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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2285. catjojo
5:08 AM GMT on August 18, 2007
Surf's up !Be careful in the carrib............
Conditions at 42059 as of
0450 GMT on 08/18/2007: Unit of Measure: English Metric Time Zone: Station Local Time Greenwich Mean Time [GMT] British Summer Time [GMT+1] Eastern Greenland [GMT-1] Azores [GMT-2] Western Greenland [GMT-3] Atlantic Standard [GMT-4] US/Eastern Standard US/Central Standard US/Mountain Standard US/Pacific Standard Alaska Standard [GMT-9] Hawaii-Aleutian Standard [GMT-10] Samoa Standard [GMT-11] International Date Line West [GMT-12] Western European [GMT+0] Central European [GMT+1] Eastern European [GMT+2] Moscow [GMT+3] USSR Zone 3 [GMT+4] USSR Zone 4 [GMT+5] USSR Zone 5 [GMT+6] USSR Zone 6 [GMT+7] China Coast [GMT+8] Japan Standard [GMT+9] Guam Standard [GMT+10] GMT+11 International Date Line East [GMT+12]
Click on the graph icon in the table below to see a time series plot of the last five days of that observation.

Wind Direction (WDIR): NNE ( 20 deg true )
Wind Speed (WSPD): 36.9 kts
Wind Gust (GST): 48.6 kts
Wave Height (WVHT): 22.6 ft
Dominant Wave Period (DPD): 13 sec
Average Period (APD): 8.8 sec
Atmospheric Pressure (PRES): 29.61 in
Pressure Tendency (PTDY): -0.14 in ( Falling Rapidly )
Air Temperature (ATMP): 81.1 F
Water Temperature (WTMP): 83.8 F
Dew Point (DEWP): 73.2 F
Heat Index (HEAT): 86.2 F
Member Since: July 11, 2006 Posts: 0 Comments: 1
2284. WatchingInHouston
5:09 AM GMT on August 18, 2007
C2News: I've tried not to chime in on posts like this... but, really... a "sad and frightening event" regarding gas prices? I think that we need to really put things in scale here - a sad and frightening event would be the people whose lives are being drastically affected by Dean... whose lives have been taken, whose livelihoods have been swept away, whose homes are no more. A sad and frightening event is the people that's already happened too and the people that it IS going to happen too.

Let's keep things in perspective here. Gas prices are a simple reflection of market supply and demand. The people that can't afford to buy gasoline take demand away from the pool, thus creating a sense of increased supply, or increasing the supply to those whom can afford it. The natural market reaction to this is lower prices.

Sorry for the OT post, folks.
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2282. weathersp
1:14 AM EDT on August 18, 2007
How low can ya go I say how low can ya go?

Dean Buoy Pressure
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2279. Aggie92
5:10 AM GMT on August 18, 2007
Good Bull Mr. Niceville.

On a more storm related note. I work at the Riverside Campus, an old military base that has been turned into offices, wharehouses, and what not. We got an e-mail today saying that Gov. Perry has declared a State of Iminent Danger and they were going to start staging supplies and search and rescue aircraft at Riverside Campus. Sounds like our State Gov't is on the ball.
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2276. weatherwonderer
5:09 AM GMT on August 18, 2007
good night atmoaggie. Good luck tomorrow.
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2273. Spoon
5:12 AM GMT on August 18, 2007
Has anyone done the math -- what time will Dean be closest to 42059?
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2272. KnowYourRole
1:12 AM EDT on August 18, 2007
later nola70119.
2270. punkasshans
5:10 AM GMT on August 18, 2007
The SREF (short range ensemble) has an average 4 day position in the central gulf. The models are moving north, and the entire Texas region needs to be getting ready, or at least have a plan of action. The NGM has also shifted far north compared to the last run (just north of Jamaica now), along with the GFS as already discussed.
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2269. KnowYourRole
1:10 AM EDT on August 18, 2007
Posted By: Daveg at 1:09 AM EDT on August 18, 2007.
Gah...nevermind on that slight WNW turn...was yet another wobble. Crazy hurricane.


Unless you see it in about 3-4 frames, it's not even worth mentioning a possible turn. I still have yet to see it move off 15N since about 8:00pm EST.
2267. JFLORIDA
5:10 AM GMT on August 18, 2007
so hurricane force winds out 60 mi from the center now.
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2266. bappit
5:07 AM GMT on August 18, 2007
Interesting disclaimer on the model plot Skyepony posted.

If anything on this graphic causes confusion, ignore the entire product.
Member Since: May 18, 2006 Posts: 10 Comments: 6147
2264. Metallica1990
5:10 AM GMT on August 18, 2007
Posted By: nola70119 at 5:10 AM GMT on August 18, 2007.

What time is the next GFDL?


5 am i think
2263. MrNiceville
5:08 AM GMT on August 18, 2007
Atmo - I've been in the regular population toooooo long - LOL - and married and MSU graduate. She has had a detrimental influence on me, but I still proudly display my memorabilia, have taught my kids to "saw Varsity's horns off", and taught them that it's TU, not UT....
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2262. nola70119
5:09 AM GMT on August 18, 2007
What time is the next GFDL?
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2261. iahishome
5:09 AM GMT on August 18, 2007
Newest Buoy data is in:

Conditions at 42059 as of
0450 GMT on 08/18/2007:
Unit of Measure: Time Zone:

Wind Direction (WDIR): NNE ( 20 deg true )
Wind Speed (WSPD): 36.9 kts
Wind Gust (GST): 48.6 kts

Wave Height (WVHT): 22.6 ft

Dominant Wave Period (DPD): 13 sec
Average Period (APD): 8.8 sec
Atmospheric Pressure (PRES): 29.61 in
Pressure Tendency (PTDY): -0.14 in ( Falling Rapidly )
Air Temperature (ATMP): 81.1 F
Water Temperature (WTMP): 83.8 F
Dew Point (DEWP): 73.2 F
Heat Index (HEAT): 86.2 F

Let's hope we see some unexpected drops.
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2259. nola70119
5:06 AM GMT on August 18, 2007
By the way, is it any surprise that the NHC forecast outperforms the models....they forecast after looking at the models, not before they come out, right?
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2258. C2News
1:07 AM EDT on August 18, 2007
With gas prices as high as they are now, a cat 5, even just a major hurricane in the Gulf would cause major price hikes that would take many people off the streets as far as driving goes...many middle class families would not be able to afford it, let alone lower class families...it would be a sad and frightening event that may be enevitable
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2256. Daveg
5:08 AM GMT on August 18, 2007
Gah...nevermind on that slight WNW turn...was yet another wobble. Crazy hurricane.
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2255. sammo
5:08 AM GMT on August 18, 2007
Posted By: exexec at 5:04 AM GMT on August 18, 2007.
Can't believe anyone would ever cheer for a hurricane. My parents' house was blasted during Ivan. We nearly lost everything we had. It's easy to cheer for disaster when you believe you are invincible -- and have no morals at the same time.

If that applies to you and bothers you, good. It should.


True. There's a fine line btw weather freak and cane cheerleader. Some here cross it...
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2254. KnowYourRole
1:07 AM EDT on August 18, 2007
Posted By: DG136 at 1:06 AM EDT on August 18, 2007.
Interesting how the NHC newest run is way right of the others (notice up in Master's entry he says the NHC tends to out preform the models).

I may be color blind, but it appears on that graphic that the NHC shows landfall around the US/Mexico border. The one all the way to the right is not the NHC


the one to the right, the CLP5 has not moved all day.
2253. moonlightcowboy
5:05 AM GMT on August 18, 2007
Hey, Niceville! Prolly resting a lil easier now. Jamaica, Caymans, Mexico...maybe a lit south Texas,heh? Just know that it's going to be a bad one for someone!

The GFDL is coming back around!
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2252. MrNiceville
5:02 AM GMT on August 18, 2007
I consider anyone that attended a "real" aggie - I should have appended LOL to the end of the comment - apologies...

It doesn't matter how you support our school - just that you support it! I have ties as well, not going back that far, though! Sounds like a proud heritage.

Seriously - I'm sure that the Met School will have interesting things on their web site if the storm winds up coming that way. If you need info here are a few links...

MLC

Patrap

StormW

Tropical Lagniappe
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2251. FMTXWMAN
5:04 AM GMT on August 18, 2007
I do not know about anyone else, but it seems from the wv imagery over Florida, that the ULL is starting to sink to the southwest. Which could be in response to Dean and other forces acting on it over the continental US. If things evolve this way dean could be punted north due to the effect of which I can not remember the name of.

All we need is a cat 5 to wipe out Houston's oil facilities. Then again there'd be a silver lining where it may finally force the government to do something about the refinery crunch.
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2249. DG136
5:04 AM GMT on August 18, 2007
Interesting how the NHC newest run is way right of the others (notice up in Master's entry he says the NHC tends to out preform the models).

I may be color blind, but it appears on that graphic that the NHC shows landfall around the US/Mexico border. The one all the way to the right is not the NHC
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2248. C2News
1:04 AM EDT on August 18, 2007
Posted By: Metallica1990 at 1:04 AM EDT on August 18, 2007.
Posted By: C2News at 5:02 AM GMT on August 18, 2007.

For me, I've been through Frances, Jeanne

Power out for 2 days in N.E. Florida...


I was only like 11 or 12 then

I was 14 and being outta school was awesome lol


Duval County closed schools for a week for Frances, a day for Charley, and 4 days for Jeanne...and we are where "Florida Begins"
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2247. nola70119
5:04 AM GMT on August 18, 2007
The NHC is a forecast track, not a model......
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2246. Aggie92
5:05 AM GMT on August 18, 2007
Howdy, atmo.
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2245. atmoaggie
5:04 AM GMT on August 18, 2007
I am with you aggie92, non-reg, bit I did say howdy, dammit.
Member Since: August 16, 2007 Posts: 6 Comments: 12463
2244. nola70119
5:02 AM GMT on August 18, 2007
Houston, Western Louisiana, Brownsville, take your pick.....if you don't like choices talk about a ULL or He-heberts box.
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2243. guygee
5:00 AM GMT on August 18, 2007
leelee75k - It is the high to the west combined with the ULL now beginning to cross the FL peninsula that is pushing that dying MCS down from AL-GA into the Fl panhandle.
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2241. Spoon
5:02 AM GMT on August 18, 2007
42059 just updated again. Hanging in there..
42059
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2240. exexec
5:00 AM GMT on August 18, 2007
Can't believe anyone would ever cheer for a hurricane. My parents' house was blasted during Ivan. We nearly lost everything we had. It's easy to cheer for disaster when you believe you are invincible -- and have no morals at the same time.

If that applies to you and bothers you, good. It should.
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2239. Skyepony (Mod)
5:00 AM GMT on August 18, 2007
scratch that..lol
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2238. Metallica1990
5:02 AM GMT on August 18, 2007
THEY ARE LMAO
2236. C2News
1:01 AM EDT on August 18, 2007
For me, I've been through Frances, Jeanne

Power out for 2 days in N.E. Florida...


I was only like 11 or 12 then
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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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