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

Share this Blog
3
+

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

Reader Comments

Comments will take a few seconds to appear.

Post Your Comments

Please sign in to post comments.

or Join

Not only will you be able to leave comments on this blog, but you'll also have the ability to upload and share your photos in our Wunder Photos section.

Display: 0, 50, 100, 200 Sort: Newest First - Order Posted

Viewing: 1535 - 1485

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34 | 35 | 36 | 37 | 38 | 39 | 40 | 41 | 42 | 43 | 44 | 45 | 46 | 47 | 48 | 49 | 50 | 51 | 52 | 53 | 54 | 55 | 56 | 57 | 58 | 59 | 60 | 61 | 62 | 63 | 64 | 65 | 66 | 67 | 68 | 69 | 70 | 71Blog Index

1535. Drakoen
2:12 AM GMT on August 18, 2007
The ULL level low over the Bahamas has picked up some speed. may not have any affect on dean.
Member Since: Posts: Comments:
1534. kev22
2:12 AM GMT on August 18, 2007
There is nothing to prevent it from strengthening in the near term. It's going to reach Cat 5 status. How long it maintains it may be a question.

I think it will reach five too. But those mountains can do a number pretty quickly if it gets too close.
Member Since: Posts: Comments:
1533. MelbourneTom
2:11 AM GMT on August 18, 2007
UW - CIMSS
ADVANCED DVORAK TECHNIQUE
ADT-Version 7.2.1
Tropical Cyclone Intensity Algorithm

----- Current Analysis -----
Date : 18 AUG 2007 Time : 011500 UTC
Lat : 14:54:17 N Lon : 65:28:09 W


CI# /Pressure/ Vmax
6.1 / 948.2mb/117.4kt


6hr-Avg T# 3hr-Avg T# Adj T# Raw T#
5.8 6.1 6.2 6.7

Member Since: Posts: Comments:
1532. kmanislander
2:09 AM GMT on August 18, 2007
Hi Littlefish

Scary times in the Caribbean my friend. The price we pay for living in the tropics.

Dean has a small but intense core of very high winds. If that condition maintains we can survive a near miss of about 60 miles without too much damage. Gotta hope !
Member Since: Posts: Comments:
1531. Caymanite
2:05 AM GMT on August 18, 2007
Good evening all. I have just completed ALL perparations for Dean and returned home to see that it was for good cause. Only a miracle can keep us from getting sig effect from him now. Seems like a lot of folks were planning to party tonite and leave preps for tomorrow and I hope that they will get them completed as it looks now like we will be severely impacted. Will stay in touch as best as possible during the event and definitely up until power is lost. Having just recovered completely from Ivan, this really is not a joke.
Member Since: Posts: Comments:
1530. Metallica1990
2:11 AM GMT on August 18, 2007
I'm thinking 5 by next advisory
Member Since: Posts: Comments:
1529. WPBHurricane05
10:11 PM EDT on August 17, 2007
If the NHC goes with the CONU, they will shift the track south.
Member Since: Posts: Comments:
1528. Xion
2:07 AM GMT on August 18, 2007
No eyewall replacement cycle in site.

I hope the HH have plenty of fuel or science will cry.

CI# /Pressure/ Vmax
6.1 / 948.2mb/117.4kt


Another .2 in a 1/2 hour period!!!!!!!!!!!!!!!!!
Member Since: Posts: Comments:
1527. littlefish
2:11 AM GMT on August 18, 2007
kman, that was waht I wa ssaying- the south Low may be what is shifting the track south, not the North high. Hope you're ready for a ride out there! Yikes...
Member Since: Posts: Comments:
1526. bluehaze27
2:11 AM GMT on August 18, 2007
The ull was supposed to have dissipated by now.
Member Since: Posts: Comments:
1525. comtrader
2:08 AM GMT on August 18, 2007
littlefish,
my guess is that without the low off of florida, dean would have no chance to make it into the gulf. it all hinges on whether or not that low gets close enough in time and space to pull dean northwards.
d
Member Since: Posts: Comments:
1524. KnowYourRole
10:10 PM EDT on August 17, 2007
Posted By: kev22 at 10:07 PM EDT on August 17, 2007.
I just thought I'd throw in my 2 cents. Intensity forecasts are notoriously innacurate. This thing might well make Category Five. It might also unexpectedly weaken to a 2 or 3. Let's just sit back, see what track it takes at what strength, and comment from there. It would save alot of bandwidth. In the meantime, let's all agree to hope for the best.


There is nothing to prevent it from strengthening in the near term. It's going to reach Cat 5 status. How long it maintains it may be a question.
Member Since: Posts: Comments:
1523. rodrigo0
2:09 AM GMT on Agosto 18, 2007
I work for the media here in Mexico and I have access to photowires... I will upload more pictures to Flickr but only for friends.

Add me as a friend in flickr to see more HQ pictures in the future.

http://www.flickr.com/photos/ebrmx/
Member Since: Posts: Comments:
1522. Drakoen
2:10 AM GMT on August 18, 2007
Most of the models have Dean hiting Mexico.
Member Since: Posts: Comments:
1521. littlefish
2:07 AM GMT on August 18, 2007
LOL SJ- love that technology huh! I was just mentioning the southerly low because of the amount of convection being pulled in by Dean from down there. Looks like there may be some interacting. The other thing I'm watching is LB way out at 15N 32W approx (moving so probably not there anymore exactly). No convection but a bit of circltn.

The other thought on the S low is that the models changed to south in last run even though the north ULL ahdn't hardly budged. Had me scratch my head until I saw the south inflows or unless the ULL north gets squished into oblivion by highs.
Member Since: Posts: Comments:
1520. bappit
2:07 AM GMT on August 18, 2007
At least Dean strengthened after passing through the Antilles.
Member Since: May 18, 2006 Posts: 10 Comments: 5960
1519. HurricaneDean2007
10:09 PM EDT on August 17, 2007
that ULL is drifting westward VERY slowly...
Member Since: Posts: Comments:
1518. WeafhermanNimmy
2:09 AM GMT on August 18, 2007
Hurricane Dean is now a potent cat 4 hurricane with winds up to 145 mph.
Member Since: Posts: Comments:
1517. nola70119
2:08 AM GMT on August 18, 2007
Looks like a slight move back to North in the last frames....
Member Since: June 16, 2006 Posts: 0 Comments: 1560
1516. KnowYourRole
10:08 PM EDT on August 17, 2007
Posted By: StormJunkie at 10:07 PM EDT on August 17, 2007.
lol LF, I am so wore out from that java issue I am just not with it. Take a java loop away from a stormjunkie and it is like beating him in the head with a bat!


I'm still having problems with mine, although not as frequently.
Member Since: Posts: Comments:
1515. DG136
2:08 AM GMT on August 18, 2007
I could be wrong, but 14.9N is the opposite of direction of north. The longer it treks west, the better it looks for the US
Member Since: Posts: Comments:
1514. kmanislander
2:05 AM GMT on August 18, 2007
Drak

Very interesting. There was a small ULL that was tracking W with Dean from about 36 hrs ago just to Dean's SW. Perhaps this is exerting some steering.

I wonder if the models will pick up on this with the next set of runs as Dean will soon be below the curve
Member Since: Posts: Comments:
1513. weathersp
10:08 PM EDT on August 17, 2007
Oh I think it is rapidly intensifying...

Dean
Member Since: January 14, 2007 Posts: 17 Comments: 4140
1512. StormJunkie
2:07 AM GMT on August 18, 2007
Welcome CTodd :~)

Quick Links

Select the first link in the model section. This is the FSU Experimental model page. For all models except for the GFDL and HWRF, I set the field to 850mb vorticity to view potential genesis or track and size of tropical systems. Select animate then scroll right and page through the model run. The surface maps are also good to look at as the 850mb map will sometimes show features which are not at the surface. The GFS, Ukmet, GFDL & HWRF run four times a day; 00z, 06z, 12z, and 18z. The 00z runs usually come out around 2am Est, the 06z around 8am Est, the 12z around 2pm Est, and the 18z around 8pm Est. The CMC, Nogaps and mm5fsu only run at 00z and 12z. The FSU model site can depict the strength of a system which is something you donít get with the line models. There is a great link that shows the mb to ft comparison in the learning section. Also the GFDL and HWRF only work with the field set to Surface Pressure and they only run for active storms. The NWS NCEP model page contains the long range GFS and the NAM as well as several other models. The South Florida Water Management page has a nice spaghetti plot showing most all of the models together. The Weather Underground Tropical section also has some nice spaghetti plots of several of the major models. The GFDL track can usually be found here before it can be seen on the other sites.
Member Since: Posts: Comments:
1511. HurricaneDean2007
10:07 PM EDT on August 17, 2007
It will become a Five, weaken back down to Three or Four, then become a Five again and cross the Yucatan Channel between Yucatan and Cuba and then hit texas.
Member Since: Posts: Comments:
1510. nolesjeff
2:08 AM GMT on August 18, 2007
Thanks metallica and everyone else
Member Since: Posts: Comments:
1509. WPBHurricane05
10:08 PM EDT on August 17, 2007
Wilma was september, wasnt it?

Missed the August part, but no Wilma was October.
Member Since: Posts: Comments:
1508. floridafisherman
2:07 AM GMT on August 18, 2007
wilma was an oct storm
Member Since: Posts: Comments:
1507. Metallica1990
2:07 AM GMT on August 18, 2007
Posted By: nolesjeff at 2:07 AM GMT on August 18, 2007.

Posted By: WPBHurricane05 at 2:05 AM GMT on August 18, 2007.

FYI
Strongest Atlantic storm on record for August was Allen (1980) at 899mb with winds at 190mph.

I remember that one. A big high pressure system and drought in Texas ate that storm up before it made landfall.


They go by pressure. The strongest Atlantic storm is Wilma (2005) with 882mb.

Wilma was september, wasnt it?


October
Member Since: Posts: Comments:
1506. FatPenguin
2:05 AM GMT on August 18, 2007
Posted By: WPBHurricane05 at 2:05 AM GMT on August 18, 2007.

FYI
Strongest Atlantic storm on record for August was Allen (1980) at 899mb with winds at 190mph.

I remember that one. A big high pressure system and drought in Texas ate that storm up before it made landfall.


They go by pressure. The strongest Atlantic storm is Wilma (2005) with 882mb.
++++++++++++++++++++++++++++++++++++++

I was talking about strongest for the month of August.
Member Since: Posts: Comments:
1505. kev22
2:05 AM GMT on August 18, 2007
I just thought I'd throw in my 2 cents. Intensity forecasts are notoriously innacurate. This thing might well make Category Five. It might also unexpectedly weaken to a 2 or 3. Let's just sit back, see what track it takes at what strength, and comment from there. It would save alot of bandwidth. In the meantime, let's all agree to hope for the best.
Member Since: Posts: Comments:
1504. Drakoen
2:06 AM GMT on August 18, 2007
17/2345 UTC 14.9N 65.1W T6.0/6.0 DEAN -- Atlantic Ocean
Member Since: Posts: Comments:
1503. afs
2:04 AM GMT on August 18, 2007
This is starting to look bad.

Member Since: Posts: Comments:
1502. StormJunkie
2:06 AM GMT on August 18, 2007
lol LF, I am so wore out from that java issue I am just not with it. Take a java loop away from a stormjunkie and it is like beating him in the head with a bat!
Member Since: Posts: Comments:
1501. bappit
2:06 AM GMT on August 18, 2007
Galveston looks like it always did to me. Dean is days away if it even comes close.
Member Since: May 18, 2006 Posts: 10 Comments: 5960
1500. nolesjeff
2:06 AM GMT on August 18, 2007
Posted By: WPBHurricane05 at 2:05 AM GMT on August 18, 2007.

FYI
Strongest Atlantic storm on record for August was Allen (1980) at 899mb with winds at 190mph.

I remember that one. A big high pressure system and drought in Texas ate that storm up before it made landfall.


They go by pressure. The strongest Atlantic storm is Wilma (2005) with 882mb.

Wilma was september, wasnt it?
Member Since: Posts: Comments:
1499. Drakoen
2:06 AM GMT on August 18, 2007
Member Since: Posts: Comments:
1497. WatchingInHouston
2:01 AM GMT on August 18, 2007
Posted By: WatchingInHouston at 5:10 PM CDT on August 17, 2007.
TxKiwi - I put together an animated GIF of the forecast history... here's the link:

Link

what a loser...You stole that from NHC and claimed as yours.Click

Here is NHC Link


FWIW, I never claimed that it was MINE, just that I made the looping image... which, I did.. OBVIOUSLY with graphics from the NHC. The reason that I did so is because the NHC link fails to load for me, regardless of the browser. It sits in an endless loop attempting to load the images.

1495. bappit
2:02 AM GMT on August 18, 2007
What did the Yucatan do to Gilbert? I think it was cat 3 at the second landfall.
Member Since: May 18, 2006 Posts: 10 Comments: 5960
1494. littlefish
2:04 AM GMT on August 18, 2007
I think Dean is being pulled a bit south by the south low (LOL if I repeat enough maybe someone will chime in). STAY SAFE kman and Cayman! My goodness, this thing looks dangerous. Glad it isn't over land right now...
Member Since: Posts: Comments:
1493. URAKAN
1:59 AM GMT on August 18, 2007
Hello everyone. I live in Miami and have been following Dean for a couple of days. However, I haven't let my guard down. I'm still wary of last minute track shifts a'la Charley. Anyway, here's a news headline that can really puts things in perspective for Jamaica...Wow!...

Link
Member Since: Posts: Comments:
1491. bluehaze27
2:03 AM GMT on August 18, 2007
Moohlight, I thought you were refering to the talk about the oother storm forming. I don't want to talk politics or wars or anything else, but tropical weather. Dean isn't the only game in town even though it is the most prominent.
Member Since: Posts: Comments:
1490. bollidear
1:56 AM GMT on August 18, 2007
Has anyone any suggestions on what Storm Sturge we can expect on Grand Cayman (south side)?
Member Since: Posts: Comments:
1489. WPBHurricane05
10:04 PM EDT on August 17, 2007
FYI
Strongest Atlantic storm on record for August was Allen (1980) at 899mb with winds at 190mph.

I remember that one. A big high pressure system and drought in Texas ate that storm up before it made landfall.


They go by pressure. The strongest Atlantic storm is Wilma (2005) with 882mb.
Member Since: Posts: Comments:
1488. tallahasseecyclone
2:02 AM GMT on August 18, 2007
Posted By: TexasRiverRat at 2:02 AM GMT on August 18, 2007.

I just dont see the Yucatan knocking that much breath out of Dean?

----If it passes over the peninsula, it will drastically weaken the storm. Land is friction.
Member Since: Posts: Comments:
1487. Drakoen
2:04 AM GMT on August 18, 2007
Posted By: kmanislander at 2:03 AM GMT on August 18, 2007.

Drak

Does that image mean that Dean is still below 15N?


Yes.
Member Since: Posts: Comments:
1486. nolasoci
2:03 AM GMT on August 18, 2007
Louisiana and Mississippi hotels filling up fast for next week for a just in case senerio.
Member Since: Posts: Comments:
1485. KnowYourRole
10:03 PM EDT on August 17, 2007
Posted By: TexasRiverRat at 10:02 PM EDT on August 17, 2007.
I just dont see the Yucatan knocking that much breath out of Dean?


No way to know. Depends on how long it is over the Yucatan for one, and where exactly it crosses.
Member Since: Posts: Comments:

Viewing: 1535 - 1485

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34 | 35 | 36 | 37 | 38 | 39 | 40 | 41 | 42 | 43 | 44 | 45 | 46 | 47 | 48 | 49 | 50 | 51 | 52 | 53 | 54 | 55 | 56 | 57 | 58 | 59 | 60 | 61 | 62 | 63 | 64 | 65 | 66 | 67 | 68 | 69 | 70 | 71Blog Index

Top of Page

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.

Local Weather

Overcast
60 °F
Overcast