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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1635. nolasoci
2:30 AM GMT on August 18, 2007
Good luck Jamacian Grl.. Please get to higher ground and stay very safe. If you can leave the island please do
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1634. atmoaggie
2:29 AM GMT on August 18, 2007
I suppose that particular Gore voter left, or maybe I simply shut him up.

Back to DEAN!

Look at this freakin wind field! (By way of CSU, thank you) The hurricane force wind area has really expanded!

Link
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1633. i12BNEi
2:27 AM GMT on August 18, 2007
Last few frames looks pretty bad to me.
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1631. ForecasterColby
2:29 AM GMT on August 18, 2007
You know, looking at the satellite, I'm suprised. Dean is well-organized, but not what I would expect from a Cat 4-5 storm. I mean, consider the incredible symmetry and deep convection of Katrina/Rita/Wilma/Gilbert/Sepat et al at their peaks. Dean's CDO is elongated and the banding has actually deteriorated a bit.
1630. Wundermobay
2:30 AM GMT on August 18, 2007
JamaicanGir where in the Island are you.
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1628. bappit
2:23 AM GMT on August 18, 2007
szqrn1: None of the models have taken the center of the storm to New Orleans or Mississippi since it intensified. Most of the models take it into Mexico. Not much chance of it going that far east and north it would seem. The NHC forecast is shown here.
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1627. JamaicanGir
9:26 PM EST on August 17, 2007
Good evening all

wacthing, waiting and praying from here in jamaica. not really looking good for us here.

Thanks for all those who have us in thier prayers
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1626. kmanislander
2:28 AM GMT on August 18, 2007
yea Caymanite, I have a new driver and want to take some money off the usual group. Looks like that will have to wait LOL
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1625. carolina90s
2:29 AM GMT on August 18, 2007
Hi,new here. Lived in the eastern coastal plain of NC throughout the 90s...got very personal with quite a few hurricanes. For Guerra and Bappit...if this hits Texas I think it will be very reminiscent of the Dennis Floyd 1-2 punch to NC...Horrible flooding well inland. Atmoaggie..Mountaintop glaciers melting all over the world revealing artifacts 1000s of years old???
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1624. Drakoen
2:28 AM GMT on August 18, 2007
I'm out for night...later
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1623. Daveg
2:25 AM GMT on August 18, 2007
One thing I noticed about this blog, is earlier (just today) the models where trending North, and a lot of folks started screaming about how LA was doomed and all that. Now the models have shifted a bit south again, and there is all this screaming about folks in Mexico being doomed.

My point is, can we have some leveled headedness (not a word, but sounds good) about this whole thing? Everyone should watch Dean real close, as the models could easily shift north again. Deep Breaths. :)
Member Since: September 23, 2005 Posts: 0 Comments: 426
1622. Drakoen
2:27 AM GMT on August 18, 2007
THe GFS has shifted further to the west and south than before. U.S. looks Safe for now.
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1621. AnthonyJKenn
2:22 AM GMT on August 18, 2007
So far, szgrn, it's looking more and more like NOLA and MS are more in the clear, at least from a direct hit. But remain cautious and be ready just in case things change. Even a NoTex or CenTex hit could bring flooding and squally weather as far east as where you are, and there is the real possibility of costal flooding...though you would be far from the bigger winds.

But for the most part, things are looking a whole lot better than it was this morning. At least for now.


Anthony
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1619. kmanislander
2:25 AM GMT on August 18, 2007
StuccoMan

Not from the inside my friend, the outside !
You would be surprised how many here kept the ocean out with silicone and duct tape.
As long as a door or window does not break you can in fact keep water out of a home surrounded by water by sealing dryer vents,caulking around doors and windows etc. I would rather spend a week removing silicone than 6 months rebuilding a flooded home
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1617. nolasoci
2:26 AM GMT on August 18, 2007
SQZ...

NOLA is not completely out of the woods. I know the Louisiana State Police have been cleaning the ContraFlow lanes out. I just say be prepared.
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1616. Skyepony (Mod)
2:20 AM GMT on August 18, 2007
Dropsonde to the eye.

Dropsonde Observations
Storm Name: DEAN (04L)
Mission Number: 05
Flight ID: AF302
Observation Number: 11
Time: 0100Z
Latitude: 14.8N
Longitude: 65.5W
#NAME?
Surface: 937 mb; Temp: 80F; Dewpt: 78F; NW (310) @ 8 mph
1000mb height: Unavailable
925mb height: 381 ft; Temp: 78F; Dewpt: 77F; NW (310) @ 9 mph
850mb height: 2831 ft; Temp: 78F; Dewpt: 67F; W (280) @ 15 mph
700mb height: 11703 ft; Temp: 69F; Dewpt: 47F; WNW (300) @ 17 mph
500mb height: Unavailable
400mb height: Unavailable
300mb height: Unavailable
250mb height: Unavailable
200mb height: Unavailable
EYE SPL 1483N06549W 0119 MBL WND 30008 AEV 00000 DLM WND 29
509 937737 WL150 31008 082 =

937mb winds: NW (310) @ 8 mph
850mb winds: W (280) @ 15 mph
775mb winds: NW (315) @ 13 mph
746mb winds: WNW (285) @ 12 mph
697mb winds: WNW (300) @ 18 mph
#VALUE!
Member Since: August 10, 2005 Posts: 161 Comments: 37300
1615. Wundermobay
2:24 AM GMT on August 18, 2007
It looks like a grave situation as the best shelters here in Jamaica are schools, and are built to winds up to cat.3
so it seems not even our SHELTERS will be safe from Dean.
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1614. StormJunkie
2:24 AM GMT on August 18, 2007
Ok y'all, I am going to take a nap before the 2am model runs come out. See if I can't get that Java bat out of my head!

In the mean time, here is some really cool MIMIC imagery from Dean starting to strengthen! The next MIMIC run should be really interesting!

Winds and waves starting to come up pressure starting to fall. 42059
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1613. extreme236
2:27 AM GMT on August 18, 2007
is it just me or is dean looking a tad smaller
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1611. StuccoMan
9:23 PM CDT on August 17, 2007
Posted By: Caymanite at 9:21 PM CDT on August 17, 2007.
Hi Afs, the standard of housing here is EXTRMELY high and I will be staying in a very strong concrete home with shutters and on high ground. Being a very nautical community MOST people have a real understanding of these systems but lots of expats from elsewhere that think its an excuse to party. The Govt is very good at making preps and emegency plan is one of the best anywhere.


I have seen allot of concrete structures wash out from underneath and collapse.Remember a structure is only as good as its foundation.make sure you are far away from any kind of wash out area and at least 60 feet above sea level.
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1610. Drakoen
2:26 AM GMT on August 18, 2007
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1609. weathersp
10:24 PM EDT on August 17, 2007
Posted By: MelbourneTom at 10:24 PM EDT on August 17, 2007.

Is there a link to support the 140+ MPH winds?


Dean 142mph
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1608. bluehaze27
9:25 PM EST on August 17, 2007
melbournetom here is the special statement from NHC Link
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1607. Metallica1990
2:25 AM GMT on August 18, 2007
theres got to be a spot of 155+ mph in there somwhere if not then this is a impressive looking cat 4
1606. strangesights
2:21 AM GMT on August 18, 2007
Many places could be at risk, points south of yucatan for example could have landfall too: Hondurus, Belize, Nicaraugua ... Prayers for all ... Hispanola ... Jamaica
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1605. drj27
2:25 AM GMT on August 18, 2007
so everyone here is the florida panhandle out of the woods now
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1604. extreme236
2:25 AM GMT on August 18, 2007
Posted By: MelbourneTom at 2:24 AM GMT on August 18, 2007.

Is there a link to support the 140+ MPH winds?


Yes, the national hurricane center site
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1602. Caymanite
2:25 AM GMT on August 18, 2007
Hey Kman I am done cause entire family including wife, kids, sisters, mom here this time. Hope you didnt have a plan for 18 holes tomorrow cause everything closed. LOL
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1600. Xion
2:23 AM GMT on August 18, 2007
dont they have a second plane they can send out

They didn't for Wilma I guess. They missed it's final (lowest pressure) burst of intensification).

If they were smart (had the resources) they would have another one en route as this plane runs low on fuel.
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1599. comtrader
2:20 AM GMT on August 18, 2007
littlefish
the ull is moving slowly south along the fla coast. the gfs prediction is that is crosses over the southern tip of fla and into the gulf. if it gets farther south than the southern tip of fla i'd say the odds of it catching dean go up significantly. the miss, according to the current solution is not by that much.
d
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1597. weatherwonderer
2:22 AM GMT on August 18, 2007
One thing I noticed about intensifying hurricanes at this level (cat 3 and above)is the size. They get smaller and just spin up tight. Dean is doing that now and from the looks of it, it isn't done yet.
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1596. moonlightcowboy
2:24 AM GMT on August 18, 2007
Have a good sleep, StormW. Thanks, ALWAYS!
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1595. BeenThereinMiami
2:24 AM GMT on August 18, 2007
NDBC Buoy due west of Dean

Link


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1594. kmanislander
2:23 AM GMT on August 18, 2007
WPBH

Right now I will take either N or S, just not a steady 275/280 degrees !
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1593. Prgal
2:23 AM GMT on August 18, 2007
Patriots, I think that the melting of the ice caps affects everyone.
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1592. MelbourneTom
2:23 AM GMT on August 18, 2007
Is there a link to support the 140+ MPH winds?
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1590. StuccoMan
9:20 PM CDT on August 17, 2007
Posted By: kmanislander at 9:20 PM CDT on August 17, 2007.
WPBH

No I will not be leaving. I am flying my wife and children out tomorrow afternoon. After I secure my home I will be leaving for a secure CAT5 purpose built bunker.

My home is only about 400 feet from the ocean and had 6 feet of salt water go through it in Ivan. Wasn't a lot of fun looking down your stair well watching all your possessions float out through the french doors !

This time the home will be virtually hermetically sealed with windows and doors siliconed etc. . The structure can handle CAT %winds and where I am the waves are not a problem but the surge is.

Don't worry, I am not going to play hero.


LOL at sealing a house with silicone from inside.Good luck with that.
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1589. Drakoen
2:23 AM GMT on August 18, 2007
Posted By: WPBHurricane05 at 2:23 AM GMT on August 18, 2007.

Stay safe kman.

As for the models, they seem to be shifting south.


yep.
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1587. Dan187
2:19 AM GMT on August 18, 2007
recon as of 10:20 is at 13.5 north, 65.38 west, flying east.
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1586. WPBHurricane05
10:22 PM EDT on August 17, 2007
Stay safe kman.

As for the models, they seem to be shifting south.
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About

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.