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: 2135 - 2085

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

2135. VEROBEACHFL1
4:33 AM GMT on August 18, 2007
thx c2
Member Since: Posts: Comments:
2134. nola70119
4:32 AM GMT on August 18, 2007
No support for the NW turn in models or discussion......all the pros are confident in 48hr track.
Member Since: Posts: Comments:
2133. Metallica1990
4:33 AM GMT on August 18, 2007
Posted By: 7544 at 4:33 AM GMT on August 18, 2007.

dont forget its in the herbert box here too hmmmmmmmm


no its not it passed it to the south

and its hebert box not herbert box
2131. i12BNEi
4:32 AM GMT on August 18, 2007
Just north of DEAN isn't the steering almost due north?
Member Since: Posts: Comments:
2130. VEROBEACHFL1
4:31 AM GMT on August 18, 2007
-----sounds ok peeps but sometime--whether gradual or slightly gradual--- DEAN is going to show a more northernly NW track within 24-36 hrs....... and most likely all before 80W...
---thats just me--------
--- i could be wrong as we are all having fun with it of course----landfall-- thats another story...........
Member Since: Posts: Comments:
2129. Canenut
4:33 AM GMT on August 18, 2007
1) Yes latest (0Z) GFS run is further north, and is back to where it was at 2am on the 17th.

2) I haven't seen ANY 0Z GFDL run anywhere (PSU server, OSU Server, so at least for me it might be a suprise.

3) The FSU MM5 shows Dean riding 15N for about 2-3 more hours then nudging WNW

4) If anyone has the 0Z GFDL please lemme have the link.
Member Since: Posts: Comments:
2128. 7544
4:32 AM GMT on August 18, 2007
dont forget its in the herbert box here too hmmmmmmmm
Member Since: May 6, 2007 Posts: 0 Comments: 6690
2126. Metallica1990
4:30 AM GMT on August 18, 2007
Posted By: VegasRain at 4:30 AM GMT on August 18, 2007.

Posted By: watchingnva at 4:23 AM GMT on August 18, 2007.

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???

Dean is about to go through an eyewall replacement cycle. It now has an inner eyewall and an outer eyewall, and the inner eyewall is beginning to collapse. The new eye will be much larger once it starts to take over. The cloud tops have warmed and you can clearly make out the two eyewalls on the San Juan Radar.


that was my second thought
i know what an eye wall replacement cycle is i was just wondering if it was dry air getting to but thanks for telling me

i guess im only good at 3 hr forecast points lmao
2125. 7544
4:30 AM GMT on August 18, 2007
dean is also getting alot more convection to the north thats what im worry about it might start to do the unexpected and throw every met a big loop here . no sleep tonight hehehe
Member Since: May 6, 2007 Posts: 0 Comments: 6690
2124. C2News
12:31 AM EDT on August 18, 2007
Posted By: VEROBEACHFL1 at 12:30 AM EDT on August 18, 2007.
---vero im intending to agree with you here the ull is digging to the south into cuba this is the player tonight as dean gets closer to 75 and he might do the nw turn . but 90% of the others are saying no.
---SIGH- YES, I KNOW---- im the oddball/target---- shoot your darts here--LOL


I agree with you vero...
Member Since: Posts: Comments:
2122. watchingnva
4:29 AM GMT on August 18, 2007
i wouldnt be surprised to see dean weaken a bit with a bit more of a wnw track over the next 6 hours or so...a lil dry air still bothering him...but...I have a feeling as he gets closer to jamaica...hes gonna bomb again...will have to wait and see...
Member Since: Posts: Comments:
2121. howarjo1943
4:28 AM GMT on August 18, 2007
noted wunderadmin

we are eclipsed!!!!
Member Since: Posts: Comments:
2120. VegasRain
4:26 AM GMT on August 18, 2007
Posted By: watchingnva at 4:23 AM GMT on August 18, 2007.

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???


Dean is about to go through an eyewall replacement cycle. It now has an inner eyewall and an outer eyewall, and the inner eyewall is beginning to collapse. The new eye will be much larger once it starts to take over. The cloud tops have warmed and you can clearly make out the two eyewalls on the San Juan Radar.
Member Since: Posts: Comments:
2119. Hellsniper223
4:27 AM GMT on August 18, 2007
After Dean's first real eyewall replacement cycle, I expect the windfield in the system to greatly increace in size. After the cycle dean's eye should also greatly increase in size. This should be An Ivan/Katrina like storm in the next 12 hours as this occurs.
Member Since: Posts: Comments:
2118. VEROBEACHFL1
4:29 AM GMT on August 18, 2007
---vero im intending to agree with you here the ull is digging to the south into cuba this is the player tonight as dean gets closer to 75 and he might do the nw turn . but 90% of the others are saying no.
---SIGH- YES, I KNOW---- im the oddball/target---- shoot your darts here--LOL
Member Since: Posts: Comments:
2117. weatherwonderer
4:24 AM GMT on August 18, 2007
This storm is weird. Itseems like it picks strength in the day and early evening instead of growing stronger as it approaches diurnal max. Man it is struggling to move North. This thing has been booking 280 for a long time. Doesn't look like Cancun will be the place to go in a couple of days. Still, the ULL lurks as the only factor to change things.
Member Since: Posts: Comments:
2116. Daveg
4:28 AM GMT on August 18, 2007
Possible every so slight WNW turn....maybe...or it could just be a wobble. Need some more images in the loop first.
Member Since: Posts: Comments:
2115. nola70119
4:27 AM GMT on August 18, 2007
GFS moved back north.........the models can't get a good fix.
Member Since: Posts: Comments:
2112. 7544
4:25 AM GMT on August 18, 2007
vero im intending to agree with you here the ull is digging to the south into cuba this is the player tonight as dean gets closer to 75 and he might do the nw turn . but 90% of the others are saying no.
Member Since: May 6, 2007 Posts: 0 Comments: 6690
2110. VEROBEACHFL1
4:25 AM GMT on August 18, 2007
---it will make it to the buoy---thats what like 90 miles away or so--------- its gonna be a great reading----- did u notic the word 'GRADUAL"
Member Since: Posts: Comments:
2109. wederwatcher555
4:25 AM GMT on August 18, 2007
gfs has dean only scraping the top of the yucatan on this latest run. if the gfdl sticks to its guns things are going to get interesting
2108. Justwondering
4:22 AM GMT on August 18, 2007
I'm hearing conflicting thoughts and would like to clarify. Is the GFS aligning more North\North East with GFDL or is GFS going back south?
Member Since: Posts: Comments:
2107. mikester
4:25 AM GMT on August 18, 2007
I live south of syracuse and a town called marathon got hit by the storm with 70+ mph gusts. I live in pitcher and my parents told me they had alot of wind and lightening out there.
Member Since: Posts: Comments:
2106. Metallica1990
4:24 AM GMT on August 18, 2007
Posted By: watchingnva at 4:23 AM GMT on August 18, 2007.

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???


the southwest eyewall looks like its weakening i could be wrong
2105. Randyman
4:25 AM GMT on August 18, 2007
An excellent look at Dean I posted earlier...


Link
Member Since: Posts: Comments:
2104. nola70119
4:25 AM GMT on August 18, 2007
Flat screen, round earth....
Member Since: Posts: Comments:
2103. Cachito
4:17 AM GMT on August 18, 2007
mikester: I'm in Rochester. Raining like a cow peeing on a flat rock today, but I don't believe the gusts reached 70 mph.


bappit: Thanks for the info. I'll go back and check the pages you mentioned.
Member Since: Posts: Comments:
2102. H2OMaker
4:23 AM GMT on August 18, 2007
Someone have a GFDL model run link? I use the one's from the Tropics homepage, maybe I'm missing something?
Member Since: Posts: Comments:
2100. atmoaggie
4:24 AM GMT on August 18, 2007
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...

shear anomaly
Member Since: August 16, 2007 Posts: 6 Comments: 12461
2097. VEROBEACHFL1
4:23 AM GMT on August 18, 2007
it WILL gradually move NW in the next few hours............ its not going to ride the line of 15.........
Member Since: Posts: Comments:
2096. katadman
4:11 AM GMT on August 18, 2007
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: Posts: Comments:
2095. nola70119
4:23 AM GMT on August 18, 2007
Link
Member Since: Posts: Comments:
2093. Relix
4:04 AM GMT on August 18, 2007
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: Posts: Comments:
2092. getalife
4:19 AM GMT on August 18, 2007
A hit on Brownsville would be small compared to a Galveston hit.
Member Since: Posts: Comments:
2091. watchingnva
4:22 AM GMT on August 18, 2007
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: Posts: Comments:
2090. mikester
4:21 AM GMT on August 18, 2007
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: Posts: Comments:
2089. nola70119
4:21 AM GMT on August 18, 2007
According to NHS there is nothing except internal dynamics and land to reduce the intensity of the storm....
Member Since: Posts: Comments:
2088. TheCaneWhisperer
4:21 AM GMT on August 18, 2007
I hope so too KY! Every inch west means a larger chance to miss for you.
Member Since: Posts: Comments:
2087. VEROBEACHFL1
4:21 AM GMT on August 18, 2007
IM not buying it--- im sticking to my NNW as usual--i know--im out of the norm--but thats what i see........
Member Since: Posts: Comments:
2086. cirrocumulus
4:21 AM GMT on August 18, 2007
JFlorida,

You are correct. There is a slight move to the northwest on satellite!
Member Since: Posts: Comments:

Viewing: 2135 - 2085

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

Mostly Cloudy
70 °F
Mostly Cloudy