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) +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
Categories: Climate Change
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302. SWFLdrob 17. elokuuta 2007 klo 21:03 (GMT)    
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.
303. Metallica1990 17. elokuuta 2007 klo 21:04 (GMT)    
the eye is actually slightly south of 15
304. StuccoMan 17. elokuuta 2007 klo 21:04 (GMT)    
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
305. weatherboyfsu 17. elokuuta 2007 klo 21:04 (GMT)    
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......

Member Since: 17.07.2005 Posts: 0 Comments: 1025
306. TXKiwi 17. elokuuta 2007 klo 21:04 (GMT)    
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!
308. Dropsonde 17. elokuuta 2007 klo 21:05 (GMT)    


Vis of Dean at 2015Z. The eye is clearing itself out.
Member Since: 22.08.2006 Posts: 10 Comments: 414
310. getalife 17. elokuuta 2007 klo 21:05 (GMT)    
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.
311. Metallica1990 17. elokuuta 2007 klo 21:06 (GMT)    
finally someone sees my comment lol thanks for agreeing weatherboy
312. whirlwind 17. elokuuta 2007 klo 21:06 (GMT)    
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...


313. H2PV 17. elokuuta 2007 klo 21:06 (GMT)    
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.
314. welshcayman 17. elokuuta 2007 klo 21:06 (GMT)    
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.
315. leftyy420 17. elokuuta 2007 klo 21:06 (GMT)    
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
Member Since: 24.08.2005 Posts: 35 Comments: 1987
317. Crisis57 17. elokuuta 2007 klo 21:07 (GMT)    
Dean is taking a peak at us
Link
318. Inyo 17. elokuuta 2007 klo 21:07 (GMT)    
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?
Member Since: 3.09.2002 Posts: 42 Comments: 765
320. GPTGUY 17. elokuuta 2007 klo 21:09 (GMT)    
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
Member Since: 26.08.2005 Posts: 0 Comments: 391
321. StormJunkie 17. elokuuta 2007 klo 21:09 (GMT)    
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: 17.08.2005 Posts: 26 Comments: 15218
324. boobless 17. elokuuta 2007 klo 21:10 (GMT)    
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
325. rwdobson 17. elokuuta 2007 klo 21:11 (GMT)    
"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.
Member Since: 12.06.2002 Posts: 0 Comments: 1574
326. Cavin Rawlins 17. elokuuta 2007 klo 21:11 (GMT)    
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

Member Since: 24.07.2005 Posts: 407 Comments: 19076
328. GetReal 17. elokuuta 2007 klo 21:12 (GMT)    
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!!!
Member Since: 4.07.2005 Posts: 204 Comments: 8196
330. hu2007 17. elokuuta 2007 klo 21:14 (GMT)    
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)
Member Since: 6.08.2007 Posts: 0 Comments: 195
331. whirlwind 17. elokuuta 2007 klo 21:14 (GMT)    
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...
332. Metallica1990 17. elokuuta 2007 klo 21:14 (GMT)    
i think cat 4 by next advisory possibly cat 5 by tomorrow this thing looks like it could explode at anytime
334. Crisis57 17. elokuuta 2007 klo 21:15 (GMT)    
clearly see the eye
335. HurricaneDean2007 17. elokuuta 2007 klo 21:16 (GMT)    
Tell me...when is Dean going to go NW?
337. nola70119 17. elokuuta 2007 klo 21:16 (GMT)    
NHC forecaster Avila says the Bahamas ULL will not in itself steer but may weaken and allow a ridge to form, which (I guess) dictate the western motion after Jamaica. I think they are unsure of what is going to happen really....
Member Since: 16.06.2006 Posts: 0 Comments: 1535
338. StormJunkie 17. elokuuta 2007 klo 21:16 (GMT)    
Going to be interesting to see the 18z runs...Only three more hours for them...
Member Since: 17.08.2005 Posts: 26 Comments: 15218
340. rwdobson 17. elokuuta 2007 klo 21:18 (GMT)    
Hmm, looks like Dean is right now on the 15th parallel and exactly where NHC predicted it to be. Guys, you gotta learn not to read too much into these little wobbles.
Member Since: 12.06.2002 Posts: 0 Comments: 1574
341. wederwatcher555 17. elokuuta 2007 klo 21:18 (GMT)    
doesnt the 18z gfs start to come out now?
342. Cavin Rawlins 17. elokuuta 2007 klo 21:19 (GMT)    
Powerful Dean continues through the Caribbean

Member Since: 24.07.2005 Posts: 407 Comments: 19076
343. boobless 17. elokuuta 2007 klo 21:19 (GMT)    
iceman
Of course the flip side of that coin is the ULL could exert a S-SSW push as they draw nearer. Then we're inline with the consensus track
345. WPBHurricane05 17. elokuuta 2007 klo 21:19 (GMT)    
The NHC is fairly good when the track comes to 48 hours. Once we get passed that, the error starts to become larger.

Don't focus on the wobbles so hard. You cant make the storm go WNW or NW.
Member Since: 31.07.2006 Posts: 55 Comments: 7895
346. Crisis57 17. elokuuta 2007 klo 21:20 (GMT)    
classic Hurricane look, Dean is looking awesome look at his banding
wow
347. rwdobson 17. elokuuta 2007 klo 21:20 (GMT)    
You can check the status of the model runs here. Looks like the 18z GFS is running now.

Link
Member Since: 12.06.2002 Posts: 0 Comments: 1574
349. HurricaneDean2007 17. elokuuta 2007 klo 21:21 (GMT)    
I wish it would start going WNW, I don't want it to hit the Yucatan.
350. DG136 17. elokuuta 2007 klo 21:21 (GMT)    
Those cloud tops sure are cooling off, and the eye is trying to clear out. Are there any bouys in the vacinity of Dean? I'd be interested to see what the pressure is doing.
351. Melagoo 17. elokuuta 2007 klo 21:22 (GMT)    
Look at Africa making waves

wide view Look at Africa again
Member Since: 31.07.2006 Posts: 19 Comments: 1510

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About JeffMasters
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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