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

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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

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335. HurricaneDean2007
5:15 PM EDT on August 17, 2007
Tell me...when is Dean going to go NW?
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334. Crisis57
9:15 PM GMT on August 17, 2007
clearly see the eye
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332. Metallica1990
9:13 PM GMT on August 17, 2007
i think cat 4 by next advisory possibly cat 5 by tomorrow this thing looks like it could explode at anytime
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331. whirlwind
9:12 PM GMT on August 17, 2007
Most models are usually too far to the west on tracks. Canes end up going east most of the time.


StormKat-- where R U ?? Talk to us...
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330. hu2007
9:13 PM GMT on August 17, 2007
Tonight
Cloudy. Numerous showers and scattered thunderstorms until early morning...then showers and scattered thunderstorms late in the night. Windy. Some thunderstorms may produce gusty winds and heavy rainfall. Lows 78 lower elevations ranging to 66 higher elevations. East winds 20 to 30 mph with gusts to around 50 mph. Chance of rain 90 percent.
Saturday
Cloudy. Showers and scattered thunderstorms until late afternoon...then numerous showers and scattered thunderstorms late in the afternoon. Breezy. Some thunderstorms may produce gusty winds and heavy rainfall. Highs 86 lower elevations ranging to 78 higher elevations. East winds 15 to 25 mph. Chance of rain 90 percent.
ZIP Code Detail
Saturday Night
Mostly cloudy. Numerous showers and scattered thunderstorms early in the evening...then isolated showers in the late evening and overnight. Isolated thunderstorms early in the morning. Some thunderstorms may produce gusty winds and heavy rainfall early in the evening. Lows 79 lower elevations ranging to 67 higher elevations. Southeast winds 5 to 15 mph. Chance of rain 70 percent.
Sunday
Variably cloudy with isolated showers and thunderstorms early in the morning...then variably cloudy with scattered showers in the late morning and afternoon. Highs 88 lower elevations ranging to 81 higher elevations. East winds 10 to 15 mph. Chance of rain 40 percent.

this is for puerto rico at 5:00pm, fais better for us :) (hu2007-pr)
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328. GetReal
9:10 PM GMT on August 17, 2007
Posted By: welshcayman at 9:06 PM GMT on August 17, 2007.

then we might as well scrap the entire NHC and start watching ants and squirrels to tell the weather.


Hey there now watch what you say about the squirrels there! I have been known to check on my son's hampster to verify the approach of a storm!!!
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326. Weather456
9:10 PM GMT on August 17, 2007
African Wave Update

Satellite imagery, 315K potential vorticity charts and 700 mb wind analysis through 1800 UTC indicate that a tropical wave is near 31-32W south of 22N. The last visible loops of the day of the Eastern Atlantic clearly depicts low-mid level cyclonic turning just to the west of the Cape Verde. This wave continues to be envelop in very dry African dust and thus convective active activity remains absent. Another interesting feature is that QuikSCAT shows a second possible circulation within the ITCZ band in the image below.

by 456

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325. rwdobson
9:08 PM GMT on August 17, 2007
"this doesn't make sense to me.. what about the ocean? That is wet and high pressure areas exist there! Does moisture realy decrease high pressure formation?"

things are different over land vs over sea. over land, dry soil = hot weather = strong upper level ridges. part of the reason the southeast is baking so bad is b/c of the drought there. that's also where there is a strong ridge. but things are different over the ocean.
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324. boobless
8:37 PM GMT on August 17, 2007
In a previous post I tried to express concern regarding the formation of the ULL. To my untrained eye, it was poorly defined and late in developing.

Surprise, surprise, there it is in about the exact spot predicted per models. I guess I relied too much on WV imagery (pretty pictures). Should have focused on 500 or 700 mb levels to "see" this ULL. Not much good consistent upper air data once you leave the coast behind in my defense.

A track forecast would be much simpler with out it. Dean would just bump along under the ridge untill landfall on the Yucatan, then a short trip to the Mexican coast and we're onto other things.

It appears the ULL is moving slightly slower then Dean and would catch up (at the same longitude) around 120 hrs from this post time. Steering influence would be felt by Dean at 48-60 hrs (wild-a$$ guess again).

Maybe this is what is behind the GFDL's outlier track. A slow but increasing influence on Dean to turn to the right resulting in landfall on the North-Central Gulf Coast.

Butt who nose
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321. StormJunkie
9:06 PM GMT on August 17, 2007
What's up lefty, good to see ya.

Don't think I'll make this one lefty, but if I should I will be there 4-5 days. Going to stay and volunteer for at least three days afterwards.

Back to working this issue, see y'all in a little while!
Member Since: August 17, 2005 Posts: 26 Comments: 16502
320. GPTGUY
4:06 PM CDT on August 17, 2007
I remember in 2005 the GFDL handled Katrina better than any other model and called for its WSW movement over S FLA while the other models had it going west or WNW over FLA..and the initial NHC landfalls were in the FLA panhandle..and we see how that turned out...and Dean is still far out..things can change
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318. Inyo
8:05 PM GMT on August 17, 2007
Posted By: Michael at 8:04 PM GMT on August 17, 2007.
The ground is soaked plenty of moisture all over the state, high pressure really cant take hold because wet soil rises and creates clouds/rain, so the weakness is here


this doesn't make sense to me.. what about the ocean? That is wet and high pressure areas exist there! Does moisture realy decrease high pressure formation?
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317. Crisis57
9:07 PM GMT on August 17, 2007
Dean is taking a peak at us
Link
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315. leftyy420
9:04 PM GMT on August 17, 2007
weatherboyfsu

i feel ya. we will see. i am up for as far south as florida and the panhandle. i am def go if you want a partner. i ahve money saved just to chase this year.


stormjunkie

same to you. if you wnat to huit the gulf coast i am up for it. just don't wnat to go alone. need some oen to call the wife when i get blown away
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314. welshcayman
8:59 PM GMT on August 17, 2007
Posted By: OUFan919 at 8:57 PM GMT on August 17, 2007.

What the heck is wrong with the NHC?? I see it at 15.3N right now, they have it at 15N. They have it at 15.5N in 12 hours. No way. It will be close to 16.0N in 12 hours at this pace.


I appreciate that sometimes it is hard to tell where the centre is and sometimes people have different opinions on this.

However, if we have really reached the point where either;

a) we believe the NHC does not know how to tell where the centre of storm is, or
b) we believe the NHC is not telling the truth about where the centre of a storm is,

then we might as well scrap the entire NHC and start watching ants and squirrels to tell the weather.
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313. H2PV
8:52 PM GMT on August 17, 2007
40 inches of rain (1,000 millimeters) predicted for parts of Taiwan from Sepat.

Link

In the Philippines, rains exacerbated by Typhoon Sepat continued to soak Manila and surrounding provinces on Friday after the cyclone brought the capital to a near standstill two days earlier, with major roads in the vicinity under water up to 5 feet (1.5 metres) deep in places.
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312. whirlwind
9:04 PM GMT on August 17, 2007
I guess today is the night where u want to stay up. Tonight is when he will explode.....and when he enters the GOM.


Cannot hit FL eh? Prob not east coast..... maybe panhandle...


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311. Metallica1990
9:05 PM GMT on August 17, 2007
finally someone sees my comment lol thanks for agreeing weatherboy
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310. getalife
8:57 PM GMT on August 17, 2007
Florida will NOT get hit. Just my opinion. But yes, it doesn't matter what anyone says it will go where the heck it wants to. No one will have a great idea until later this weekend so I think everyone should just relax and keep their eyes on it, lol.
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308. Dropsonde
9:05 PM GMT on August 17, 2007


Vis of Dean at 2015Z. The eye is clearing itself out.
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306. TXKiwi
9:02 PM GMT on August 17, 2007
The Kiwi Box is similar to the Hebert box...

100% of hurricanes that hit TX go through the GOM.

This does not mean that what goes through the GOM hits TX!
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305. weatherboyfsu
8:59 PM GMT on August 17, 2007
Metallica.......... I agree with you......I made some comments earlier today and there was some replies with opinions just like mine.





Lefty420......It all depends on timing and location.....If its in Florida then its almost a definite.....In Texas probably not... Got some things going on at the homefront financially that i can be gone to long.......I will definitely give it my best......

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304. StuccoMan
4:02 PM CDT on August 17, 2007
Posted By: Relix at 4:01 PM CDT on August 17, 2007.
It is going WNW. Baah... Dean is such an awesome system. Still... i see it still going WNW, any of the most experienced members here might give me some insight? I see it at 15.4 right now.


HUH the storm is at 15N and not no 15.4 unless you are looking at a different storm or archives.This storm is at 15N
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303. Metallica1990
9:03 PM GMT on August 17, 2007
the eye is actually slightly south of 15
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302. SWFLdrob
9:01 PM GMT on August 17, 2007
agree with A4...the eye seems to have reappeared right on 15N and has been moving W along the 15N line the last couple of frames.
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300. StormJunkie
9:02 PM GMT on August 17, 2007
Afternoon all!

Still working my dang java issue, but am very close to having it resolved soon!!!

I do see Dean is growing to be a monster. Have missed so much today though...Arghh!

See y'all in an hour or so

Easily find preparedness info, forecast models, and imagery. These are the many links that are posted here time and time again.

Quick Links
Member Since: August 17, 2005 Posts: 26 Comments: 16502
299. Melagoo
9:01 PM GMT on August 17, 2007
Sepat

Sepat
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298. MTJax
9:01 PM GMT on August 17, 2007
THE GFDL SHOWS A MORE NORTHWESTERLY TRACK ACROSS EXTREME WESTERN CUBA AND THE CENTRAL GULF OF MEXICO. WHILE THIS SOLUTION IS OUTSIDE THE OVERALL MODEL GUIDANCE ENVELOPE...IT CAN NOT BE RULE OUT COMPLETELY SINCE THIS MODEL HAS AN EXCELLENT FORECAST TRACK
HISTORY. THE OFFICIAL TRACK FORECAST IS AN UPDATE OF THE PREVIOUS
ONE AND FOLLOWS THE MODEL CONSENSUS.

THE BOTTOM LINE IS THAT DEAN IS EXPECTED TO BE A DANGEROUS HURRICANE THROUGH THE NEXT SEVERAL DAYS...AND ALL INTERESTS IN THE CARIBBEAN SEA AND THE GULF OF MEXICO SHOULD CLOSELY MONITOR THE PROGRESS OF DEAN.


$$
FORECASTER AVILA
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297. Relix
8:58 PM GMT on August 17, 2007
It is going WNW. Baah... Dean is such an awesome system. Still... i see it still going WNW, any of the most experienced members here might give me some insight? I see it at 15.4 right now.
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296. Dropsonde
8:58 PM GMT on August 17, 2007
The eye is clearing. (WV image) Look for a bomb out tonight and a clear eye by 5 a.m.
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295. A4Guy
8:58 PM GMT on August 17, 2007
He hit 15N...and the last few frams of the sat loop have him traveling due W along 15N. I don't see a northward component...which is what the NHC needs to see - cosnsitent motion - before adjsuting tracks...especially when the modes are in such good agreement near term.
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293. Metallica1990
8:56 PM GMT on August 17, 2007
Posted By: SquirrelRJ at 8:55 PM GMT on August 17, 2007.

Ill take a bet it doesn't hit FL.


betting on landfalls is foolish!
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292. paulfrmpasschristian
2:50 PM CST on August 17, 2007
interesting post on the putor models Dr. I do hope the NHC is right on this one. I don't feel like gutting another house
291. littlefish
8:55 PM GMT on August 17, 2007
Hello SJ- looks like the 15N and 64.5W coords are just slightly north of forecast 15N and 65.5 W...
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290. Xion
8:56 PM GMT on August 17, 2007
Hmmmm I thought Gilbert had the lowest measured pressure in the Atlantic...Wilma????

You're new to this hurricane stuff, aren't you?

Wilma beat Gilbert with 882 mb compared to 888 mb.
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289. TX
8:54 PM GMT on August 17, 2007
Dean may have already killed several people indirectly...media-fueled awareness could be inducing heart-attacks for those with heart conditions that flip the channels
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288. OUFan919
8:57 PM GMT on August 17, 2007
What the heck is wrong with the NHC?? I see it at 15.3N right now, they have it at 15N. They have it at 15.5N in 12 hours. No way. It will be close to 16.0N in 12 hours at this pace.
Member Since: July 31, 2007 Posts: 0 Comments: 329
287. pcolabaygm
8:52 PM GMT on August 17, 2007
Coastal Water Temperatures
Place: Temperature:
Pensacola, FL 93 F / 33.9 C
Panama City Beach, FL 89 F / 31.7 C

Panhandle H20 temps are higher than I've ever seen. I do not think we will worry too much at this time about Dean. I will be hoping for a couple of early season cold fronts in September though to cool down our waters.
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286. sammo
8:56 PM GMT on August 17, 2007
Posted By: MichaelSTL at 8:51 PM GMT on August 17, 2007.
think it's interesting to note that Dean will graze (may already be in) Hebert box #1

Remember - it is 9 out of 10 storms that hit Florida passed through it, not that 9 out of 10 storms that passed though it hit Florida. Completely different meanings.

Right on MichaelSTL - exactly my point.
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285. SquirrelRJ
8:56 PM GMT on August 17, 2007
Wilma at 882mb is the record low in the atlantic.
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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

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