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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951. Tropicnerd13 18. elokuuta 2007 klo 00:04 (GMT)
i still think the storm will go more north than mexico. jmho. i also have the next set of model runs in 2 days or less. that is what they will be.

952. TheCaneWhisperer 18. elokuuta 2007 klo 00:03 (GMT)
I feel for them as well Amy! They have been blasted over the past several years. Direct hit on Jamacia, Caymans and Cozumel and Cancun of all places, hurts. Nature of the beast and your chosen destination I guess. Floridians like myself are breathing a sigh of relief and taking a break. Especially when every credible forecaster says your the bullseye this year. Dean is days away from a major strike to landmass, sit back and observe. Take advantage, it's looking to be crazy from here on out. Family in Jamacia is evacuating as we speak and I know K-Man is up to the same.

953. WPBHurricane05 18. elokuuta 2007 klo 00:04 (GMT)
On television they say the fact that the storm is slowing in forward motion means it may be about to have a change in course. Is that true? That wouldnt be good. The GFDL had Dean slowing down. Member Since: 31.07.2006 Posts: 56 Comments: 8004

954. mgreen91 18. elokuuta 2007 klo 00:04 (GMT)
Posted By: Amystery at 11:53 PM GMT on August 17, 2007. I feel sorry for Jamica, Yucatan and then Mexico...wish it would just die.....but better them then us(sounds bad, but oh well) THAT WAS VERY MEAN... Member Since: 4.08.2006 Posts: 0 Comments: 290

955. tallahasseecyclone 18. elokuuta 2007 klo 00:04 (GMT)
How much of a pressure drop is this from last check. I think that 130 mph may be a little conservative.

956. NASA101 18. elokuuta 2007 klo 00:05 (GMT)
oops...130 mph is still CAT 3. looks like some of us got it wrong..!? Member Since: 16.08.2007 Posts: 0 Comments: 276

957. adrianalynne 18. elokuuta 2007 klo 00:05 (GMT)
If any part of Florida of should be worried, I think its the Panhandle Member Since: 7.08.2006 Posts: 0 Comments: 134

958. Dropsonde 18. elokuuta 2007 klo 00:05 (GMT)
Hi StormW. Yes I check your blog whenever I go online and see an update to it. Your views as a met are among those that I put the most confidence in. Congrats on making the featured list. Member Since: 22.08.2006 Posts: 10 Comments: 414

959. Skyepony (Mod) 18. elokuuta 2007 klo 00:06 (GMT)
Storm DEAN: Observed by AF #302 Storm #04 In Atlantic Ocean Total Flights For Storm #04: 05 Date/Time of Recon Report: August 17, 2007 23:32:00 Zulu Position Of The Center: 14 � 52 ' N 065 � 02 ' W (14.87� N 65.03� W) Minimum Height Measured At Standard Level Of N/A Millibars: 2632 Meters (Normal: N/A Meters) Maximum Surface Winds Were Estimated At: 119 Knots (136.85 MPH) Estimated Surface Winds Were Measured At: 006 Nautical Miles (6.9 miles) From Center At Bearing 302� Maximum Flight Level Winds Near Center Were 130 Knots (149.5 MPH) From 048� Maximum Flight Level Winds Were Measured 010 Nautical Miles (11.5 Miles) From Center At Bearing 309� Minimum Pressure: 946 Millibars (27.934 Inches) Maxium Flight Level Temperature / Pressure Altitude Outside The Eye: 8�C (46.4�F) / 3045 Meters Maximum Flight Level Temperature / Pressure Altitude Inside The Eye: 18�C (64.4�F) / 3045 Meters Dewpoint Temperature / Sea Surface Temperature Inside The Eye: 13�C (55.4�F) / NA�C (NA�F) Eye Wall Was Characterized As Being: CLOSED Eye Form Was Characterized As Being: 16 Center Fix Established Using: Penetration Radar Wind Pressure Temperature Center Fix Established At Level(s): 700 Millibars Navigational Accuracy Measured At: 0.02 Nautical Miles Meteorological Accuracy Measured At: 2 Nautical Miles Other Information: 1: Maximum Flight Level Winds Were 130 KT NW Quadrant at 23:29:00 Member Since: 10.08.2005 Posts: 145 Comments: 29944

960. waccamaw16 18. elokuuta 2007 klo 00:06 (GMT)
looks like the ull is not moving on the last couple of loops on the satellite. it could be stopping because of the little frontal boundry thats in s.carolina to alabama and that might be stopping the ull from moving at this time , but that could change later

961. efallon28 18. elokuuta 2007 klo 00:06 (GMT)
Posted By: cirrocumulus at 12:02 AM GMT on August 18, 2007. One statistic I found fascinating was that of the previous ten wettest Julys on record in Texas, six had major hurricanes hit the Texas Gulf Coast the same year. Texas had one of the wettest Julys ever this year. Did you ever think that maybe that's why they were record months? I mean, these storm do drop a lot of rain. Just a thought. Member Since: 12.07.2005 Posts: 0 Comments: 105

962. OUFan919 18. elokuuta 2007 klo 00:06 (GMT)
NHC said winds are AT LEAST 130mph...So they could be around 135-140. My taking of what that means. Member Since: 31.07.2007 Posts: 0 Comments: 329

963. Crazman 18. elokuuta 2007 klo 00:06 (GMT)
135mph MISPRINT ON NHC Member Since: 3.08.2006 Posts: 0 Comments: 32

964. Cavin Rawlins 18. elokuuta 2007 klo 00:06 (GMT)
WC saying 135 mph Member Since: 24.07.2005 Posts: 407 Comments: 19076

965. Xion 18. elokuuta 2007 klo 00:06 (GMT)
135 mph now. Member Since: 29.08.2006 Posts: 0 Comments: 726

966. extreme236 18. elokuuta 2007 klo 00:07 (GMT)
nvm dean has 135mph winds Member Since: 2.08.2007 Posts: 19 Comments: 19234

967. zingocat 18. elokuuta 2007 klo 00:07 (GMT)
When I visited Jamica about 10 years ago I asked some locals if they were worried about hurricanes. These young people said no, we are too far south to get them. Member Since: 15.07.2007 Posts: 0 Comments: 170

968. quakeman55 18. elokuuta 2007 klo 00:07 (GMT)
Interesting how they say "at least"...that's the first time I've seen them do that. So they know for sure they are actually greater than 130MPH...maybe that's why they are calling it a Cat 4, even though 130MPH is a high-end Cat 3. Member Since: 31.03.2002 Posts: 1 Comments: 1276

969. VEROBEACHFL1 18. elokuuta 2007 klo 00:06 (GMT)
HI all-- i still think the more northernly it will go--gradually -- any of the models show this? just popped in for a second--watching the marlins and the giants.....

970. scottflorida 18. elokuuta 2007 klo 00:07 (GMT)

971. StormJunkie 18. elokuuta 2007 klo 00:07 (GMT)
We are now in the 1km view. Images will update much more often! Member Since: 17.08.2005 Posts: 26 Comments: 15240

973. Cavin Rawlins 18. elokuuta 2007 klo 00:08 (GMT)
REPEATING THE 800 PM AST POSITION...14.9 N...65.1 W. MOVEMENT TOWARD...WEST NEAR 19 MPH. MAXIMUM SUSTAINED WINDS...135 MPH. MINIMUM CENTRAL PRESSURE...946 MB. Member Since: 24.07.2005 Posts: 407 Comments: 19076

974. Dan187 18. elokuuta 2007 klo 00:07 (GMT)
REPORTS FROM AN AIR FORCE RESERVE RECONNAISSANCE AIRCRAFT INDICATE THAT MAXIMUM SUSTAINED WINDS HAVE INCREASED TO AT LEAST 135 MPH...215 KM/HR...WITH HIGHER GUSTS. DEAN IS NOW A CATEGORY FOUR HURRICANE ON THE SAFFIR-SIMPSON HURRICANE SCALE. SOME ADDITIONAL STRENGTHENING IS FORECAST DURING THE NEXT 24 HOURS. was corrected

975. Cavin Rawlins 18. elokuuta 2007 klo 00:08 (GMT)
Dean also slowed to 19 mph Member Since: 24.07.2005 Posts: 407 Comments: 19076

976. quakeman55 18. elokuuta 2007 klo 00:08 (GMT)
Ah, okay. I get it now. Member Since: 31.03.2002 Posts: 1 Comments: 1276

977. tallahasseecyclone 18. elokuuta 2007 klo 00:08 (GMT)
Seems to be wrapping in a little dry air on the east side.

978. extreme236 18. elokuuta 2007 klo 00:08 (GMT)
REPORTS FROM AN AIR FORCE RESERVE RECONNAISSANCE AIRCRAFT INDICATE THAT MAXIMUM SUSTAINED WINDS HAVE INCREASED TO AT LEAST 135 MPH...215 KM/HR...WITH HIGHER GUSTS. DEAN IS NOW A CATEGORY FOUR HURRICANE ON THE SAFFIR-SIMPSON HURRICANE SCALE. SOME ADDITIONAL STRENGTHENING IS FORECAST DURING THE NEXT 24 HOURS. Notice how they said "at least" so perhaps they are still finding higher winds Member Since: 2.08.2007 Posts: 19 Comments: 19234

979. obxrox 18. elokuuta 2007 klo 00:09 (GMT)
latest GFDL shows landfall in vicinity of Freeport, TX with 150+ mph surface winds, Wed 6AM...that's the outlier model. all other model consensus is south. will be interesting to see how the trends change and models shift. my hope is that all in this storm's path fare well and are safe, wherever it ends up.

980. AnthonyJKenn 18. elokuuta 2007 klo 00:09 (GMT)
Not neccessarily, Donna..remember that Dean was booking it at nearly 25mph earlier, more likely, it's slowing to a more normal rate of speed. 17 mph is still rather quick for a hurricane, especially one that is rapidly intensifying as Dean is. Anthony Member Since: 20.09.2005 Posts: 0 Comments: 187

983. StuccoMan 18. elokuuta 2007 klo 00:09 (GMT)
E-mail Advisories GIS Data \| RSS XML/RSS logo Help with Advisories Marine Forecasts Atlantic and E Pacific Forecast and Analysis Tools Help with Marine Hurricane Awareness Be Prepared \| Learn Frequent Questions AOML Research Hurricane Hunters Saffir-Simpson Scale Forecasting Models Eyewall Wind Profiles Glossary/Acronyms Storm Names Breakpoints Hurricane History Seasons Archive Forecast Accuracy Climatology Most Extreme About the NHC Mission and Vision Personnel \| Visitors Library Joint Hurr Testbed The NCEP Centers NOAA Locator WX4NHC Radio Contact Us � Help FirstGov.gov is the U.S. Government's official Web portal to all Federal, state and local government Web resources and services. Hurricane DEAN Public Advisory Home Public Adv Fcst/Adv Discussion Wind Probs Maps/Charts Archive US Watch/Warning 000 WTNT34 KNHC 180004 TCPAT4 BULLETIN HURRICANE DEAN INTERMEDIATE ADVISORY NUMBER 19A...CORRECTED NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL042007 800 PM AST FRI AUG 17 2007 ...CORRECTED MAXIMUM WIND SPEED TO 135 MPH... ...DEAN REACHES CATEGORY FOUR STRENGTH AS ITS CENTER PASSES SOUTH OF THE VIRGIN ISLANDS...

984. KYhomeboy 18. elokuuta 2007 klo 00:09 (GMT)
Amystery...excuse me? You didn't mention the Cayman Islands...but Jamaica and the other countires are our neighbours. So yes I do take offence. Hope nothing comes knocking on your door to kill you...but thats just me...I wishcast to preserve life...not to take it. Your clearly young and immature so I will let it go :)

985. weatherguy03 18. elokuuta 2007 klo 00:09 (GMT)
New blog up! With pretty maps!..LOL Enjoy. Member Since: 5.07.2005 Posts: 581 Comments: 29681

986. presslord 18. elokuuta 2007 klo 00:10 (GMT)
it appears the wave @ 35w x 14n is doing push ups and taking it's vitamins.... Member Since: 13.08.2007 Posts: 0 Comments: 10404

987. Crisis57 18. elokuuta 2007 klo 00:10 (GMT)
Posted By: StormW at 12:07 AM GMT on August 18, 2007. Posted By: DonnaGalveston at 12:03 AM GMT on August 18, 2007. On television they say the fact that the storm is slowing in forward motion means it may be about to have a change in course. Is that true? Most of the time yes...or it means steering currents are getting weak. I feel the slowdown is from that ULL we've been talking of. If you look at water vapor, the big ridge over the U.S. is centered over Texas. The flow on the east sied of it is from NNE TO SSW. Right now, Dean is in a position to where it can't get steered right away by the ridge until it deals with the flow around the ULL. The ridge will have to slide east and repalce that ULL. Go to water vapor, loop it and do a closeup. You should be able to see what I'm talking about. Thanks Storm lets me know im not going crazy that the ULL isn't moving guys

988. Cavin Rawlins 18. elokuuta 2007 klo 00:10 (GMT)
Wow dean maybe the first cat 5 since wilma 2005 Member Since: 24.07.2005 Posts: 407 Comments: 19076

989. dean2007 18. elokuuta 2007 klo 00:10 (GMT)
The winds are 135mph and it is a category four hurricane the pressure has dropped from 961mb to 946mb thats a 15mb drop in the last three hours.

990. Metallica1990 18. elokuuta 2007 klo 00:10 (GMT)
Posted By: Metallica1990 at 10:59 PM GMT on August 17, 2007. Posted By: ThePainkiller at 10:58 PM GMT on August 17, 2007. Recon is on its way out to Dean now. It will be intresting to see what they find. I say CAT 4 winds of 140< pressure <945 I was close :)

991. DonnaGalveston 18. elokuuta 2007 klo 00:10 (GMT)
Thank you StormW for that very detailed answer! Half of it did go over my head though!

992. Tropicnerd13 18. elokuuta 2007 klo 00:11 (GMT)
ok my models are coming soon. yes, they are just lines on paper. that is what models are. lol. but seriously, i think the modles will change to this soon. now they say 135 mph winds. sounds like rapid intensification is occuring..... again not wishcasting. you can see my prediction getting more true with the recent info. i am not trolling or wishcasting. i am not trying to make anyone feel bad either, or make anyone afraid or scared or worried in any way. just stating what i think on paper.

993. cirrocumulus 18. elokuuta 2007 klo 00:12 (GMT)
So much for the GFS on the remnants of Erin. The storm is pulled north rather than west as the GFS forecasted. Remnants of Erin are centered over Reagan County according to Midland/Odessa radar. Member Since: 30.09.2005 Posts: 0 Comments: 1606

994. Crisis57 18. elokuuta 2007 klo 00:12 (GMT)
Also Storm i think whats left of Erin is playing a part in that as well

996. MysteryMeat 18. elokuuta 2007 klo 00:12 (GMT)
Gotta love how every cone drawn by commenters manage to include New Orleans, even though the official ones, at most, get to the Texas-Louisiana border. Member Since: 25.09.2005 Posts: 0 Comments: 253

997. Tropicnerd13 18. elokuuta 2007 klo 00:14 (GMT)
gfdl has it as a cat 5 soon. but that is the old model run. they need to update the gfdl run video thing.

998. paulfrmpasschristian 18. elokuuta 2007 klo 00:14 (GMT)
Storm w ..what do you thinK? is gfdl more wrong than the rest??

999. Crisis57 18. elokuuta 2007 klo 00:14 (GMT)
nice graphic Tropic

1000. ClearH2OFla 18. elokuuta 2007 klo 00:15 (GMT)
hey Storm W how goes it.

1001. errantlythought 18. elokuuta 2007 klo 00:15 (GMT)
Not sure where people are getting SW movement, radar out of PR definately points at a roughly 280 movement still. Member Since: 27.08.2005 Posts: 0 Comments: 191

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