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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1285. bappit
1:22 AM GMT on August 18, 2007
I like the global warming posts because they cool off some of the hype about Dean.
Member Since: May 18, 2006 Posts: 10 Comments: 6061
1284. atmoaggie
1:21 AM GMT on August 18, 2007
sorry, now I'm done...regardless of whatever/whoever rebuts
Member Since: August 16, 2007 Posts: 6 Comments: 12463
1281. catjojo
1:22 AM GMT on August 18, 2007
Thanks Chuckie... I was going from memory on the interstate but I knew I still had a link to it.
Member Since: July 11, 2006 Posts: 0 Comments: 1
1280. WPBHurricane05
9:22 PM EDT on August 17, 2007
Eastern time is currently in daylight savings time, AST is the same as EDT. Next advisory is at 11pm.
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1279. atmoaggie
1:18 AM GMT on August 18, 2007
Posted By: bappit at 1:15 AM GMT on August 18, 2007.

A rebuttal does not refute another's argument. There is ample evidence that climate change is occurring.


Like what? Melting ice we didn't measure until within the last 30 to 40 years? Airport temperature measurents made in different places with different instruments all while the grass/trees around them turned into asphalt and they measured a 1 degree C change in 100 years? That is within the error, standard deviation, and instrument biases for the last 100 years too. Sure something is happening, the ice is melting, so? I expect that it has melted before.
Member Since: August 16, 2007 Posts: 6 Comments: 12463
1278. cormit
1:13 AM GMT on August 18, 2007
Recon just passing throgh shows max flight level wind of 136 kt and lowest pressure of 935.8 mb.
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1277. KEEPEROFTHEGATE (Mod)
1:07 AM GMT on August 18, 2007
track mark
15,67
16.1,72 C5/H/D
16.5,75
17.2,77 C5/H/D
17.2,79
18,81 C4/H/D
19,62
21,85
21,86 C3/H/D
23,88
25,90 C4/H/D
27,91
29,92 C5/H/D
29,93
29,94 C4/H/D
30,95 FINAL DESINATION MOVIN INLAND
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1276. kimpy
1:19 AM GMT on August 18, 2007
this was discovered in the Library of Congress:

A headline in the Nov. 2, 1922 edition of The Washington Post reads: "Arctic Ocean Getting Warm; Seals Vanish and Icebergs Melt." This was one of several articles from this era about "global warming". Also noted - Four of the 10 hottest years in the U.S. were actually in the 1930s, with 1934 the hottest of all.
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1273. KnowYourRole
9:20 PM EDT on August 17, 2007
Posted By: bekroweather at 9:19 PM EDT on August 17, 2007.
Dean seems to be moving due west the last couple of hours, which has brought him south of the forecasted track.


Difference between yesterday and today is that it seems to be moving almost directly west now, rather than wobbling around WNW.
1272. MikeOhio
1:20 AM GMT on August 18, 2007
Posted By: fldude99 at 1:18 AM GMT on August 18, 2007.

If this isn't global warming I don't know what is


What's the point of bringing this up now?
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1271. Metallica1990
1:20 AM GMT on August 18, 2007
yep swflboy i was thanks again :)
1270. PensacolaBuoy
8:14 PM CDT on August 17, 2007
StuccoMan, I think your Dennis comparison is an excellent one. Compact storm... big damage over relatively small area. I don't fully understand the dynamics of what makes a storm blossom into the Gargantuan storm size that Katrina and Rita were. Heat content of the gulf? I guess we'll see. If it stays small, we're in much better shape. Size really matters when it comes to major hurricanes!
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1269. 53rdWeatherRECON
1:21 AM GMT on August 18, 2007
THIS IS WHAT DEAN WILL LOOK LIKE IN THE MORNING. THIS IS WILMA WHEN SHE BROKE ALL THOSE RECORDS.
http://en.wikivisual.com/images/f/fa/Wilma1315z-051019-1kg12.jpg
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1268. catjojo
1:20 AM GMT on August 18, 2007
Xion, try these as well.

Link

Link
Member Since: July 11, 2006 Posts: 0 Comments: 1
1267. TheCaneWhisperer
1:19 AM GMT on August 18, 2007
Yes SaBen! 11pm eastern
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1266. Masquer08er
1:15 AM GMT on August 18, 2007
People write theses on the subject of global warming without convincing the other side. No one will change their opinion due to a post here.
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1263. ChuckieTodd
8:20 PM CDT on August 17, 2007
Actually, catjojo, that was Highway 90 not Interstate 10. Either way, it was a barge on a highway. not something I want to go through again.
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1262. Bobbyweather
9:19 PM EDT on August 17, 2007
Dean has t# of 6.0 and has winds of Flossie!
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1261. bekroweather
1:08 AM GMT on August 18, 2007
Dean seems to be moving due west the last couple of hours, which has brought him south of the forecasted track.
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1260. tallahasseecyclone
1:14 AM GMT on August 18, 2007
Alexandra Steele is to Maria Shriver as Dean is to Wilma...Only time will tell if either of the previous will overcome the latter.
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1259. bappit
1:18 AM GMT on August 18, 2007
Cool post CajunSubbie!
Member Since: May 18, 2006 Posts: 10 Comments: 6061
1258. eaglesrock
9:19 PM EDT on August 17, 2007
Dean is rapidly intensifying!

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1257. Metallica1990
1:19 AM GMT on August 18, 2007
enough global warming stuff back to dean
1255. nolesjeff
1:17 AM GMT on August 18, 2007
Posted By: bappit at 1:15 AM GMT on August 18, 2007.

A rebuttal does not refute another's argument. There is ample evidence that climate change is occurring

Then why did you choose to rebut? there is ample evidence there isnt! so how about we drop it
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1254. 7544
1:17 AM GMT on August 18, 2007
just a question i know when canes get this big they might stall if dean does stalls before 75 west . what will it mean
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1253. WildHorseDesertTx
8:17 PM CDT on August 17, 2007
Posted By: whipster at 8:15 PM CDT on August 17, 2007.
Going outside now to start my Prius. I hope I'm not too late!

(sarcasm)

Yeah and when the Ice Age (tm) starts up it's gonna be your fault too!
(sarcasm again)
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1252. Metallica1990
1:17 AM GMT on August 18, 2007
Thanks
1251. fldude99
1:16 AM GMT on August 18, 2007
If this isn't global warming I don't know what is
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1250. SaBenDa
1:16 AM GMT on August 18, 2007
Gang,

Next major update @ 11PM Eastern..Is the correct???

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1249. CajunSubbie
1:17 AM GMT on August 18, 2007
I love Rita's Path Projections.. It makes you feel confident in the models/NHC :(

http://www.nhc.noaa.gov/archive/2005/RITA_graphics.shtml
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1248. tampahurricane
1:15 AM GMT on August 18, 2007
because the storm should keep around the same forward speed while the ULL seems to be slowing that means that they will interact before the modles say there going to.
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1247. tharsheblow
1:16 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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1245. Metallica1990
1:16 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
1244. cirrocumulus
1:11 AM GMT on August 18, 2007
Eyewallreplacement: It does appear on the latest water vapor loops that Dean will soon be pulled a little farther north under the influence of the ULL. The ULL this season has been stagnant and less likely to budge. The models did not factor that in. This season is slightly different and we could see something change in the next twelve hours on track forecasts. I still think Texas is possible but so is Louisiana now that Dean is about to be slightly influenced by the remote edges of the ULL as portrayed by clouds over Jamaica moving north and northeast!
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1243. Cheyanne
1:03 AM GMT on August 18, 2007
Posted By: coffeecrusader at 1:02 AM GMT on August 18, 2007.

GFDL has shifted a little further south on the 18z run. If that track holds true Houston is in the line of fire.

Are you trying to give me a stroke? LOL We're already soaked! I lived here my entire life..32 years and have NEVER seen so much rain during the summer (except Allison). lol Yesterday was HORRIBLE. I'm scared, my kids are terrified and my husband is just pissed. lol Think I can pray it away?????
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1242. whipster
7:13 PM CST on August 17, 2007
Going outside now to start my Prius. I hope I'm not too late!

(sarcasm)
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1241. catjojo
1:07 AM GMT on August 18, 2007
My comparison to New Orleans was the terrible death and destruction of homes and lives, a good example of what Faethe is referring to is the tremendous force of the surge..... In comparison did you see the photo of the Casino Barge in Gulfport, Ms. that was planted onto interstate 10 ? check this link for some photosLink
Member Since: July 11, 2006 Posts: 0 Comments: 1
1240. JLPR
1:14 AM GMT on Agosto 18, 2007
getting decent winds here in Carolina,PR
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1239. bappit
1:09 AM GMT on August 18, 2007
A rebuttal does not refute another's argument. There is ample evidence that climate change is occurring.
Member Since: May 18, 2006 Posts: 10 Comments: 6061
1238. howarjo1943
1:10 AM GMT on August 18, 2007
I saw where someone said earlier that a small cat 5 is not too bad. That guy needs to ask those who experienced Camille, Andrew, and Charley how bad a minicane can be.
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1237. nolesjeff
1:13 AM GMT on August 18, 2007
Posted By: howarjo1943 at 1:08 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.

Exactly, you can twist it anyway you want, cold front moving through the northeast now. iceage coming
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1236. obxrox
1:09 AM GMT on August 18, 2007
say the current GFDL track comes to pass with landfall in TX and/or LA...

in addition to the natural and human devastation, we'll have a big reduction and/or damage to gas and oil refining infrastructure. stir that up with the growing credit crunch and continued softening of the mortgage and equity markets, and what do we have?.....a big CF and it won't be pretty. i'd prefer that the GFDL remain the outlier and ultimately incorrect model.
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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.