Dr. Jeff Masters' WunderBlog

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

Posted 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

Categories: Climate Change

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3301. sporteguy03 2:30 PM GMT on August 18, 2007
Drak, Coordinates 11N 30W Member Since: July 7, 2005 Posts: 0 Comments: 4824

3302. KYhomeboy 2:31 PM GMT on August 18, 2007
Yea we do have caves...but sadly not enough for 54,000 people! lol

3303. labsr4me 2:30 PM GMT on August 18, 2007
Posted By: StormJunkie at 2:29 PM GMT on August 18, 2007. labs, I think that image may be stretching the blog for anyone in IE, any chance the width could be reduced? 640 width is always a good number for all browsers and screen resolutions. sorry

3305. youngw3ath3rman 2:32 PM GMT on August 18, 2007
Is there anything coming off of Africa that looks interesting? Member Since: September 17, 2006 Posts: 0 Comments: 81

3307. CJ5 2:33 PM GMT on August 18, 2007
Posted By: StormJunkie at 9:18 AM CDT on August 18, 2007. I know CJ! Dean is a mystery for know as far as Mex and the Conus go. SW told me yesterday that he was looking to 2 pints to help give his guidance. Jamaica and the Yucatan...I think those are good points to watch as well. I agree. Contrasted against a storm like 04Jeanne or even Katrina, the dynamics with Dean seem almost as simple as they could be with any storm but even that is difficult. It makes you appreciate the complexity of nature. Member Since: July 4, 2007 Posts: 0 Comments: 1709

3308. Drakoen 2:33 PM GMT on August 18, 2007
Just looks like convection associated with a tropical wave and the ITCZ... Member Since: October 28, 2006 Posts: 57 Comments: 29010

3309. bajelayman2 2:34 PM GMT on August 18, 2007
lowerbamagirl: Not an Invest yet. Way it looks, I agree, probably will be soon. Here is the Navy site. Keep checking every few hours and you will know when an Invest: http://www.nrlmry.navy.mil/tc_pages/tc_home.html Member Since: August 13, 2007 Posts: 0 Comments: 468

3310. welshcayman 2:34 PM GMT on August 18, 2007
Posted By: raindancer at 2:28 PM GMT on August 18, 2007. ScoobaSteve - The Cayman people tend to fare hurricanes quite well. There are series of natural caves on the islands, which have in times past been used for shelter... Actually the caves are only on the sister island Cayman Brac and although they were once used as shelter the Brac now has modern shelters. Most of us just stay in our homes. All new construction on the island (and there was a lot after Ivan) is built to Dade County standards. Most of the condo developments are built from solid concrete, have hurricane rated roofs, and plenty of inside rooms (bathrooms, walk in closets) that have no windows so they can be used as 'safe' rooms if things really hit the fan. For those in lesser quality housing there are excellent shelters here and the infrastructure is simply amazing here. During the peak of Hurricane Ivan we were still able to talk to others using our cell phones. Not many countries around the world have phone systems that would continue to operate during and after a direct Cat 5 hit I am guessing.

3311. Stormchaser2007 2:34 PM GMT on August 18, 2007
All i have to say is WOW!! Member Since: June 9, 2007 Posts: 4 Comments: 15243

3312. noleman 2:34 PM GMT on August 18, 2007
Looks like the track of Dean needs to be tweaked this morning . Im in PC, FL and I hope this just means bigger waves and not a trend.

3313. ScoobaSteve 2:34 PM GMT on August 18, 2007
ScoobaSteve - The Cayman people tend to fare hurricanes quite well. There are series of natural caves on the islands, which have in times past been used for shelter... raindancer: Thanks for your answer. Where are the caves you speak of? I've been there 9 times on dive trips and was unaware of them. Good to know they have a place to take shelter.

3314. weatherwonderer 2:35 PM GMT on August 18, 2007
Neponset, correct it would just zoom straight up North if weren't for the blocking high pressure ridge. Sorry if my over simplification caused you problems. I would be surprise given what I have been seeing that Dean passes South of Jamaica but since waves of high pressure or weakness thereof could put it N or S of the island. It is unlikely that huge deviations would occur but If I were in Eastern Cuba I would be paying very close attention right now. Member Since: July 16, 2005 Posts: 0 Comments: 167

3315. weatherboykris 2:35 PM GMT on August 18, 2007
They've made the NE turn...heading towards the eye. Member Since: December 9, 2006 Posts: 125 Comments: 11343

3316. extreme236 2:35 PM GMT on August 18, 2007
Posted By: Drakoen at 2:33 PM GMT on August 18, 2007. Just looks like convection associated with a tropical wave and the ITCZ... Yep, but it is something to watch because the gfs and cmc develop it Member Since: August 2, 2007 Posts: 19 Comments: 19234

3317. TerraNova 2:35 PM GMT on August 18, 2007
Im sorry to say this but right now the truth is that Dean is at a borderline Category 5 (it'll likely be classified as a 5 soon) and Jamaica and the Caymans will get hammered whether it hits as a 5 or 4. People are going to get hurt. Member Since: July 30, 2007 Posts: 76 Comments: 4058

3318. Pedibrainpa 2:35 PM GMT on August 18, 2007
Why is there such a discrepancy in the forecasted path between the 3D GFDL model and the GFDL model on the "computer models" page on wunderground? Thanks! Amy

3321. weatherboykris 2:37 PM GMT on August 18, 2007
We'll see if it's a Cat 5 when the plane gets to the eye... Member Since: December 9, 2006 Posts: 125 Comments: 11343

3322. nola70119 2:36 PM GMT on August 18, 2007
Dean's been moving almost NW for eight hours....three hours prior to that it was moving due W. Member Since: June 16, 2006 Posts: 0 Comments: 1535

3324. StormJunkie 2:38 PM GMT on August 18, 2007
No problem labs, I run FireFox, but I do remember how frustrating it used to be when I ran IE. Thanks again ☺ And one more request for all... I think that when new folks sign up they automatically show up hidden if you have your filter set to "show below average". If you set your filter this way then you know who those folks are and then it is easier to give them +'s to get them out of the "below average" setting. I have seen some great posts that are showing up as below average just because the folks are new. Anywho, back to your regularly scheduled Dean... Member Since: August 17, 2005 Posts: 26 Comments: 15218

3325. weatherboykris 2:38 PM GMT on August 18, 2007
leftovers....you need to consider that by the time the radar beam gets to the eye,it's many miles up in the air. Member Since: December 9, 2006 Posts: 125 Comments: 11343

3326. raindancer 2:38 PM GMT on August 18, 2007
welsh - yup / concur... I suspect Jamaica could be in much worse shape, though an eye passing just to the north of the island would be much better news. Member Since: September 14, 2001 Posts: 0 Comments: 79

3327. weatherboykris 2:38 PM GMT on August 18, 2007
I don't use my filter SJ. Member Since: December 9, 2006 Posts: 125 Comments: 11343

3328. Drakoen 2:39 PM GMT on August 18, 2007
Posted By: extreme236 at 2:35 PM GMT on August 18, 2007. Posted By: Drakoen at 2:33 PM GMT on August 18, 2007. Just looks like convection associated with a tropical wave and the ITCZ... Yep, but it is something to watch because the gfs and cmc develop it If more computer models develop the wave then i will be interested. Member Since: October 28, 2006 Posts: 57 Comments: 29010

3329. KennerLA70065 2:40 PM GMT on August 18, 2007
We're all anxiously watching the storm here in New Orleans. For the sake of the Flood Control system, we're all hoping that if it makes landfall in the area, that the eye is at least to the west of Grand Isle and Port Fouchon. This keeps the peak surge area on the west side of the mississippi and limits the amount of water that will get pushed into the lake to more manageable levels. Having relatives on Grand Cayman that weathered Ivan (they're new house lost its roof and they had to run, through the storm, to the old house on their property that extended family was living in) I can only hope that the storm either passes them on the north side, or, very far to the south. Whatever happens, I wish luck to those in Dean's pass and safety to the flight crews that are drilling holes in Dean's clouds right now to help us be safe. Member Since: August 17, 2007 Posts: 0 Comments: 1

3330. noleman 2:41 PM GMT on August 18, 2007
I wasnt too concerned last night. Now with this new movement and the fact the ULL looks to have some pull on Dean I think its time for gas and water.

3331. StormJunkie 2:41 PM GMT on August 18, 2007
Welcome Pedi ☺ I think due to the angle it is very hard to interpret track forecast from the 3d GFDL. Just my guess. Member Since: August 17, 2005 Posts: 26 Comments: 15218

3332. youngw3ath3rman 2:40 PM GMT on August 18, 2007
could someone send me the website to the models of the gfs, gfdl, nogas, and the rest of em Member Since: September 17, 2006 Posts: 0 Comments: 81

3333. Drakoen 2:41 PM GMT on August 18, 2007
Member Since: October 28, 2006 Posts: 57 Comments: 29010

3335. stormhank 2:41 PM GMT on August 18, 2007
Dean isnt moving due west anymore? wonder if that will change path projections on models later today? Member Since: September 8, 2005 Posts: 0 Comments: 1375

3336. sporteguy03 2:42 PM GMT on August 18, 2007
Drak, The GFDL shows that convection heading towards FL in the loop. Member Since: July 7, 2005 Posts: 0 Comments: 4824

3337. StormJunkie 2:42 PM GMT on August 18, 2007
youngwx- Info on model pages and imagery pages... Quick Links Select the first link in the model section. This is the FSU Experimental model page. For all models except for the GFDL and HWRF, I set the field to 850mb vorticity to view potential genesis or track and size of tropical systems. Select animate then scroll right and page through the model run. The surface maps are also good to look at as the 850mb map will sometimes show features which are not at the surface. The GFS, GFDL, and HWRF run four times a day; 00z, 06z, 12z, and 18z. The 00z runs usually come out around 2am Est, the 06z around 8am Est, the 12z around 2pm Est, and the 18z around 8pm Est. The CMC, Nogaps and mm5fsu only run at 00z and 12z. The FSU model site can depict the strength of a system which is something you don�t get with the line models. There is a great link that shows the mb to ft comparison in the learning section. Also the GFDL and HWRF only work with the field set to Surface Pressure and they only run for active storms. The NWS NCEP model page contains the long range GFS and the NAM as well as several other models. The South Florida Water Management page has a nice spaghetti plot showing most all of the models together. The Weather Underground Tropical section also has some nice spaghetti plots of several of the major models. The GFDL track can usually be found here before it can be seen on the other sites. Select the first link in the imagery section. This is the Global Hydrology and Climate Data Center. There are several rows of maps. The first column is visible imagery. The second infrared and the third is water vapor. The first row is the W Atl view and the frames update most often and also has the highest max zoom. The next active row down does not have the same zoom level and the images update every 30 minutes. The Carib row uses a different color scale on the IR imagery and shows more whites and reds with weaker convection. Select the map you wish t o view. Below the image that comes up are options that will allow to change size, number of frames, zoom level, quality, etc. There is also a box that on SOME maps will allow you to turn on lat/lon lines. Set these parameters the way you choose and then click the area on the map you wish to view. Make sure you select the animate feature if you wish to see a loop. Allow loop to load and enjoy. This site releases images prior to any other site as far as I know. Member Since: August 17, 2005 Posts: 26 Comments: 15218

3338. Miamiweather 2:42 PM GMT on August 18, 2007
could someone post a link to stormw synopsis

3339. raindancer 2:43 PM GMT on August 18, 2007
Just to clarify... NONE of the models call for a due west movement of Dean. ALL call for WNW movement - which is exactly what Dean is doing... Member Since: September 14, 2001 Posts: 0 Comments: 79

3340. weatherwonderer 2:43 PM GMT on August 18, 2007
I concur Kenner, that would the end of NO if Dean kept its strength and Made landfall near it. Highly unlikely but not impossible. Member Since: July 16, 2005 Posts: 0 Comments: 167

3341. Drakoen 2:43 PM GMT on August 18, 2007
Posted By: sporteguy03 at 2:42 PM GMT on August 18, 2007. Drak, The GFDL shows that convection heading towards FL in the loop. time frame is not with the other models. Member Since: October 28, 2006 Posts: 57 Comments: 29010

3342. NOWCAST 2:43 PM GMT on August 18, 2007
Dean is not moving due west anymore NHC just said that.. 11:00 update should be interesting. Member Since: August 11, 2007 Posts: 0 Comments: 10

3343. DonnaGalveston 2:43 PM GMT on August 18, 2007
Hello, how are things looking for Galveston this morning?

3344. jake436 2:43 PM GMT on August 18, 2007
Dean is about 4-5 days away from any possible US landfall. That said, I can't help but remember the forecast for Katrina 4-5 days out. Every model, AND the NHC, TWC, and all the "experts" had it going to Apalachicola, FL. I guess what I'm trying to say is this:There's no need in panicking along the northern GOM, but keep an eye on things. On Monday, we'll all have a better idea of what's going to happen...BE PREPARED! Member Since: August 31, 2006 Posts: 0 Comments: 271

3345. youngw3ath3rman 2:43 PM GMT on August 18, 2007
thanks Member Since: September 17, 2006 Posts: 0 Comments: 81

3346. pcshell 2:44 PM GMT on August 18, 2007
ok i have been watchin for days as people keep saying its going north as usual with any storm but i have never seen forward motion down to 18 mph with dean before he has always been just cruisin through this whole time not that i am saying this is whats happening now but in the past when storms slow down in the carribean its so they can turn which makes me nervous praying for everyone in the path of this monster

3347. StormJunkie 2:45 PM GMT on August 18, 2007
SW analysis That link can also be found on that Quick Links link I just posted. As well as the Dr's blog, imagery, models, marine data, wind data, preparedness info, and some other great info. Basically, it contains the links most often posted in here. Member Since: August 17, 2005 Posts: 26 Comments: 15218

3348. OUFan919 2:45 PM GMT on August 18, 2007
Deans pressure is down a mb to 929, according to the weather channel on there website Member Since: July 31, 2007 Posts: 0 Comments: 329

3349. nola70119 2:45 PM GMT on August 18, 2007
I'd say right now its toward the right part of the NHC cone.....so yeah, maybe certainly we need to keep paying attention here in LA. I think the real test comes tommorow night though.... Member Since: June 16, 2006 Posts: 0 Comments: 1535

3351. Neponset 2:47 PM GMT on August 18, 2007
weatherwonder No problem, I don't have much to contribute here and I thought it would be fun to use a word that is fundamental to the forces at work here. M. Coriolis said that bodies in motion in the northern hem. would curve to the right -not shoot straight for the pole.

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