Dr. Jeff Masters' WunderBlog

Which model do you trust? And, Arctic sea ice reaches a record minimum

Posted by: Dr. Jeff Masters, 17. elokuuta 2007 klo 19:33 (GMT)

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

Categories: Climate Change

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2701. katadman 18. elokuuta 2007 klo 08:42 (GMT)
Well, if there is any movement toward the north, I can't tell it. Member Since: 7.09.2006 Posts: 0 Comments: 1081

2702. sflhurricane 18. elokuuta 2007 klo 08:42 (GMT)
In the new discussion for Dean, the NHC still believes the ULL will be moving west.. but one can clearly see the ULL moving SW... Hmmm? Member Since: 25.08.2006 Posts: 0 Comments: 355

2703. VEROBEACHFL1 18. elokuuta 2007 klo 08:42 (GMT)
omg---and im not getting paid? lol

2704. bekroweather 18. elokuuta 2007 klo 08:43 (GMT)
Hello everyone, indeed it looks that with the last few satellite frames the center of Dean has move decisively to NW. It's first time really that the storm has been N of 15. Given the Forecast Points, however, it's still on track according to the latest NHC prediction.

2706. katadman 18. elokuuta 2007 klo 08:44 (GMT)
Makes the GFDL of yesterday morning look pretty accurate. Member Since: 7.09.2006 Posts: 0 Comments: 1081

2707. VEROBEACHFL1 18. elokuuta 2007 klo 08:44 (GMT)
--i think we are going to see a slight change in the next0----maybe 11am update-------

2708. sflhurricane 18. elokuuta 2007 klo 08:45 (GMT)
Katadman, here, you'll see the Northern movement PR radarLink Member Since: 25.08.2006 Posts: 0 Comments: 355

2709. MauiHawk 18. elokuuta 2007 klo 08:45 (GMT)
YAWN lots of wishcasting going on tonight.....yall have watched too many loops, yall are going loopy.....Dean is goin W into Mexico. That seems to me the most likely bit of conjecture I've seen all evening. (Though a cat 5 storm hitting anywhere is not a yawn... and remember the spring breakers need somewhere to go next year)

2710. VEROBEACHFL1 18. elokuuta 2007 klo 08:45 (GMT)
at 67w

2711. VEROBEACHFL1 18. elokuuta 2007 klo 08:46 (GMT)
im sorry--maui---i agreed with you up until that comment-----

2712. VEROBEACHFL1 18. elokuuta 2007 klo 08:47 (GMT)
--its too early------ for a mexico predict------

2713. redrobin 18. elokuuta 2007 klo 08:48 (GMT)
NOT wishcasting- The hit will be in TX, by what is current at this time.

2714. katadman 18. elokuuta 2007 klo 08:48 (GMT)
Hard to tell if that is just a wobble or not. Seemed to me to dip a tad back SW at the very end of the loop.? Member Since: 7.09.2006 Posts: 0 Comments: 1081

2715. MauiHawk 18. elokuuta 2007 klo 08:49 (GMT)
In the new discussion for Dean, the NHC still believes the ULL will be moving west.. but one can clearly see the ULL moving SW... Hmmm? SF, but your argument was that you thought the ULL wasn't doing what the NHC expected it to. They certainly would have mentioned that if it were the case. And the long term track would have been nudged N not S if it were the case. Whether or not it appears like it to you, logic says the ULL must be doing what the NHC expects it too-- and they have a heck of a lot more experience at interpreting these maps than us...

2716. VEROBEACHFL1 18. elokuuta 2007 klo 08:49 (GMT)
its too early for a nailed down landfall-- but i respect your opinion 100%

2717. silverstripes 18. elokuuta 2007 klo 08:49 (GMT)
Amystery, I like your thinking. HAHA. I came up with my new descriptions earlier today since everybody kept saying it was moving W-NW. IF it was truly moving W-NW then that can mean anywhere from 271 degrees all the way to 314. Big difference there so. NW = 315 WNW = 292.5 WWNW = 281.25 WWWNW = 275.6 HAHA. SO it has been moving mostly W with some WWWWNW and sometimes WWNW throughout it's life. Ok I must be bored. Member Since: 26.07.2006 Posts: 5 Comments: 594

2718. redrobin 18. elokuuta 2007 klo 08:50 (GMT)
150 mile winds-15.1 n

2719. samiam1234 18. elokuuta 2007 klo 08:51 (GMT)
guys dean has gone through an entire day of slowing down.. it stated this morning motoring at 25 mph and has come down to 17 mph in a matter of 24 hours.. will this speed reduction continue, and stay this way, is something reducing it for the short term and will it pick up speed again.. or is this the speed it will stay at.. also if its going to keep slowing down, will that help it go North or does speed have nothing to do with the track. thanks Member Since: 13.08.2007 Posts: 0 Comments: 133

2720. GPTGUY 18. elokuuta 2007 klo 08:51 (GMT)
Posted By: katadman at 3:48 AM CDT on August 18, 2007. Hard to tell if that is just a wobble or not. Seemed to me to dip a tad back SW at the very end of the loop.? yeah kat I agree..thats what i was looking at..wanted to make sure before I posted but you beat me too it lol Member Since: 26.08.2005 Posts: 0 Comments: 391

2721. VEROBEACHFL1 18. elokuuta 2007 klo 08:53 (GMT)
WNW WILL STICK---JUST WAIT---ITS A WEEBLE WOOBLEY STORM -------not a sharp N movement --but gradually to the west NW --is that y all of u put like 5 w's in front of it --to express a west but slight movement north? -----example---WWWWWNW?

2722. sflhurricane 18. elokuuta 2007 klo 08:53 (GMT)
Maui.. I doubt the NHC would discuss how they were wrong about the movement of the ULL...The ULL, according to them was supposed to move across Southern FL and into the Gulf and dissipate.. Its clear that that the ULL isn't showing signs of weakening and is moving SW.. Im just wondering why the NHC doesnt believe this feature will be a player in the future path of Dean Member Since: 25.08.2006 Posts: 0 Comments: 355

2723. MauiHawk 18. elokuuta 2007 klo 08:53 (GMT)
im sorry--maui---i agreed with you up until that comment----- No need to be sorry :D I'm sure Cancun is rooting for you. My feeling is simply that as much as I like to poor over this stuff and pretend I can understand what's going on and what it all means, the NHC is pretty darn good at this stuff and I'll always be inclined to believe them over my own musings.

2724. redrobin 18. elokuuta 2007 klo 08:56 (GMT)
Slow down---south Speed up---North So far that is what they are saying here in Houston

2725. VEROBEACHFL1 18. elokuuta 2007 klo 08:58 (GMT)
well--its all IMO---- like i said before we ALL have 1 thing on ALL our sides and opinions------------ ----TIME! :)

2726. MauiHawk 18. elokuuta 2007 klo 08:59 (GMT)
Maui.. I doubt the NHC would discuss how they were wrong about the movement of the ULL I really don't think the NHC takes things so personally. They are constantly discussing what happens that isn't expected and how it influences their forcast. For example here: http://www.nhc.noaa.gov/archive/2007/al04/al042007.discus.016.shtml? The discuss why their intenisty forcast came up short owing to dry air, and why they thought the track needed to be moved N because of more interaction with the ULL than previously thought.

2728. redrobin 18. elokuuta 2007 klo 09:00 (GMT)
Good Luck Vero- I am off to work...:(

2729. VEROBEACHFL1 18. elokuuta 2007 klo 09:00 (GMT)
ahhh the 5am-- do they hold my WNW movement? or did they keep it at WEST?

2730. VEROBEACHFL1 18. elokuuta 2007 klo 09:01 (GMT)
DEAN IS MOVING TOWARD THE WEST NEAR 17 MPH...28 KM/HR. A GENERAL WESTWARD TO WEST-NORTHWESTWARD MOTION IS EXPECTED DURING THE NEXT 24 HOURS. ON THIS TRACK...THE CORE OF THE HURRICANE WILL BE MOVING SOUTH OF THE DOMINICAN REPUBLIC LATER TODAY AND SOUTH OF HAITI TONIGHT.

2731. katadman 18. elokuuta 2007 klo 09:01 (GMT)
What time will the new computer models come out? The NHC apparently relies heavily on them for their own track. Also, they will have all the new data factored in, si'? Member Since: 7.09.2006 Posts: 0 Comments: 1081

2732. samiam1234 18. elokuuta 2007 klo 09:01 (GMT)
I am from Galveston and am somewhat prepared.. but I had a gut feeling that we here will not see any signs of this storm... and the more I see the latest the more confident I feel about this.. I am getting more and more happier for us, but the poor ppl have Mexico will pay the price for this.. I think this will end up going a bit more in the central mexico region and not effect even the Southern Texas part, other then a little rain and some wind. Member Since: 13.08.2007 Posts: 0 Comments: 133

2733. hurricanehamster 18. elokuuta 2007 klo 09:01 (GMT)
whats deans strenth?

2735. stormybil 18. elokuuta 2007 klo 09:02 (GMT)
looks like the eye has just went over 15n now

2736. sflhurricane 18. elokuuta 2007 klo 09:02 (GMT)
I guess.. but I still wonder about this ULL lol And I agree, the NHC does an amazing job and I take their word over mine anyday, but I know the basics of weather and how it applies to hurricanes so Im wondering why they aren't stating how the ULL is moving SW, creating a close call between it and Dean.. rather than continue to discuss how its moving West, when its definitely not... I'll see tomorrow I guess Member Since: 25.08.2006 Posts: 0 Comments: 355

2737. VEROBEACHFL1 18. elokuuta 2007 klo 09:04 (GMT)
NHC being cautious-- and rightlfully so--- pretty good info at the 5am :)

2738. Jaxen 18. elokuuta 2007 klo 09:05 (GMT)
Dean rode 15N from 64W to past 67 ... how can you say that moving "all the way up" to 15.1 is the start of WNW movement? As for the slowdown from 25 to 17mph movement is normalization to me ... 25 is like breakneck speed. Once it settles in at 15-17 for a while, nobody will think anything of it again. As I sign off for a while, here's an ugly thought ... even IF it misses Jamaica AND IF if it misses the Yucatan, THEN it will hit Texico as a Cat 5. Somebody is getting a Cat 5 hurricane. damn Member Since: 12.07.2005 Posts: 0 Comments: 16

2739. MauiHawk 18. elokuuta 2007 klo 09:06 (GMT)
I'll see tomorrow I guess Indeed... we all will. I'm calling it a night. Later... (and gl Jamaica)

2740. sflhurricane 18. elokuuta 2007 klo 09:06 (GMT)
If you extrapolate Deans last few frame movements, the storm would be heading towards Hispanolia.. kinda crazy.. Here, check Member Since: 25.08.2006 Posts: 0 Comments: 355

2741. katadman 18. elokuuta 2007 klo 09:07 (GMT)
Certainly they're cautious. They don't want to appear as flighty as we are! LOL Member Since: 7.09.2006 Posts: 0 Comments: 1081

2742. VEROBEACHFL1 18. elokuuta 2007 klo 09:08 (GMT)
jaxen=== not sure what u mean but the NHC seems to agree........ --DEAN IS MOVING TOWARD THE WEST NEAR 17 MPH...28 KM/HR. A GENERAL WESTWARD TO WEST-NORTHWESTWARD MOTION IS EXPECTED DURING THE NEXT 24 HOURS. ON THIS TRACK...THE CORE OF THE HURRICANE WILL BE MOVING SOUTH OF THE DOMINICAN REPUBLIC LATER TODAY AND SOUTH OF HAITI TONIGHT. -the key here is within the next 24 hours...........

2743. stormybil 18. elokuuta 2007 klo 09:09 (GMT)
thanks sf you can really see that north jog with that one .

2744. VEROBEACHFL1 18. elokuuta 2007 klo 09:10 (GMT)
---- i guess some people didnt see this coming??? ----- --i think that last report might peed some peeps off but i dont know y...........

2745. samiam1234 18. elokuuta 2007 klo 09:10 (GMT)
I dont think this is hitting Texas.. there will be Texas wishcasters all day tommorow.. who just like to see drama unfold and have something to talk about.. but this storm is clearing heading due West, the eye might not even hit Jamaica, rather go south of it and it looks like it will hit further south on the Yucatan as the models are showing.. this will not only reduce the storm once it enters the gulf... but will clearly make this a Mexico Cane. Member Since: 13.08.2007 Posts: 0 Comments: 133

2746. sflhurricane 18. elokuuta 2007 klo 09:10 (GMT)
Uh oh Vero... Checking out PR's radar again, and the "wobble" back to the NW continues.. very interesting Member Since: 25.08.2006 Posts: 0 Comments: 355

2747. stormybil 18. elokuuta 2007 klo 09:12 (GMT)
the cone will be alot further north today i say at 5pm if the motion continues

2748. VEROBEACHFL1 18. elokuuta 2007 klo 09:12 (GMT)
well----to the people who think their WEST movement will stick--- good luck---cause i sure as heck DO NOT--------

2749. sflhurricane 18. elokuuta 2007 klo 09:12 (GMT)
Samiam, dont be so sure with this, or any storm...They all find a way to fool us all Member Since: 25.08.2006 Posts: 0 Comments: 355

2750. GPTGUY 18. elokuuta 2007 klo 09:12 (GMT)
yeah SF I see it too..it looks like its bouncing Member Since: 26.08.2005 Posts: 0 Comments: 391

2751. sflhurricane 18. elokuuta 2007 klo 09:13 (GMT)
stormybill, you still here the rumblings out there?... That ULL has the air really unstable out here Member Since: 25.08.2006 Posts: 0 Comments: 355

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