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

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2051. Spoon 18. elokuuta 2007 klo 04:14 (GMT)
42059 just updated

2052. mikester 18. elokuuta 2007 klo 04:14 (GMT)
Hey chachito i am also in nystate. Up hear all we get is strong cold fronts in the summer. Around my area it is been active today with thunderstorms producing 70+mph wind gusts. Member Since: 4.04.2005 Posts: 1 Comments: 133

2054. Masquer08er 18. elokuuta 2007 klo 04:14 (GMT)
Why not list everything you, personally, are doing to stop GW and reduce greenhouse emmissions? As we know, change starts with you and me. That might be more productive than arguing who's right. Even if you don't believe in GW, conservation is a good thing. BTW, isn't there a hurricane? Member Since: 16.08.2007 Posts: 0 Comments: 388

2055. Blink 18. elokuuta 2007 klo 04:14 (GMT)
Wow... Been working all weekend long and just got some time tonight to pass by and see what Dean is doing. No surprise, I knew this storm was gonna be a monster and my worst fear came true. Im on the west coast of Fl. and right now Im not too worried about us over here but for the folks in the carribean. Cat.5 Hurricane projected? I hope folks in its wrath are prepared for this. been looking at some models and looks like a yucatan hit for now. Few models take it towards Tx and LA. Will watch it very closely this weekend. Link

2056. wederwatcher555 18. elokuuta 2007 klo 04:14 (GMT)
new gfs significantly north from previous run. but remember the previous run 18z was extremely different than the past couple days. the latest run is back to the consensus of N.mex-S.tex brownsville area

2057. bappit 18. elokuuta 2007 klo 04:14 (GMT)
There were some posts earlier tonight around pages 27 to 30 I think from people in P.R. They said they had no problems. Member Since: 18.05.2006 Posts: 3 Comments: 4389

2058. nola70119 18. elokuuta 2007 klo 04:14 (GMT)
GFDL and GFS just got closer......GFS moved way north to where UKMET is. Member Since: 16.06.2006 Posts: 0 Comments: 1535

2060. AndyN 18. elokuuta 2007 klo 04:15 (GMT)
GFDL is historically the most accurate Member Since: 29.12.2005 Posts: 1 Comments: 551

2061. Justwondering 18. elokuuta 2007 klo 04:16 (GMT)
Hey Nola: Would you pass along that link, please? I'm digging through the NCEP pages and not finding that one. Thanks

2062. Canenut 18. elokuuta 2007 klo 04:16 (GMT)
Well the 00z GFS has landfall once again ~50 miles south of Brownsville, TX. The model has reverted back to the original thinking last seen in the 06Z run, 18 hours of goofiness, then oops, never mind.....

2064. VEROBEACHFL1 18. elokuuta 2007 klo 04:17 (GMT)
i see it now-- yeah looks to be a gradual shift to the NW till 80W ......then what.......

2065. nola70119 18. elokuuta 2007 klo 04:17 (GMT)
Stop. Member Since: 16.06.2006 Posts: 0 Comments: 1535

2066. KnowYourRole 18. elokuuta 2007 klo 04:17 (GMT)
Posted By: JFLORIDA at 12:14 AM EDT on August 18, 2007. So, where is Dean headed? Is he expected to track northwestward? Ok I wont start again - but i still think on the radar the NW component of motion is reoccurring. Hasn't moved off of 15N all night. I'm not sure why you think it's headed NW.

2067. chicagowatcher 18. elokuuta 2007 klo 04:17 (GMT)
Wind gusts almost to 50 knts on that buoy too. Don't know how long it will last, but will be interesting to watch... Member Since: 28.08.2005 Posts: 0 Comments: 153

2068. nola70119 18. elokuuta 2007 klo 04:19 (GMT)
All bets off according to NHS.....west and north Gulf are all equally at risk, too many variables to make an intelligent guess according to forecaster Knapp. Member Since: 16.06.2006 Posts: 0 Comments: 1535

2069. bappit 18. elokuuta 2007 klo 04:19 (GMT)
WatchingInHouston, cool map! Glad it has a zoom button. LOL Member Since: 18.05.2006 Posts: 3 Comments: 4389

2070. wederwatcher555 18. elokuuta 2007 klo 04:19 (GMT)
this thing has the possibility of being very ugly. yes brownsville itself would be a disaster but the yucatan would take some of the punch out of dean. if this moves just a LITTLE north let alone the GFDL track, nothing will slow down dean and all hell will break lose. it only takes a little movement North

2071. Spoon 18. elokuuta 2007 klo 04:20 (GMT)
50?? I only see close to 40kts at the buoy.

2072. VEROBEACHFL1 18. elokuuta 2007 klo 04:20 (GMT)
OMG-- are u really stuck on the EASTERN track? I dont think so-- istill saw ULL there and it slowed a bit also--- that NW movement is in play from now till about 80w or so......... its not be-lining east--thats for sure......

2073. nola70119 18. elokuuta 2007 klo 04:20 (GMT)
NHS had 15N at 2am.....its right where its supposed to be. Member Since: 16.06.2006 Posts: 0 Comments: 1535

2074. atmoaggie 18. elokuuta 2007 klo 04:20 (GMT)
We are getting all excited about Dean's ramping intensity, but take a look (Thanks to CSU). he has not entered the higher areas of heat content yet. A little more shear would help knock him down, though, and that may be in the works... Member Since: 16.08.2007 Posts: 6 Comments: 12461

2075. cirrocumulus 18. elokuuta 2007 klo 04:21 (GMT)
What a difference six hours makes! The GFS has changed its mind and says Dean is heading farther north than before! The ULL is starting show its effects and the westerly push on some ULL forecasts has started to change the plots. Member Since: 30.09.2005 Posts: 0 Comments: 1606

2076. WunderBlogAdmin (Admin) 18. elokuuta 2007 klo 04:21 (GMT)
Good evening all. We'd like to ask that the topic of conversation move to the storms, since the topic of the ice caps has descended into conversation that doesn't belong here. The traffic here is very high and we are being extra strict over thee weekend as Dean approaches. If you must chat, use our chatroom. Otherwise, review the Rules of the Road. Thanks and enjoy the blogs.

2077. 7544 18. elokuuta 2007 klo 04:21 (GMT)
should there be any reason to concerned that the ull is digging deep south to cuba and dean is getting close to it .could this be the time that dean might turn more to the nw or north . Member Since: 6.05.2007 Posts: 0 Comments: 5925

2078. bappit 18. elokuuta 2007 klo 04:22 (GMT)
Extra! Extra! National Data Buoy Center is running a special on Dean. List of all reports in Dean's vicinity is here. Member Since: 18.05.2006 Posts: 3 Comments: 4389

2079. Metallica1990 18. elokuuta 2007 klo 04:22 (GMT)
eye is about to close or weaken

2080. KnowYourRole 18. elokuuta 2007 klo 04:22 (GMT)
Posted By: nola70119 at 12:20 AM EDT on August 18, 2007. NHS had 15N at 2am.....its right where its supposed to be. imagine that=)

2081. silverstripes 18. elokuuta 2007 klo 04:22 (GMT)
Here is recent imagery (12:01 Eastern). Link Click on Dean and it will zoom in on him. Member Since: 26.07.2006 Posts: 5 Comments: 594

2083. WatchingInHouston 18. elokuuta 2007 klo 04:22 (GMT)
Bappit - For those that are unfamiliar with the structures in the GOM, it's really amazing how densely populated it is with structure.

2084. chicagowatcher 18. elokuuta 2007 klo 04:22 (GMT)
LOL sorry spoon, I stand corrected. almost 40 it is... was hard to read the graph with all the GW hot air obscuring the screen... Member Since: 28.08.2005 Posts: 0 Comments: 153

2086. cirrocumulus 18. elokuuta 2007 klo 04:22 (GMT)
JFlorida, You are correct. There is a slight move to the northwest on satellite! Member Since: 30.09.2005 Posts: 0 Comments: 1606

2087. VEROBEACHFL1 18. elokuuta 2007 klo 04:22 (GMT)
IM not buying it--- im sticking to my NNW as usual--i know--im out of the norm--but thats what i see........

2088. TheCaneWhisperer 18. elokuuta 2007 klo 04:23 (GMT)
I hope so too KY! Every inch west means a larger chance to miss for you.

2089. nola70119 18. elokuuta 2007 klo 04:23 (GMT)
According to NHS there is nothing except internal dynamics and land to reduce the intensity of the storm.... Member Since: 16.06.2006 Posts: 0 Comments: 1535

2090. mikester 18. elokuuta 2007 klo 04:23 (GMT)
What is really puzzling is the current track of west on 15n. It hasn't moved much at all over that last few hours. Something is blocking it from taking a north turn. As long as whatever is stopping him from going north stays there he is most likely going to hit mexico. Member Since: 4.04.2005 Posts: 1 Comments: 133

2091. watchingnva 18. elokuuta 2007 klo 04:23 (GMT)
Posted By: Metallica1990 at 4:22 AM GMT on August 18, 2007. eye is about to close or weaken why??...bc the cloud tops have warmed up a bit??? Member Since: 7.09.2005 Posts: 3 Comments: 1310

2092. getalife 18. elokuuta 2007 klo 04:24 (GMT)
A hit on Brownsville would be small compared to a Galveston hit.

2093. Relix 18. elokuuta 2007 klo 04:24 (GMT)
Reporting from Puerto Rico: I live in the north coast of the island, close to San Juan, and a few minutes ago I got a gust reading of an impressive 47 miles... yep, 47. Immediately there was a widespread blackout with no power for a minute or so. Right now it JUST got back, but it was... "nice" seeing something exciting =P Member Since: 3.08.2006 Posts: 0 Comments: 2358

2095. nola70119 18. elokuuta 2007 klo 04:24 (GMT)
Link Member Since: 16.06.2006 Posts: 0 Comments: 1535

2096. katadman 18. elokuuta 2007 klo 04:24 (GMT)
Want to add my prayers and wishes for safety for all those in Dean's path. Our hope is that you will be spared loss of any kind. Will someone tell me what is the geographical relationship between Dean and the ULL that would cause the turn north. How far southwest does the low have to move in order to effect Dean's path? I realize that it also depends on Dean's forward speed. What is the minimum degrees north of the storm that the ULL must reach in order to have that effect? Member Since: 7.09.2006 Posts: 0 Comments: 1081

2097. VEROBEACHFL1 18. elokuuta 2007 klo 04:24 (GMT)
it WILL gradually move NW in the next few hours............ its not going to ride the line of 15.........

2100. atmoaggie 18. elokuuta 2007 klo 04:24 (GMT)
Anomalously high shear begins before the Yucatan channel. Will Dean catch up to it? Also note the anomalously lower shear off of Africa, where that wave is... Member Since: 16.08.2007 Posts: 6 Comments: 12461

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