Dr. Jeff Masters' WunderBlog

Which model do you trust? And, Arctic sea ice reaches a record minimum

Posted by: Dr. Jeff Masters, 17. elokuuta 2007 klo 19:33 (GMT)

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

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251. sammo 17. elokuuta 2007 klo 20:49 (GMT)
I think it's interesting to note that Dean will graze (may already be in) Hebert box #1 - as a cat3, of course. Will be interesting to see where it goes... Member Since: 30.08.2006 Posts: 0 Comments: 149

252. DeepintheHearta 17. elokuuta 2007 klo 20:49 (GMT)
weatherboy, the GFDL's accuracy beats the #2 and #3 most accurate models by a grand total of 15 miles. there is little reason to suspect that it is significantly more accurate than the other solutions, virtually all of which plot an entirely different solution for the effects of the ULL. this doesn't mean GFDL is wrong, of course, but it is obviously an outlier at this point and should be treated as such. I guess we'll know more in 10 minutes.

253. CFL 17. elokuuta 2007 klo 20:49 (GMT)
new trackLink

254. Relix 17. elokuuta 2007 klo 20:49 (GMT)
Yup, I know they will be doing that at 8PM, they want to make sure of certain things I guess. And WTF... NHC says 15, but... are they reading the southernmost part of the eye of something? I don't know, I see it at around 15.2-15.3. Whatever... they are the ones with the experts. Member Since: 3.08.2006 Posts: 0 Comments: 2358

255. diabeticstorm 17. elokuuta 2007 klo 20:49 (GMT)
Well I'm not focusing on Florida anymore. You guys can wish all you want. That's just silly. And yes, I know Florida is a GOM state, but you know what I meant!!

256. weatherboyfsu 17. elokuuta 2007 klo 20:49 (GMT)
One more time!!!!!!! The bottom line is that Dean is expected to be a dangerous hurricane through the next several days...and all interests in the Caribbean Sea and the Gulf of Mexico should closely monitor the progress of Dean. Member Since: 17.07.2005 Posts: 0 Comments: 1025

257. sporteguy03 17. elokuuta 2007 klo 20:50 (GMT)
The steering pattern continues to be controlled by the high pressure system to the north of the hurricane and the mid to upper-level low over the southwestern Atlantic and Florida. Now they said it ULL controlling steering with High. Member Since: 7.07.2005 Posts: 0 Comments: 4824

258. snowboy 17. elokuuta 2007 klo 20:51 (GMT)
REPEATING THE 500 PM AST POSITION...15.0 N...64.5 W. MOVEMENT TOWARD...WEST NEAR 21 MPH. MAXIMUM SUSTAINED WINDS...125 MPH. MINIMUM CENTRAL PRESSURE...961 MB. Member Since: 21.09.2005 Posts: 10 Comments: 2546

259. Metallica1990 17. elokuuta 2007 klo 20:51 (GMT)
Posted By: diabeticstorm at 8:49 PM GMT on August 17, 2007. Well I'm not focusing on Florida anymore. You guys can wish all you want. That's just silly. And yes, I know Florida is a GOM state, but you know what I meant!! Dont focus on anything in the US yet its still too early to tell

260. Keys99 17. elokuuta 2007 klo 20:51 (GMT)
The NWS Key West site 4pm forcast discussion gives some insight as to what they think the ULL will do. just thie forcast though Member Since: 16.08.2007 Posts: 0 Comments: 132

262. C2News 17. elokuuta 2007 klo 20:52 (GMT)
Posted By: snowboy at 4:51 PM EDT on August 17, 2007. REPEATING THE 500 PM AST POSITION...15.0 N...64.5 W. MOVEMENT TOWARD...WEST NEAR 21 MPH. MAXIMUM SUSTAINED WINDS...125 MPH. MINIMUM CENTRAL PRESSURE...961 MB. So, that was the position close to an hour ago... Member Since: 17.07.2006 Posts: 73 Comments: 622

263. atmoaggie 17. elokuuta 2007 klo 20:52 (GMT)
check message, guygee Member Since: 16.08.2007 Posts: 6 Comments: 12461

264. MTJax 17. elokuuta 2007 klo 20:52 (GMT)
This image from the NECP should give a clear indication of the areas it could go. There are no certain paths 5 days out. The possible paths are in the image

265. thewebisode 17. elokuuta 2007 klo 20:52 (GMT)
Well I'm not focusing on Florida anymore. You guys can wish all you want. That's just silly. And yes, I know Florida is a GOM state, but you know what I meant!! Well, it's not so much a wish really, I mean even the NHC has Key West in the cone, and this is from an older track. With the trend of the storm riding the northern track of the forecast, it is most likely more of Florida will be included in the NHC cone sometime this weekend if not before. Member Since: 15.08.2007 Posts: 0 Comments: 6

266. StuccoMan 17. elokuuta 2007 klo 20:53 (GMT)
LOL these blogs continue to amaze me.Here is some good information.I have been tracking storms on the computer for almost 10 years and watching the models on allot of them.My past experience is If you are in the models track 6-7 days out.Than you are almost 100 percent guaranteed to not get this storm.I would be shocked if this storm hit Houston or Galveston and that is just straight up. All these people making claims that Florida and NO is 100 percent clear need your head examined.People look at where this storm is at. It is just now crossing into the Caribbean.It has 5 days to get to the Yucatan.Allot of weather patterns can greatly change and shoot this storm up the middle of the Gulf.The NHC does not give ceartian forecast past 5 days for a reason.there 3 day forecast are usually dead on and Texas is well beyond a 6-7 day landfall. Lets not be ignorant and say you know where this storm is going because no one knows for sure.Way to many clusters and disagreements in the models right now and NHC said yesterday the forecast was more ceartian than today.So much can change in 48 hrs and dean wont even be halfway thou the Caribbean. Texas wishcasters need to relax and just pay more attention to the 3- 4 day outlook and not the 6-7

267. PalmBeachWeatherBoy 17. elokuuta 2007 klo 20:53 (GMT)
what a suprise another track shift, damn jamaica is in for trouble Member Since: 30.08.2006 Posts: 1 Comments: 433

268. gsueagle07 17. elokuuta 2007 klo 20:53 (GMT)
Sounding more and more like a Yucatan and Mexico storm....and I believe tomorrow you will see the GFDL come back in line with all the other ones......

269. weatherboyfsu 17. elokuuta 2007 klo 20:53 (GMT)
and all interests in the Caribbean Sea and the Gulf of Mexico should closely monitor the progress of Dean. I believe someone already said that earlier today.......Hmmmmmmmmmm............. Who was that????????????? lol.......... Anybody giving any Million to One bets on it not hitting florida? Member Since: 17.07.2005 Posts: 0 Comments: 1025

270. whirlwind 17. elokuuta 2007 klo 20:53 (GMT)
This looks to be an exciting storm. Sorry for those that feel differently.... Dean WILL break record books..... Maybe take over #1 spot over Wilma for lowest pressure? Imagine if Dean reaches 180-200 mph?? forget Katrina....

271. StormJunkie 17. elokuuta 2007 klo 20:53 (GMT)
Afternoon all! Still working my dang java issue, but am very close to having it resolved soon!!! I do see Dean is growing to be a monster. Have missed so much today though...Arghh! See y'all in an hour or so Easily find preparedness info, forecast models, and imagery. These are the many links that are posted here time and time again. Quick Links Member Since: 17.08.2005 Posts: 26 Comments: 15218

272. Xion 17. elokuuta 2007 klo 20:54 (GMT)
Dean could break records. Just hope he breaks a very important record. Strongest storm ever that killed nobody. Be safe people,Dean looks like a mean beast. Too late. He already killed one person. :( But maybe he will beat Wilma (probably after an eyewall replacement) without hurting anybody in the process, just like Wilma did out there. :) Member Since: 29.08.2006 Posts: 0 Comments: 726

273. missippinumismatist 17. elokuuta 2007 klo 20:54 (GMT)
I'm not an expert, but I've watched enough of these things turn N as they pass Cuba that I will stock up tonight. I'm in South MS and I have a BAD feeling about this. Some swore RITA would hit the middle of TX until it knocked on LA's front door.

274. TX 17. elokuuta 2007 klo 20:54 (GMT)
some are in the discussion to blast others who are freaked out...the discussion is alive only because of concerned/freaked out people. fear is a precursor for motivation and that is what keeps some people going while for others it drags them down, and those who it drags down arent the ones who are adding anything worthwhile to the discussion...ill keep my worries, continue to lose sleep, monitor tell-tale signs all-around, and maintain my insatiable appetite for weather-related discussion. Those who agree will continue to dismiss polarized and erroneous dissenters of a mass consensus who are rationaly ignorant towards opined science-skeptics. i too am skeptical, but not here to discourage people and their postings. For the depth and breadth of all you contributors surpasses anything ive ever been a part of on a consistent and altruistic basis.

275. leftyy420 17. elokuuta 2007 klo 20:55 (GMT)
weatherboyfsu us landfall u still looking to chase. i am debating going to the gulf coast but might if i can find a partner Member Since: 24.08.2005 Posts: 35 Comments: 1987

276. gsueagle07 17. elokuuta 2007 klo 20:55 (GMT)
Hmmmm I thought Gilbert had the lowest measured pressure in the Atlantic...Wilma????

278. Unlabled 17. elokuuta 2007 klo 20:55 (GMT)
I really think that we will know where this is going between 80N-85N Member Since: 26.08.2005 Posts: 0 Comments: 12

279. HurricaneDean2007 17. elokuuta 2007 klo 20:55 (GMT)
I am starting to doubt that Dean will even hit the Yucatan at all.Probably will pass between Yucatan and Cuba.

280. SquirrelRJ 17. elokuuta 2007 klo 20:55 (GMT)
Ill take a bet it doesn't hit FL.

281. ecflawthr 17. elokuuta 2007 klo 20:56 (GMT)
rita is a good example. they evacuated houston and she went north Member Since: 4.09.2006 Posts: 1 Comments: 201

282. Unlabled 17. elokuuta 2007 klo 20:55 (GMT)
errr make that west Member Since: 26.08.2005 Posts: 0 Comments: 12

283. Xion 17. elokuuta 2007 klo 20:56 (GMT)
This looks to be an exciting storm. Sorry for those that feel differently.... Dean WILL break record books..... Maybe take over #1 spot over Wilma for lowest pressure? Imagine if Dean reaches 180-200 mph?? forget Katrina.... Unfortunately they can't have a plane in their 24/7, so they might miss the lowest pressure. Just like they did with Wilma which must have bottomed out at least a little below 882 mb. Member Since: 29.08.2006 Posts: 0 Comments: 726

285. SquirrelRJ 17. elokuuta 2007 klo 20:57 (GMT)
Wilma at 882mb is the record low in the atlantic.

286. sammo 17. elokuuta 2007 klo 20:57 (GMT)
Posted By: MichaelSTL at 8:51 PM GMT on August 17, 2007. think it's interesting to note that Dean will graze (may already be in) Hebert box #1 Remember - it is 9 out of 10 storms that hit Florida passed through it, not that 9 out of 10 storms that passed though it hit Florida. Completely different meanings. Right on MichaelSTL - exactly my point. Member Since: 30.08.2006 Posts: 0 Comments: 149

287. pcolabaygm 17. elokuuta 2007 klo 20:57 (GMT)
Coastal Water Temperatures Place: Temperature: Pensacola, FL 93 �F / 33.9 �C Panama City Beach, FL 89 �F / 31.7 �C Panhandle H20 temps are higher than I've ever seen. I do not think we will worry too much at this time about Dean. I will be hoping for a couple of early season cold fronts in September though to cool down our waters. Member Since: 13.10.2003 Posts: 0 Comments: 0

288. OUFan919 17. elokuuta 2007 klo 20:57 (GMT)
What the heck is wrong with the NHC?? I see it at 15.3N right now, they have it at 15N. They have it at 15.5N in 12 hours. No way. It will be close to 16.0N in 12 hours at this pace. Member Since: 31.07.2007 Posts: 0 Comments: 329

289. TX 17. elokuuta 2007 klo 20:57 (GMT)
Dean may have already killed several people indirectly...media-fueled awareness could be inducing heart-attacks for those with heart conditions that flip the channels

290. Xion 17. elokuuta 2007 klo 20:57 (GMT)
Hmmmm I thought Gilbert had the lowest measured pressure in the Atlantic...Wilma???? You're new to this hurricane stuff, aren't you? Wilma beat Gilbert with 882 mb compared to 888 mb. Member Since: 29.08.2006 Posts: 0 Comments: 726

291. littlefish 17. elokuuta 2007 klo 20:57 (GMT)
Hello SJ- looks like the 15N and 64.5W coords are just slightly north of forecast 15N and 65.5 W...

292. paulfrmpasschristian 17. elokuuta 2007 klo 20:57 (GMT)
interesting post on the putor models Dr. I do hope the NHC is right on this one. I don't feel like gutting another house

293. Metallica1990 17. elokuuta 2007 klo 20:57 (GMT)
Posted By: SquirrelRJ at 8:55 PM GMT on August 17, 2007. Ill take a bet it doesn't hit FL. betting on landfalls is foolish!

295. A4Guy 17. elokuuta 2007 klo 21:00 (GMT)
He hit 15N...and the last few frams of the sat loop have him traveling due W along 15N. I don't see a northward component...which is what the NHC needs to see - cosnsitent motion - before adjsuting tracks...especially when the modes are in such good agreement near term. Member Since: 23.06.2006 Posts: 0 Comments: 646

296. Dropsonde 17. elokuuta 2007 klo 21:01 (GMT)
The eye is clearing. (WV image) Look for a bomb out tonight and a clear eye by 5 a.m. Member Since: 22.08.2006 Posts: 10 Comments: 414

297. Relix 17. elokuuta 2007 klo 21:01 (GMT)
It is going WNW. Baah... Dean is such an awesome system. Still... i see it still going WNW, any of the most experienced members here might give me some insight? I see it at 15.4 right now. Member Since: 3.08.2006 Posts: 0 Comments: 2358

298. MTJax 17. elokuuta 2007 klo 21:01 (GMT)
THE GFDL SHOWS A MORE NORTHWESTERLY TRACK ACROSS EXTREME WESTERN CUBA AND THE CENTRAL GULF OF MEXICO. WHILE THIS SOLUTION IS OUTSIDE THE OVERALL MODEL GUIDANCE ENVELOPE...IT CAN NOT BE RULE OUT COMPLETELY SINCE THIS MODEL HAS AN EXCELLENT FORECAST TRACK HISTORY. THE OFFICIAL TRACK FORECAST IS AN UPDATE OF THE PREVIOUS ONE AND FOLLOWS THE MODEL CONSENSUS. THE BOTTOM LINE IS THAT DEAN IS EXPECTED TO BE A DANGEROUS HURRICANE THROUGH THE NEXT SEVERAL DAYS...AND ALL INTERESTS IN THE CARIBBEAN SEA AND THE GULF OF MEXICO SHOULD CLOSELY MONITOR THE PROGRESS OF DEAN. $$ FORECASTER AVILA

299. Melagoo 17. elokuuta 2007 klo 21:02 (GMT)
Sepat Member Since: 31.07.2006 Posts: 19 Comments: 1510

300. StormJunkie 17. elokuuta 2007 klo 21:02 (GMT)
Afternoon all! Still working my dang java issue, but am very close to having it resolved soon!!! I do see Dean is growing to be a monster. Have missed so much today though...Arghh! See y'all in an hour or so Easily find preparedness info, forecast models, and imagery. These are the many links that are posted here time and time again. Quick Links Member Since: 17.08.2005 Posts: 26 Comments: 15218

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