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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1584. Drakoen
2:22 AM GMT on August 18, 2007
Very defined eye.
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1583. mikester
2:20 AM GMT on August 18, 2007
Man good thing typhoon sepat went through eye wall replacement causing it to weaken alot. If it had not Taiwan would not be taken so easy by the force of this storm. I am still waiting for dean to become as big as sepat was. Sepat was an impressive storm.
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1582. Prgal
2:22 AM GMT on August 18, 2007
Yes, we just have a nice breezy night here. I love it!
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1581. guerra2100
9:19 PM CDT on August 17, 2007
Bappit, ever heard of the Galveston storm or the Corpus Christi storm, that for decades were the nation's deadliest natural disasters?

Neither was a slow-moving tropical storm.

Having personally lived through nine hurricanes, beginning with Beulah, and I posted what I did and very specifically warned of a "Katrina-level disaster" because I know the Rio Grande Valley -- on both sides of the border -- well enough to realize that it's evacuation infrastructure has grown ill suited to handle the massive relocation that will be required, also on both sides.

Everyone has heard of Brownsville and Matamoros, both of which are among their respective countries' fastest growing urban areas. But few Americans realize that, for example, more than 2 million people live within a 50-mile radius of McAllen. And that's up the road a ways.

And as was pointed out earlier, unlike what happened when Bret came in the late 1990s during Texas' second-worst drought, thereby causing little damage, South Texas soils are pretty soaked already.

If Erin caused massive flooding, a big storm shortly thereafter can only be worse.
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1579. szqrn1
2:19 AM GMT on August 18, 2007
OK gonna try again...I am only a nurse...addicted to following storm but know very little. Does anyone who knows a whole lot think there is a chance this will hit New Orleans or MS? (the latter being my home)
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1578. Metallica1990
2:21 AM GMT on August 18, 2007
Posted By: Xion at 2:21 AM GMT on August 18, 2007.

If you missed Wilma's intensification, then this is your second chance.

Except it won't even near Wilma's intensity. Especially since HH can't stay there forever.


dont they have a second plane they can send out
1577. Drakoen
2:20 AM GMT on August 18, 2007
Posted By: littlefish at 2:19 AM GMT on August 18, 2007.

Drak, that N ULL aint moving very fast. But Dean looks to be slowing a bit. And the hammer above the ULL's head is gonna squish it if it doesn't move (the jet pulling down from up north some dryer air).


I am talking about the ULL over the Florida, not the one to the NNE of Dean. That one is moving out as the models predicted.
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1576. kmanislander
2:20 AM GMT on August 18, 2007
Caymanite

I know you will be ready. I will be at CUC from Sunday afternoon and will have my cell with me. Stay in touch
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1575. KnowYourRole
10:20 PM EDT on August 17, 2007
Posted By: kmanislander at 10:20 PM EDT 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.


good luck kmanislander. I hope you are able to get you and your family out safely and there is no damage to your home.
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1574. littlefish
2:19 AM GMT on August 18, 2007
Uh-oh wife is calling. Time to cook dinner (BBQ). Will tyr to come back in a bit. Ya LB is around 15N 32W, a tiny puff of convection over its NE side I believe. Not sure if it still ahs COC.
1573. JLPR
2:18 AM GMT on Agosto 18, 2007
i get what happend here in PR the slight change to the south passing through the 15N instead of 15.5 has the convection south from the forecast.
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1572. Caymanite
2:16 AM GMT on August 18, 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.
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1571. Xion
2:20 AM GMT on August 18, 2007
If you missed Wilma's intensification, then this is your second chance.

Except it won't even near Wilma's intensity. Especially since HH can't stay there forever.
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1570. Daveg
2:20 AM GMT on August 18, 2007
Posted By: WPBHurricane05 at 2:17 AM GMT on August 18, 2007.

Looking at the latest models looks like the US is in good shape.


Probably a bit to early to declare that yet, and even if we are safe, it means someone else is not. We should always remember that.

One thing for sure, he looks impressive on Sat, and is head due west. Link
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1569. moonlightcowboy
2:17 AM GMT on August 18, 2007
Yeah, knew someone was gonna say "Blue Mountains" ....been there! That doesn't help any of them that live there with a Cat 5 landfalling! It might slightly help the Caymans, but Dean would only strengthen after hitting the high TCHP in on the west end of Jamaica! Still be a Cat 5 after it rips through Jamaica, Caymans on it's way to the Yucatan! Look at a TCHP chart!
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1568. TayTay
2:15 AM GMT on August 18, 2007
Cat. 4 now. Looks like Dean might have that shot at being a category 5. Still has a ragged looking eye. I don't think there's an eyewall replacement anytime soon.
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1567. kmanislander
2:14 AM GMT on August 18, 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 5 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.
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1566. kev22
2:15 AM GMT on August 18, 2007


The mountains of Jamaica. I think some go to 5 or 6 thousand feet. That can cause alot of disruption if Dean crosses it.
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1565. bluehaze27
2:19 AM GMT on August 18, 2007
Dr. Masters need to update the winds on his chart Dean 145.
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1564. weatherguru
2:19 AM GMT on August 18, 2007
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
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1563. littlefish
2:15 AM GMT on August 18, 2007
Drak, that N ULL aint moving very fast. But Dean looks to be slowing a bit. And the hammer above the ULL's head is gonna squish it if it doesn't move (the jet pulling down from up north some dryer air).
1562. StormJunkie
2:17 AM GMT on August 18, 2007
The other thing I'm watching is LB

Speaking of scratching my head, LB? It has been bothering me all day. I am telling ya, this java thing threw me off today!
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1561. weathersp
10:16 PM EDT on August 17, 2007
I FOUND IT 142 MPH!!!!

Storm DEAN: Observed By Air Force #302
Storm #04 in Atlantic Ocean1
Maximum Flight Level Winds Were 138KT (158.7mph 255.6km/h) In NE Quadrant At 01:12:20 Z
Estimated Max Surface Winds 124.2KT (142.8mph 230.0km/h) *
Date/Time of Recon Report: Friday, August 17, 2007 9:15:00 PM (Sat, 18 Aug 2007 01:15:00 UTC)
Position of the center: 14 51' N 065 29' W (14.9N 65.5W) [See Map]
Surface Winds Were Estimated At: 111KT (127.65MPH 205.6km/h)
Estimated Surface Winds Were Measured 011nm (12.65miles) From Center At Bearing 044
Maximum Flight Level Winds Near Center Were 138KT (158.7mph 255.6km/h) From 136
Maximum Flight Level Winds Were Measured 011nm (12.6 miles) From Center At Bearing 044
Minimum pressure: 937 mb (27.67in)
Eye Wall Was Characterized As Being: CLOSED
Eye Form Was Characterized As Being , 15
Center Fix Established Using: Penetration Radar Wind Pressure Temperature
Center Fix Established At Level(s): 700mb
Navigational Accuracy Measured At 0.02nm
Meteorological Accuracy Measured At 2nm
* = Estimated Surface Winds are assumed 90% of Max Flight Level Winds
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1560. ForecasterColby
2:18 AM GMT on August 18, 2007
Just got back, good lord. This could surpass Wilma on a longer-term intensification, although not the absurd speed of it. I fully expect Cat 5 tonight.
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1557. bappit
2:18 AM GMT on August 18, 2007
I like the disclaimer on the plot of various model tracks.

This plot does not display official storm information. Use for informational purposes only. DO NOT USE FOR LIFE AND DEATH DECISIONS!
Member Since: May 18, 2006 Posts: 10 Comments: 6011
1556. Metallica1990
2:14 AM GMT on August 18, 2007
unless its shifted its track or slowed down at 11 it should be near

14.9N
65.96W

i just want to see how good i am at forecasting lol
1555. floridafisherman
2:16 AM GMT on August 18, 2007
hi guru. i live in lehigh and is watching dean closely
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1554. Tropicnerd13
2:16 AM GMT on August 18, 2007
dean now with 145 according to twc
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1553. KnowYourRole
10:16 PM EDT on August 17, 2007
Posted By: Caymanite at 10:12 PM EDT on August 17, 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.


good luck to you and your family.
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1552. nolesjeff
2:16 AM GMT on August 18, 2007
Posted By: moonlightcowboy at 2:15 AM GMT on August 18, 2007.

You're prolly right, Drakoen!

kev22, what mountains? There's isn't a pebble in sight of Jamaica!

Blue mountains, 6000 feet
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1551. WPBHurricane05
10:16 PM EDT on August 17, 2007
Looking at the latest models looks like the US is in good shape.
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1550. 7544
2:16 AM GMT on August 18, 2007
the ull thats was over fla is digging south to cuba dean has to catch up with soon
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1549. afs
2:16 AM GMT on August 18, 2007
Caymanite...

How are you guys set for reinforced concrete shelters? I'd personally be avoiding riding this Dean out in a wood frame building.
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1547. KnowYourRole
10:15 PM EDT on August 17, 2007
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.
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1546. franck
2:11 AM GMT on August 18, 2007
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.
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1545. tharsheblow
2:14 AM GMT on August 18, 2007
Looks like a Cat 5 to me, beautiful presentation.

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1544. atmoaggie
2:14 AM GMT on August 18, 2007
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: August 16, 2007 Posts: 6 Comments: 12461
1543. moonlightcowboy
2:14 AM GMT on August 18, 2007
You're prolly right, Drakoen!

kev22, what mountains? There's isn't a pebble in sight of Jamaica!
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1542. nolesjeff
2:12 AM GMT on August 18, 2007
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
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1541. Baybuddy
2:12 AM GMT on August 18, 2007
I wonder how the hurricane hunter's plane ever leaves the ground with the weight of all those big brass balls?
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1540. Tazmanian
7:12 PM PDT on August 17, 2007
Posted By: Drakoen at 7:11 PM PDT on August 17, 2007.

Most of the models have Dean hiting Mexico.


thats old
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1539. weatherguru
2:13 AM GMT on August 18, 2007
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
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1538. SWFLdrob
2:13 AM GMT on August 18, 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?
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1537. Wundermobay
2:13 AM GMT on August 18, 2007
Hello all,
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1536. WPBHurricane05
10:13 PM EDT on August 17, 2007
Hey kman, did you leave your island?
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1535. Drakoen
2:12 AM GMT on August 18, 2007
The ULL level low over the Bahamas has picked up some speed. may not have any affect on dean.
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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.

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