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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2435. TheCaneWhisperer
6:18 AM GMT on August 18, 2007
Family in South Coast JamaicanGir, little SSW of Santa Cruz.
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2433. louisianaweatherguy
6:15 AM GMT on August 18, 2007
Dean is going to be a Mexico Hurricane if in continues on a Bee-line track into Mexico.... But I think Louisiana needs to watch it go well south of Jamaica before we can breathe a sigh of relief...

Looking good so far for New Orleans...

Although, I have been watching the flow to the north of Dean (The High forcing it westward)... During the last few satellite runs I noticed the clouds above stop going from East to West and I watched them start going Southeast to Morthwest....

COuld that be a sign that Dean will try a WNW jog in few hours???

Time will tell...
Member Since: July 9, 2007 Posts: 0 Comments: 692
2432. Dropsonde
6:23 AM GMT on August 18, 2007
Crisis57: As of the last water vapor satellite before the blackout, the ULL appeared to be partially over Florida.
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2431. KEEPEROFTHEGATE (Mod)
6:17 AM GMT on August 18, 2007
drop
some of those temp in west carb and gom are at 32 degees c we are the first to see what kind of monsters these hot waters creates.
Member Since: July 15, 2006 Posts: 163 Comments: 52230
2430. Crisis57
6:23 AM GMT on August 18, 2007
Posted By: VEROBEACHFL1 at 6:21 AM GMT on August 18, 2007.

HI ALL -- back again---i fell asleep at the keyboard--my fiance came in and woke me up--LOL--YAWWWN-- CRISIS--its still there but it looks like a slight movement to the west--verify it for me?
--we are gonna see a slight change in course soon------IMO-- maybe by 67W or a bit after..... GRADUAL NW shift--ill try to stay up for that..if possible....


i do see it has moved but very slowly nothing thats racing off
2429. OUFan919
6:21 AM GMT on August 18, 2007
What I think too weathersp. I just think they want to make sure it keeps those winds for a few hours before they do the full update at 5am. I think they will update it then to Category 5!
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2427. WeatherSpotter
6:20 AM GMT on August 18, 2007
HH has Cat 5 intensity winds factored at Surface... Its a Cat 5

I see Cat 5 at the 5 am advisory.
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2426. DanielPC
1:18 AM CDT on August 18, 2007
I topped off my tank tonight - was very happy with 2.629. Though I plan on staying, if this thing gets to the Gulf, gas prices will go up due to GOM production being shut-in.

I filled up my tank, too, even though I'm in the Florida Panhandle, and the gas prices here already are rising. The Associated Press is reporting that oil is now going up because of evacuations on the gulf oil/gas-exploration platforms.
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2424. KoritheMan
6:20 AM GMT on August 18, 2007
Anybody else think Dean is Category 5 but the NHC wants to make sure it is for sure a Cat 5 before they declare it?

Yeah, I think so. But yes, a pressure drop is probably what they are waiting for.

If an EWRC does not occur today, with warmer waters ahead of it, and land not being a huge issue right now, Dean could break or tie Wilma's record low pressure of 882 mb, IMO.
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2423. stormybil
6:19 AM GMT on August 18, 2007
weathersp at 6:18 AM GMT on August 18, 2007.

the eye is half over 15n now

Based on what? All of the satellite images I have seen are 2 hrs old.

i check this one too you can clearly see it

Link
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2422. VEROBEACHFL1
6:18 AM GMT on August 18, 2007
HI ALL -- back again---i fell asleep at the keyboard--my fiance came in and woke me up--LOL--YAWWWN-- CRISIS--its still there but it looks like a slight movement to the west--verify it for me?
--we are gonna see a slight change in course soon------IMO-- maybe by 67W or a bit after..... GRADUAL NW shift--ill try to stay up for that..if possible....
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2421. weathersp
2:19 AM EDT on August 18, 2007
Anybody else think Dean is Category 5 but the NHC wants to make sure it is for sure a Cat 5 before they declare it?

Heck by the NHC'own Hurricane Hunter Criteria for Flight level winds to surface winds and the latest Hurricane Hunter Data it is a Cat. 5!
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2420. TX2AK
6:19 AM GMT on August 18, 2007
For all the Texans out there, here is a map I made showing the historical likelihood of storms in the Atlantic Basin eventually making landfall along the Texas coast. It shows the climatological probability (as a percentage) of all tropical storms and hurricanes passing within 50 miles of a point eventually striking Texas. The current position (2 a.m. EDT on 8/18/07) of Dean is superimposed on the map. As you can see, Dean is within a fairly narrow swath (south of Hispaniola to the tip of the Yucatan) of the Caribbean that consistently produce land falling storms for Texas.
Dean Probability Map
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2419. JamaicanGir
1:17 AM EST on August 18, 2007
Been thru Andrew in Miami and i parked as close as possible to the wall with the sides to the wall allowing the aerodynamics to go over the vehicle.
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2417. OUFan919
6:18 AM GMT on August 18, 2007
Anybody else think Dean is Category 5 but the NHC wants to make sure it is for sure a Cat 5 before they declare it?
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2416. weathersp
2:17 AM EDT on August 18, 2007
the eye is half over 15n now

Based on what? All of the satellite images I have seen are 2 hrs old.
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2415. Crisis57
6:18 AM GMT on August 18, 2007
is there any update on the ULL
2414. Crisis57
6:16 AM GMT on August 18, 2007
Posted By: Fl30258713 at 6:16 AM GMT on August 18, 2007.

Posted By: WatchingInHouston at 5:57 AM GMT on August 18, 2007.

Haven't gone through any major canes... question for those that have - what do you do with your vehicles? I don't feel comfortable leaving mine at ground level... I imagine that a multi-level parking garage would be fine?


I have two vans that I park in front of my house to use as wind breaks in order to help prevent the wind from pushing up on the edge of my roof over my porch.


i do the same or i park it in the parking garage at a local mall
2413. JamaicanGir
1:16 AM EST on August 18, 2007
TCW i am on the northwest coast of the island ( Montego Bay)
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2412. stormybil
6:16 AM GMT on August 18, 2007
the eye is half over 15n now
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2411. Fl30258713
6:05 AM GMT on August 18, 2007
Posted By: WatchingInHouston at 5:57 AM GMT on August 18, 2007.

Haven't gone through any major canes... question for those that have - what do you do with your vehicles? I don't feel comfortable leaving mine at ground level... I imagine that a multi-level parking garage would be fine?



I have two vans that I park in front of my house to use as wind breaks in order to help prevent the wind from pushing up on the edge of my roof over my porch.





Member Since: July 24, 2006 Posts: 1 Comments: 981
2410. JamaicanGir
1:15 AM EST on August 18, 2007
Thanks iahishome
preparing for the worst and hoping for the best
good night
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2409. TheCaneWhisperer
6:14 AM GMT on August 18, 2007
There has been no visible eye is what I meant kori. Pop out for a frame or two and then cloud covered again.
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2408. Twisterman555
6:14 AM GMT on August 18, 2007
Posted By: WeatherSpotter at 6:13 AM GMT on August 18, 2007.

According to HH Dean is a Cat 5 but NHC is not ready to make it that determination yet.


Ya I saw that the HH had 154kts.
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2407. Dropsonde
6:10 AM GMT on August 18, 2007
I just looked at the satellites on the Navy site, and I am simultaneously awed and horrified. We'd better pray for an EWRC tomorrow, or this thing is going to break records tomorrow night. It still hasn't even hit the hottest water yet.
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2406. TheCaneWhisperer
6:11 AM GMT on August 18, 2007
Morning yourself JamaicanGir! That's all you can be, prepared. Where is your location on the island (N,S,E,W).
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2405. KoritheMan
6:12 AM GMT on August 18, 2007
Never has been Colby, Cat 2 with no clear eye? This last run is the first time it has been able to maintain a clear eye.

Charley never had a huge eye on satellite, either. Probably below 10 nm. Yet it was at 150 mph, just like Dean.
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2404. kev22
6:08 AM GMT on August 18, 2007
Have to say... this system's signature is turning quite beautiful. I still think Katrina was the most beautifully developed storm or at least the most threatening looking in the Atlantic Basin in modern times.
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2403. WeatherSpotter
6:12 AM GMT on August 18, 2007
According to HH Dean is a Cat 5 but NHC is not ready to make it that determination yet.
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2402. Crisis57
6:11 AM GMT on August 18, 2007
Very mature Hurricane and look at that long tail

Dean
2401. wolfshadow
6:11 AM GMT on August 18, 2007
weathersp.. you have a link to that HH info?
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2400. Twisterman555
6:12 AM GMT on August 18, 2007
Wow, I see Dean is almost a Cat5!
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2399. Crisis57
6:10 AM GMT on August 18, 2007
Hey guys whats is the latest on the ULL
2398. TheCaneWhisperer
6:08 AM GMT on August 18, 2007
Never has been Colby, Cat 2 with no clear eye? This last run is the first time it has been able to maintain a clear eye.
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2397. mikester
6:06 AM GMT on August 18, 2007
Off topic real quick does chat work with firefox on the site?
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2395. JamaicanGir
1:07 AM EST on August 18, 2007
morning TCW i am as prepared as i can be
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2394. H2OMaker
6:00 AM GMT on August 18, 2007
The question about vehicles has been one of my big one's to my employer down here in Texas City for our hurricane crews. Our parking lot is about 6.5' above sea level. They kinda shrug and deflect the question. I don't think I'll be working hurricane duty this year, certainly not after our engineering study came back stating that our building would not withstand a minimal cat3 wind loading.
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2393. stormchaser254
6:06 AM GMT on August 18, 2007
How favorable are the conditions for the African wave to develop? Thanks guys good luck on Dean whoever is in its path.
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2392. WatchingInHouston
6:03 AM GMT on August 18, 2007
Justwondering - I stayed put for the Rita evacuation... thankfully. I did direct a local family member out to San Antonio via 59S and they encountered very little traffic most of the way, while everything else was gridlocked.

I'd like to think that our officials have learned from past experiences and will implement things a bit sooner and take a firmer stance on who needs to leave and when.

I'd love to get data on the average number of vehicles on the road per family. I have a sneaking hunch that many multi-vehicle families took as many cars out as possible greatly contributing to the congestion.

I topped off my tank tonight - was very happy with 2.629. Though I plan on staying, if this thing gets to the Gulf, gas prices will go up due to GOM production being shut-in.
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2391. ForecasterColby
6:04 AM GMT on August 18, 2007
I'm really quite surprised at Dean's intensity. It's not really that spectacular on satellite.
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2390. TheCaneWhisperer
6:02 AM GMT on August 18, 2007
That would be my post too JamaicanGir! Could be a Cat5 direct hit, hopefully your prepared. I have family there also, they are on their way out for a couple weeks.
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2389. Crisis57
6:05 AM GMT on August 18, 2007
Posted By: weathersp at 6:04 AM GMT on August 18, 2007.

Hey guys checking in whats the status on Dean

Cat 5 According to the Hurricane Hunters (159 MPH) but NHC won't call it yet...


wow looks incredible
2388. rlpellegrin
6:03 AM GMT on August 18, 2007
Does anyone think that this could still come close to SE Louisiana? Thanks for all the amazing info on this blog. I have learned soooo much!
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2387. iahishome
6:03 AM GMT on August 18, 2007
Latest Buoy readings... it's still hanging on:

Conditions at 42059 as of
0550 GMT on 08/18/2007:


Wind Direction (WDIR): N ( 10 deg true )
Wind Speed (WSPD): 38.9 kts
Wind Gust (GST): 46.6 kts
Wave Height (WVHT): 26.9 ft
Dominant Wave Period (DPD): 14 sec
Average Period (APD): 9.3 sec
Atmospheric Pressure (PRES): 29.50 in
Pressure Tendency (PTDY): -0.22 in ( Falling Rapidly )
Air Temperature (ATMP): 81.0 F
Water Temperature (WTMP): 83.8 F
Dew Point (DEWP): 75.0 F
Heat Index (HEAT): 86.7 F
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2386. weathersp
2:03 AM EDT on August 18, 2007
Hey guys checking in whats the status on Dean

Cat 5 According to the Hurricane Hunters (159 MPH) but NHC won't call it yet...
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2385. TexJonnie
6:01 AM GMT on August 18, 2007
Posted By: WatchingInHouston at 5:57 AM GMT on August 18, 2007.
"Justwondering: Can't say that I entirely agree with his predictions either... :) But, it seems to be fairly objective, which I respect. Being inland a bit (Galleria area), I'll probably stay in town for the duration of this, if it heads our way. Need to stock up on supplies tomorrow while the gettings good... I'd hate to get all of the no-good snacks, ya know? :)

Haven't gone through any major canes... question for those that have - what do you do with your vehicles? I don't feel comfortable leaving mine at ground level... I imagine that a multi-level parking garage would be fine?"

I live near D.W. Hooks Airport. I plan to stay as well. Keeping my car in the garage. My house is elevated from the road and my driveway is near the top of the slope of my road... don't foresee water coming up to my door if Dean hits, but then this will be my first hurricane to live through here in Houston. Been in this area for 12 years.
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About JeffMasters

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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