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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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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2834. WeatherSpotter
10:15 AM GMT on August 18, 2007
He's a BIG boy now, right up there with the biggest.
Do you have link? I must have read earlier discussion, it said cat 4 and 937 thanks


Flight level indiciated Cat 5 Storm but dropsonde data didn't supply conveniencing data for Cat 5 at surface.

Currently a Cat 4 @ 930 MB at the surface while they know while we know its a Cat 5
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2833. bobcane
10:11 AM GMT on August 18, 2007
If 307 deg WNW holds (confirmed on radar returns out of PR) this storm will go north of Jamaca into Cuba from this current position. Over the Isle of Youth north of the Yucatan channel. Emerge into the gulf at north of 23 deg. That's the significance of this change in direction seen on radar in the last 1-2 hours.
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2832. nolesjeff
10:13 AM GMT on August 18, 2007
Posted By: bajelayman2 at 10:08 AM GMT on August 18, 2007.

Jeez, just read the discussion. CAT 5 and 930MB.

He's a BIG boy now, right up there with the biggest.
Do you have link? I must have read earlier discussion, it said cat 4 and 937 thanks
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2831. WeatherSpotter
10:10 AM GMT on August 18, 2007
weatherspotter, can you please explain your reasoning as to why Mexico is not part of your percentage.. I would thik they have better then 70%, just because Dean is slowing down and the high that builds up early next week pushes Dean further down south towards Central Mexico..

I'm only considering Gulf Coast states because I actually don't think this storm will hit Mexico.

Its changed direction earlier than previously thought and if that ULL beats Dean then the ULL will turn the Hurricane into a curve.

While mexico is important and I don't want them or anyone else to be hit I just feel this will be a US Landfall.
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2830. SWFLdrob
10:08 AM GMT on August 18, 2007
bob...just like it was south of the track for about 10 hours yesterday as it was sliding due west. They shifted the track south a bit because of it...and now it is north again. NHC just can't win ;)

Finally has some northweard tilt to it...that jog perfect west was unexpected.
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2829. samiam1234
10:07 AM GMT on August 18, 2007
weatherspotter, can you please explain your reasoning as to why Mexico is not part of your percentage.. I would thik they have better then 70%, just because Dean is slowing down and the high that builds up early next week pushes Dean further down south towards Central Mexico..
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2828. bajelayman2
10:06 AM GMT on August 18, 2007
Jeez, just read the discussion. CAT 5 and 930MB.

He's a BIG boy now, right up there with the biggest.
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2827. bobcane
10:04 AM GMT on August 18, 2007
On the NHC satellite, the eye is clearly norh of the NHC track now. They have a little hurricane icon at 15.1 and the storm is at 15.3 in that position. Movement of WNW can now be confirmed.
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2825. bajelayman2
9:49 AM GMT on August 18, 2007
Official forecast has it going through Jamaica.

Poor Jamaica, another Andrew? And it is projected on the South side, which means that it will get the worst quadrant being the right front as I was told here, no? And still the big tail. Today is the first low cloud day in Barbados since Wednesday, rained a lot yesterday, all the tail.

Take care guys & gals there.

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2824. hurricane667
10:02 AM GMT on August 18, 2007
when do the huurricane hunters go out next 12z?
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2823. WeatherSpotter
10:01 AM GMT on August 18, 2007
I sure would hate to see this storm wreck havoc in the Gulf Coast... I have friends in the area of Baton Rouge and hope for their sake as friends it misses that NO/BR area.

When Katrina hit I had an opportunity to respond with FEMA when they was looking for emergency responders to assist in the efforts and I was stupid for not going.

If this does happen again I will make every effort to respond with FEMA this time and not have another chance of losing out on this once ( or twice ) in a life time event.
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2822. GPTGUY
5:00 AM CDT on August 18, 2007
Weatherspotter it made sense..like I said its getting late..and if the ULL takes its time moving out or is drifting WSW..those numbers dont seem to far off
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2821. WeatherSpotter
9:59 AM GMT on August 18, 2007
Amy

Mine
Mexico- 68%
Texas: 25%
Louisiana: 3%
Mississippi: 2%
Alabama: 1%%
Florida: 1%


It is evident your being ignored in this forum by reading past responses of others in the room.
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2820. VEROBEACHFL1
9:57 AM GMT on August 18, 2007
AMY i but only have this last entry for you---and you can scramble the letters together to figure it out----its not a met term either--------




-----------S T F U------------- goodnight all----till tomorrow---well, ur, um--i guess thats today--lol nite/morn--:)
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2819. WeatherSpotter
9:55 AM GMT on August 18, 2007
Thanks

I hope what I've said makes sense...

Man those last frames are definately showing a consistant WNW to NW motion compared to earlier while it was due W.

Knowing our luck it'll miss the YP and Cuba and go between there in the caribbean and keep its strength and hit stronger than Katrina did on the gulf coast.
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2818. VEROBEACHFL1
9:55 AM GMT on August 18, 2007
oh yes---that is almost a fact---well---heck--it is !! LOL later katadman.................
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2816. katadman
9:52 AM GMT on August 18, 2007
Hey, I enjoyed blogging with each of you, but am yawning way too often to stay up any longer. See you tomorrow. You realize that regardless of direction, we may very well have a cat 5 on our hands later this evening!

Goodnight all.
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2815. WeatherSpotter
9:52 AM GMT on August 18, 2007
---i think he means each one out of a possible 100%----individually---not as a whole group-----

Right out of a 100% chance for each state those are my predictions per each 100% percentile for each state listed.
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2814. GPTGUY
4:54 AM CDT on August 18, 2007
LOL VERO I didn't..took me a few to figure it!
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2813. GPTGUY
4:52 AM CDT on August 18, 2007
I gotcha Weatherspotter..I see how youre figuring it..my fault its late
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2812. VEROBEACHFL1
9:53 AM GMT on August 18, 2007
lol@weatherspotter----i understood the first chart---BTW :)
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2811. WeatherSpotter
9:49 AM GMT on August 18, 2007
Right well it should add up to 100% but we look at it as the percentages of it striking a certain area.

If you want me to redo these to match 100% then here are as follows:

Texas: 40%
Louisiana: 25%
Mississippi: 15%
Alabama: 10%
Florida: 10% ( Depending on the curve )
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2810. GPTGUY
4:51 AM CDT on August 18, 2007
yeah VERO i see...like everyone else said its getting late and hrs of watching loops makes you think differently...lol
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2809. VEROBEACHFL1
9:49 AM GMT on August 18, 2007
---i think he means each one out of a possible 100%----individually---not as a whole group-----
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2808. GPTGUY
4:46 AM CDT on August 18, 2007
Weatherspotter what you said makes sense..but its misleading to put percentages for states...for example 60% for Louisiana and 40% for Mississippi...If Dean were to strike somewhere near NOLA or a little east of there..Mississippi would be on the east side and get the full effects of the east and ne quadrant of the storm..just as much of an impact as Louisiana
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2807. nrtiwlnvragn
9:48 AM GMT on August 18, 2007
West, No Northwest, No west

If he only knew what he started

radar
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2806. katadman
9:47 AM GMT on August 18, 2007
That's 235%. I don't understand.
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2805. SWFLdrob
9:46 AM GMT on August 18, 2007
hey weather spotter...shouldn't those percentages all add up to 100%? Looks like you're working on a 235% scale ;)
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2803. WeatherSpotter
9:46 AM GMT on August 18, 2007
I have got a couple of question... with Erin crossing the GOM last week.. is there still plenty of moist in there for Dean to build up more convection and continue increasin in size.. according to NHC there were buoys 200 miles away from COC that had 59 mph average for 1 minute.. in comparison how does Dean stand against Titans like Katrina and Rita, in size only and how large do you expect this system to get??


Plenty of moisture... Erin was nothing merely but a weak Low Level Storm and while it did have a ton of rain it did nothing on deep level water temperatures.
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2802. VEROBEACHFL1
9:45 AM GMT on August 18, 2007
swfldrob---Also, the models and NHC track all have some northern movement in its tracks, not straight west. Will have to wait to see, but too early to call a prolonged NW motion IMO.

---IMO--WNW not a NW till at least 80w or right before
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2801. bobcane
9:44 AM GMT on August 18, 2007
The radar returns have been consistant now. There have been slight moves to west, then correction to the north again, but overall the storm is now moving in the direction of 307 deg, 13 deg of 320 which is NW. It is WNW at the moment. No longer W. It is headed for 16N now
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2800. WeatherSpotter
9:35 AM GMT on August 18, 2007
Thoughts?

Its Massive!!!

Uhm I think you nailed the NW/WNW right on the nailhead - GJ with that analysis.

My thoughts are as follows:

This storm has the potential to break records as what happened in 2005. The storm isn't even in the peak temp of water in the deep layers of the caribbean.

If this storm keeps this WNW to NW then we will definately see a projected path shift towards the N that will be more influxed of TX,LA ( Possibly Another NOLA strike ) all depends on how strong that ULL is and what happens if the ULL beats the Hurricane since it is now slowing down which also isn't good for anyone in its path.

Following is my percentages of landfall for US:

Texas - 80%
Louisiana - 60%
Mississippi - 40%
Alabama - 35%
Florida - 20% ( But can change depending on how large the curve is )
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2799. samiam1234
9:42 AM GMT on August 18, 2007
Bobcane do you think this is a temporary jog to the north or is there really no way to tell that?
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2798. bobcane
9:40 AM GMT on August 18, 2007
The source for 307 deg is my own analysis using a rose tool attached with my GR2AE radar software. You put a compas rose on the screen as an overlay on your radar and plot the direction. The software is very accurate.
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2797. samiam1234
9:38 AM GMT on August 18, 2007
sorry didnt read that... you said 16 degrees.. I thought it was 16 North.. getting a bit sleepy.. does that confirm a WNW movement though??
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2796. katadman
9:36 AM GMT on August 18, 2007
The WNW movement is consistent with ALL the models as far as I can see. So it really doesn't lend more credence to one path or the other. The real divergence in the paths won't be noticeable for quite some time.
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2795. VEROBEACHFL1
9:38 AM GMT on August 18, 2007
?? it shouldnt cross 16 till at LEAST somewhere in the 69-71
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2794. nolesjeff
9:35 AM GMT on August 18, 2007
Posted By: Amystery at 9:22 AM GMT on August 18, 2007.

if Dean was going to FL...Drak, jp, hurricane23 the whole Florida gang would be here, and this blog would be double....have you noticed all the Florida regulars are nowhere to be found? lol(they are looking for a spin in the wave off africa)


What is your problem, where are you from? Every day I come on here you are bashing Florida! You have an issue, sounds like you are bitter or jealous, but it has gotten old!
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2793. bobcane
9:38 AM GMT on August 18, 2007
Who you talking to samiam
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2792. bobcane
9:36 AM GMT on August 18, 2007
Dean is most like Gilbert and Allen before it at the moment. Something Like Ivan as well. Similar to Katrina in size I guess if we need to compare it to something in recent legend.
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2791. samiam1234
9:35 AM GMT on August 18, 2007
no way COC is at 16 Degrees in 2 hours from 15.1?? thats not even WNW thats more North then West.. can you site your source.
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2790. samiam1234
9:30 AM GMT on August 18, 2007
I have got a couple of question... with Erin crossing the GOM last week.. is there still plenty of moist in there for Dean to build up more convection and continue increasin in size.. according to NHC there were buoys 200 miles away from COC that had 59 mph average for 1 minute.. in comparison how does Dean stand against Titans like Katrina and Rita, in size only and how large do you expect this system to get??
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2789. noshoes
9:28 AM GMT on August 18, 2007
I'm Florida, and I am here...paying close attention.
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2788. bobcane
9:33 AM GMT on August 18, 2007
Just reconfirmed the 307 deg movement in the last hour on GR2AE radar. 16 deg shy of NW at the moment.
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2787. VEROBEACHFL1
9:33 AM GMT on August 18, 2007
ty weatherspotter-- any thoughts?
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2786. katadman
9:25 AM GMT on August 18, 2007
No, no, my friend, you misunderstand me. I mean the GRINGO Mexico wishcasters. There are people who will pick a position and hang onto it for dear life just for the sake of saying they were right without backing their position with any useful meteorological data. That goes for every possible path. There was some jack-ass kid on a couple of days ago that would assume any position at all just to start arguments. He even changed his identity a couple of times to keep the ruse going. It seems that those types are going to continue to plague us here for the duration. Sad, don't you think?
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2785. WeatherSpotter
9:26 AM GMT on August 18, 2007
Yep,

I agree with Vero its turning NW/WNW direction especially in the last couple frames of this.

Link

Very evident of that in the Infrared/Satellite views.
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About

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.