmpasschristian at 1:04 AM GMT on August 18, 2007.

mettalica - sorry;sick minds think alike

I would like to throw him in the trunk of a car and drive around middle America...we could spell a word with the tracking a make history.:)


ROTFLMAO oh thats funny

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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.