Dr. Jeff Masters' WunderBlog

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

Posted by: Dr. Jeff Masters, 7:33 PM GMT on August 17, 2007

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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1801. bluehaze27 3:14 AM GMT on August 18, 2007
baybuddy, no. We have gotten taller to keep our heads above the floods. (facitiousness)Just look at the dutch---the tallest people on earth. Member Since: March 26, 2007 Posts: 0 Comments: 794

1804. iTeachSWLa 3:13 AM GMT on August 18, 2007
Does anyone happen to know how many meteorologists are at TWC? Gosh, that's driving me crazy!

1806. Metallica1990 3:15 AM GMT on August 18, 2007
Posted By: Metallica1990 at 2:53 AM GMT on August 18, 2007. Posted By: Metallica1990 at 2:46 AM GMT on August 18, 2007. Posted By: Metallica1990 at 2:18 AM GMT on August 18, 2007. unless its shifted its track or slowed down at 11 it should be near 14.9N 65.96W i just want to see how good i am at forecasting lol damn i was right 14.9N 65.9W woo hoo :) I love the fact that my post was ignored

1807. Masquer08er 3:15 AM GMT on August 18, 2007
I too am afirm believer in GW and absolutely have not cast my lot politically What does Bush have to do with this? Member Since: August 16, 2007 Posts: 0 Comments: 388

1808. CuriuosGa 3:15 AM GMT on August 18, 2007
on the lighter side.. if it wasn't for global warming we would still be in the ice age

1809. VegasRain 3:16 AM GMT on August 18, 2007
Posted By: Daveg at 3:10 AM GMT on August 18, 2007. Look at this spread...insane I tell ya...INSANE! The Colorado State website wont allow you to post images directly from their site. You will have to copy and paste a link to their main page. Tropical Cyclone Guidance Model Website Member Since: October 24, 2005 Posts: 12 Comments: 455

1810. moonlightcowboy 3:16 AM GMT on August 18, 2007
iTeach, they claim over 100 meteorologists! Member Since: July 9, 2006 Posts: 179 Comments: 28121

1812. BigToe 3:16 AM GMT on August 18, 2007
Posted By: DestinJeff at 3:14 AM GMT on August 18, 2007. all this ice cap talk is making me long for the days of the "first" posts Posted By: Rick54 at 3:14 AM GMT on August 18, 2007. If you can show me some melting glaciers or ice caps in the tropics I will cease my arguement. Mt. Kilamanjaro Now thats good bloggin' Member Since: June 12, 2006 Posts: 0 Comments: 239

1814. Crisis57 3:16 AM GMT on August 18, 2007
Posted By: VegasRain at 3:11 AM GMT on August 18, 2007. As I typed that last message about Dean's wobble to the west being temporary, Dean is now back on a more WNW track in the last few frames. i see that also

1815. Justwondering 3:16 AM GMT on August 18, 2007
The GFDL late cycle track I just saw (and can't seem to post) hasn't moved hardly at all from their earlier track. GFDL still seems to have it set on about Corpus Christi. Has anyone got a link for a dissenting GFDL?

1816. drj27 3:15 AM GMT on August 18, 2007
so my question is is the florida panhandle out of the woods will we have any affects from dean Member Since: August 25, 2006 Posts: 0 Comments: 98

1817. DatagirlWPB 3:17 AM GMT on August 18, 2007
jamaican girl i was in Jamaica on vacation when Gilbert hit. there was no evacutation from the oceanside resort. took five days to get out. Member Since: August 2, 2006 Posts: 0 Comments: 34

1818. Daveg 3:17 AM GMT on August 18, 2007
Posted By: VegasRain at 3:16 AM GMT on August 18, 2007. The Colorado State website wont allow you to post images directly from their site. You will have to copy and paste a link to their main page. Thanks VegasRain...I didn't know that! Member Since: September 23, 2005 Posts: 0 Comments: 426

1819. bluehaze27 3:17 AM GMT on August 18, 2007
sullivan, I took it as an acknowledgement of hell to pay. If that's not what you meant than you should clarify. Otherwise, don't I look foolish. At least I can show some humility if I'm wrong which is hard to find on this site. I can eat crow to and will readily acknowledge it if necessary. Member Since: March 26, 2007 Posts: 0 Comments: 794

1820. Twisterman555 3:17 AM GMT on August 18, 2007
Posted By: iTeachSWLa at 3:13 AM GMT on August 18, 2007. Does anyone happen to know how many meteorologists are at TWC? The Weather Channel on wikipedia Member Since: August 28, 2006 Posts: 0 Comments: 11

1821. HiWay 3:17 AM GMT on August 18, 2007
Mother nature has ALWAYS been pissed off Well wouldn't you be pissed off too if a buncha upright apes started using tools and blowing holes in the sides of you and digging out vast portions of you to meld into machines that screw with your balanced atmosphere, as well as living longer than they are supposed to and overpopulating? :) Member Since: August 17, 2007 Posts: 0 Comments: 55

1824. BigToe 3:18 AM GMT on August 18, 2007
OK Metallica1900..... You NAILED it. Member Since: June 12, 2006 Posts: 0 Comments: 239

1825. sullivanweather 3:18 AM GMT on August 18, 2007
Blue Haze, Think about what the prevailing winds are in the Arctic. Now think about what would happen if there was no more sea-ice up there? Member Since: March 8, 2007 Posts: 269 Comments: 12491

1826. Dan187 3:19 AM GMT on August 18, 2007
last couple frames on IR show some warming of the cloud tops, and pressure remained about the same last 2 (936, 937). I believe the intensification phase has slowed/stopped currently, although I believe it will only be temporary.

1828. Daveg 3:19 AM GMT on August 18, 2007
No wobble....due west... Link Member Since: September 23, 2005 Posts: 0 Comments: 426

1829. bluehaze27 3:19 AM GMT on August 18, 2007
baybuddy, that was a joke as well. Geez. Since when did I EVER say anyone was an idiot. Ya'll need to takle a chill pill. Member Since: March 26, 2007 Posts: 0 Comments: 794

1830. scaldisnoel 3:19 AM GMT on August 18, 2007
drj27, We don't even know if it is going to hit the Yucatan, let alone Florida. So, keep your eyes on the news, don't believe too much of the wild speculation on this site, and be prepared in case it does head toward FL. Member Since: September 3, 2003 Posts: 0 Comments: 59

1831. atmoaggie 3:19 AM GMT on August 18, 2007
H2PV, glad to see someone on your side of the aisle not afraid to do a little research on their own, refreshing. You seem to have your mind made up about this as much as the fact that sun will rise tomorrow, so I'll not try to change your opinion. Yes, water vapor is what is in clouds and is what is seen by the IR channels on NOAA's images. Yes we are detecting and measuring CO2, methane and a host of other gases via satellite. And finally, yes, water vapor is the single most effective greenhouse gas, i.e. my low temps of ~83 in humid South LA. I only ask of you one thing. Please do not stop your researching. We must be tenacious to see through the motivations of our sources, be it grant money or ad sales. We must also be careful not to make too many assumptions about other's assumptions, specifically on the other side of the aisle. Lastly, this is not the forum for me to respond to most of your comments, but as a single example, I want you to be aware that NOAA has discovered that some of the ship reports from the days of old claim a lat/long location from the middle of the Sahara. Some of the data needs to questioned more thoroughly than it has. Member Since: August 16, 2007 Posts: 6 Comments: 12461

1832. AndyN 3:19 AM GMT on August 18, 2007
Also according to the NHC Dean is getting bigger....I also noticed T Stoems firing this evening in South Georgia and East Alabama....counter clockwise cloud motion seems to indicate ULL is making a move West..... Member Since: December 29, 2005 Posts: 1 Comments: 551

1834. JamaicanGir 3:19 AM GMT on August 18, 2007
DatagirlWPB where on the island were you

1835. Metallica1990 3:19 AM GMT on August 18, 2007
Posted By: BigToe at 3:18 AM GMT on August 18, 2007. OK Metallica1900..... You NAILED it. even though i think that was sarcasm thanks

1837. drj27 3:21 AM GMT on August 18, 2007
do you think its going to decrease in the longitude Member Since: August 25, 2006 Posts: 0 Comments: 98

1838. weatherwonderer 3:21 AM GMT on August 18, 2007
Another article daveg: http://www.ipcc.ch/SPM2feb07.pdf As for the Vikings, all hail can I have another? Blue and Sul people will believe what they want. Even if they have to dig deep to find support for their opinion. Member Since: July 16, 2005 Posts: 0 Comments: 167

1839. bluehaze27 3:21 AM GMT on August 18, 2007
Sullivan what is your point? I don't understand. Do you believe the ice caps are melting? I do. Do you believe in global warming? I do. I'm not following you. Member Since: March 26, 2007 Posts: 0 Comments: 794

1840. whipster 3:21 AM GMT on August 18, 2007
Nudging to the N in the last few frames IMO Member Since: August 14, 2007 Posts: 0 Comments: 422

1841. Baybuddy 3:22 AM GMT on August 18, 2007
People always talk about massive flooding when the glaciers melt. If the ice is floating why would the sea level increase? Also, the Bonneville Salt Flats were caused by glaciers. Who's fault is that? Member Since: June 26, 2006 Posts: 0 Comments: 1115

1842. Metallica1990 3:22 AM GMT on August 18, 2007
Posted By: DestinJeff at 3:21 AM GMT on August 18, 2007. metallica, please post your landfall coordinate so we can all go back to our regulatry scheduled lives lol im not going that far

1843. Justwondering 3:22 AM GMT on August 18, 2007
Sorry about that. Let me try to post the link to Colorado State's Late Cycle page. If it won't post again, here's the site: http://euler.atmos.colostate.edu/~vigh/guidance/northatlantic/track_late1.png

1844. drj27 3:22 AM GMT on August 18, 2007
sorry guys for all the questions i just became a member the other day so nice to meet everybody Member Since: August 25, 2006 Posts: 0 Comments: 98

1845. Crisis57 3:23 AM GMT on August 18, 2007
Posted By: whipster at 3:21 AM GMT on August 18, 2007. Nudging to the N in the last few frames IMO i see it

1847. AndyN 3:22 AM GMT on August 18, 2007
I noticed my popsicle melts faster...Is that indicative of global warming? Member Since: December 29, 2005 Posts: 1 Comments: 551

1848. Masquer08er 3:23 AM GMT on August 18, 2007
There's a good reason he posted the Arctic ice extent info That reminds me....I need another Stoli rocks Member Since: August 16, 2007 Posts: 0 Comments: 388

1849. bluehaze27 3:24 AM GMT on August 18, 2007
Baybuddy, I think one issue is the salinity question with ice cap melting. if the salinity falls the ocean currents can stop and we actually may find ourselves in an ice age which is antithetical to ice cap melting and global warming. Member Since: March 26, 2007 Posts: 0 Comments: 794

1850. drj27 3:24 AM GMT on August 18, 2007
yea sorry thats what i meant but ill keep watching it looks like its going to become a cat 5 pretty soon Member Since: August 25, 2006 Posts: 0 Comments: 98

1851. DatagirlWPB 3:24 AM GMT on August 18, 2007
jamaicangirl yep in negril. Gilbert taught me to respect Hurricanes. also been thru Frances, Jeanne,Wilma. good luck Member Since: August 2, 2006 Posts: 0 Comments: 34

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