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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1085. DonnaGalveston
12:34 AM GMT on August 18, 2007
deadmandancing, I wish I could get my mind off of it, but I am trying to stay informed and learn as much as possible. I am trying not to freak out about it. Even if I go out everyone around town is talking about it already.
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1084. KRL
12:31 AM GMT on August 18, 2007
Whoa, speaking of earthquakes. Saudi Arabia just had a 4.3 shaker. I think that's a first. Never seen one happen there before that I can recall.

Hmmmm. The earth is really off kilter recently.
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1083. Metallica1990
12:35 AM GMT on August 18, 2007
Posted By: howarjo1943 at 12:35 AM GMT on August 18, 2007.

In the past cat 5's in the east carib don't last long and do not become strong cat 5's(sub 900mb), in the west carib however...


Times change

I think tomorrow will be a very busy day
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1082. Xion
12:34 AM GMT on August 18, 2007
a say cat 5 by noon tommorow...and by noon on sunday it will have 180 mph winds with a pressure below 900

I don't know.

Eyewall replacement cycles like to interrupt the storms quite a bit when they reach OMGWTF intensities. And usually once they undergo them, they never regain more than their former strength (because of land interaction or just taking too much time).
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1081. AnthonyJKenn
12:28 AM GMT on August 18, 2007
LAJoe...the GDFL tab is from this morning; the latest model run (18z) is the one showing a shift south towards a Freeport/Port O'Connor/Matagorda Bay landfall.

Ignore that tab, it is outdated as of the 5 PM advisory.


Anthony
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1080. gustypr
12:28 AM GMT on August 18, 2007
Just a coment according to the San Juan Long Range Radar Link Dean's eye is not where the NHC locates it.The wall appeers that it's barely reaching 64.8-64.9. The radar is barely 7 minutes behind present time. I'm confused
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1078. howarjo1943
12:32 AM GMT on August 18, 2007
In the past cat 5's in the east carib don't last long and do not become strong cat 5's(sub 900mb), in the west carib however...
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1077. Skyepony (Mod)
12:22 AM GMT on August 18, 2007
HHmm the high directly North of Dean has certainly weakened alot today. That High is soppose to move in over FL following the ULL. Hope the high doesn't weaken much more, specially we know how strong canes like to go N & will break down a weak ridge to get there. Also the ULL just east of FL~ click -3 hrs a few times. What was lastnight a solid 500mb ULL is getting to be a 700mb midlevel low pretty quick. The High to the east should have kept it from working to the surface at all, another testament to how weak the high North of Dean got the last 1/2 day or so.
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1076. Tropicnerd13
12:14 AM GMT on August 18, 2007
ok guys sorry if i made anyone upset in any way im going to go before someone gets offended. bye guys!
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1075. Metallica1990
12:32 AM GMT on August 18, 2007
I say Cat 5 by 5 am 175< by 5 pm or earlier and a close to if not record low pressure by 8 pm tomorrow
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1074. cormit
12:33 AM GMT on August 18, 2007
Recon is making another pass through now, should be into the eyewall within another 45 minutes.
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1073. SaBenDa
12:33 AM GMT on August 18, 2007
Gang,

I assume the planes are leaving from Keesler in Biloxi...Where to find a posted schedule?
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1072. JLPR
12:33 AM GMT on Agosto 18, 2007
someone said diurnal max
that could help a lil bit
it may get to 5 between tonight and tomorrow
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1071. leftyy420
12:29 AM GMT on August 18, 2007
interested in the next gfdl run. i always follow the gfdl as many in here know.

dean is looking fierce indeed
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1070. H2PV
12:31 AM GMT on August 18, 2007
Nice "ROOSTER TAIL" forming up behind DEAN. In the case of IVAN the rooster tail grew to be many hundreds of miles long. CAT 5's really churn out a big wake behind them.

http://www.h2-pv.us/wiki_100mpg/img/wiki_up/20070817_2315_04LDEAN.jpg

http://www.h2-pv.us/wiki_100mpg/img/wiki_up/ft.jpg
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1069. deadmandancing
12:32 AM GMT on August 18, 2007
@Donna:

Hey, there. I am a Mississippian who, while not on the Coast, but about 90 miles inland, witnessed the incredible damage from Katrina first hand. It was impressive even here in Hattiesburg. I love this site and was one of the most prepared people I know when Katrina came to town precisely because of my monitoring of this site.

That being said, though, may I suggest that you go and have a nice night out or partake of your favorite activity? You sound like you are very well prepared and proactive as concerns this storm. I can't think of any more prep you can do at this time. As real new data comes out only a couple of times a day, many of us here like to spend the rest of the time pontificating with more or less expertise and managing to scare the heck out of ourselves.

Sounds like you are on top of things, girl--now it is time to get your mind off of it for a while (I know its hard :)
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1068. howarjo1943
12:29 AM GMT on August 18, 2007
Cat 5 is immenent. Is there a recon still out there right now to get the pressure when this thing reaches its max.
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1067. SaBenDa
12:30 AM GMT on August 18, 2007
Where is Nash Roberts when you need him!
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1066. mgreen91
12:29 AM GMT on August 18, 2007
CNN just stated Dean is a Cat 4 headed to the U.S
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1064. moonlightcowboy
12:30 AM GMT on August 18, 2007
Forget 70w, not happening! Dayum! Double dayum! I don't think it's gonna catch the tail of the trough! Jamaica, Caymans, prolly southwards of them maybe now. GFDL will come back around southwards. Mexico, lower Texas, heads up!
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1063. tallahasseecyclone
12:26 AM GMT on August 18, 2007
Blanco is already asking for federal aid. I love it how we take the lessons learned from the past to the extreme
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1061. KRL
12:24 AM GMT on August 18, 2007
I agree Kman. The worst are earthquakes. They can zap you at any time with zero warning. I was in the 6.9 Northridge Quake in Jan '94. That thing was a monster and I said never again and moved out of Los Angeles that year. Can you imagine, 4:30 AM and your whole house starts shaking up and down like the world's ending. Thirteen years later and I can still feel that in my mind. You never forget an event like that. We were only 3 miles from the epicenter and got the full on jolts. Scary as hell.

So, I decided Hurricanes in FL was much more to my liking. LOL They really aren't all that bad as long as you live in a well constructed home and you don't get a Cat 4 or 5 head on. And at least, unlike quakes, you get ample warning.
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1060. DocBen
12:28 AM GMT on August 18, 2007
obxrox - "what could be behind this increase in intense hurricanes?....."

http://www.wunderground.com/education/webster.asp

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1059. ebzz
8:27 PM EDT on August 17, 2007
Posted By: watchdog40 at 8:27 PM EDT on August 17, 2007.
I live around Pensacola and the news said if it stalls it could change direction and make a northward turn, that we should not let our guard down. It this still possible?

It's possible but probably very unlikely. But it still can happen. Look at wilma last year (different conditions but still), it went all the way to the yucatan and curved back to florida.
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1058. JLPR
12:24 AM GMT on Agosto 18, 2007
there is a 40barb on the quikscat on the one in the coast of Africa
weird but no circulation with it
Link
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1057. staggalee
12:27 AM GMT on August 18, 2007
Correct me if I'm wrong but if Dean started slowing down wouldn't that put more distance between it and the ULL and allow the High over the Atlantic to build more in front of it to the west....thus allowing Dean to continue on its WNW trek to the Yucatan and Mex/Tex border?
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1056. bbesse
12:27 AM GMT on August 18, 2007
fox news just said that it was going to strike from mexico to the top coastal areas of texas. it is funny how they know for sure that is where it is going,i hate that because it could turn and hit someone else and catch them off guard,because of weather men that says it is going right in a location that is 96 to 120 hrs away according to the speed of the storm

If this one catches any coastal area off guard, shame on them! I'm in MS, and there is no way this one is catching anyone off guard.
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1055. Fl30258713
12:28 AM GMT on August 18, 2007
tallahasseecyclone

I think it has to do with the dry air disappearing in Dean's path

Dean
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1054. Metallica1990
12:27 AM GMT on August 18, 2007
It looks like a 5 now! man this one storm makes up for all of last year
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1053. strangesights
12:22 AM GMT on August 18, 2007
Praying for all in Dean's path ... time to get prepared ... adios folks
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1052. StormJunkie
12:26 AM GMT on August 18, 2007
LA joe, 12Z was 8am Est. The one 18z is 2pm. The 00z runs just started at 8:00.

It takes the global models a long time to ingest all that data...
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1051. sunshineandshowers
12:23 AM GMT on August 18, 2007
woah..some people are really getting carried away.
yes dean is looking pretty bad, but there's a huge difference between 135mph and a wilma. then again wilma only needed 30 hours to drop from 982 to 882.
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1050. littlefish
12:23 AM GMT on August 18, 2007
The ULL aint moving much west so I'm suspecting the models are weakening it and pushing it slightly more north away from Dean. Otherwiae I think they'd be computing the lack of west moveemnt and shifting things slightly west. So I'm guessing dissipation and more north mvmnt for ULL. Anybody? I see a microburst of convection around wave off Africa LOL. TINY burst. 15N 32W.
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1049. watchdog40
12:25 AM GMT on August 18, 2007
I live around Pensacola and the news said if it stalls it could change direction and make a northward turn, that we should not let our guard down. It this still possible?
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1047. KEEPEROFTHEGATE (Mod)
12:25 AM GMT on August 18, 2007
e beez C5/H/D 16.1,72
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1046. HurricaneJoe
12:27 AM GMT on August 18, 2007
diurnal max time
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1045. bbesse
12:24 AM GMT on August 18, 2007
Here is a question for someone with good experience: On television they said watch the shape of the eye for hints on change of course. They looked at the radar for Puerto Rico and said the eye appears to have a bit of a northwest slant, meaning the storm could turn in that direction shortly. Does that make sense?

It only makes sense to someone on television looking for ratings. In my opinion it's just a scare tactic. They are grasping for something to scare everyone including the east coast. Even though the models (based on physics) are showing a very southern TX or Mexico landfall, they will stab at something irrelevant.
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1044. SWFLdrob
12:26 AM GMT on August 18, 2007
holy crap


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1043. Metallica1990
12:25 AM GMT on August 18, 2007
you know if the pressure keeps droping as fast as it is we could be dealing with explosive deepening
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1042. StormJunkie
12:23 AM GMT on August 18, 2007
I agree 1943, Dean is riding a line a hair under 15N. Due W.

Gonna have to gain some lat if is is going to hit the forecast points.

Headed for his next buoy snack...
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1041. Crazman
12:23 AM GMT on August 18, 2007
Donna Yes that is VERy true, a hurricane usually stretches the direction it will move. Floyd was an excellent example. It stretched taller right before it moved north. It is the direction of the air flow that influences shape of the storm, so if the gap between the ull and high weakened for example and dean were to slip off to sea, it would probably stretch tall and thinner and maybe slant NE.
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1040. extreme236
12:25 AM GMT on August 18, 2007
nice point keeperofthegate. a couple weeks ago people were like:

"this season is a bust"

"this season is a bust"

and i havent seen any of those people since
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1039. louisianaweatherguy
12:21 AM GMT on August 18, 2007
I've watched Dean move straight WEST... not WNW or not WSW... If he's gonna wobble it will be to the WNW to try and find a weakness...

That's what we're wondering.... WILL DEAN FIND HIS WEAKNESS and go further to the NW AFTER JAMAICA OR NOT??

... The Million Dollar Question
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1038. IMA
12:25 AM GMT on August 18, 2007
KATADMAN

You can see pictures of what Erin did to our bridge last night. Keep in mind that the bridge is (was) about 6 to 6.5 feet from the creek bed, where my son and I played on Wednesday. Also, the water has gone down many feet, which you can see in some of the pictures.

I'm planning on going to bed early tonight so I can start getting things in order tomorrow. Today was a bust because I was recovering from yesterday! lol


Link

-- it's continued on page 2 and later I'll have more added, now that the water has receded another foot & you can see the "holes".
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1037. LAJoe
12:25 AM GMT on August 18, 2007
Correct me if I am wrong but the time of initiation on the GFDL on the computer model page that shows landfall in Tx is at 2:00 pm AST. If you go to the GFDL tab which was initiated at 1200 Z 7:00 pm AST it shows landfall in LA. I believe that is the latest run!!!!!!!!
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1036. howarjo1943
12:19 AM GMT on August 18, 2007
Too many things have to happen with that upper low for Dean to hit the northern Gulf Coast. The percentages say go with the Yucatan/ mex/S tex landfall. I usually disagree with the NHC(especially when they classify occluded fronts topical systems) but they are doing a good job on this difficult storm. They are under a lot of pressure with a storm like this. They have time to watch that low and if things change, they will shift the track giving anyone in Deans path ample time to leave.
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1035. KEEPEROFTHEGATE (Mod)
12:17 AM GMT on August 18, 2007
it will achieve 165 mph winds at its peak then the slow decrease in wind an overall storm intensity will begin to come down it funny about a week ago of all the gripe as to where was the season well i guess its here and in a big way
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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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