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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1884. VegasRain
3:19 AM GMT on August 18, 2007
Posted By: Daveg at 3:19 AM GMT on August 18, 2007.

No wobble....due west...
Link

Dean won't be on a due west course. That would take it along 15N until it reached Honduras. The westward track is only temporary, and from the latest NHC update it is traveling 275 or slightly north of due west. I suppose wobble is a bad term for it, but temporary jog is more accurate.

A good indication of where a storm will go is the outflow pattern surrounding a hurricane. It will point in the general direction of where the storm is going or is about to go. Right now the outflow is traveling Northwestward towards Haiti, so a more WNW track should follow.

Check out this image of Hugo as it approached South Carolina:

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1883. ChuckieTodd
10:31 PM CDT on August 17, 2007
Just like ice cream:

We need a bigger cone...
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1881. H2OMaker
3:28 AM GMT on August 18, 2007
http://euler.atmos.colostate.edu/~vigh/guidance/northatlantic/track_early1.png

Notice the CLIPPER5 in this multi track map, it's the real northern outlier.

Alas, I may be mistaken but isn't CLP5 one of NOAA's tracks?
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1880. nola70119
3:27 AM GMT on August 18, 2007
No one is betting on everything the NHC 11pm advisory says:

THE CHANCES OF TROPICAL STORM FORCE WINDS ARE
SIMILAR AT EACH LOCATION ALONG THE ENTIRE WESTERN AND NORTHERN
COASTS OF THE GULF OF MEXICO...AND IT IS TOO EARLY TO DIFFERENTIATE
THE RISK OF HURRICANE FORCE WINDS BETWEEN ANY OF THESE LOCATIONS.

In other words, regardless of the cone, this forecaster says its TOO EARLY TO MAKE A REASONABLE GUESS. (My caps)
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1878. Crisis57
3:29 AM GMT on August 18, 2007
Posted By: Michael at 3:29 AM GMT on August 18, 2007.

WNW componet is going to start taken over throughout the morning hours and thats crucial. Due west motion is about to end.


where is the ULL located also is crucial
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1876. moonlightcowboy
3:28 AM GMT on August 18, 2007
Posted By: JamaicanGir at 3:27 AM GMT on August 18, 2007.
DatagirlWPB

thanks, was here in gilbert in Montego Bay, was in So. MIami for andrew, in Montego Bay for Ivan,

not looking forward to Dean


Posted By: moonlightcowboy at 3:26 AM GMT on August 18, 2007.
Please tell Lloydie and Paula up at 3Dives, hello and to be safe! Best folks, best jerk chiken and lobster in Negril!

....be safe, Jamaicagirl!
Member Since: July 9, 2006 Posts: 184 Comments: 29610
1870. sullivanweather
3:25 AM GMT on August 18, 2007
Again...


Think about the prevailing wind direction in the arctic. If you take the ice away it changes the ocean currents up there because now you have open water instead of ice.
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1868. ChuckieTodd
10:26 PM CDT on August 17, 2007
why do people keep comparing katrina to the most powerful storms of all time.For the love of god katrina was a 3 when it hit and was only devastating in wide range due to new orleans in a soup bowl.If you want to compare it to a more noteable hurricane how about andrew or wilma.
Katrina was a 3 and thats that.


I'm not sure that category is all there is to a storm. The surge built when Katrina was bigger than a 3 thus caused more damage than Camille, a category 5. I use Camille because it was so close to the same landfall as Katrina.
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1867. JamaicanGir
10:25 PM EST on August 17, 2007
DatagirlWPB

thanks, was here in gilbert in Montego Bay, was in So. MIami for andrew, in Montego Bay for Ivan,

not looking forward to Dean
1865. bluehaze27
10:26 PM EST on August 17, 2007
rick54 explain.
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1864. weatherwonderer
3:24 AM GMT on August 18, 2007
Andy, I feel sorry for your popsicle. Maybe your just getting older now and beginning to realize that time flys. Especially when you are eating such a delicious object. Get two the next time.
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1863. AndyN
3:25 AM GMT on August 18, 2007
BayBuddy: Two stick...No expense spared here.
Member Since: December 29, 2005 Posts: 1 Comments: 551
1862. bluehaze27
10:26 PM EST on August 17, 2007
whipster, why yes it would.
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1861. Rick54
10:25 PM CDT on August 17, 2007
Baybuddy, I think one issue is the salinity question with ice cap melting. if the salinity falls the ocean currents can stop and we actually may find ourselves in an ice age which is antithetical to ice cap melting and global warming.

That would only be a local phenomenon.

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1860. presslord
11:23 PM EDT on August 17, 2007
Dr. masters isn't veering off course with the ice issue...read he piece...it's clear why he brings it up and what he's suggesting/posting...
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1859. moonlightcowboy
3:24 AM GMT on August 18, 2007
Please tell Lloydie and Paula up at 3Dives, hello and to be safe! Best folks, best jerk chiken and lobster in Negril!
Member Since: July 9, 2006 Posts: 184 Comments: 29610
1857. GetReal
3:19 AM GMT on August 18, 2007
There is doubt going to be an old fashion western, Showdown Tomorrow at First Light, in the central Caribbean between Dean and the much written about ULL that refuses to give space!

Who will win, and most importantly who will loose, will be determined!!! Tune in all day tomorrow and cheer, or hiss for either side...
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1856. wederwatcher555
3:24 AM GMT on August 18, 2007
i cant believe the spread between gfs and gfdl is so big. i mean HUGE. by late tomorrow one of them will have to give in in a big way and everyone is betting on the gfdl doing it
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1852. Baybuddy
3:24 AM GMT on August 18, 2007
Andy, is it a one stick popsicle or two stick?
Member Since: June 26, 2006 Posts: 0 Comments: 1115
1851. DatagirlWPB
3:24 AM GMT on August 18, 2007
jamaicangirl
yep in negril. Gilbert taught me to respect Hurricanes. also been thru Frances, Jeanne,Wilma. good luck
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1850. drj27
3:23 AM GMT on August 18, 2007
yea sorry thats what i meant but ill keep watching it looks like its going to become a cat 5 pretty soon
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1849. bluehaze27
10:22 PM EST on August 17, 2007
Baybuddy, I think one issue is the salinity question with ice cap melting. if the salinity falls the ocean currents can stop and we actually may find ourselves in an ice age which is antithetical to ice cap melting and global warming.
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1848. Masquer08er
3:22 AM GMT on August 18, 2007
There's a good reason he posted the Arctic ice extent info

That reminds me....I need another Stoli rocks
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1847. AndyN
3:22 AM GMT on August 18, 2007
I noticed my popsicle melts faster...Is that indicative of global warming?
Member Since: December 29, 2005 Posts: 1 Comments: 551
1845. Crisis57
3:22 AM GMT on August 18, 2007
Posted By: whipster at 3:21 AM GMT on August 18, 2007.

Nudging to the N in the last few frames IMO


i see it
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1844. drj27
3:20 AM GMT on August 18, 2007
sorry guys for all the questions i just became a member the other day so nice to meet everybody
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1843. Justwondering
3:22 AM GMT on August 18, 2007
Sorry about that. Let me try to post the link to Colorado State's Late Cycle page. If it won't post again, here's the site:

http://euler.atmos.colostate.edu/~vigh/guidance/northatlantic/track_late1.png

Link
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1842. Metallica1990
3:20 AM GMT on August 18, 2007
Posted By: DestinJeff at 3:21 AM GMT on August 18, 2007.

metallica,

please post your landfall coordinate so we can all go back to our regulatry scheduled lives


lol im not going that far
1841. Baybuddy
3:19 AM GMT on August 18, 2007
People always talk about massive flooding when the glaciers melt. If the ice is floating why would the sea level increase? Also, the Bonneville Salt Flats were caused by glaciers. Who's fault is that?
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1840. whipster
9:21 PM CST on August 17, 2007
Nudging to the N in the last few frames IMO
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1839. bluehaze27
10:20 PM EST on August 17, 2007
Sullivan what is your point? I don't understand. Do you believe the ice caps are melting? I do. Do you believe in global warming? I do. I'm not following you.
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1838. weatherwonderer
3:17 AM GMT on August 18, 2007
Another article daveg:
http://www.ipcc.ch/SPM2feb07.pdf

As for the Vikings, all hail can I have another?

Blue and Sul people will believe what they want. Even if they have to dig deep to find support for their opinion.
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1837. drj27
3:19 AM GMT on August 18, 2007
do you think its going to decrease in the longitude
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1835. Metallica1990
3:19 AM GMT on August 18, 2007
Posted By: BigToe at 3:18 AM GMT on August 18, 2007.

OK Metallica1900..... You NAILED it.


even though i think that was sarcasm thanks

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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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