Little change to Isaac, but intensification coming; Joyce forms

By: Dr. Jeff Masters , 3:13 PM GMT on August 23, 2012

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Tropical Storm Isaac is a large and impressive-looking storm on satellite images, but data from the Hurricane Hunters reveal that Isaac remains a minimal-strength tropical storm with 40 mph winds, as it heads westward across the Eastern Caribbean. An Air Force Reserve hurricane hunter aircraft which completed its mission into Isaac at 8 am EDT found top winds at the surface near 40 mph, and highest winds at their 5,000 foot flight level of 47 mph. A NOAA hurricane hunter aircraft flying at 10,000 feet has found top winds of 47 mph at that altitude. The Hurricane Hunters found a broad area of light winds with a central pressure of 1003 mb. The aircraft did not observe an eyewall trying to form, and recent microwave satellite images also show no signs of an eyewall forming. There does not appear to be much in the way of dry air near the core of Isaac, as seen on water vapor satellite loops, which is a big switch from what we've seen previously. Visible satellite loops show that Isaac has a much more symmetric circular cloud pattern, and has developed a Central Dense Overcast (CDO) of high cirrus clouds, the hallmark of an intensifying storm. These clouds have very cold cloud tops, indicating that the updrafts creating them are quite strong. An analysis of upper level winds from the University of Wisconsin CIMSS shows that an upper-level pattern of outflow supportive of significant strengthening has developed this morning, with an upper-level outflow channel now well-established to the north, and a new outflow channel opening to the south. Radar imagery from Puerto Rico shows some weak low-level spiral bands that are slowing intensifying and becoming more organized.


Figure 1. Morning radar image of Isaac taken from the Puerto Rico radar. Isaac's rain bands are weak, but are starting to take on a more spiraling shape.

Intensity forecast for Isaac
Isaac has consistently confounded predictions that it would intensify, but all the potential factors inhibiting intensification seem to have diminished to the point where intensification has to occur. Wind shear is low, 5 - 10 knots, and ocean temperatures are warm, 29°C, and these warm waters extend to great depth, giving the storm a high total heat content to work with. These factors, combined with the favorable upper-level outflow pattern and more symmetric cloud pattern, support intensification, and all of the intensity models except the HWRF model predict intensification of Isaac to a strong tropical storm or Category 1 hurricane by Friday afternoon. The latest 8 am EDT run of the SHIPS model predicts that wind shear will be light to moderate, 5 - 15 knots, for the next five days. The 11 am EDT wind probability forecast from NHC predicted a 34% chance that Isaac will become a hurricane by Friday afternoon, and a 6% chance it will be a Category 2 or stronger hurricane then. By Friday afternoon, Isaac will likely be close enough to Southwest Haiti that the inner core will be disrupted, and the storm will likely be a 45 - 55 mph tropical storm on Saturday and Sunday as it moves over Cuba. Once Isaac pops off the coast of Cuba into the Florida Straits, it will be over very warm waters of 31 - 32°C (88 - 90°F), wind shear will be light to moderate, and the upper-level wind pattern favorable for intensification, with low wind shear due to an upper-level anticyclone over the storm. It will probably take at least 24 hours with the storm's center over water for it to become a hurricane.

Impact of Isaac on the Islands
The south coast of Puerto Rico should see Isaac's heaviest rains and strongest winds beginning near 8 pm EDT tonight, with tropical storm-force winds of 40 - 45 mph potentially affecting the southwest portion of the island. The San Juan airport may be able to stay open during Isaac's passage, but with delays when spiral bands move overhead.

Heavy rains and tropical storm-force winds should arrive on the southern coast of the Dominican Republic late tonight, and the Santo Domingo airport will probably be closed on Friday. Rainfall amounts of 8 - 12 inches will likely affect the Dominican Republic Thursday through Saturday, creating dangerous flash floods and mudslides.

Isaac is potentially a very dangerous storm for Haiti, where 400,000 people still live outside underneath tarps in the wake of the 2010 earthquake. Heavy rains from Isaac will begin on Friday morning in Haiti, and last through Sunday. Rainfall amounts of 8 - 12 inches are possible, which will be capable of causing extreme flooding on the vegetation-denuded slopes of Haiti. It will be a major challenge to keep those Haitians living outside safe, if rainfall amounts of 5 - 10 inches occur.

Impact on Florida, Cuba, Jamaica, and the Bahamas
Florida, Cuba, Jamaica, and the Bahamas are all at risk of receiving flooding rains and high winds from Isaac. The latest set of 00Z (8 pm EDT) and 06Z (2 am EDT) model runs for Isaac are fairly unified for the coming three days, showing a west-northwestward track over Southwest Haiti and into Western Cuba. At the 4 - 5 day forecast period for Sunday and Monday, the models have come into better agreement, and have shifted west some. Our best-performing model, the ECMWF, has now shifted Isaac's path more to the east, but still is the westernmost of the models, predicting a landfall for Isaac near the Alabama/Florida border on Wednesday. While we do still have some models predicting a path up the east coast of Florida, model consensus now favors a path up the west coast of Florida through the Gulf of Mexico. The recent reformation of Isaac's center more to the south supports the idea that Isaac will take a track more to the west through the Gulf of Mexico. Since this now means a final landfall for Isaac in the Florida Panhandle is likely, the storm will probably have an extra day over water, increasing the odds that it will become a Category 2 or stronger hurricane before this final landfall. The NOAA jet is scheduled to fly into the storm this afternoon, to do a large-scale dropsonde mission to aid model forecasts. These missions can improve model forecasts by 10 - 20%, so the model runs that will be available early Friday morning should have increased reliability.

Impact on Tampa, Florida
The Republican National Convention begins on Monday in Tampa, Florida. The latest 11 am EDT wind probability forecast from NHC gives Tampa a 15% chance of receiving tropical storm-force winds and a 1% chance of receiving hurricane-force winds on Monday. The latest model tracks for Isaac suggests that the trough of low pressure pulling the storm to the north will not be strong enough to give Isaac a northeastward component of motion when it crosses Tampa's latitude. Thus, Isaac will have difficulty making a direct hit on Tampa without passing over a considerable amount of land first, making a multi-billion dollar hurricane disaster in Tampa very unlikely. I put the odds of a mass evacuation occurring during the convention at 1%; a limited evacuation of people in the Tampa Bay area living in mobile homes in low-lying areas is probably about 5 - 10 % likely. I have detailed information on Tampa's storm surge vulnerability in a post from last week.


Figure 2. Morning satellite image of Tropical Storm Joyce.

Tropical Storm Joyce forms in the Central Atlantic
The season's tenth named storm of the year, Tropical Storm Joyce, has formed in the Central Atlantic. Joyce's formation on August 23 puts 2012 in a tie for second place with 1995 for earliest formation date of the season's tenth storm. Only 2005 had an earlier appearance of the season's tenth storm, when Tropical Storm Jose formed at 2 pm EDT on August 22. None of the models show that Joyce will be a threat to the Lesser Antilles Islands, but it may be a storm that will affect Bermuda. It is possible that Joyce will complicate the track forecast for Isaac 4 - 5 days from now, when the storms may be close enough together to interact.

Jeff Masters

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Geeeezzzzzzzzz,Getting nasty in here over a storms track? Please people,Lets keep it all nice.Differing opinions are one thing...but the tone seems nasty? No?
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What Isaac would be working with in the Gulf:

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Will be interesting to see what the data will show in advance of the 5:00 advisory discussion. The current NHC plot assumes hurricane status before Haiti. If his circulation remains disorganized, any interaction with Haiti will disrupt it more than currently anticipated and everything will certainly have to be recalculated at that point. His window for better organization before Hispanola is closing.......Then again, he did very well last evening in terms of convective bursts. The next 24 hours are critical.
Member Since: August 8, 2006 Posts: 0 Comments: 8706
Planning our strategy before heading out to TS Isaac

Peple who are risking their lives for keep us informed thanks
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1670. nolajet
Quoting HurricaneHunterJoe:
Has Isaac done a u-turn and is now heading east?


That would shut this blog down... however, I didn't see that when I looked.
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1669. LargoFl
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Can we confirm wth is the swirl close to the SW portion of Puerto Rico? is this the real deal or not. Because if it is then the NHC track makes sense and the models, if that aint it, this thing is totally unorganized and going hellava lot farther west.
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Quoting KeyWestwx:
hi, could someone link the latest animated GFS model for me. I'm at work and don't have time to search it.
thanks!


Can find the GFS either on Huffman's page, or the NCEP page under models. That link will save you from having to search for most anything you need for tracking and makes it easy to navigate the various imagery, wind, and model sites.

So Isaac is looking pretty rough ATM. Also see that recon must have had some issues with equipment and are headed home. They never really got in to the southern side of the storm at all. A little disappointing.
Member Since: August 17, 2005 Posts: 26 Comments: 15626
Quoting sporteguy03:
In two hours we will have the 18z GFS to discuss.


And blog mayhem to go with it.
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Hoping that euro track is just an anomaly of some sort. Has Isaac coming right over my house. Guess I'll be monitoring the situation more closely now as I thought it was going into Florida. Wow I hate hurricanes.
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Quoting RitaEvac:




If anything this could be the old LLC racing off to the WNW...with the main vorticity and convergence further south with the MLC around 15.3-15.6 this is where the new center will likely take residence.
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These missions can improve model forecasts by 10 - 20%, so the model runs that will be available early Friday morning should have increased reliability.
Member Since: August 13, 2007 Posts: 0 Comments: 10479
1662. LargoFl
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Quoting watchingnva:
this thing looks like it wants to decouple... just sayin...
Not sure it was ever coupled to begin with. :)
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Has Isaac done a u-turn and is now heading east?
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Quoting IceCoast:
Rough day for Taiwan.





Any day that involves a pinhole eye is likely not a good one...unless you're a chaser!
Member Since: August 28, 2006 Posts: 6 Comments: 2895
Quoting angiest:




That's way too much time in those warm gulf waters for my taste.
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Quoting TropicalAnalystwx13:
Meanwhile, the costliest hurricane ever to hit the United States was born in one hour seven years ago.

ZCZC MIATCDAT2 ALL
TTAA00 KNHC DDHHMM
TROPICAL DEPRESSION TWELVE DISCUSSION NUMBER 1
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 PM EDT TUE AUG 23 2005

DATA FROM AN AIR FORCE RESERVE UNIT RECONNAISSANCE AIRCRAFT...ALONG
WITH OBSERVATIONS FROM THE BAHAMAS AND NEARBY SHIPS...INDICATE THE
BROAD LOW PRESSURE AREA OVER THE SOUTHEASTERN BAHAMAS HAS BECOME
ORGANIZED ENOUGH TO BE CLASSIFIED AS TROPICAL DEPRESSION TWELVE.
THE INITIAL INTENSITY OF 30 KT IS BASED RECON WINDS OF 39 KT AT 800
FT...AND SHIP A8CI9 REPORTING 30-KT SUSTAINED WINDS AT 18Z IN THE
NORTHEAST QUADRANT. UPPER-LEVEL OUTFLOW IS WEAK...BUT IMPROVING AS
A SMALL ANTICYCLONE HAS BEEN DEVELOPING ABOVE THE LOW-LEVEL CENTER.

THE INITIAL MOTION ESTIMATE IS AN UNCERTAIN 310/07. THE LOW-LEVEL
CENTER HAS BEEN REFORMING WITHIN A LARGE CLEAR AREA NOTED IN
SATELLITE IMAGERY. HOWEVER...FLIGHT-LEVEL RECON WINDS CLEARLY
INDICATE A BROAD BUT OTHERWISE WELL-DEFINED LOW-LEVEL WIND FIELD.
THERE HAVE BEEN SEVERAL SMALL VORTICES DEVELOP WITHIN THE
CONVECTION IN THE EASTERN SEMICIRCLE AND THEN ROTATE WESTWARD OUT
FROM UNDER THE CONVECTION. THE INITIAL POSITION IS ROUGHLY THE
GEOMETRIC CENTER OF ALL THE SMALL SWIRLS...BUT SOME RE-ORGANIZATION
OF THE CENTER WITHIN THE CONVECTION IS POSSIBLE. TD-12 IS EXPECTED
TO CONTINUE MOVING SLOWLY NORTHWESTWARD TOWARD A WEAKNESS IN THE
MID-LEVEL SUBTROPICAL RIDGE. THIS WEAKNESS SHOWS UP BEST IN 500 MB
DATA...AND THEN DISAPPEARS BELOW AND ABOVE THAT LEVEL. BY 36-48
HOURS...ALL OF THE GLOBAL MODELS AND THE GFDL MODEL FORECAST THE
WEAKNESS TO FILL AND BE REPLACED BY A BROAD EAST-WEST ORIENTED
RIDGE. THIS SHOULD HELP TO DRIVE THE CYCLONE MORE WESTWARD ACROSS
SOUTHERN FLORIDA IN 60-72 HOURS...AND THEN INTO THE EASTERN GULF OF
MEXICO BY 96 HOURS. THIS SCENARIO IS CONSISTENT WITH THE NHC MODEL
CONSENSUS AND THE DEVELOPING SYNOPTIC PATTERN.

THE INTENSITY FORECAST IS A LITTLE TRICKY DUE TO THE UNCERTAINTY ON
EXACTLY WHEN A WELL-DEFINED CENTER WILL DEVELOP AND HOW SOON
CONVECTION WRAPS AROUND THE WEST SIDE OF THE CIRCULATION. THE
UPPER-LEVEL FLOW IS FORECAST TO REMAIN STRONGLY DIFLUENT FROM THE
NORTH FOR THE NEXT 24-36 HOURS...AND THEN BECOME NORTHEASTERLY TO
EASTERLY AFTER THAT. SINCE THE SHEAR IS ALSO FORECAST TO REMAIN
RELATIVELY LOW AT AROUND 10 KT AND SSTS WILL BE NEAR 31C UNDER THE
CENTER...AT LEAST STEADY INTENSIFICATION APPEARS TO BE IN ORDER. IF
CENTRAL CONVECTION DEVELOPS WITHIN THE NEXT 24 HOURS...THEN THIS
SYSTEM COULD REACH HURRICANE STRENGTH BEFORE IT MAKES LANDFALL. THE
OFFICIAL INTENSITY FORECAST IS SLIGHTLY LOWER THAN THE SHIPS MODEL.

THE NWS RULES GOVERNING THE NAMING OF TROPICAL CYCLONES SPECIFY
THAT...WITHIN A BASIN...WHEN A CYCLONE FORMS FROM THE REMNANT OF A
PREVIOUSLY EXISTING CYCLONE...THE OLD NAME/NUMBER IS RETAINED.
TROPICAL DEPRESSION TWELVE HAS A COMPLEX GENESIS THAT LIKELY
INCLUDES A MID-LEVEL REMNANT OF FORMER TROPICAL DEPRESSION TEN. A
REVIEW OF SATELLITE AND RAWINSONDE DATA OVER THE PAST WEEK OR SO
SUGGESTS THAT A SECOND DISTURBANCE APPROACHED AND COMBINED WITH THE
MID-LEVEL REMNANT OF TROPICAL DEPRESSION TEN ON 20 AUGUST. BECAUSE
IT IS IMPOSSIBLE TO DETERMINE WHICH OF THESE TWO SYSTEMS IS
ASSOCIATED WITH TODAY'S GENESIS...WE HAVE ELECTED TO USE THE
DESIGNATION TWELVE RATHER THAN TEN FOR THE NEW DEPRESSION. THIS
SITUATION DIFFERS FROM LAST YEAR'S REGENERATION OF IVAN...IN WHICH
THE LOW-LEVEL REMNANT OF THAT SYSTEM REMAINED A DISTINCT FEATURE
THAT COULD BE FOLLOWED CONTINUOUSLY UNTIL IT REGENERATED.

FORECASTER STEWART


FORECAST POSITIONS AND MAX WINDS

INITIAL 23/2100Z 23.2N 75.5W 30 KT
12HR VT 24/0600Z 24.0N 76.5W 35 KT
24HR VT 24/1800Z 25.0N 77.7W 40 KT
36HR VT 25/0600Z 25.7N 78.5W 45 KT
48HR VT 25/1800Z 26.0N 79.4W 60 KT
72HR VT 26/1800Z 26.3N 81.0W 50 KT...INLAND
96HR VT 27/1800Z 26.5N 83.5W 60 KT
120HR VT 28/1800Z 27.5N 86.0W 65 KT

$$



Hard to believe that poor looking TD became a hurricane that caused significant damage in Miami in so short a period of time..
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In two hours we will have the 18z GFS to discuss.
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1655. dearmas
G-IV Mission what time does it start?? TIA
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Quoting KeyWestwx:
hi, could someone link the latest animated GFS model for me. I'm at work and don't have time to search it.
thanks!


click here
Member Since: August 17, 2009 Posts: 0 Comments: 249
1653. emguy
Quoting hurricanejunky:


Were you referring to what looked like a weak COC near the SW tip of PR?


I certainly was. Radar shows it, and satellite does support it. This is either an elongated system, a binary system, or we have a complete decouple going down before our eyes. Which actually wouldn't be a complete shock. There was the highly unexpected and unforcasted decouple of Hurricane Chris near Puerto Rico (I want to say that was in 2006).
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Link
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that spin on PR radar is not the LLCOC guys
Member Since: June 13, 2009 Posts: 2 Comments: 10852
Quoting Tazmanian:




i have a idea whats send JFV and jason out there and they can tell us what the storm is doing


Sounds great TAZ, lol.
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Quoting doabarrelroll:


Yes and the costliest one before that made landfall 20 years ago tomorrow.
Remember it well
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Quoting TropicalAnalystwx13:

Not sure how you're getting it's not viable...it's definitely possible if the storm misses the trough which it seems to be doing right now.
Seems to be doing right now? Lol wut?

The Euro is the one and only model that has the cyclone moving into the northwestern Gulf of Mexico. At this point in time, that solution just by no means is likely, unless it remains very weak and embedded within shallow zonal steering to the point that it cruises along the southern Cuban coast.
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Quoting ProgressivePulse:
Maybe it's so favorable that any one vortex can't absorb the others? I'm running out of ideas.




i have a idea whats send JFV and jason out there and they can tell us what the storm is doing
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1645. Stats56
Quoting Bluestorm5:
It was post 1492...


Just hide it, then np
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Land interaction could be Isaacs best friend. A lot of times when tropical systems traverse over land there core comes together quite nice on the other side
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Another 12z GFS Ensemble shows Joyce a lot stronger:

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Quoting RitaEvac:
uh oh....seeing low level rotation SW of PR, looking obvious, but we'll see



With that radar, I wouldn't be surprised to see Isaac as a naked swirl sometime early tonight, then all of the sudden he gets his act together late tonight. we shall see.
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Maybe it's so favorable that any one vortex can't absorb the others? I'm running out of ideas.
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Quoting ILikeIke:
lol and jonny depp behind that
Captain Sparrow
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From Firsthand Weather
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Quoting mojofearless:


How is that funny, fellow Louisianian? I've been watching the Euro for days - it had NOLA in the crosshairs for a number of runs, and now it's showing more of a panhandle hit. Which is east last time I checked. Furthermore, the GFS has shifted west over the past few days. So what am I missing here? I did actually sleep, so maybe I missed something.


You should check the 12z Euro, which shows a Texas/Louisiana border landfall...as a major, I think.

Here's the Link
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Quoting Hurricanes101:


Euro just went to LA/TX border, much further west than it has been


Ahhhh - So I DID miss something. Thanks for the clarification. Silly me - see what happens when I actually try to go do things all functional and real time- real life and such. I leave for two hours and Argh! I miss the subtle shifts. My apologies to Louisiana boy 44 for my bewilderment.
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Quoting hurricanejunky:


Were you referring to what looked like a weak COC near the SW tip of PR?


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Quoting mcluvincane:


Big one of what??


Dont quote him and bait him like I did lol..mistake on my part....admin should be in shortly
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1633. LargoFl
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hi, could someone link the latest animated GFS model for me. I'm at work and don't have time to search it.
thanks!
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Quoting MiamiHurricanes09:
Lol, the ECMWF isn't even a viable option, I don't even know why it's getting much credence om the blog.

Will be more than happy to choke on crow if it verifies though.


thank you me as well....someone else said it earlier too...its not going to RUN INTO THE GD ridge over the southern plains for cryin out loud....track favors are north or straight west from haiti and beyond...get it through your heads.....im going to romanellis for tequila and steak to calm myself!
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Quoting mojofearless:


How is that funny, fellow Louisianian? I've been watching the Euro for days - it had NOLA in the crosshairs for a number of runs, and now it's showing more of a panhandle hit. Which is east last time I checked. Furthermore, the GFS has shifted west over the past few days. So what am I missing here? I did actually sleep, so maybe I missed something.


Sorry I did not clarify I was not laughing at you I was laughing because the 12Z Euro has shifted WAY west with its track...that is why I did not get why you said east... lol
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1629. angiest
Quoting cat6band:


Dang...that's def more west than I expected....


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Quoting CJ5:


Considering all major model put the storm in your front door, yes, I would make some preparations.
Thank you...I haven't had to stock up much since Wilma creamed the island.I have a feeling the stores are being gutted as I type.
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Quoting MiamiHurricanes09:
Lol, the ECMWF isn't even a viable option, I don't even know why it's getting much credence om the blog.

Will be more than happy to choke on crow if it verifies though.


Look at the Doctor's post and you'll see why.

On average, it beats the NHC and the GFS after 72 hours.
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Quoting emguy:


Check out the radar and see...There is other rotation...suggesting the system is either highly elongated, or we have a binary low. This storm is a hot mess right now.


Were you referring to what looked like a weak COC near the SW tip of PR?
Member Since: August 28, 2006 Posts: 6 Comments: 2895
Quoting MiamiHurricanes09:
Lol, the ECMWF isn't even a viable option, I don't even know why it's getting much credence om the blog.

Will be more than happy to choke on crow if it verifies though.

Not sure how you're getting it's not viable...it's definitely possible if the storm misses the trough.
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Quoting MississippiWx:
12z GFS Ensembles at 132 hours:



Dang...that's def more west than I expected....
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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.