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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785. Baybuddy
11:27 PM GMT on August 17, 2007
Donna always err on the side of caution. If you are full of nervous energy, you can get all of your important documents and prepare them to travel. I feel tupperware works well. Also, if you have any valuables in a safe deposit at a bank close to the coast, I would pull it.
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784. Patchmedic
11:30 PM GMT on August 17, 2007
Donna is your husband on a DMAT team?
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783. WPBHurricane05
7:30 PM EDT on August 17, 2007
Just as I thought....even the GFDL is joining the crowd.....Mexico/Texas border is your landfall....

Link? The GFDL I'm looking at has it in Louisiana.
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782. JRRP
11:15 PM GMT on Agosto 17, 2007
This afternoon here in Santo Domingo
we had winds from NE 45K-50Km/h
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781. JLPR
11:30 PM GMT on Agosto 17, 2007
well i see a cloud comming from the east here in carolina PR and the wind has picked up a lil bit
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780. medicroc
11:27 PM GMT on August 17, 2007
Hurricanes are like Police Chases on t.v. all of the media cover it, everyone watches and then expresses shock that someone actually got killed
I vote this as one of the greatest analogies of all time
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779. Metallica1990
11:30 PM GMT on August 17, 2007
anyone wanna take a guess at how wide the eye is?
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778. Neponset
11:27 PM GMT on August 17, 2007
I live in Charleston S.C, and do not have a dog in this fight, but I take this stuff very seriously. We are in sort of a holding pattern as we watch this storm progress and I think there is a little space for the periphials of living with storms. I evacuated for Hugo and lived/worked thru the aftermath. Some one earlier mentioned differiculty of returning to their homes after an evacuation - this can be a real problem. The folks who had homes on the barrior islands were not permitted to return for repair work/salvage of stuff for many weeks. My refuge for Hugo was 75-100 miles inland and we got hammered - need to go inland and to left of anticipated path.
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777. Metallica1990
11:29 PM GMT on August 17, 2007
np and best of luck to you
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776. gatagus07
11:28 PM GMT on August 17, 2007
Just as I thought....even the GFDL is joining the crowd.....Mexico/Texas border is your landfall....
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775. tristanh72
11:27 PM GMT on August 17, 2007
I am going to go try to relax a bit. When will there be another update? I need to follow this very closely.

A very good idea on both counts. Mentally prepare, relax, nothing you can do about it anyways. Someone else can tell you the model times, keep an eye on them, that's all we can do.
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774. BigToe
11:29 PM GMT on August 17, 2007
Nice Link water vapor loop. shows the ull e of Fl. Just toggle back & forth.
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773. cirrocumulus
11:26 PM GMT on August 17, 2007
I'm still sticking with a Texas landfall even though the GFS is still in Mexico. I think Dean will catch a little more of the ULL at the huge forward momentum of 22mph and it tilted farther north on a jog earlier today.
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772. DonnaGalveston
11:27 PM GMT on August 17, 2007
Thank you Metallica1990, I will stay around until it comes in. This has made me a very nervous person. My husband is a doctor, so I believe if we evacuate we may be able to get back into town easier should the storm hit.
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771. bekroweather
11:24 PM GMT on August 17, 2007
Is there a link for the 18Z GFDL? Is it out?
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770. Metallica1990
11:27 PM GMT on August 17, 2007
next update will be within the hour
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769. Baybuddy
11:26 PM GMT on August 17, 2007
This placehas actually slowed down. I thought it crashed for a sec...
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768. DonnaGalveston
11:26 PM GMT on August 17, 2007
I am going to go try to relax a bit. When will there be another update? I need to follow this very closely.
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767. wederwatcher555
11:25 PM GMT on August 17, 2007
the 18z gfs is crazy. it has dean going completely west and then turning sw instead of nw like the other models
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766. cirrocumulus
11:23 PM GMT on August 17, 2007
icepilot: And there you have it: The huge air conditioner Dean is about to work overtime on the melting ice.
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765. Metallica1990
11:24 PM GMT on August 17, 2007
anyone wanna take a guess at how wide the eye is?
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764. StormJunkie
11:22 PM GMT on August 17, 2007
Well this kept telling me that I had "virtual machines running too many instances of java"...

I have known of a memory problem with Java for sometime and have a link that will help fix it. I'll post that when I get off this dang laptop!
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763. DonnaGalveston
11:21 PM GMT on August 17, 2007
Our neighborhood home owners association has scheduled an emergency meeting on Sunday afternoon to discuss Dean.
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762. Baybuddy
11:21 PM GMT on August 17, 2007
Hurricanes are like Police Chases on t.v. all of the media cover it, everyone watches and then expresses shock that someone actually got killed.
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761. snowboy
11:21 PM GMT on August 17, 2007
with the pinhole eye, Dean is at least Cat4 by now..
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760. icepilot
5:21 PM CST on August 17, 2007
Re:Arctic sea ice shrinks to record low

The loss of so much summer sea ice is very frightening. What’s really amazing is the sat picture which apparently shows open water in McClure Strait, between Banks Island and Melville Island,

I was aboard the USCGC Polar Sea which transited the NW passage above Canada in the summer of 1985.
We had to go through the Prince of Wales Strait, East of Banks Island because McClure Strait was packed with a jumble of multi year ice – we tried McClure Strait but could make no headway through the thick rubble of multi yr ice. This is significant as I had personally seen the Polar Sea transit 5-6 ft thick Ice at 10 Kts and had personally driven through ridges of ice up to 100 ft (measured) thick (albeit - there was some open water on the other side, so the ice had somewhere to move to which helped it break) The ship, Polar Sea, is a Polar Class Icebreaker and is one of the 2 most powerful non-nuclear Icebreakers in the world. Her sister ship Polar Star is the other - 13000 tons, 399 feet long and 60,000+ HP – 75k Hp in short bursts)

If the world’s glaciers are keeping pace (and it seems they are) we could see the ocean levels rise faster than anyone has yet predicted. While the melting sea ice won’t affect sea levels - think of ice in a glass of water, as the ice melts the water level stays the same – the added fresh water and lack of cooling effect will effect water circulation, and the reduction in the reflection of the sun’s energy just adds to the equation. Melting ice cover on Greenland and Antarctica are sure to follow.


I have watched Arctic sea ice conditions since the early 80’s. I have 6 yrs of service on Polar Icebreakers and 6 years doing Oceano data collection and tracking Icebergs in the North Atlantic for the International Ice Patrol. My career as a Oceano tech spans 20 yrs. And this scares the *&^% out of me.

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759. Xion
11:16 PM GMT on August 17, 2007
Wow.

The ADT's latest estimate absolutely plummeted (rose in intensity) in T#, especially when lookin at the graph HERE.

It estimates wind speeds of 117 knots. That would make it a Cat 4.
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758. Pachanga
11:20 PM GMT on August 17, 2007
Governor declares state of emergency

To me that’s just another example of her incompetence. IMO, it's way too early to declare such an emergency, just think of the panic this will cause those who went through Rita and Katrina. I wouldn’t be surprised if this state of emergency declaration doesn’t cause someone to literally be scared to death before Dean even entered the GOM.
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757. JFLORIDA
11:21 PM GMT on August 17, 2007
Probably the thing keeping Dean on its due westward path now is the Bermuda high it seems. Dean is just Due South of its center. I think it will start back on its more WNW motion soon as it passes the point that the high stretches to the south the most – unless it continues to move with it west.
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756. silverstripes
4:20 PM PDT on August 17, 2007
SJ,

I know I recently allowed the auto update of Java to occur and I think that coincides with the problems I was having with it loading properly.
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755. nawlinsdude
11:18 PM GMT on August 17, 2007
WOW She did. I thought that was a joke. Unbelievable
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754. wederwatcher555
11:20 PM GMT on August 17, 2007
on the 18z run the GFS has become an outlier
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753. ezziboo
11:15 PM GMT on August 17, 2007
Just saw the link about the Louisiana governor declaring a state of emergency....which means that, because I'm employed by a Louisiana social service agency, I have to pack a bag and wait to be called out to man a shelter...even if the storm would be headed straight for my area...not fun.
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752. HurricaneJoe
11:20 PM GMT on August 17, 2007
any ideas on if dean will hit LA?
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751. nrtiwlnvragn
11:15 PM GMT on August 17, 2007
Short term on radar looks moving due west

Link
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750. cirrocumulus
11:13 PM GMT on August 17, 2007
The 12 hour models on the remnants of Erin were incorrect by eight hours. None of the computer models picked up the remnants moving farther into the Texas panhandle before 7 p.m. And yet the remnants were already in those areas at 11 a.m. It's going to be hard to predict where Dean strikes if the models can't get the next 24 on Erin!
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749. snowboy
11:18 PM GMT on August 17, 2007
west is 270 degrees, northwest 315 degrees, wnw is 292.5 degrees
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748. WPBHurricane05
7:19 PM EDT on August 17, 2007
is Dean a boy or girl? I'm curious

A boy. During odd years it goes Girl, Boy, Girl, Boy and in even years it goes Boy, Girl, Boy, Girl.
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747. HurricaneParty
11:17 PM GMT on August 17, 2007
HurricanePary I didn't believe it until I saw it. All I can say is, wow.

I know. We'll be rid of her soon.

The porridge is too hot, the porridge is too cold.. poor woman just can't seem to get it just right.
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746. StormJunkie
11:15 PM GMT on August 17, 2007
ss, I used one that will allow my ip to be shown...Not positive that was it though, but I can not think of anything else.

LF, yea, hopefully the GFS and Ukmet will be a little more true to life at 18z.

As for the cmc, put it down and back away slowly, you can get tore up from all the crack it has had this season...

Almost back to my normal pc!!!
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745. Johnhopefan
11:16 PM GMT on August 17, 2007
I don't see this year breaking the Cat 5 record of 2005, but all you need in one, and we have it. I do have a very eeire feeling about Dean and Houston, but this is jus my opinion.

One model does show two systems behind Dean right when it is approaching the coast, one in a Katrina position near the keys, one north of Puerto Rico. Thus, Gabrielle & Felix
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744. iahishome
11:13 PM GMT on August 17, 2007
Looks like Hurricane Hunters are back in Dean... They're not really aptly named are they?

Finding the hurricane isn't really that hard... Flying through it and surviving it is the hard part. God bless 'em.

Data will continue to get better and less errors in the track... If you live on gulf coast, I'd go fill up some gas tanks and then get a good night's sleep... You could wake up tomorrow and the tracks might all lead to Mexico.
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743. Weather456
11:18 PM GMT on August 17, 2007
is Dean a boy or girl? I'm curious
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742. bekroweather
11:15 PM GMT on August 17, 2007
18Z GFS
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741. Melagoo
11:18 PM GMT on August 17, 2007
Many tracks of a wide differences

tracks
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740. tampahurricane
11:12 PM GMT on August 17, 2007
if this thing were to tack a north turn the ULL would have to eat away at the high to make a weakness for it to turn to the north.
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739. Metallica1990
11:17 PM GMT on August 17, 2007
Posted By: silverstripes at 11:17 PM GMT on August 17, 2007.

If you want to get real technical I made up my own way it is traveling. WWWNW, which is 277.5 degrees :)


nice lol
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737. WPBHurricane05
7:15 PM EDT on August 17, 2007
HurricanePary I didn't believe it until I saw it. All I can say is, wow.
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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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