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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3085. watchingnva
1:07 PM GMT on August 18, 2007
peurto rico is about to have a very heavy squall line /rain band come through over the next couple of hours...
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3084. Pipewhale
1:04 PM GMT on August 18, 2007
Not to belittle the effects Dean is having, but does anyone have any thoughts on the blob at about 10N 35W?

I can't find a loop so I can't tell if it's just a flair up or something else. Thoughts?
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3083. Kaea
7:07 AM MDT on August 18, 2007
Looks like Dean missed Roatan, at least directly - anybody know if that's correct? I have a friend who is there for a diving vacation. Thanks.
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3082. atmoaggie
1:02 PM GMT on August 18, 2007
OK...However, if that's the case shouldn't those anamolies occur from the radar location down in League City which would be further south? If you notice there were two of them right along I-10.

We may not be calling the same thing an anomaly. I think I see some of what you mean, that ring almost seems centered on 290/45/Westheimer area. Now I have no answer. Could it be a mushroom cloud? Sorry, not real funny. I tried, at least.
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3081. StormJunkie
1:05 PM GMT on August 18, 2007
The MIMIC imagery is impressive this morning. Shows the start of the WNW-NWish movement. it also shows the eyewall intensifying and contracting.
Member Since: August 17, 2005 Posts: 26 Comments: 16874
3080. Masquer08er
1:04 PM GMT on August 18, 2007
WatchingnVA, Hope you're right. Those folks in Haiti/DR would be devistated.
Member Since: August 16, 2007 Posts: 0 Comments: 397
3079. SEFL
12:59 PM GMT on August 18, 2007
"Never would have guessed hail in a hurricane. Never seen it myself, but I don't go out side during storms."

In an interview on last night with an HH pilot he talked about the wind and rain and hail hitting the windscreen when they fly into hurricane. Of course this is at 10,000 feet!!!
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3078. VegasRain
1:04 PM GMT on August 18, 2007
Posted By: dmaddox at 1:04 PM GMT on August 18, 2007.

oh wow!! the weather channel has put mike seidel in the direct path of a potential category 5 hurricane in montego bay, jamaica!!! WHAT!??


When I heard that last night, I thought TWC must be out of their minds!! I hope that they have him in a strong concrete reinforced building above 20 feet at least. That seems idiotic to send someone into the direct path of a Catagory 5 hurricane.
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3077. PensacolaDoug
1:05 PM GMT on August 18, 2007
oh wow!! the weather channel has put mike seidel in the direct path of a potential category 5 hurricane in montego bay, jamaica!!! WHAT!??


What a cool job!
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3076. StormJunkie
1:04 PM GMT on August 18, 2007
waccamaw16, Welcome ☺

Quick Links-You want the last part about the South Fla Water Mang site...Go there and select Storm 04 at the top of the page.

Select the first link in the model section. This is the FSU Experimental model page. For all models except for the GFDL and HWRF, I set the field to 850mb vorticity to view potential genesis or track and size of tropical systems. Select animate then scroll right and page through the model run. The surface maps are also good to look at as the 850mb map will sometimes show features which are not at the surface. The GFS, GFDL, and HWRF run four times a day; 00z, 06z, 12z, and 18z. The 00z runs usually come out around 2am Est, the 06z around 8am Est, the 12z around 2pm Est, and the 18z around 8pm Est. The CMC, Nogaps and mm5fsu only run at 00z and 12z. The FSU model site can depict the strength of a system which is something you donít get with the line models. There is a great link that shows the mb to ft comparison in the learning section. Also the GFDL and HWRF only work with the field set to Surface Pressure and they only run for active storms. The NWS NCEP model page contains the long range GFS and the NAM as well as several other models. The South Florida Water Management page has a nice spaghetti plot showing most all of the models together. The Weather Underground Tropical section also has some nice spaghetti plots of several of the major models. The GFDL track can usually be found here before it can be seen on the other sites.
Member Since: August 17, 2005 Posts: 26 Comments: 16874
3075. waccamaw16
1:03 PM GMT on August 18, 2007
thank you wecouldoit
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3074. EllistonVA
12:56 PM GMT on August 18, 2007
steel - that sounds like great advice. I'm used to winter storms that come out of nowhere - or at the most you get a day's notice. Where we live we can lose power for days and we live on a mountain that we ca't get off of. So we always have all of our supplies ready, gas for the generator and we just don't worry about it.

You have more to worry about with an evacuation, but the idea of having everything ready well in advance so that you are ready to go and then just kicking back and watching to see if you have to is the way to go.
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3073. dmaddox
1:01 PM GMT on August 18, 2007
oh wow!! the weather channel has put mike seidel in the direct path of a potential category 5 hurricane in montego bay, jamaica!!! WHAT!??
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3072. watchingnva
1:02 PM GMT on August 18, 2007
d.r. and haiti will be fine here....tropical force winds of course...but the eye will pass well south...right now its a crap shoot for jamaica...could directly hit...could just miss to the north or south...we will just have to wait and see...
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3071. JRRP
12:59 PM GMT on Agosto 18, 2007
THE RADAR OF DOMINICAN REPUBLIC
IS DAMAGE
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3070. TXMET
12:54 PM GMT on August 18, 2007
Looking at the WV loop this morning, the ULL is hanging in there and has nudged a little further west. It's interesting that the models (including the GFDL) seem to be minimizing its potential effect. What do you think?
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3069. welshcayman
1:01 PM GMT on August 18, 2007
I am really hoping that the movement to the North continues now. The latest track is the worst possible one for us being that any storm that passes South of us causes the most damage.

I just bought 5 cartons of cigarettes though so with those and the 50 gallons of water I have I think I should be good to go.
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3068. StormJunkie
12:56 PM GMT on August 18, 2007
Welcome holyd ☺

srada, I think in Deans case the ULL is what will ultimately decide the outcome. Help me out here maggie, If the ULL were to stay slow Dean could get caught up in front of it and then get "tugged" N. If the ULL travels in tandem then Dean continues W at a decent rate of speed. Not likely to happen in this case, but if Dean/a storm were to get behind an ULL then it would likely be pulled N and then W if it could get over the top of it? Y'all correct/help me understand here, thanks
Member Since: August 17, 2005 Posts: 26 Comments: 16874
3067. PensacolaDoug
1:01 PM GMT on August 18, 2007
I've had Puerto Rico radar up all morning. Good view

Likewise, but we're gonna need a new one soon.
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3066. srada
1:00 PM GMT on August 18, 2007
good morning,

steve lyons saying storm has jumped to the north which makes a difference in the islands getting hit, hummmmm
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3065. Randyman
12:56 PM GMT on August 18, 2007
Posted By: atmoaggie at 12:48 PM GMT on August 18, 2007.

Someone please explain to me what is this on the Houston/Galveston radar loop...I see this every now and then...it always appears to dissipate most of the rain within it's vicinity...

That could the HGX radar folks changing the VCP (Volume Coverage potential) which is a fancy way of saying the elevation angles of the radar. They change it lower at time when there is no nearby rainfall so more vertical structure in an event futher away can be seen and accept that buildings/ birds, and the like will show up near the radar (all of the light blue). Why the concentric ring moving away from the radar? No real sure. Could have been the VCP change itself.


OK...However, if that's the case shouldn't those anamolies occur from the radar location down in League City which would be further south? If you notice there were two of them right along I-10.
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3064. pottery2
8:54 AM AST on August 18, 2007
Mornin'all.
Last night I spent 3 hours looking at the most incredible light-show over the mountains of the Paria Peninsula, Venezuela. I am in Trinidad, 7 miles from there.
I have never in my 57 years seen lightening like that. The sky looked like a disco with all the strobes no, and on fast-forward.
I would not be suprised to hear bad news out of there today.
How can the sky generate this much electricity, for such a continuous period ??
Incredible stuff!!!!
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3063. KYhomeboy
12:57 PM GMT on August 18, 2007
dmad...Dean will track on a westward to west-northwestward direction...so some northerly component is expected. Don't consider it a permanent change in direction though....Dean has moved due wedt for many hours...than changed to almost due northwest....so expect it to very...but mostly stay on track
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3062. Masquer08er
12:58 PM GMT on August 18, 2007
P'cola,

I've had Puerto Rico radar up all morning. Good view.
Member Since: August 16, 2007 Posts: 0 Comments: 397
3061. PensacolaDoug
12:57 PM GMT on August 18, 2007
What are the chances of the ULL shifting and changing the course of Dean?

The NHC seems awfully confident of they're track. I wouldn't bet against them. We have seen big track adjustments be fore tho....
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3060. Masquer08er
12:57 PM GMT on August 18, 2007
Thanks WPB and SJ.
Member Since: August 16, 2007 Posts: 0 Comments: 397
3059. watchingnva
12:54 PM GMT on August 18, 2007
def. much more north of track in the short term...looks to be at 16.2-16.6 when it will cross over 70 at this direction and speed...a norther pass of jamaica would be great for the island...
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3058. Wecouldoit
12:52 PM GMT on August 18, 2007
waccamaw16... If you want most of the models...go to http://euler.atmos.colostate.edu/~vigh/guidance/
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3057. PensacolaDoug
12:54 PM GMT on August 18, 2007
Anybody got a link to a Haiti or Dominican Republic radar?
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3056. dmaddox
12:54 PM GMT on August 18, 2007
one other note..it appears the track of dean is definitely, finally beginning to have a northerly component. at first i thought it may be a "jog" or "jump" but dont think it is. has anyone else noticed this??

http://www.meteo.psu.edu/~gadomski/SAT_CARIBWIDE/anim8ir.html
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3055. StormJunkie
12:52 PM GMT on August 18, 2007
Morning y'all

I see the GFDL shifted S a little, but I would expect more changes over the next couple of days.

Welcome 08er ☺
As for storms going N, they always want to, but if there is a high above them then they can't. So no, it is not just a GOM/Carib thing. Just that the CATL has a high over it more often then the Carib and Gom. The storm needs a weakness to travel in to. Last year there ws a weakness in the CATL that sent mpst storms out to sea.
Member Since: August 17, 2005 Posts: 26 Comments: 16874
3054. holydiver
12:53 PM GMT on August 18, 2007
What are the chances of the ULL shifting and changing the course of Dean?
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3053. steelmagnolia44
12:39 PM GMT on August 18, 2007
BiloxiGirl,

I agree with you about the time frame for predictions and about the unexpected changes.

I remember Bob Breck standing there with great confidence and telling everyone Katrina would be a Florida storm!

I was very concerned yesterday about Dean, and this morning I feel a little better about it. Yesterday I thought I don't have the energy to go through this again.

I did start getting ready for Katrina early because of Stormtop's prediction on this blog. I had a head start of several days. I remember Camille. All we can do is have the basic preparations in place and if there is an unexpected change, then we are prepared to take action. Watching this all day when a more accurate prediction is still days away is not very productive. We know Dean is a threat. We won't help ourselves by becoming wiped out emotionally before it even gets into the Gulf. We will need all that energy. Prepare the basics and have a plan.

steel
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3052. atmoaggie
12:53 PM GMT on August 18, 2007
Then what you doing posting a WDSU Nash Roberts thing?
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3051. watchingnva
12:49 PM GMT on August 18, 2007
wow...just studying the radar images along with sat. frames....it looks like the new outer eye is going to be huge....look for overall cdo (cloud field) to expand out in a big way over the next 6-12 hours...should be interesting to watch...
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3050. srada
12:52 PM GMT on August 18, 2007
Not sure. There are too many variables which controls where a storm goes. Sometimes the sinking air around intense hurricane will create its own high pressure system steering it west, or sometimes intense hurricanes will weaken the ridge allowing it to turn north.

so in deans case, is it making its own steering pattern?
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3049. bobw999
8:53 AM EDT on August 18, 2007
WPB, you in NOLA area? where? Covington here. Born in NOLA, raised in BR.

Nope. I'm in West Palm Beach (hence the WPB).
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3048. atmoaggie
12:51 PM GMT on August 18, 2007
WPB, you in NOLA area? where? Covington here. Born in NOLA, raised in BR.
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3047. ecflawthr
12:50 PM GMT on August 18, 2007
anything new on the low behind dean?
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3046. ncstorm
12:46 PM GMT on August 18, 2007
You know, i sit here and observed some of the comments on here and sometimes you just have to laugh, when people post comments of experts saying it looks like it wont come your way, people get mad because "how dare they not considered us in the strike zone" but yet you act so scared of a hurricane hitting you, which one do you want?
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3045. WPBHurricane05
8:49 AM EDT on August 18, 2007
WPB,

The stronger = north theory, is that only true for GOM and Carib. storms?


Not sure. There are too many variables which controls where a storm goes. Sometimes the sinking air around intense hurricane will create its own high pressure system steering it west, or sometimes intense hurricanes will weaken the ridge allowing it to turn north.
Member Since: July 31, 2006 Posts: 56 Comments: 8112
3044. dmaddox
12:51 PM GMT on August 18, 2007
point noted 1900, but i still have a hard time believing that. how can that be?? i think there has to be a mistake somewhere.... as a "general" rule, i like to follow this table for pressure esp. in the "southern" tropics. it seems most accurate there:

scroll to bottom:
http://weather.unisys.com/hurricane/index.html
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3043. EllistonVA
12:45 PM GMT on August 18, 2007
jamweather - I am so sorry to hear that it doesn't appear that people are preparing. I always worry about the people on the islands in these storms. In the US we can just go 100 miles inland to get out of the path, not so on an island. You will all be in my prayers.
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3042. watchingnva
12:47 PM GMT on August 18, 2007
no problem...just take care of yourself and stay safe...

when will you be signing off of here and bunkering down...whats your plan???
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3041. atmoaggie
12:43 PM GMT on August 18, 2007
Someone please explain to me what is this on the Houston/Galveston radar loop...I see this every now and then...it always appears to dissipate most of the rain within it's vicinity...

That could the HGX radar folks changing the VCP (Volume Coverage potential) which is a fancy way of saying the elevation angles of the radar. They change it lower at time when there is no nearby rainfall so more vertical structure in an event futher away can be seen and accept that buildings/ birds, and the like will show up near the radar (all of the light blue). Why the concentric ring moving away from the radar? No real sure. Could have been the VCP change itself.
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3040. Masquer08er
12:42 PM GMT on August 18, 2007
WPB,

The stronger = north theory, is that only true for GOM and Carib. storms?
Member Since: August 16, 2007 Posts: 0 Comments: 397
3039. Wecouldoit
12:36 PM GMT on August 18, 2007
Based on latest sat images...it does appear to have jogged NW...Jamaica will need more, but that is in the right direction...
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3038. WPBHurricane05
8:45 AM EDT on August 18, 2007
Member Since: July 31, 2006 Posts: 56 Comments: 8112
3037. jamweather
12:45 PM GMT on August 18, 2007
Posted By: watchingnva at 12:45 PM GMT on August 18, 2007.
jam....we will be praying for ya...and hoping for the best...unfortunantly...it doesnt look good for ya...


thanx
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3036. waccamaw16
12:45 PM GMT on August 18, 2007
can someone post the link of the newest models were every model is on the page?
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3035. 1900hurricane
7:41 AM CDT on August 18, 2007
Katrina had a pressure at 920 mbs, and it was a CAT 3!
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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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