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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1724. scott39
Isaac isnt even a teenager in respects to devolopement. The Eastern Caribbean is notorious for limiting the maturing of a TC. Isaac is not dealing with the dry air very well for right now. The reason the models blow it up in the GOM, is because the enviroment will allow Isaac to mature to a strong hurricane. This is what the EURO has seen all along. Dont expect any significant developement of Isaac until Saturday at the earliest....or may wait until it reaches the GOM.
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Quoting StormJunkie:


Already airborne. Been taking obs for the past 3 hours.

There you are! H1900 says no mention of the alien blob attack today. Vaya con dios, HHs, and stay away from any straight up jet columns!
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Quoting Levi32:
Keep in mind the recon last night found the mid-level center as low as the 850mb level without a surface reflection. Puerto Rico radar hints that the recon may have found a mid-level center again this afternoon, with the surface reflection still displaced northward. Either that, or the surface circulation has two lobes, one south, and one north. There's definitely something closer to Puerto Rico though. It might be an extension trough that harmlessly rotates around the circulation and becomes nothing, but there's definitely something messy still going on with Isaac.
Strange how he is having a hard time pulling it together... There's seems to be a new element or ingredient that the models are not factoring in.. maybe something with climate change...I'm pontificating about it though if he doesn't get his act together we are all better for it. Especially for us sitting ducks in the Fl Keys
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Good afternoon all. I was just thinking, wouldn't it be CRAZY if the Euro is right and Isaac does come up the Louisiana/MS border (just like Katrina did) on the 7th Anniversary of Katrina, next week on Wednesday, August 29th, 2012???
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1719. Levi32
Quoting CJ5:


The RGB shows no sign of rotation in that area, either from the upper or lower level clouds.


I've been double and triple questioning myself on this all morning, but peering beneath the milky mid-level clouds south of PR, the surface circulation is definitely either elongated that direction or actually is there. I can almost see a swirl as the cloud deck thins.

Rapid-scan visible loop
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Quoting clwstmchasr:
Great news for the Caymans. Current track leaves Isaac over 350 miles to the East and North (and on the weaker side of the storm). Last thing they need is a major hurricane.
I see what you did there.
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Quoting Levi32:
Keep in mind the recon last night found the mid-level center as low as the 850mb level without a surface reflection. Puerto Rico radar hints that the recon may have found a mid-level center again this afternoon, with the surface reflection still displaced northward. Either that, or the surface circulation has two lobes, one south, and one north. There's definitely something closer to Puerto Rico though. It might be an extension trough that harmlessly rotates around the circulation and becomes nothing, but there's definitely something messy still going on with Isaac.


If that is the true center than this storm is in horrible shape
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Quoting Levi32:


It also could affect the short-term track significantly for the residents of Hispaniola if Isaac picks a different surface center to consolidate around.


The "center" you are referring to is also moving rapidly due west and very far to the north. It is more than likely a lobe rotating around a common center, just as the case has been for a while now.
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1715. WunderAlertBot (Admin)
JeffMasters has created a new entry.
Quoting RitaEvac:
uh oh....seeing low level rotation SW of PR, looking obvious, but we'll see

I see it too but is it elongated to the south or solo?
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Quoting jonelu:
Whats your best guess on how much rain we are gonna git here in Palm Beach?
I'm sorry jonelu....It's all up in the air right now.....So many variables right now
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1712. LargoFl
Quoting KeyWestwx:
Cute!
yeah there are some funny hurricane pics out there on the web, with all this doom and gloom we need a laugh or two huh
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Quoting MississippiWx:


The point to take home is that Isaac is highly disorganized and this limits the chances of him strengthening very much for a while.


I'm sorry...but....we're going to have to ask you to leave....as that comment is contrary to the preferred narrative around here....
Member Since: August 13, 2007 Posts: 0 Comments: 10492
Quoting TropicalAnalystwx13:

Yeah...don't ask me where my head was just then, lol. I removed it as soon as re-reading it.

As for the ECMWF, it shows the Bermuda ridge re-building as the trough lifts out. This would force it on a more westward path as the model shows.
Let me put it this way, it would take a major hurricane and some massive ridge humping in order for Isaac to get that far west. The Floridian peninsula as a category 2 is as far as I would go, and that's being generous.

...coming from one of the much more liberal guys on this blog too.
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1709. CJ5
Quoting emguy:


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).


The RGB shows no sign of rotation in that area, either from the upper or lower level clouds.
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1708. GetReal
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Quoting SFLWeatherman:
From Firsthand Weather


Looks like it came from First Drawing Weather...
Member Since: August 28, 2006 Posts: 6 Comments: 2899
1706. Levi32
Quoting MississippiWx:


The point to take home is that Isaac is highly disorganized and this limits the chances of him strengthening very much for a while.


It also could affect the short-term track significantly for the residents of Hispaniola if Isaac picks a different surface center to consolidate around.
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new Vortex Message about 7 minutes old



Product: Air Force Vortex Message (URNT12 KNHC)
Transmitted: 23rd day of the month at 20:14Z
Aircraft: Air Force Aircraft (Last 3 digits of the tail number are 300)
Storm Number & Year: 09L in 2012
Storm Name: Isaac (flight in the North Atlantic basin)
Mission Number: 7
Observation Number: 13
A. Time of Center Fix: 23rd day of the month at 19:20:20Z
B. Center Fix Coordinates: 15°40'N 66°34'W (15.6667N 66.5667W)
B. Center Fix Location: 193 miles (310 km) to the S (190°) from San Juan, Puerto Rico (USA).
C. Minimum Height at Standard Level: 1,451m (4,760ft) at 850mb
D. Estimated (by SFMR or visually) Maximum Surface Wind: 35kts (~ 40.3mph)
E. Location of the Estimated Maximum Surface Wind: 64 nautical miles (74 statute miles) to the NE (36°) of center fix
F. Maximum Flight Level Wind Inbound: From 145° at 29kts (From the SE at ~ 33.4mph)
G. Location of Maximum Flight Level Wind Inbound: 66 nautical miles (76 statute miles) to the NE (36°) of center fix
H. Minimum Sea Level Pressure: 1004mb (29.65 inHg)
I. Maximum Flight Level Temp & Pressure Altitude Outside Eye: 17°C (63°F) at a pressure alt. of 1,524m (5,000ft)
J. Maximum Flight Level Temp & Pressure Altitude Inside Eye: 17°C (63°F) at a pressure alt. of 1,524m (5,000ft)
K. Dewpoint Temp (collected at same location as temp inside eye): 17°C (63°F)
K. Sea Surface Temp (collected at same location as temp inside eye): Not Available
L. Eye Character: Not Available
M. Eye Shape: Not Available
N. Fix Determined By: Penetration, Radar, Wind and Pressure
N. Fix Level: 850mb
O. Navigation Fix Accuracy: 0.02 nautical miles
O. Meteorological Accuracy: 10 nautical miles
Remarks Section:
Maximum Flight Level Wind: 47kts (~ 54.1mph) in the east quadrant at 18:12:00Z
Maximum Flight Level Temp: 18°C (64°F) which was observed 31 nautical miles (36 statute miles) to the NNE (25°) from the flight level cente
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The low level center is just to the SW of puerto. You'll also see in the 5:00pm a shift to the west in track.
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1703. jonelu
Quoting PalmBeachWeather:
Remember it well
Whats your best guess on how much rain we are gonna git here in Palm Beach?
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Quoting Levi32:
Keep in mind the recon last night found the mid-level center as low as the 850mb level without a surface reflection. Puerto Rico radar hints that the recon may have found a mid-level center again this afternoon, with the surface reflection still displaced northward. Either that, or the surface circulation has two lobes, one south, and one north. There's definitely something closer to Puerto Rico though. It might be an extension that harmlessly rotates around the circulation and becomes nothing, but there's definitely something messy still going on with Isaac.


yeah huge center swirling south of PR...no convection, but mid level swirl moving towards the low level one...also does it seem isaac has slowed quite a bit?
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Quoting Levi32:
Keep in mind the recon last night found the mid-level center as low as the 850mb level without a surface reflection. Puerto Rico radar hints that the recon may have found a mid-level center again this afternoon, with the surface reflection still displaced northward. Either that, or the surface circulation has two lobes, one south, and one north. There's definitely something closer to Puerto Rico though. It might be an extension that harmlessly rotates around the circulation and becomes nothing, but there's definitely something messing going on with Isaac.


The point to take home is that Isaac is highly disorganized and this limits the chances of him strengthening very much for a while.
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1700. Gearsts
Quoting Levi32:
Recon last night found the mid-level center as low as the 850mb level without a surface reflection. Puerto Rico radar hints that the recon may have found a mid-level center again this afternoon, with the surface reflection still displaced northward. Either that, or the surface circulation has two lobes, one south, and one north. There's definitely something closer to Puerto Rico though. It might be an extension that harmlessly rotates around the circulation and becomes nothing, but there's definitely something messing going on with Isaac.
Thats a good thing right?
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The EURO is even trending west now. It bears repeating as this is the best model overall!
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Quoting FLSurf:
First time. Wahoooooooo! Go North!
"WHAT"?
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Quoting Levi32:
Recon last night found the mid-level center as low as the 850mb level without a surface reflection. Puerto Rico radar hints that the recon may have found a mid-level center again this afternoon, with the surface reflection still displaced northward. Either that, or the surface circulation has two lobes, one south, and one north. There's definitely something closer to Puerto Rico though. It might be an extension that harmlessly rotates around the circulation and becomes nothing, but there's definitely something messing going on with Isaac.


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1694. CJ5
Quoting wunderkidcayman:
that spin on PR radar is not the LLCOC guys


That is correct
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Ok just went to Publix and *gasp* people where there...buying water and stuff...wow.

It must be about time to run around the neighborhood screaming "we're all gonna die! Taste the rainbow before it's too late!" Just kidding, but I have really wanted to do that when there is a gloom and doom forecast for the Bay Area. At least people are out getting stuff, just in case:)
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Quoting stormchaser19:
Planning our strategy before heading out to TS Isaac

Peple who are risking their lives for keep us informed thanks

Do you know if the HHs have said anything about last night's run, around the water cooler?
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The EURO shows two lows at 24 hrs. So it mat take awhile to get going.

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Quoting LargoFl:
Cute!
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Quoting nrtiwlnvragn:


Just exactly how does that work? What kind of data? What do the models do with it?



:)


it's just like vitamins...they eat the data....and it makes them stronger ;-)
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1688. FLSurf
First time. Wahoooooooo! Go North!
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Quoting emguy:


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).


Except that you forgot to check base velocity tool.

If you had done that, you'd see no "circulation" exists at that point, and all the winds are blowing away from the radar station.
Member Since: January 25, 2012 Posts: 33 Comments: 1520
1686. CJ5
If you watch the RGB, you can clearly see the rotation of the lower level clouds. Based on that, it appears to me that the "center" is under the newest small convection blow up, around 15N.
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1685. dearmas
Quoting StormJunkie:


Already airborne. Been taking obs for the past 3 hours.


oops Thanks ;)
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Looks like Isaac is starting to move more poleward?

Link
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1683. Levi32
Keep in mind the recon last night found the mid-level center as low as the 850mb level without a surface reflection. Puerto Rico radar hints that the recon may have found a mid-level center again this afternoon, with the surface reflection still displaced northward. Either that, or the surface circulation has two lobes, one south, and one north. There's definitely something closer to Puerto Rico though. It might be an extension trough that harmlessly rotates around the circulation and becomes nothing, but there's definitely something messy still going on with Isaac.
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He looks like an open wave
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Quoting HurricaneHunterGal:


click here
Thanks!
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Quoting presslord:
These missions can improve model forecasts by 10 - 20%, so the model runs that will be available early Friday morning should have increased reliability.


Just exactly how does that work? What kind of data? What do the models do with it?



:)
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Quoting MiamiHurricanes09:
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.

Yeah...don't ask me where my head was just then, lol. I removed it as soon as re-reading it.

As for the ECMWF, it shows the Bermuda ridge re-building as the trough lifts out. This would force it on a more westward path as the model shows.
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1678. angiest
Quoting RitaEvac:
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.


I personally don't see anything resembling a COC in the base velocity scans out of PR.
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Quoting dearmas:
G-IV Mission what time does it start?? TIA


Already airborne. Been taking obs for the past 3 hours.
Member Since: August 17, 2005 Posts: 26 Comments: 16874
1676. TXCWC
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.



#1 because it is without dispute 1 of the top 2 models in use today - the other being the GFS. If it were the NOGAPS or CMC as the lone major dynamic model showing a more west solution then you would probally have a point in the lack of viability.

#2 while most models were showing an EAST or SOUTH FLORIDA hit the Euro WAS showing a North Gulf Coast anywhere from Louisiania to Pensacola hit. Model trends the last day or so have come into much better agreement with what Euro was showing. Euro has now shifted even further west - will the models continue to follow suit and trend further west??
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Quoting wunderkidcayman:
that spin on PR radar is not the LLCOC guys


I don't know. Looks like that spin could be heading right toward the Cayman Islands.


;)
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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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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.