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: 185 - 135

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

184. hurricanehamster
8:28 PM GMT on August 17, 2007
noaa say dean will hit any where in the gulf
Member Since: Posts: Comments:
183. Crisis57
8:27 PM GMT on August 17, 2007
great link Randyman
Member Since: Posts: Comments:
181. MisterPerfect
8:26 PM GMT on August 17, 2007
Posted By: StSimonsIslandGAGuy at 8:24 PM GMT on August 17, 2007.

I ganked this from Levi32. Hope he doesn't mind, but it is the best model graphic I have ever seen.


It is pretty. And it illustrates just how big and uncertain this is right now...
Member Since: Posts: Comments:
180. sngalla
4:26 PM EDT on August 17, 2007
Florida meteorologists are saying to keep a close eye on the storm.
Member Since: February 18, 2003 Posts: 57 Comments: 5363
179. Thaale
8:23 PM GMT on August 17, 2007
1 = 69 statutes miles, benerica (or 60 nautical miles).

But though that always hold true for latitude, for longitude its less correct the further from the equator you go. At a latitude of 15, each of longitude is about 3.4% smaller than it would be at the equator.
Member Since: Posts: Comments:
178. nola70119
8:22 PM GMT on August 17, 2007
By Northerly we mean a slight adjustment that would favor the GFDL model to Louisiana and not till nexr week, and its not clear this is happening, though the current track might be slightly more N than forecast. All the models are moving Dean toward Jamaica, there is no indication of any radical movement north.
Member Since: June 16, 2006 Posts: 0 Comments: 1565
177. Dropsonde
8:26 PM GMT on August 17, 2007
I would say it's 99.5% likely that Florida is in the clear from a direct hit. I'm more worried at this point about Dean passing west of NOLA or making a direct hit on Houston.
Member Since: Posts: Comments:
176. benirica
8:24 PM GMT on August 17, 2007
i didnt take any preparations for DEAN either here in PUERTO RICO and i dont think it will matter. on the Doppler radar out of PR you can see that it did wobble to the WNW a bit but it seems that its going to the West again. you can clearly see the eye out of the long range Puerto Rido radar.
Member Since: Posts: Comments:
175. Randyman
8:26 PM GMT on August 17, 2007
Posted By: Crisis57 at 8:23 PM GMT on August 17, 2007.

Posted By: Michael at 8:14 PM GMT on August 17, 2007.

I forgot all about that, he said a huge anticyclone over Dean will over power anything and will find the weakness whereever it may be.....NW gulf? dont know

I'm not diagreeing with you at all just giving friendly observation but take a look at the link posted by Randyman and check the last frame very interesting


Here's the link for anyone who missed it...



Link
Member Since: Posts: Comments:
174. JLPR
8:25 PM GMT on Agosto 17, 2007
so its moving wnw or nw or w?
Member Since: Posts: Comments:
173. o311
4:23 PM EDT on August 17, 2007
Wouldn't the forward speed drop if a more northern track appears.
Member Since: Posts: Comments:
172. Metallica1990
8:23 PM GMT on August 17, 2007
Floridas not out of the woods till this thing passes 85 degrees long.
Member Since: Posts: Comments:
171. diabeticstorm
8:23 PM GMT on August 17, 2007
i disagree with you floridafisherman, none of the models indicate that Dean will hit florida, none of them since a few days ago. if there was a hint of dean hitting florida, it would be in the forecast cone and at least one of the models would show it. but i dont see any of them doing that. why do some people still think that florida Is NOT safe yet?? and if florida is not 100% safe, then why don't forecasters on the news say so, etc.
Member Since: Posts: Comments:
169. SherryB
8:22 PM GMT on August 17, 2007
Thanks to you too Nola....Can anyone really predict where Dean may or may not go? There are so many variables that will factor into his course and from what I have read and seen, you cannot discount ANY possible landfall in the GOM or even possibly the East Coast of FL (highly unlikely - but not to be discounted)
Member Since: Posts: Comments:
168. StormDodgerDude
3:07 PM CDT on August 17, 2007
Well here on our Ship (150 miles south of Louisiana), we will not be taking any chances. Preparations are now being taken. We should be off of our present location by late Sunday. Many of us who are "Non-Essential" will be evacuated off of this ship. Which is fine with me since I've spent the last several Major Hurricanes out here. For Once I will truly be Dodging this storm...Whew!!!
Member Since: Posts: Comments:
167. tampahurricane
8:18 PM GMT on August 17, 2007
the weather man said that there was some indications that the track was going to shift more to the north and does any one think we will see any thing here in tampa.
Member Since: Posts: Comments:
165. sngalla
4:24 PM EDT on August 17, 2007
Nothing is certain till it is over and done with.
Member Since: February 18, 2003 Posts: 57 Comments: 5363
164. weathermanwannabe
4:20 PM EDT on August 17, 2007
I would keep a close eye on the water vapor loops over the next several days in terms of this storm............
Member Since: Posts: Comments:
162. Melagoo
8:22 PM GMT on August 17, 2007
VAPOR - eye shows up here nicely


Member Since: July 31, 2006 Posts: 19 Comments: 1563
161. Relix
8:23 PM GMT on August 17, 2007
Wow, this is getting scary. News already told people to take it easy since well... just some rains and wind. But I am watching the radar, loops, etc every single minute, and in fact, its moving WNW with a slight NW wobble. Or maybe its convection fooling with my eyes. I'll admit I didn't take a single preparation to get ready for Dean.
Member Since: Posts: Comments:
160. benirica
8:23 PM GMT on August 17, 2007
its impossible for it to impact PR directly. it would need to sharply go to the NW, not happening.
the worst case scenario would maybe 16N and bring more rain then expected and some more wind.
Member Since: Posts: Comments:
159. bocaman
8:20 PM GMT on August 17, 2007
I pray for the people in Haiti, I hat to say this but I think they may be in for a direct hit. I know I'm going out on a limb early here but I think Dean is going to hit the Southern Coast of Haiti. It may be a lot stronger storm by the time it reaches Haiti too. Haiti as well as the Dominican as well as Southern Cuba and Eastern Jamaica should be making mass preparations right now.
Member Since: Posts: Comments:
158. Crisis57
8:20 PM GMT on August 17, 2007
Posted By: Michael at 8:14 PM GMT on August 17, 2007.

I forgot all about that, he said a huge anticyclone over Dean will over power anything and will find the weakness whereever it may be.....NW gulf? dont know


I'm not diagreeing with you at all just giving friendly observation but take a look at the link posted by Randyman and check the last frame very interesting
Member Since: Posts: Comments:
157. rwdobson
8:23 PM GMT on August 17, 2007
"diabetic, it is not 100% certain that fla is safe. still too early to tell"

yes, only 99% certain.
Member Since: Posts: Comments:
156. Dropsonde
8:18 PM GMT on August 17, 2007
Here is a java loop showing the movement of the ULL off the coast of Florida. It also seems that Dean is beginning another blowup, with heavy convection forming over the eye and CDO. The core of the hurricane is "rounder." Dean won't be upgraded further at 5 p.m. (the next step up from 110 kts is 115 aka Cat 4), but 11 p.m. is not out of the question.
Member Since: Posts: Comments:
155. JLPR
8:21 PM GMT on Agosto 17, 2007
If it crossed PR it would be a big desaster here i hope it keeps south and doesnt exceed the 16N mark
Member Since: Posts: Comments:
154. floridafisherman
8:20 PM GMT on August 17, 2007
diabetic, it is not 100% certain that fla is safe. still too early to tell
Member Since: Posts: Comments:
153. atmoaggie
8:16 PM GMT on August 17, 2007
And that report on the polar ice is very scary to me.

The 5C+ anomalies in the Arctic are also scary:


If you are expecting hurricanes in the Arctic, you are in the correct blog, otherwise...
Member Since: Posts: Comments:
152. auminer68
8:13 PM GMT on August 17, 2007

I just thought of something no-one's mentioned yet... It looks like Gantanamo Bay is going to at minimum feel some effects of Dean. Gitmo is on the southern coast of Cuba just barely outside the view of the San Juan radar linked by SavannahStorm at 7:49 on this thread.

link
Member Since: Posts: Comments:
151. C2News
4:20 PM EDT on August 17, 2007
What would the ULL need to do to make Dean track on a more northwesterly course?
Member Since: Posts: Comments:
150. RadarRich
8:20 PM GMT on August 17, 2007
I agree Noles
Member Since: Posts: Comments:
149. benirica
8:19 PM GMT on August 17, 2007
anyone....
1 degree = ? miles
is it 60?
Member Since: Posts: Comments:
148. SherryB
8:19 PM GMT on August 17, 2007
Thanks for your insight Littlefish! Every little bit helps!
Member Since: Posts: Comments:
146. SELouisianaGirl
8:16 PM GMT on August 17, 2007
When will we see the next computer models come out?
Member Since: Posts: Comments:
145. Relix
8:19 PM GMT on August 17, 2007
If it got to 16N we would be in MAJOR trouble JLPR =P
Member Since: Posts: Comments:
144. primez
8:17 PM GMT on August 17, 2007
What if Dean becomes a Cat 5 and strikes Haiti/D.R.?

Even a Cat 4 would wipe the Haitians out. Jeanne, as a simple Cat 1, killed 3000 of them in 2004. Imagine what a Cat 4 or 5 would do.

If you ask me, maybe it would be better off if it hit somewhere else.
Member Since: Posts: Comments:
143. sporteguy03
8:19 PM GMT on August 17, 2007
Posted By: C2News at 8:17 PM GMT on August 17, 2007.


Posted By: sporteguy03 at 4:14 PM EDT on August 17, 2007.
My met said if ULL does not cross FL all bets are off.


All bets are off of what?


The track
Member Since: Posts: Comments:
142. diabeticstorm
8:18 PM GMT on August 17, 2007
Florida is completely out of the woods now. Let's focus on the states in the Gulf.
Member Since: Posts: Comments:
141. nola70119
8:18 PM GMT on August 17, 2007
SherryB, there are no indications of final outcome past Monday.....the forecaster has less confidence longterm today than yesterday, which means that nothing is clear at this point.
Member Since: June 16, 2006 Posts: 0 Comments: 1565
139. SaBenDa
8:16 PM GMT on August 17, 2007
It should be interesting to note the gas stations this evening after the 6:00pm news
Member Since: Posts: Comments:
138. A4Guy
8:15 PM GMT on August 17, 2007
I totally trust the NHC and the models...but, as with anything weather-related, there are no absolutes, and sometimes, things truly defy logic and convention. While I don't expect Dean to make a sharp turn over Hispanola...the effects of the ULL could create a more northerly component than the models or NHC are expecting.
Member Since: Posts: Comments:
137. JLPR
8:18 PM GMT on Agosto 17, 2007
could it get to 16n while passing south of PR?
Member Since: Posts: Comments:
136. littlefish
8:14 PM GMT on August 17, 2007
SherryB I'd say no and no. The ULL wasn't really supposed to start moving W until today. It is starting to do so. but Dean is still moving faster. The ULL is squished between 2 ULHs on the east and west sides. But the east ULH is starting to shove harder into the ULL than the west ULH so hence the W motion now of the ULL. If the ULL drifts further north and west, it'll separate from Dean a bit better than if it goes due west IMO. But speed is still improtant regardless. Can Dean chase it down is the big issue. Dean is quite close to where it was forecast to be (at least over last 24 hours or so). But I'm not as smart as many on here :)

Viewing: 185 - 135

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
72 °F
Overcast