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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2535. mikester
7:03 AM GMT on August 18, 2007
Dean's eye appears to be stable. I don't see any eye reformation you guys are talking about. He finally has a nice eye.
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2533. OUFan919
7:02 AM GMT on August 18, 2007
I dunno. Im drunk and I saw something that looked like a circle appear on the San Juan radar. I might be seeing things! I was at the bar for 6 hours!
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2532. JamaicanGir
2:03 AM EST on August 18, 2007
thanks c57
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2531. StormJunkie
7:00 AM GMT on August 18, 2007
Good point JG and I would tend to agree. I think the windfield expands because typically in a cane this strong, the size of the eyewall expands after the EWRC. But if you get under it while it is under going that EWRC, it would actually be undergoing a little weakening. Now, what is really the difference between a 145mph storm and a 130-135 mph storm...Both are real nasty.
Member Since: August 17, 2005 Posts: 26 Comments: 16874
2530. VEROBEACHFL1
7:02 AM GMT on August 18, 2007
why are people in the present? im with u storyofthecane 100%.........a WNW movement is VERY SOON>............... its not going to RIDE the 15 line-GEEZ.........
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2528. KRL
7:02 AM GMT on August 18, 2007
NDBC - Latest Buoy Data Near Dean

NDBC Buoy Data Link
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2527. Crisis57
7:01 AM GMT on August 18, 2007
Posted By: TheCaneWhisperer at 6:58 AM GMT on August 18, 2007.

Small eyes—those less than 10 nmi (19 km, 12 mi) across—often trigger eyewall replacement cycles, where a new eyewall begins to form outside the original eyewall. This can take place anywhere from ten to a few hundred miles (fifteen to hundreds of kilometers) outside the inner eye. The storm develops two concentric eyewalls, or an "eye within an eye". In most cases, the outer eyewall begins to contract soon after its formation, which chokes off the inner eye and leaves a much larger but more stable eye. While the replacement cycle tends to weaken storms as it occurs, the new eyewall can contract fairly quickly after the old eyewall dissipates, allowing the storm to re-strengthen. This may trigger another cycle of eyewall replacement.[8]

Eyes can range in size from 320 km (200 miles) (Typhoon Carmen) to a mere 3 km (2 mi) (Hurricane Wilma) across.[9] While it is uncommon for storms with large eyes to become very intense, it does occur, especially in annular hurricanes. Hurricane Isabel was the eleventh most powerful Atlantic hurricane of all time, and sustained a large, 65–80 km (40–50 mi)-wide eye for a period of several days.[10]

Credit Wikipedia!


and Dean IMO might be going through another one
2526. LSU
6:59 AM GMT on August 18, 2007
????? What kind of remark is that? Its just my educated guess, quit being an arrogant prick...

I'm not being arrogant at all. I'm being sensible. Putting a track through central Florida, even the edge of a track, is simply not sensible. Unfortunately, some people read these comments and take them seriously, which is why you shouldn't post the things you do.
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2524. unknownuser
6:55 AM GMT on August 18, 2007
northern jog? if anything it appeared to me that it jogged more to the west.. thats just what i see.
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2521. sullivanweather
6:57 AM GMT on August 18, 2007
I would estimate the latest position as of 615UTC @ 15.05°N, 66.8°W
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2520. KRL
6:54 AM GMT on August 18, 2007
If Dean heads to Texas as a Cat 5, this country's oil production and refinery infrastructure will be significantly crippled in a major way.

Watch for long gas lines and sky rocketing prices like we've never seen before. I wouldn't be surprised if we go to $4 cause of this cane.
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2519. TheCaneWhisperer
6:52 AM GMT on August 18, 2007
Small eyes—those less than 10 nmi (19 km, 12 mi) across—often trigger eyewall replacement cycles, where a new eyewall begins to form outside the original eyewall. This can take place anywhere from ten to a few hundred miles (fifteen to hundreds of kilometers) outside the inner eye. The storm develops two concentric eyewalls, or an "eye within an eye". In most cases, the outer eyewall begins to contract soon after its formation, which chokes off the inner eye and leaves a much larger but more stable eye. While the replacement cycle tends to weaken storms as it occurs, the new eyewall can contract fairly quickly after the old eyewall dissipates, allowing the storm to re-strengthen. This may trigger another cycle of eyewall replacement.[8]

Eyes can range in size from 320 km (200 miles) (Typhoon Carmen) to a mere 3 km (2 mi) (Hurricane Wilma) across.[9] While it is uncommon for storms with large eyes to become very intense, it does occur, especially in annular hurricanes. Hurricane Isabel was the eleventh most powerful Atlantic hurricane of all time, and sustained a large, 65–80 km (40–50 mi)-wide eye for a period of several days.[10]

Credit Wikipedia!
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2518. JamaicanGir
1:55 AM EST on August 18, 2007
thanks SJ, just wondering as i believe each time it does the hurricane force wind field area expands, making it less and less chance that even if it moves to the north or south we would still be affected by hurricane force winds
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2516. OUFan919
6:53 AM GMT on August 18, 2007
Looks like Dean is making a wobble to the northwest. Look at the San Juan radar. I could be seeing something else but that looks like the eye appearing on the radar. I would like somebody to see this and see if they agree with me.

http://www.goes.noaa.gov/HURRLOOPS/huirloop.html

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2515. mikester
6:55 AM GMT on August 18, 2007
Wait is west texas duh. Anyways i thought erin was farther north then that.
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2514. sullivanweather
6:54 AM GMT on August 18, 2007
New 615UTC image is in and Dean is still on the 15°N parallel.

The eye has also contracted some
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2513. KEEPEROFTHEGATE (Mod)
6:48 AM GMT on August 18, 2007
soc guess what
track mark 15,66
15.5,67
16.1,72 C5/H/D
16.5,75
17.2,77 C5/H/D
17.4,79
18,81 C4/H/D
STOP....
i can take it all the way right to final destination but i wont not till it gets to 18,81
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2512. StormJunkie
6:54 AM GMT on August 18, 2007
FF, I think that is what Mike is referring to.

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2511. PRmarinaowner
6:47 AM GMT on August 18, 2007
I keep waiting for that tail to come up and smack us here in Fajardo but it seems that it doesnt want to come further north than st. croix. Do you guys think the squall line will come further north?
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2510. Crisis57
6:54 AM GMT on August 18, 2007
Posted By: StormJunkie at 6:54 AM GMT on August 18, 2007.

Don't think there is really a set cycle JG, but it basically gets so strong and intense that it can not sustain the inner wall of the eye. This collapses and then a new eye takes over. That is my understanding at least.


exactly and as long as it keeps intensifying it will go through these eyewall replacements
2509. StoryOfTheCane
6:53 AM GMT on August 18, 2007
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2508. JamaicanGir
1:52 AM EST on August 18, 2007
thanks for the explanation crisis57, any hope is a light at the end of the tunnel
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2507. mikester
6:53 AM GMT on August 18, 2007
Go through the frames and let it play the last 10 frames and you will see what i mean.
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2506. StormJunkie
6:52 AM GMT on August 18, 2007
Don't think there is really a set cycle JG, but it basically gets so strong and intense that it can not sustain the inner wall of the eye. This collapses and then a new eye takes over. That is my understanding at least.
Member Since: August 17, 2005 Posts: 26 Comments: 16874
2505. forecastFlyer
6:49 AM GMT on August 18, 2007
mikester:
What are you seeing? All I see is Erin In west Texas)
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2504. mikester
6:53 AM GMT on August 18, 2007
I don't know it just bloomed in the last few frames of infrared.
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2503. mikester
6:52 AM GMT on August 18, 2007
Sorry fixed my link in my post. Works now.
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2502. StormJunkie
6:48 AM GMT on August 18, 2007
mike, maybe remnants of Erin?
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2501. Crisis57
6:49 AM GMT on August 18, 2007
Posted By: JamaicanGir at 6:46 AM GMT on August 18, 2007.

i sincerely hope so Crisis57


Now my reason for this is the ULL over Florida is not moving as rapidly as many thought because of this at some point the storm is going to catch the ULL if it hasn't started to feel the affects of it already (notice how the forward motion of this morning 25mph has slowed to 18mph)if i'm correct and i may be wrong then this should start to suck the storm slight north of due west, thus bringing Dean slight north of the forecast track and missing Jamaica
2500. JamaicanGir
1:48 AM EST on August 18, 2007
question?? how often does the storm go thru an eye wall replacement cycle

thanks
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2499. groundman
6:49 AM GMT on August 18, 2007
Posted By: mikester at 6:43 AM GMT on August 18, 2007.
Go here and check out texas. Man something just boomed in texas.
http://weather.msfc.nasa.gov/cgi-bin/post-goes



link doesn't work, trying to go to radar, slow molasses type like satellite internet, bah humbug.
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2498. druseljic
6:49 AM GMT on August 18, 2007
ncep=National Center for Environmental Predictions
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2497. Dan187
6:47 AM GMT on August 18, 2007
looking at 2:15 image, appears somewhat more organised, but still not the coldest cloud tops, especially on the SW side.
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2496. CajunSubbie
6:47 AM GMT on August 18, 2007
louisianaweatherguy - last few frames of the radar shows like a uptick of the eye northward.. it usually has come back west by now. we'll see

http://radar.weather.gov/radar.php?rid=JUA&product=N0Z&overlay=11101111&loop=yes
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2495. sullivanweather
6:47 AM GMT on August 18, 2007
TCHP

Once Dean passes 70°W it's heading straight into an area of TCHP of 90-110kj/cm^2.

This could be where Dean reaches category 5 status.
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2494. StoryOfTheCane
6:47 AM GMT on August 18, 2007
Cat 5 landfall...

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2493. VEROBEACHFL1
6:46 AM GMT on August 18, 2007
ride the 15 line? not a chance--------- very soon it will start to go wnw.... how sharp n is a good question--- but WNW-yes...and most likely by 67W give or take 1 degree or 2
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2492. StormJunkie
6:46 AM GMT on August 18, 2007
the only factor that would prevent that is an inhibitor like a strong High.

Which the high is fairly strong, but that upper level low over Fla is really the key player from everything I have heard.
Member Since: August 17, 2005 Posts: 26 Comments: 16874
2491. StoryOfTheCane
6:45 AM GMT on August 18, 2007
yeah, Im just guessin but I could be right..never know til it happens
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2490. mikester
6:46 AM GMT on August 18, 2007
Can someone tell me what is happening in texas. The latest infrared shows a big red blob in southern texas. Any ideas what caused this?
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2489. JamaicanGir
1:45 AM EST on August 18, 2007
i sincerely hope so Crisis57
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2488. louisianaweatherguy
6:39 AM GMT on August 18, 2007
I REALLY REALLY REALLY don't see any jogs to the north... but I am noticing a major slow down... and for big hurricanes like Dean, usually track shifts are the reasons for slow downs like the one we're seeing...

We'll see if he turns WNW tonight... If dean continues WEST WEST WEST tonight, following the 15N line like a tightwire, we'll likely see even the GFDL move back down towards Mexico... and then..

It would be a great day tommorrow for Louisiana...


BUT... if Dean has slowed down to make that WNW turn now, Louisiana should probably WATCH OUT

I'm still saying tonight...

Brownsville to Houston to Lake Charles to Baton Rouge.... WATCH DEAN the next 5 days!!
Member Since: July 9, 2007 Posts: 0 Comments: 692
2487. StormJunkie
6:44 AM GMT on August 18, 2007
Dang, the GFDL even seems to have underestimated the intensity through the first 66hrs....
Member Since: August 17, 2005 Posts: 26 Comments: 16874
2486. JamaicanGir
1:42 AM EST on August 18, 2007
i lived in south miami (kendall) during Andrew and it was devastating though the infrastructures are very different from here in terms of vegetation here being much much more which can cause much more damage
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2485. Crisis57
6:42 AM GMT on August 18, 2007
i don't see the COC hitting Jamaica i honestly think it will pass north maybe even through cuba

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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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