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

Categories: Climate Change

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1501. bappit 18. elokuuta 2007 klo 02:07 (GMT)
Galveston looks like it always did to me. Dean is days away if it even comes close. Member Since: 18.05.2006 Posts: 3 Comments: 4381

1502. StormJunkie 18. elokuuta 2007 klo 02:07 (GMT)
lol LF, I am so wore out from that java issue I am just not with it. Take a java loop away from a stormjunkie and it is like beating him in the head with a bat! Member Since: 17.08.2005 Posts: 26 Comments: 15218

1503. afs 18. elokuuta 2007 klo 02:07 (GMT)
This is starting to look bad. Member Since: 28.08.2005 Posts: 0 Comments: 23

1504. Drakoen 18. elokuuta 2007 klo 02:07 (GMT)
17/2345 UTC 14.9N 65.1W T6.0/6.0 DEAN -- Atlantic Ocean Member Since: 28.10.2006 Posts: 57 Comments: 29010

1505. kev22 18. elokuuta 2007 klo 02:07 (GMT)
I just thought I'd throw in my 2 cents. Intensity forecasts are notoriously innacurate. This thing might well make Category Five. It might also unexpectedly weaken to a 2 or 3. Let's just sit back, see what track it takes at what strength, and comment from there. It would save alot of bandwidth. In the meantime, let's all agree to hope for the best.

1506. FatPenguin 18. elokuuta 2007 klo 02:07 (GMT)
Posted By: WPBHurricane05 at 2:05 AM GMT on August 18, 2007. FYI Strongest Atlantic storm on record for August was Allen (1980) at 899mb with winds at 190mph. I remember that one. A big high pressure system and drought in Texas ate that storm up before it made landfall. They go by pressure. The strongest Atlantic storm is Wilma (2005) with 882mb. ++++++++++++++++++++++++++++++++++++++ I was talking about strongest for the month of August. Member Since: 13.08.2007 Posts: 0 Comments: 307

1507. Metallica1990 18. elokuuta 2007 klo 02:08 (GMT)
Posted By: nolesjeff at 2:07 AM GMT on August 18, 2007. Posted By: WPBHurricane05 at 2:05 AM GMT on August 18, 2007. FYI Strongest Atlantic storm on record for August was Allen (1980) at 899mb with winds at 190mph. I remember that one. A big high pressure system and drought in Texas ate that storm up before it made landfall. They go by pressure. The strongest Atlantic storm is Wilma (2005) with 882mb. Wilma was september, wasnt it? October

1508. floridafisherman 18. elokuuta 2007 klo 02:08 (GMT)
wilma was an oct storm Member Since: 28.08.2005 Posts: 0 Comments: 514

1509. WPBHurricane05 18. elokuuta 2007 klo 02:08 (GMT)
Wilma was september, wasnt it? Missed the August part, but no Wilma was October. Member Since: 31.07.2006 Posts: 56 Comments: 7929

1510. nolesjeff 18. elokuuta 2007 klo 02:08 (GMT)
Thanks metallica and everyone else Member Since: 20.06.2006 Posts: 9 Comments: 1391

1511. HurricaneDean2007 18. elokuuta 2007 klo 02:08 (GMT)
It will become a Five, weaken back down to Three or Four, then become a Five again and cross the Yucatan Channel between Yucatan and Cuba and then hit texas.

1512. StormJunkie 18. elokuuta 2007 klo 02:09 (GMT)
Welcome CTodd :~) 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, Ukmet, GFDL & 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. Member Since: 17.08.2005 Posts: 26 Comments: 15218

1513. weathersp 18. elokuuta 2007 klo 02:09 (GMT)
Oh I think it is rapidly intensifying... Member Since: 14.01.2007 Posts: 17 Comments: 4112

1514. kmanislander 18. elokuuta 2007 klo 02:09 (GMT)
Drak Very interesting. There was a small ULL that was tracking W with Dean from about 36 hrs ago just to Dean's SW. Perhaps this is exerting some steering. I wonder if the models will pick up on this with the next set of runs as Dean will soon be below the curve Member Since: 19.08.2006 Posts: 0 Comments: 14939

1515. DG136 18. elokuuta 2007 klo 02:09 (GMT)
I could be wrong, but 14.9N is the opposite of direction of north. The longer it treks west, the better it looks for the US

1516. KnowYourRole 18. elokuuta 2007 klo 02:10 (GMT)
Posted By: StormJunkie at 10:07 PM EDT on August 17, 2007. lol LF, I am so wore out from that java issue I am just not with it. Take a java loop away from a stormjunkie and it is like beating him in the head with a bat! I'm still having problems with mine, although not as frequently.

1517. nola70119 18. elokuuta 2007 klo 02:10 (GMT)
Looks like a slight move back to North in the last frames.... Member Since: 16.06.2006 Posts: 0 Comments: 1535

1518. WeafhermanNimmy 18. elokuuta 2007 klo 02:10 (GMT)
Hurricane Dean is now a potent cat 4 hurricane with winds up to 145 mph. Member Since: 1.11.2003 Posts: 4 Comments: 234

1519. HurricaneDean2007 18. elokuuta 2007 klo 02:10 (GMT)
that ULL is drifting westward VERY slowly...

1520. bappit 18. elokuuta 2007 klo 02:10 (GMT)
At least Dean strengthened after passing through the Antilles. Member Since: 18.05.2006 Posts: 3 Comments: 4381

1521. littlefish 18. elokuuta 2007 klo 02:10 (GMT)
LOL SJ- love that technology huh! I was just mentioning the southerly low because of the amount of convection being pulled in by Dean from down there. Looks like there may be some interacting. The other thing I'm watching is LB way out at 15N 32W approx (moving so probably not there anymore exactly). No convection but a bit of circltn. The other thought on the S low is that the models changed to south in last run even though the north ULL ahdn't hardly budged. Had me scratch my head until I saw the south inflows or unless the ULL north gets squished into oblivion by highs.

1522. Drakoen 18. elokuuta 2007 klo 02:11 (GMT)
Most of the models have Dean hiting Mexico. Member Since: 28.10.2006 Posts: 57 Comments: 29010

1523. rodrigo0 18. elokuuta 2007 klo 02:11 (GMT)
I work for the media here in Mexico and I have access to photowires... I will upload more pictures to Flickr but only for friends. Add me as a friend in flickr to see more HQ pictures in the future. http://www.flickr.com/photos/ebrmx/

1524. KnowYourRole 18. elokuuta 2007 klo 02:11 (GMT)
Posted By: kev22 at 10:07 PM EDT on August 17, 2007. I just thought I'd throw in my 2 cents. Intensity forecasts are notoriously innacurate. This thing might well make Category Five. It might also unexpectedly weaken to a 2 or 3. Let's just sit back, see what track it takes at what strength, and comment from there. It would save alot of bandwidth. In the meantime, let's all agree to hope for the best. There is nothing to prevent it from strengthening in the near term. It's going to reach Cat 5 status. How long it maintains it may be a question.

1525. comtrader 18. elokuuta 2007 klo 02:11 (GMT)
littlefish, my guess is that without the low off of florida, dean would have no chance to make it into the gulf. it all hinges on whether or not that low gets close enough in time and space to pull dean northwards. d

1526. bluehaze27 18. elokuuta 2007 klo 02:12 (GMT)
The ull was supposed to have dissipated by now. Member Since: 26.03.2007 Posts: 0 Comments: 794

1527. littlefish 18. elokuuta 2007 klo 02:12 (GMT)
kman, that was waht I wa ssaying- the south Low may be what is shifting the track south, not the North high. Hope you're ready for a ride out there! Yikes...

1528. Xion 18. elokuuta 2007 klo 02:12 (GMT)
No eyewall replacement cycle in site. I hope the HH have plenty of fuel or science will cry. CI# /Pressure/ Vmax 6.1 / 948.2mb/117.4kt Another .2 in a 1/2 hour period!!!!!!!!!!!!!!!!! Member Since: 29.08.2006 Posts: 0 Comments: 726

1529. WPBHurricane05 18. elokuuta 2007 klo 02:12 (GMT)
If the NHC goes with the CONU, they will shift the track south. Member Since: 31.07.2006 Posts: 56 Comments: 7929

1530. Metallica1990 18. elokuuta 2007 klo 02:12 (GMT)
I'm thinking 5 by next advisory

1531. Caymanite 18. elokuuta 2007 klo 02:12 (GMT)
Good evening all. I have just completed ALL perparations for Dean and returned home to see that it was for good cause. Only a miracle can keep us from getting sig effect from him now. Seems like a lot of folks were planning to party tonite and leave preps for tomorrow and I hope that they will get them completed as it looks now like we will be severely impacted. Will stay in touch as best as possible during the event and definitely up until power is lost. Having just recovered completely from Ivan, this really is not a joke. Member Since: 9.12.2005 Posts: 0 Comments: 315

1532. kmanislander 18. elokuuta 2007 klo 02:12 (GMT)
Hi Littlefish Scary times in the Caribbean my friend. The price we pay for living in the tropics. Dean has a small but intense core of very high winds. If that condition maintains we can survive a near miss of about 60 miles without too much damage. Gotta hope ! Member Since: 19.08.2006 Posts: 0 Comments: 14939

1533. MelbourneTom 18. elokuuta 2007 klo 02:13 (GMT)
UW - CIMSS ADVANCED DVORAK TECHNIQUE ADT-Version 7.2.1 Tropical Cyclone Intensity Algorithm ----- Current Analysis ----- Date : 18 AUG 2007 Time : 011500 UTC Lat : 14:54:17 N Lon : 65:28:09 W CI# /Pressure/ Vmax 6.1 / 948.2mb/117.4kt 6hr-Avg T# 3hr-Avg T# Adj T# Raw T# 5.8 6.1 6.2 6.7 Member Since: 2.06.2007 Posts: 0 Comments: 600

1534. kev22 18. elokuuta 2007 klo 02:13 (GMT)
There is nothing to prevent it from strengthening in the near term. It's going to reach Cat 5 status. How long it maintains it may be a question. I think it will reach five too. But those mountains can do a number pretty quickly if it gets too close.

1535. Drakoen 18. elokuuta 2007 klo 02:14 (GMT)
The ULL level low over the Bahamas has picked up some speed. may not have any affect on dean. Member Since: 28.10.2006 Posts: 57 Comments: 29010

1536. WPBHurricane05 18. elokuuta 2007 klo 02:14 (GMT)
Hey kman, did you leave your island? Member Since: 31.07.2006 Posts: 56 Comments: 7929

1537. Wundermobay 18. elokuuta 2007 klo 02:14 (GMT)
Hello all,

1538. SWFLdrob 18. elokuuta 2007 klo 02:14 (GMT)
Posted By: nola70119 at 2:10 AM GMT on August 18, 2007. Looks like a slight move back to North in the last frames.... I don't see it. Link to what you're looking at?

1539. weatherguru 18. elokuuta 2007 klo 02:14 (GMT)
everyone...My local station just said that winds on dean are now at 145...this just came in from the planes....im in ft myers fl

1540. Tazmanian 18. elokuuta 2007 klo 02:14 (GMT)
Posted By: Drakoen at 7:11 PM PDT on August 17, 2007. Most of the models have Dean hiting Mexico. thats old Member Since: 21.05.2006 Posts: 5088 Comments: 111355

1541. Baybuddy 18. elokuuta 2007 klo 02:15 (GMT)
I wonder how the hurricane hunter's plane ever leaves the ground with the weight of all those big brass balls? Member Since: 26.06.2006 Posts: 0 Comments: 1115

1542. nolesjeff 18. elokuuta 2007 klo 02:15 (GMT)
Posted By: Caymanite at 2:12 AM GMT on August 18, 2007. Good evening all. I have just completed ALL perparations for Dean and returned home to see that it was for good cause. Only a miracle can keep us from getting sig effect from him now. Seems like a lot of folks were planning to party tonite and leave preps for tomorrow and I hope that they will get them completed as it looks now like we will be severely impacted. Will stay in touch as best as possible during the event and definitely up until power is lost. Having just recovered completely from Ivan, this really is not a joke. You are in our prayers. take care Member Since: 20.06.2006 Posts: 9 Comments: 1391

1543. moonlightcowboy 18. elokuuta 2007 klo 02:15 (GMT)
You're prolly right, Drakoen! kev22, what mountains? There's isn't a pebble in sight of Jamaica! Member Since: 9.07.2006 Posts: 179 Comments: 28121

1544. atmoaggie 18. elokuuta 2007 klo 02:15 (GMT)
All attempts to obfuscate and deceive have to ignore the reality of 2007 by trying to revise history of yesteryear. The same science which predicted that Sepat would intensify to 170 knots peak gusts (which did happen) has predicted DEAN would be cat 4 by it's present position. This same science makes it possible for you to send your blah-blah-blah at the speed of light through fiber optics, bounced off satellites, relayed by microwaves and conducted on copper wires. That same science SEE GREENHOUSE GASES AND INFRARED EMISSIONS. That's what you are looking at: Greenhouse gases and Infrared Emissions. It's science and it trumps your history lessons. This is your US NAVY picture of greenhouse gases by infrared emissions -- something wrong about your eyes? Sorry, everyone else, button pushed. One storm, no... one season, no ... one decade of storms reflects nothing about climate. The science behind fluid dynamical modeling of a TC is not related to guesstimating central pressure of a storm with only 2 questionable ship obs and 1 coastal observation. By the way, don't put too much faith in to seeing greenhouse gases or infrared emissions in a satellite image. High clouds, haze, sun glint, etc. all affect the image. Dealing with the way those affect satellite measurements over the ocean is what I do in processing images for SST, chlorophyll, net primary productivity, and turbidity every day. If you were actually seeing CO2 and its emissions, then you would see it in every satellite image you saw, especially at night. CO2 has an atmospheric lifetime of well over 100 years for the average molecule. It would not go away in the next satellite image, or ever for that matter. I will admit that changing the extremely complex chemical balances on Earth is dangerous business with POTENTIAL pitfalls and many unknowns. My history lessons were limited to American history mandated by the state of Texas. Your assumptions about my background are way off base. I'll have you know that I hold a BS in Atmospheric Science and MS in Atmospheric Chemistry from Texas A&M. No one wants to "revise the history of yesteryear" only accept that the historical information has its limitations. Thank you for your concern about my eyes, they are getting better. Member Since: 16.08.2007 Posts: 6 Comments: 12461

1545. tharsheblow 18. elokuuta 2007 klo 02:16 (GMT)
Looks like a Cat 5 to me, beautiful presentation.

1546. franck 18. elokuuta 2007 klo 02:16 (GMT)
Yes, it seem these storms are more easily torn apart when they are wound tight. The Yucatan should do a number on Dean...if that's where he goes in. Member Since: 30.08.2005 Posts: 0 Comments: 1150

1547. KnowYourRole 18. elokuuta 2007 klo 02:16 (GMT)
Posted By: SWFLdrob at 10:14 PM EDT on August 17, 2007. Posted By: nola70119 at 2:10 AM GMT on August 18, 2007. Looks like a slight move back to North in the last frames.... I don't see it. Link to what you're looking at? I don't see it, nor have I seen it since I got on here around 8:00pm EST.

1549. afs 18. elokuuta 2007 klo 02:16 (GMT)
Caymanite... How are you guys set for reinforced concrete shelters? I'd personally be avoiding riding this Dean out in a wood frame building. Member Since: 28.08.2005 Posts: 0 Comments: 23

1550. 7544 18. elokuuta 2007 klo 02:17 (GMT)
the ull thats was over fla is digging south to cuba dean has to catch up with soon Member Since: 6.05.2007 Posts: 0 Comments: 5925

1551. WPBHurricane05 18. elokuuta 2007 klo 02:17 (GMT)
Looking at the latest models looks like the US is in good shape. Member Since: 31.07.2006 Posts: 56 Comments: 7929

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