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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Just wondering why with this storm I haven't seen one word on what the Florida Keys should be expecting or getting prepared for ??? More talk about Tampa and Panhandle but the storm has to go through the Keys to get to either !!! Confused -__-
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Quoting TomballTXPride:

Definitely.


The devastation that Katrina caused along the Gulf coast of Mississippi, especially near Biloxi, was staggering. The flooding in NOLA b/c of the levee breaks took the media focus completely away from the Miss. Gulf Coast, but the damage along Hwy 90 was equal to Camille.

I visited NO (the Lakeshore area and the Ninth Ward) and then traveled the coast on my honeymoon on the way to Florida, and the damage was even more shocking than in New Orleans. Everything was basically wiped out along the coastline to over a mile inland from the storm surge. The wind did the rest. Even along I-10 the billboards were twisted and many down, all the gas stations at exits with no roofs or completely wrecked. When we drove to the coast we were flabbergasted with what we saw-- the media was not covering any of it as they were all in New Orleans.

Hwy. 90 was still closed and undriveable, we spent and entire day driving down exits from I-10 south to the coast. Nothing was left but piles of devastation all along Hwy 90 from Waveland to Pascagoula. It looked like it had been bombed, or hit by a tsunami.

Link
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Excellent job Levi...

Still aWaiting for the video forecasts of those doing negative criticizing of your work...

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Quoting StormJunkie:


I am generally on board with that.


if that's the case, look at this...it's south of the points Link
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thx levi for the forecast, but i trully believe based on the current steering and future that Isaac will follow the NHC track or a tad to the east but however you put it the florida keys should be ready for a direct hit from a cat 1 hurricane
Member Since: July 14, 2009 Posts: 0 Comments: 3022
Quoting yoboi:


look at it this way i live in swla and we had rita in 2005 national news was still in nola....rita the forgotten storm....


Not forgotten by all. My wife was pregnant with our second daughter when we evacuated (the decision process is discussed to an extent in one of my earliest wunderblog posts). A 10+ hour evacuation with a woman 6 months pregnant is not hard to forget. :)

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Good Afternoon Everyone!

Just stopped in for a quick minute.

Extemely impressive outflow channels are pumping and EMORMOUS amount of mass out of the broad center of Isaac. Current leg of the HH Recon shows 1004 pressure over a large stretch already well away from any center...

This storm is going to be relatively slow to spin up because it's center is so broad, but it will also conversely be very slow to spin down, even if it goes over considerable land.
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Quoting WDEmobmet:


You continue to counter the EURO with what the GFS shows at the 500mb level, and yet you fail to mention to most recent forecast of the GFS with a panhandle landfall. To me it seems that you ignore any other possiblity that counters your original forecast, no way you slice it. My personal opinion is that your forecast are biased... sorry just my views. I like your analysis truly very well put together. Better than 99% of others posted here. However you are afraid to mention anything that disagrees with you and only give attention to what benefits you.

Start the bashing--- just my constructive critizism. I still enjoy your forecasts


For one thing I was making up my forecast before the 12z GFS came out, and did not see it until after my post.

As for "bias"...there is much to be said for consistency and only slow changes in the 4-5 day forecast track. The NHC is known to be slow to change as well, and that can be a virtue. I am only 150 miles east of the model consensus at Day 5, which in reality is not that much. We have seen far bigger shifts than that, and as long as I see an eastward adjustment being a possibility, I don't want to throw my track westward only to have to yank it back. Tomorrow may be the day I have to shift if the models refuse to budge.

Here's the bottom line. What I am trying to do with my posts right now is make my forecast, but also let people that are watching me know about all of the possible scenarios and the uncertainties in the forecast such that they can be prepared and ready for what this storm may bring. My forecast cone is much bigger to the west because of the large uncertainties on that side of the track in this situation. My hope is that even if I am wrong on the exact track by 100-200 miles or so 5 days in advance, that folks that have watched/read me will have been made aware of the situation and well-informed about the possible impacts even if the exact track has to shift a bit during the final 72 hours.
Member Since: November 24, 2005 Posts: 635 Comments: 26647


IMO the LLC is at 14.9N and 66.6W.
Member Since: July 4, 2005 Posts: 204 Comments: 8874
Quoting Grothar:


that is far inland. Must have been powerful.


The eye came over our house. The storm was so large and moving slowly enough that we had at least 6 hours of extreme winds. We lost so many large oaks that we just bulldozed the area and built a pond.
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Way to stick to your reasoning Levi. If this decides to stall in the FL Straits..problem.
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Quoting StormJunkie:


I am generally on board with that.

Me too
Member Since: June 26, 2012 Posts: 0 Comments: 297
Hi guys. Long time lurker from Halifac NS on the east coast of Canada. The mets up here have started discussing a possibility of an eventual tag team hit between Joyce and Isaac depending on timing. What are your thoughts? Thanks guys. I love the knowledge I get from this site. Cheers.
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Quoting Levi32:
Good afternoon.

Blog update:

Tropical Tidbit for Thursday, August 23rd, with Video


Thanks Levi. On the models shown in your tidbit, what would be the reason some of the models, even some of the ones that take the storm further west through the gulf, turn Isaac to the NE at the end of the run... while some models do not show any recurve whatsoever? And which scenario do you see more likey... eventual turn NE or NNE, or the ridge building back in and not allowing the turn?
Member Since: August 4, 2011 Posts: 0 Comments: 631
Quoting Bluestorm5:
Inside isn't pretty, though :)



lol right.. i remember ppl thought ernesto was a hurricane(including me) at one point but ended up being pretty weak.. looks can and are deceiving...
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Well Guys, Ole Isaac has been tracking to the south & west of all HNC forecast points lately.

An example,
The Wed 11AM advisory had the cyclone forecasted 24 hours later to be @ 16.8N 64.8W.
This AM's 11AM advisory had it positioned @ 15.6N 65.4W. No even close to being in the ball park. (albeit that southward "re-positioning" yesterday)

This trend has been ongoing since the cyclone was designated a TS.

Given that this is is a short time span both the H.S.U. & the computer models are struggling with the motion & direction, something they are very very good at.
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Quoting Levi32:


Well given my current track obviously I think some slight shifts in the models back towards the east are possible, but we'll see how the G-IV runs go. Nopefully NRT will be around tonight to tell us whether the 0z runs actually got the data.
good update. props to you for still staying on the eastern side of florida despite what most of the models are showing. Hopefully the 0z rus of the GFS and Euro will receive the vital information to get a better track. although im more in line of isaac staying south of cuba but i respect your forecast because you provide plenty of info to support your projected path
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This is what Isaac did in Trinidad & Tobago:

Member Since: August 1, 2011 Posts: 28 Comments: 8009
"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."
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Quoting mississippired:


I live about 80 miles north of Waveland, MS. We had no power or water for a month.


The surge went over I-10 in some locations, you could see freezer and pieces of houses as you drove down I-10.
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Quoting StormTracker2K:


I still think it goes west along the SW FL coast but Levi has a great point. As I was watching his video Hurricane Charley came to mind. Either way FL is in big trouble whether this goes east or west.

yes your right ST..some point in florida is going to get hit..but besides that, its going to be a real rough and windy week for all of us, no matter which coast it goes up huh..and rain ..geez more rain, we dont need that anymore but..its coming anyway
Member Since: August 6, 2011 Posts: 4 Comments: 38478
I had an interesting thought recently- if tropical entities could talk, what do you think they would say?
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recon headed in recon about 200 miles sw of san juan puerto rico coming in from the northwest
Member Since: July 14, 2009 Posts: 0 Comments: 3022
These missions can improve model forecasts by 10 - 20%, so the model runs that will be available early Friday morning should have increased reliability.
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Quoting LargoFl:
thank you for that link and ty Levi, its what ive been trying to say..all of florida cannot take their eyes off this storm..some part of florida..is going to get hit by this..it has to, you have 2 highs one on either side..it can only go up between them..and florida is right in its way...watch this storm, wait and see which coast it goes up, and dont forget..it can still..go right up the middle of the state..nothing is set in stone yet.


Sadly, not all of Florida is watching. I was talking to a friend in Fort Walton Beach and she knew there was a 'storm' out there, but had no plans in place, etc.. I had to get her to make them with me on the phone and to promise to be watching carefully. Talked again last night and the topic never even came up. :(
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Ouch!



Member Since: October 26, 2011 Posts: 0 Comments: 2651
Quoting Levi32:
Good afternoon.

Blog update:

Tropical Tidbit for Thursday, August 23rd, with Video
Thanks Levi. Good job as usual. You are one of the few on this blog who actually uses the science in creating your forecasts. One piece of unsolicited advice to you...when the "resident experts" start attacking you, please let that all slide...it means nothing. I would be willing to bet that some of the NHC people read your stuff. You have the talent for this as a career if you so wish.

Thanks again.
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Just saw Levi's video which I always look forward to, but it seems that now that he has acquired more knowledge and status in the "meteorological world" he is getting more stubborn.
He is now citing the CMC as a one of the model support for his eastward path lol.
Guess he didn't get the memo of the latest 12Z GFS run showing just AL/FL border landfall, along with the Euro, UKMET.
He is also oblivious to the current westward track of Issac..
Member Since: June 26, 2012 Posts: 0 Comments: 297
746. yoboi
Quoting Levi32:


I've explained my concerns about the need for an eastward adjustment in the last several blog posts. If the models remain west after the G-IV data tonight, then I will likely have to join them, but the 4-5 day forecast still has lots of room for adjustment.



hey levi how about a little wager, I am going gom, if you win i will send some seafood gumbo, if i win ya send some king crabs....
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Quoting LargoFl:
thank you for that link and ty Levi, its what ive been trying to say..all of florida cannot take their eyes off this storm..some part of florida..is going to get hit by this..it has to, you have 2 highs one on either side..it can only go up between them..and florida is right in its way...watch this storm, wait and see which coast it goes up, and dont forget..it can still..go right up the middle of the state..nothing is set in stone yet.
I had to take my eyes off of it for an hour. I was up at 1:30am, needed nap lol
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Quoting presslord:


I normally tune out media bashing as shrill...but in this case, you are 100% correct....they did a negligent job telling the full story of that storm...


shrill/SHril/
Adjective:(of a voice or sound) High-pitched and piercing.
Verb:
Make a shrill noise.
Noun:
A shrill sound or cry.

hi press :)


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Thanks Levi good job
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Quoting BoroDad17:
One thing I think we can all agree on, Isaac is one of the most impressive looking 40-45mph tropical storms EVER.
Yes, it definitely 'wants' to have a lot of energy. Give it A for effort! I have seen storms like this in its early development only to turn into a monster storm!
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Quoting sporteguy03:


He was using the 6z run, maybe he made the video before the 12z came out?


maybe?
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740. wpb
Quoting Levi32:
Good afternoon.

Blog update:

Tropical Tidbit for Thursday, August 23rd, with Video
thanks
Member Since: May 28, 2011 Posts: 0 Comments: 573
Quoting mississippired:


I live about 80 miles north of Waveland, MS. We had no power or water for a month.


I can't find any information at the moment, but there was a small community located (IIRC) just barely on the mainland in Galveston County that didn't get electricity back from Ike for over a year. That was partially due to a disagreement over who was responsible for restoring service, but an amazing statistic nevertheless.
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Quoting jeffs713:
14.9/66.3 Or so. Tell me what you see there, when looking at the loop.


I am generally on board with that.
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Quoting Levi32:
Good afternoon.

Blog update:

Tropical Tidbit for Thursday, August 23rd, with Video

Good presentation but i missing any mention of sea surface temps (which are much higher to the west of Florida) and the size of Isaac which will compensate a great deal for mountain interaction.
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Quoting TampaFLUSA:
RT @twcMarkElliot: The "tail" of #Isaac went over Trinidad & Tobago. Reports of trees down, & main roads like this: http://bit.ly/MOR2kO


Hope Pottery did all right.
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Quoting WDEmobmet:


You continue to counter the EURO with what the GFS shows at the 500mb level, and yet you fail to mention to most recent forecast of the GFS with a panhandle landfall. To me it seems that you ignore any other possiblity that counters your original forecast, no way you slice it. My personal opinion is that your forecast are biased... sorry just my views. I like your analysis truly very well put together. Better than 99% of others posted here. However you are afraid to mention anything that disagrees with you and only give attention to what benefits you.


He was using the 6z run, maybe he made the video before the 12z came out?
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Quoting mississippired:


I live about 80 miles north of Waveland, MS. We had no power or water for a month.


I was a little north of Gulfport and went over a month w/o Power, water, gas, phone, cell service, etc...All this on top of the damage and to add insult to injury 100+ degree temps right after the storm.My family and I lived in a tent in the backyard for a month due to the oppressive heat in the house.


I know what you mean, It was hell on earth
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Quoting Hurricanes101:


Levi, do you think this "westward trend" continues or do you think it shifts back east a bit?


Well given my current track obviously I think some slight shifts in the models back towards the east are possible, but we'll see how the G-IV runs go. Nopefully NRT will be around tonight to tell us whether the 0z runs actually got the data.
Member Since: November 24, 2005 Posts: 635 Comments: 26647
Quoting BoroDad17:
One thing I think we can all agree on, Isaac is one of the most impressive looking 40-45mph tropical storms EVER.
Inside isn't pretty, though :)
Member Since: August 1, 2011 Posts: 28 Comments: 8009
Quoting Hurricanes101:


Very interesting that after all the debate about Isaac's movement that you agree he is starting to move WNW
thank you for that link and ty Levi, its what ive been trying to say..all of florida cannot take their eyes off this storm..some part of florida..is going to get hit by this..it has to, you have 2 highs one on either side..it can only go up between them..and florida is right in its way...watch this storm, wait and see which coast it goes up, and dont forget..it can still..go right up the middle of the state..nothing is set in stone yet.
Member Since: August 6, 2011 Posts: 4 Comments: 38478
730. 7544
thanks levi helps us alot good job
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1004.2 and not to the center. (16.6, 66.9)
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RT @twcMarkElliot: The "tail" of #Isaac went over Trinidad & Tobago. Reports of trees down, & main roads like this: http://bit.ly/MOR2kO
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Quoting Wxouttacontrol:
Following website chock full of graphics, forecast models, sat. images/loops, recon info, etc.

Link
FYI :there's a FB page too.
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Quoting StormTracker2K:


The NHC had it near Tampa but the forecasted landfall was actually Panama City. The NHC really busted that forecast just like they did with Debby. levi's right those mtns. across Cuba and Haiti can cause irratic shifts in the track.

Tks..I think I've blocked a lot of the details with Charlie being in NW Cape Coral.
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Quoting SouthTXWX:

Woah! a little bi-polar are we, not bashing Levi for the East C of FL? good to see the other you!


I still think it goes west along the SW FL coast but Levi has a great point. As I was watching his video Hurricane Charley came to mind. Either way FL is in big trouble whether this goes east or west.

Member Since: October 26, 2011 Posts: 0 Comments: 2651
Quoting Grothar:


Wow. Some pictures. I heard there was sever damage way inland. Is that true?


Friends of mine lived outside Jackson, in north MS, and they had severe damage, trees down, roof damage, etc.
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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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