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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3134. miken62
1:21 PM GMT on August 18, 2007
I will say many people around here don't even pay attention to storms ..I've seen TS warnings and Hurr watches go up in the past around here and it brings more people out to see the potential storm...

kind of strange up here ...they come instaed of go
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3133. Tampawxgirl
1:21 PM GMT on August 18, 2007
lmao at you and BG! Y'all are so right though. It was kind of like "if we ignore it it will go away" Like the monster under the bed when you were a kid...

To use another expression, they're ignoring the elephant in the room. :-)
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3132. watchingnva
1:21 PM GMT on August 18, 2007
the wave at 10,35 looks very interesting this morning...alot of convect...possible low tring to form...its another watch and see situation...I think has a descent chance of doing something over the next 3-4 days...as long as it continues to fire convection and organize more... we will see.
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3131. StormJunkie
1:20 PM GMT on August 18, 2007
dmadd, yes I have noticed it, I think more and more folks are using it. The '05 season peaked a lot of interest in tropical activity. It is still worth waiting on imho. Seems to be doing pretty good today as well. Better then yesterday!
Member Since: August 17, 2005 Posts: 26 Comments: 15723
3130. miken62
1:14 PM GMT on August 18, 2007
LOL; I am not being complacent... I've been here for some of the wildest winterstorms and for a few minor hurricanes Gloria/Bob..I am in Middletown RI next to Newport and about 165 ft above sea level (thank god for that).
Believe me ..if a monster were coming I'd leave; not for fear of my house flooding but Newport, Middletown and Portsmouth RI are on an island and even though the bridges are high, they would probably get damaged and then no one gets on or off....
that would suck
Member Since: January 14, 2003 Posts: 0 Comments: 213
3128. ajcamsmom
8:17 AM CDT on August 18, 2007
Gov. Blanco knows for a fact that NOLA can not handle any kind of real storm at this time. The levees are not up to par, the pipes under the City are at best leaking and many are crumbling. She is in a no win situation.
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3127. ridercs
1:19 PM GMT on August 18, 2007
new on the blog

does anyone think that the wave in the west Atlantic looks like it is developing?
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3126. comtrader
1:07 PM GMT on August 18, 2007
txmet
i dont think the models are minimizing the ull, they just have it zipping across the gulf and getting to texas fast enough so that the high can build in behind it in the gulf fast enough to keep dean from being dragged in. this is a really tricky related rates problem. my guess is that the farther south the ull goes and the slower it traverses the gulf towards texas, will determine if dean does any damage to the US. if the ull moves more slowly than forcast (or dean picks up a lot of speed) this will increase the likelihood of a US landfall. I keep checking the model predictions 6 hours out and comparing them to the water vapor loops which give a pretty good idea of the circulation around the ull. so far the ull to my eye has tracked a little slower and farther south, but at least on the last few frames appears headed more west across the southern tip of fla. this is a hell of a race, where a lot of lives and countless dollars are on the line.
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3125. watchingnva
1:16 PM GMT on August 18, 2007
ok...im gonna take back my ewrc statement earlier...if you study the images closely...it looks as if dean tightened its eye real tight and it just took the rest of the storm a lil longer to speed up and catch up...the inner eyewall looks strong as ever and tightening/strengthening even more as we speak...I do still feel that an ewrc will be happening this evening or overnight...
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3124. welshcayman
1:16 PM GMT on August 18, 2007
It is abhorent to send a reporter to a place where a Cat 5 storm is about to land. With the camera and sound crew that is probably 3-4 more mouths to feed and people to protect for the emergency services.

I could understand if they were there for a scientific reason but it is simply for ratings and nothing else.

My respect for TWC just keeps falling. Do they not think that there would be a local Jamaican reporter on the ground that could have provided them with the same service via sattelite feed?
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3123. WhereIsTheStorm
1:12 PM GMT on August 18, 2007
Posted By: welshcayman at 1:03 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.


I am hoping that the storm goes north of you as well. Considering the models and everything the best we can hope for is a wobble to the North and hope it stays that way before exiting the islands. You know you can always use the cigarettes and water as bartering chips for food.
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3121. dmaddox
1:19 PM GMT on August 18, 2007
StormJunkie, i have used the GHCC alot in recent years during tropical season but this year it seems particular sluggish and even unavailable at times. have you noticed this? im a bit disappointed. :(

http://wwwghcc.msfc.nasa.gov/GOES/
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3120. StormJunkie
1:17 PM GMT on August 18, 2007
Hey Lalady :~)

lmao at you and BG! Y'all are so right though. It was kind of like "if we ignore it it will go away" Like the monster under the bed when you were a kid...
Member Since: August 17, 2005 Posts: 26 Comments: 15723
3119. atmoaggie
1:15 PM GMT on August 18, 2007
atmoaggie - Foolish would be an improvement to her reputation.

True, very true. lol Evens word not recommended on a family oriented blog would be an improvement at this point.
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3117. PBG00
1:15 PM GMT on August 18, 2007
She.. sorry, Obviously I am not from there..

Yeah, definatly looking a bit foolish. Problem with that is, if she hypes it up, and it doen't come(and right now odds are it wont, but i realize it still could)..Then you have those people settling into complacency..again.
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3116. LADobeLady
8:16 AM CDT on August 18, 2007
Posted By: BiloxiGirl at 8:15 AM CDT on August 18, 2007.

atmoaggie - Foolish would be an improvement to her reputation.


She is incompetent, indesisive, selfserving, and an idiot.

Thank GOD she is not running.

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3115. tinkahbell
1:12 PM GMT on August 18, 2007
I have a friend that is supposed to leave for Cancun on Sunday/Monday. Looks like she will be at the inservice training for the start of the school year, eh?
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3114. russh46
1:16 PM GMT on August 18, 2007
We haven't heard from Ray Nagan yet probably later today....lol
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3113. canewatch
1:12 PM GMT on August 18, 2007
dmaddox, I noticed the change. After the jog a couple of hours ago it shifted back on track but, if you lay a straight edge on the eye for the last couple hours, the track appears to be toward the western tip of Cuba.
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3112. StormJunkie
1:15 PM GMT on August 18, 2007
ewolk, I don't think the cone will shift without the models first shifting.

But, from what I have seen from the last few days of GFDL I don't think a turn should be discounted.
Member Since: August 17, 2005 Posts: 26 Comments: 15723
3111. Masquer08er
1:14 PM GMT on August 18, 2007
About Gov. Blanco, After her fiasco, she is probably a little gun shy in regards to hurricanes.
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3110. BiloxiGirl
1:14 PM GMT on August 18, 2007
atmoaggie - Foolish would be an improvement to her reputation.
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3109. weathermanwannabe
9:11 AM EDT on August 18, 2007
Amazing how the ULL over Florida earnestly moved west overnight as "predicted" by NHC with the high building in behind it....With the models in good agreement for now, and with this type of intensity, I would get out of Jamaica and Cayman if I could....Bad call on the part of Weather Channel...I wonder if they drew straws....
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3108. Crawls
1:13 PM GMT on August 18, 2007
I think Gov. Blanco is making sure she covers her tail. The fiasco around Katrina will not be forgotten anytime soon.
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3107. watchingnva
1:10 PM GMT on August 18, 2007
the wnw direction right now really doesnt influence anything 3+ days out....it will just shift the track (short term (1-3days)) slightly to the north...dean could also go due west again in a couple hours...you will never know untill it happens...
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3106. LADobeLady
8:13 AM CDT on August 18, 2007
Posted By: PBG00 at 8:12 AM CDT on August 18, 2007.

Masquer08erDid you see where Gov. Blanco declared a state of emergecy in LA because of Mean Dean.

Jumping the gun a bit, isn't he?


She (Gov Blankstare/ Blanco) is a dolt and trying to recover from her horrible indecisive immage she got from her reaction to Katrina.
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3105. ewolk08
1:10 PM GMT on August 18, 2007
what is the likelyhood of a shift in its track to the north and what would that do to the modules and cone
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3103. atmoaggie
1:13 PM GMT on August 18, 2007
Jumping the gun a bit, isn't he?

She...wants to avoid yet another instance where she did nothing at all. Setting herself up to look a little foolish, here, though.
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3102. Masquer08er
1:12 PM GMT on August 18, 2007
Biloxi,

Don't blame you one bit!
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3101. UnderstandingFL
1:09 PM GMT on August 18, 2007
VegasRain, I completely agree with your post.

I can't believe he went, either.
3100. StormJunkie
1:09 PM GMT on August 18, 2007
I think in Deans case the ULL is what will ultimately decide the outcome. Help me out here maggie or anyone, 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: 15723
3099. weathersp
9:11 AM EDT on August 18, 2007
Posted By: srada at 9:11 AM EDT on August 18, 2007.

Shows the start of the WNW-NWish movement. it also shows the eyewall intensifying and contracting.

So if this direction continues, wouldnt that be bad for the LA/MS/Al and the florida panhandle then and not so much for TX/MX?


No not necessarily.. its bad for Jamaica, Hispaniola and Caymans.
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3098. atmoaggie
1:11 PM GMT on August 18, 2007
you people in harms way gotta move to Rhode Island ....nothing too crazy ever happens here

...except hurricanes when the Bermuda high is slightly more north than usual and they wipe long island down to sand and flood Providence and there is violence in the streets and looting. All of the above HAS happened! Do not be complacent.
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3097. PBG00
1:11 PM GMT on August 18, 2007
Masquer08erDid you see where Gov. Blanco declared a state of emergecy in LA because of Mean Dean.

Jumping the gun a bit, isn't she?
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3096. WhereIsTheStorm
1:06 PM GMT on August 18, 2007
Hey Jamweather, The people who don't believe that HUR DEAN is coming and obviously in denial. I have heard the statment many times that Jamiaca never gets hit the storms alwasy go around. I bring up HUR Gilbert and state the storm went from one end of the island to the other in 1988 and I get a look like my speaking a foreign language. I can only hope these people have somewhere to go once the rain starts as there will be no time after that for storm preperation as it will be there. The best you can do is make sure are prepared and that you, your family, loved ones, and close friends are safe. Our prays are with you. Hope to hear from you as soon as the storm passes and the electricity comes back on.
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3095. Tampawxgirl
1:09 PM GMT on August 18, 2007
This northerly "jog" isn't looking good. I have a friend/co-worker who may still be there. I need to find out if he's returned to the states yet.
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3094. fldude99
1:07 PM GMT on August 18, 2007
its amazing how once you feel like a storm isnt coming your way you no longer pay attention to it and go on with life-until the next one
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3093. srada
1:09 PM GMT on August 18, 2007
Shows the start of the WNW-NWish movement. it also shows the eyewall intensifying and contracting.

So if this direction continues, wouldnt that be bad for the LA/MS/Al and the florida panhandle then and not so much for TX/MX?



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3092. JamaicanGir
8:09 AM EST on August 18, 2007
Good morning all,
Siedel here in Montgo Bay could be a bad sign,but at least it's not cantore :-) all is calm right now
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3091. CJ5
8:09 AM CDT on August 18, 2007
Holy exploding, Batman. I got busy yesterday to find a near Cat5 this am. I guess it wasn't to unexpected but it did beef up pretty quickly.
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3090. StoryOfTheCane
1:10 PM GMT on August 18, 2007
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3089. BiloxiGirl
1:02 PM GMT on August 18, 2007
Masquer08erDid you see where Gov. Blanco declared a state of emergecy in LA because of Mean Dean.

I saw it but anything Blanco does doesn't mean much to me. Her reaction post Katrina was less than impressive. Anybody can whine. I'll listen to Barbour.
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3088. atmoaggie
1:09 PM GMT on August 18, 2007
I wonder if TWC upped their life insurance policy on Sidell.
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3087. miken62
1:07 PM GMT on August 18, 2007
you people in harms way gotta move to Rhode Island ....nothing too crazy ever happens here
Member Since: January 14, 2003 Posts: 0 Comments: 213
3086. Tampawxgirl
1:07 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 they won't do for media coverage *rolls eyes*
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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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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.