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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2885. Weather456
11:09 AM GMT on August 18, 2007
Good morning, OMG! Dean is almost a cat 5 very unexpected this early
Member Since: July 24, 2005 Posts: 407 Comments: 19076
2884. C2News
7:08 AM EDT on August 18, 2007
Sorry if I seemed like I was wishcasting...I merely pointed out what I saw...
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2883. extreme236
11:09 AM GMT on August 18, 2007
it looks like recon will be flying into dean in about an hour
Member Since: August 2, 2007 Posts: 19 Comments: 19234
2882. IKE
6:06 AM CDT on August 18, 2007
It's moving basically like the NHC said it was going to move. Just about all of the computer models take Dean into Mexico...other than the GFDL which is trending further south and is getting closer to making landfall in Mexico from what it was showing yesterday...those are the facts.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
2881. extreme236
11:06 AM GMT on August 18, 2007
wow, that wave at 35w has just about a favorable enviroment all the way to the antilles. shear is ranging from 5-10kts at this time and only a spot or two of 20kt shear. there are some spots of increasing shear though for it...
Member Since: August 2, 2007 Posts: 19 Comments: 19234
2879. Masquer08er
10:58 AM GMT on August 18, 2007
Hurricane23, The NHC is great. This is a deviation, though, if only for a moment.
Member Since: August 16, 2007 Posts: 0 Comments: 397
2878. PalmHarbor
11:00 AM GMT on August 18, 2007
Is dean still behind the uul that is supposed to keep him going west? (I am terrible at map deciphering) thanks!
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2877. extreme236
10:59 AM GMT on August 18, 2007
Posted By: Miamiweather at 10:59 AM GMT on August 18, 2007.

hey23 good morning quick question what do you think of the wave in the central atlantic


good morning to you as well. i am thinking that if the wave keeps getting more convection around its circulation, then it might become an invest perhaps. conditions are favorable for development, so there isnt much stopping it from developing
Member Since: August 2, 2007 Posts: 19 Comments: 19234
2876. guygee
10:51 AM GMT on August 18, 2007
I looks to me that a weakness has formed between the high steering Dean and the trough to the northwest. I see the early morning NHC track has shifted north, but Dean is still curving above the track. I don't agree with the NHC's current straight line to the Yucatan, and I think that they are going to have to make another shift north sometime today. By the end of the day the whole nation is going to be aware of the danger approaching from the SE.
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2875. Miamiweather
10:58 AM GMT on August 18, 2007
hey23 good morning quick question what do you think of the wave in the central atlantic
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2874. jj292
10:54 AM GMT on August 18, 2007
If this isn't just a jog, Dean is moving north of the forecast track at around 305 to 310 degrees. It almost looks like he is going to plow into the southern half of Haiti.

It could be just a jog or wobble. We will have to wait to see what it looks like in a few hours.
2873. extreme236
10:54 AM GMT on August 18, 2007
i know this is off-topic from dean, but the wave at about 35w is looking interesting this morning. it has more convection than yesterday but just remains disorganized
Member Since: August 2, 2007 Posts: 19 Comments: 19234
2872. CycloneOz
10:54 AM GMT on August 18, 2007
Good Morning everyone.
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2871. hurricane23
6:53 AM EDT on August 18, 2007
Posted By: C2News at 6:52 AM EDT on August 18, 2007.

Posted By: hurricane23 at 6:50 AM EDT on August 18, 2007.
Dean is right on track with the current forcast thinking....Here is a close-up infrared view of dean with the NHC'S forcast points.

I think it is slightly north or the forecast point


Hurricanes do not travel in a straight line and so far the NHC has done a fantastic job on deans track.
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2870. Masquer08er
10:50 AM GMT on August 18, 2007
Lokk at the updated (10:15) floater loop. It is north of the track. If its a jog, he's wearing Nikes.
Member Since: August 16, 2007 Posts: 0 Comments: 397
2869. C2News
6:51 AM EDT on August 18, 2007
Posted By: hurricane23 at 6:50 AM EDT on August 18, 2007.
Dean is right on track with the current forcast thinking....Here is a close-up infrared view of dean with the NHC'S forcast points.


I think it is slightly north or the forecast point
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2868. Proplayer
10:49 AM GMT on August 18, 2007
it is dark I hit the wrong keys but you get what I mean
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2867. C2News
6:48 AM EDT on August 18, 2007
It does seem Dean has taken a movement to the nw/wnw...and imagery confirms it. Bob Stokes of TWC said it is a good thing if Dean slams the Yucatan Peninsula. All they do is read off of teleprompters.
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2866. GPTGUY
5:49 AM CDT on August 18, 2007
something along the lines of what Mitch in 1998 did when it hit Honduras
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2865. hurricane23
6:49 AM EDT on August 18, 2007
Dean is right on track with the current forcast thinking....Here is a close-up infrared view of dean with the NHC'S forcast points.

ffff
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2864. GPTGUY
5:47 AM CDT on August 18, 2007
I can't imagine the horror if a cat.4/borderline cat. 5 would do if it hit DR and Haiti!!
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2863. PalmHarbor
10:45 AM GMT on August 18, 2007
Morning Everyone, I just woke up to a radar image of Dean looking like he was going alot more north that previously, is this just a wobble or the possible shift people have been talking about for days?
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2862. WatchingInHouston
10:44 AM GMT on August 18, 2007
It's going to be a very, very interesting 36-48 hours to say the least...

Off-handedly, I can't help but comment how much quicker this blog and the NHC animated-graphics load at 5:45AM CST.
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2861. Proplayer
10:42 AM GMT on August 18, 2007
we can only wait the 3 day mark will tell all like I sard brfore it is like a spinning top it mite just hit the ULL and go west or just go through it only time will tell
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2860. Masquer08er
10:40 AM GMT on August 18, 2007
JJ, Yes indeed. This loop really woke me up with a start
Link
Member Since: August 16, 2007 Posts: 0 Comments: 397
2859. jj292
10:36 AM GMT on August 18, 2007
If it truley changed course to 307, that is going to put the D.R. and Haiti in trouble now as well.

Remember what Jean did to Haiti a few years ago? And that was just a tropical storm at the time.
2858. WeatherSpotter
10:37 AM GMT on August 18, 2007
I just see a US landfall will occur with this storm.

Guess we will see in the end.
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2857. Masquer08er
10:35 AM GMT on August 18, 2007
Obx, I was thinking the same thing, but didn't want to say.
Member Since: August 16, 2007 Posts: 0 Comments: 397
2856. bobcane
10:34 AM GMT on August 18, 2007
The direction of Dean over the last 1 hour from radar returns is 303 deg WNW.
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2855. redrobin
10:30 AM GMT on August 18, 2007
Long time no post everybody. Hope all are well. I'm now in Bahrain... I lived the Katrina dream in Diamondhead, MS just north of Bay of St Louis. If a strong 3 or 4 hits your coastal area, be prepared for no water or electricity for 2 weeks or longer.

This is my scenario for Dean: The "Bahama" ULL is moving SW across SE FL/W Bahamas toward (in my opinion)the Yucatan. As the ULL moves SW, ridge will build back into the SE US and East Gulf of Mexico from W Atlantic. Dean will track across W Caribbean and track along the SE to NW flow created between the ULL and the Atlantic ridge. Dean will brush NE Yucatan and W cuba as it transits the Yucatan Channel. As Dean enters well into the Gulf of Mex, the Ridge, continuing to build as the ULL slides into Bay of Campeche and mainland Mexico, will re flatten Dean's track to a more WNW trajectory toward the NW Gulf of Mex. I see a Corpus Christi to Galveston cone, centered on Matagorda Bay.

I think Southerly shear will increase on Dean as it approaches the west Caribbean, which will limit Dean from approaching "extreme" (ie record setting) Cat 5 status. Dean will make US landfall (if it follows above steering scenario) as a strong CAT 3 or weak 4 as (relatively) cooler water temps inhibit the storm from maintaining Strong 4 or 5 strength.

I think this is the solution the GFDL is going with. The models with the more southerly track solutions are (I believe) predicated upon Dean tracking in front of the ULL. I agree w/ the GFDL, that the ULL will cross in front of Dean setting up the NW steering flow into the Gulf I discussed above.

I Agree With All of the above!!!! Lord I was starting to think I was really off on my thoughts. Thanks
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2854. obxrox
10:22 AM GMT on August 18, 2007
good morning...

looks like we have either a jog or movement to the WNW or NW..here's the NHC 12 hour plot:

12HR VT 18/1800Z 15.6N 69.6W 130 KT

So about 7.5 hours away and it looks like Dean is approaching 15.4 in the last sat image...I think we'll see the NHC model track bumped farther N and E...could be the GFDL coming to pass...we'll see
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2853. nolesjeff
10:30 AM GMT on August 18, 2007
sorry, that earlier post meant he was getting close to that buoy. sorry, was misleading
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2852. nolesjeff
10:28 AM GMT on August 18, 2007
No, southwest florida, how about you
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2851. C2News
6:27 AM EDT on August 18, 2007

Posted By: bobcane at 6:26 AM EDT on August 18, 2007.
C2NEWS, the storm changed direction overnight. Now 307 deg WNW. Opens up a more northern direction now.


Posted By: SWFLdrob at 6:26 AM EDT on August 18, 2007.
Posted By: C2News at 10:24 AM GMT on August 18, 2007.

So, what has happened overnight?

finally got divorced from the 15N line...has a bit more N in the westerly motion now. Stronger, NHC almost made it a cat5 at the 5 a.m. advisory. No big change in the track/cone.



Thanks guys. I though it would soon add a more northerly component...well my oven is dinging, biscuits ready be back soon :)
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2850. Masquer08er
10:19 AM GMT on August 18, 2007
BobCane,

Just got here. I was checking the loops and pr radar and saw the same wnw movement. This doesn't look good for Cuba. This may be a little break for Jamaica,though.
Member Since: August 16, 2007 Posts: 0 Comments: 397
2849. wxgssr
9:53 AM GMT on August 18, 2007
Long time no post everybody. Hope all are well. I'm now in Bahrain... I lived the Katrina dream in Diamondhead, MS just north of Bay of St Louis. If a strong 3 or 4 hits your coastal area, be prepared for no water or electricity for 2 weeks or longer.

This is my scenario for Dean: The "Bahama" ULL is moving SW across SE FL/W Bahamas toward (in my opinion)the Yucatan. As the ULL moves SW, ridge will build back into the SE US and East Gulf of Mexico from W Atlantic. Dean will track across W Caribbean and track along the SE to NW flow created between the ULL and the Atlantic ridge. Dean will brush NE Yucatan and W cuba as it transits the Yucatan Channel. As Dean enters well into the Gulf of Mex, the Ridge, continuing to build as the ULL slides into Bay of Campeche and mainland Mexico, will re flatten Dean's track to a more WNW trajectory toward the NW Gulf of Mex. I see a Corpus Christi to Galveston cone, centered on Matagorda Bay.

I think Southerly shear will increase on Dean as it approaches the west Caribbean, which will limit Dean from approaching "extreme" (ie record setting) Cat 5 status. Dean will make US landfall (if it follows above steering scenario) as a strong CAT 3 or weak 4 as (relatively) cooler water temps inhibit the storm from maintaining Strong 4 or 5 strength.

I think this is the solution the GFDL is going with. The models with the more southerly track solutions are (I believe) predicated upon Dean tracking in front of the ULL. I agree w/ the GFDL, that the ULL will cross in front of Dean setting up the NW steering flow into the Gulf I discussed above.
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2848. bajelayman2
10:24 AM GMT on August 18, 2007
nolesjeff, are you in Jamaica? If so, best wishes for a safe time.
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2847. SWFLdrob
10:24 AM GMT on August 18, 2007
Posted By: C2News at 10:24 AM GMT on August 18, 2007.

So, what has happened overnight?

finally got divorced from the 15N line...has a bit more N in the westerly motion now. Stronger, NHC almost made it a cat5 at the 5 a.m. advisory. No big change in the track/cone.
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2846. bobcane
10:24 AM GMT on August 18, 2007
C2NEWS, the storm changed direction overnight. Now 307 deg WNW. Opens up a more northern direction now.
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2845. Melagoo
10:25 AM GMT on August 18, 2007
Jamaica is going to get flattened ... :c(
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2844. GPTGUY
5:25 AM CDT on August 18, 2007
ok C2 just checking..thanks
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2843. C2News
6:24 AM EDT on August 18, 2007
Posted By: GPTGUY at 6:23 AM EDT on August 18, 2007.
I just heard on TWC that Louisiana's governor issued a state of emergency for LA. has anyone heard about that yet...or am I just late!


Somemone posted that last night...
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2842. C2News
6:22 AM EDT on August 18, 2007
So, what has happened overnight?
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2841. nolesjeff
10:21 AM GMT on August 18, 2007
Conditions at 42059 as of
0950 GMT on 08/18/2007:

Wind Direction (WDIR): NW ( 310 deg true )
Wind Speed (WSPD): 52.4 kts
Wind Gust (GST): 66.0 kts
Wave Height (WVHT): 28.9 ft
Dominant Wave Period (DPD): 13 sec
Average Period (APD): 8.7 sec
Atmospheric Pressure (PRES): 28.77 in
Pressure Tendency (PTDY): -0.62 in ( Falling Rapidly )

He is getting close
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2840. GPTGUY
5:22 AM CDT on August 18, 2007
I just heard on TWC that Louisiana's governor issued a state of emergency for LA. has anyone heard about that yet...or am I just late!
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2839. bajelayman2
10:21 AM GMT on August 18, 2007
10 miles across, that is what I just read about Andrew, same 10 miles.
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2838. nolesjeff
10:20 AM GMT on August 18, 2007
Posted By: bajelayman2 at 10:18 AM GMT on August 18, 2007.

http://www.nhc.noaa.gov/text/refresh/MIATCDAT4+shtml/180833.shtml?

5 am advisory

Thanks
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2837. nolesjeff
10:17 AM GMT on August 18, 2007
Discussion also said eye was 10 nautical miles across, that is pretty tight. I would say an eyewall replacement will happen sometime today
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2836. bajelayman2
10:16 AM GMT on August 18, 2007
http://www.nhc.noaa.gov/text/refresh/MIATCDAT4+shtml/180833.shtml?

5 am advisory.
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2835. bajelayman2
10:09 AM GMT on August 18, 2007
SINCE UPPER-LEVEL WINDS ARE FORECAST TO REMAIN FAVORABLE...THE
INTENSITY FORECAST CALLS FOR A GRADUAL INCREASE IN STRENGTH THROUGH
72 HR DUE TO INCREASING SEA SURFACE TEMPERATURES AND MAXIMUM
POTENTIAL INTENSITY.


Wow, and with Jamaica at 18.15 77.3 it is scheduled to get 135knot(155mph) winds.

Andrew had winds at landfall of 165mph? I guess still stronger and probably bigger too?
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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.