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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Quoting lowerbamagirl:
Can someone please explain why Isaac is not likely to strengthen when he reaches the gulf? As I have always understood, the warmer the water the more likely for strengthening. The water is very warm over the gulf right now. I do understand if he stays near the West coast of Florida the land interaction will weaken him. However, if he follows the western most part of the cone, what is to prevent rapid intensification?

I vividly remember Dennis (the first hurricane I did NOT evacuate for). Went to bed to a cat 2 and had a friend call me at 4 am to tell me he was a cat 5. By then it was too late to get out.


I honestly do not know. The NHC is being too conservative IMO. Instead of a Cat 1, I'd expect a Cat 2 in the eastern Gulf, maybe stronger.
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Quoting WDEmobmet:


Someone would really have to explain to me the reasoning behind such a planned course. Makes ZERO since to me


Sampling the high which is guiding Isaac. Actually makes perfect sense that this is where the G-IV mission would be.
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Quoting AAPLTrader:
I am very appreciative and respect LEVI and his daily updates. He is very analytical. However he has been very consistent on his forecast for Isaac moving EAST of Florida. I certainly am interested to see if he sticks with his forecast in today's post and look forward to his daily updates.
AAPL.I see you quickly changed your tune after you were ganged up on...And rightfully so I might add...Levi does a wonderful job... I'm sure you could do better.....NOT
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quit the member bashing now
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Quoting angiest:
FWIW, hurricanealley.net's latest forecast track (NOT official):



Remember when Katrina crossed Florida. It made that dip to the southwest... That small dip completely changed it's trajectory to the northern gulf coast. That is what is happening now. That's factored into hurricane alley's track and that is what the NHC sees, as well. If Isaac continues to move west, expect the NHC to shift again to the west. Eventually the models will converge. Current location of the center, combined with all of the atmospheric data coming in will line things up. Central Gulf is in the crosshairs...
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hmm Hurricane Alleys forecast track wow thats like a mix of Gustav and Fay (08)
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The FIM8 is a very good model. This presentation shows that even if Isaac goes directly over Hispaniola and reaches SW Florida, there will still be extreme weather on the Southeast coast. Something to which most of the experts agree, including the WC.

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Quoting TomballTXPride:
Now VERY interesting the GFS is taking him much further west of the west coast of Florida this time, since usually it's the 06Z & 18Z runs that have the westward bias.

Oh boy. Time to really start thinking about getting preparations in...


Wow lol, knew someone would post this

That is not MUCH further west as you are saying, its still in the window that the GFS has been in for days now
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216. wxmod
These Atlantic storms are made of mud.

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Quoting emcf30:


Here is the projected flight path



Someone would really have to explain to me the reasoning behind such a planned course. Makes ZERO since to me
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When a storm is going to possibly threaten the West Palm Beach area, FPL uses our north parking lot as a staging area. They did it last year when Irene looked as if she could be a potential threat. So far, no call from FPL.
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Quoting presslord:
It takes a great deal of testicular fortitude to do what Levi does...and none whatsoever to take asshat pot shots at him...


As the blog turns. The majority of the people here couldn't do anywhere near the level of analysis that he does. At least he backs up his claims with good science, whether right or wrong. I challenge anyone else to try to do better. Sad.
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Quoting Beachfoxx:
Hey Viking!

Long time no see.... the concern I have is if Issac hits us the ground is so saturated that we may see trees topple over, we've had soooo much rain!

Heck the bay is stained with the tannins and is orange/brown now. I was hoping for the rest of the season to be sunshine and no canes.... Guess we are going to have to keep a close eye on Issac.





Yeah, I was looking for Crab Island to be nice over the Labor Day weekend but if this happens it will be a mess and the water will be littered with debris. Keep moving West Isaac or make that turn to the East please! I'm starting to not like "I" storms very much. I'll have to move everything out of my garage and into a storage unit North of Hwy 98 because my garage will most likely flood with anything Cat 2/3 or above. Dennis put about 30 inches of murky Sound water into my garage. Luckily we had just moved in and I put all the moving boxes into the house which is elevated. The walls in my garage are cement up to 5' so I just had to pressure wash all the muck out of the garage after Dennis.
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Some here think envy is a horrible thing to waste when it comes to their nitpicking of Levi. He puts himself out there time and time again. He is a huge asset here and yet I here him criticized ten times more than he is ever given thanks for his tireless work. While going to college full time no less. Thanks Levi and those who respect what he does.
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Bravo Chicklit!! Message 197.
I couldn"t state your message any better.
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Quoting AAPLTrader:
LEVI has to eat crow today. For 3 days he predicted a path EAST of Florida.




Ban this clown

Levi does more to educate the posters of this blog than anyone other than the Doc himself.
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Quoting AAPLTrader:
I am very appreciative and respect LEVI and his daily updates. He is very analytical. However he has been very consistent on his forecast for Isaac moving EAST of Florida. I certainly am interested to see if he sticks with his forecast in today's post and look forward to his daily updates.
You should stick to trading, let Levi stick to forecasting! Troll.
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Quoting hurricanejunky:

Yes, it is today.

000
NOUS42 KNHC 231503
REPRPD
WEATHER RECONNAISSANCE FLIGHTS
CARCAH, NATIONAL HURRICANE CENTER, MIAMI, FL.
1100 AM EDT THU 23 AUGUST 2012
SUBJECT: TROPICAL CYCLONE PLAN OF THE DAY (TCPOD)
VALID 24/1100Z TO 25/1100Z AUGUST 2012
TCPOD NUMBER.....12-096

I. ATLANTIC REQUIREMENTS
1. TROPICAL STORM ISAAC
FLIGHT ONE --TEAL 73 FLIGHT TWO --NOAA 49--
A. 24/1800Z,25/0000Z A. 25/0000Z
B. AFXXX 1209A ISAAC B. NOAA9 1309A ISAAC
C. 24/1630Z C. 24/1730Z
D. 17.5N 71.2W D. NA
E. 24/1730Z TO 25/0000Z E. NA
F. SFC TO 10,000 FT F. 41,000 TO 45,000 FT

FLIGHT THREE --TEAL 71-- FLIGHT FOUR --NOAA 49--
A. 25/0600Z,1200Z A. 25/1200Z
B. AFXXX 1409A ISAAC B. NOAA9 1509A ISAAC
C. 25/0400Z C. 25/0530Z
D. 18.6N 73.5W D. NA
E. 25/0530Z TO 25/1200Z E. NA
F. SFC TO 10,000 FT F. 41,000 TO 45,000 FT

2. SUCCEEDING DAY OUTLOOK: CONTINUE 6-HRLY FIXES.
A G-IV MISSION DEPARTING 25/1730Z AND 26/0530Z.


Here is the projected flight path

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Quoting AussieStorm:


I understand that, but even a few lines at the bottom could of been enough. Not to mention a Cat 4 that is going to loop around and make landfall again then loop around and hit again, I think that could help with people widening there tropical storm knowledge. It's not just the ATL that has it's season right now.

This is both beautiful and frightening at the same time



Totally. I follow tropical formation all year round, either hemisphere, any ocean/sea. That's why my sign up date was at the end of the season, I was trying to comment about something, but my old browser would never let me sign on.
Pre-internet in the states in the 90's, TWC used to annoy me that they didn't have a tropical report in the Atl off season LOL
They do get some crazy storms WPac. A few blogs ago people were talking about a doom cat7 storm or some such. If that were to happen anywhere, surely it would be over there!?
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Can someone please explain why Isaac is not likely to strengthen when he reaches the gulf? As I have always understood, the warmer the water the more likely for strengthening. The water is very warm over the gulf right now. I do understand if he stays near the West coast of Florida the land interaction will weaken him. However, if he follows the western most part of the cone, what is to prevent rapid intensification?

I vividly remember Dennis (the first hurricane I did NOT evacuate for). Went to bed to a cat 2 and had a friend call me at 4 am to tell me he was a cat 5. By then it was too late to get out.
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198. 7544
looks like gfs says south fl again how many days is this ?
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Quoting palmpt:


You are so right. Levi is extremely good... He'll adjust. He'll be a star... He already is.


He does nice videos and makes good speeches, but so far he's 0/2 when it comes to forecast track. And this is not a character assault. Just stating the facts.
Like somebody said. Pay attention to the NHC.
Which is what he is always saying he doesn't always agree with. This is fine.
And no harm done since all this stuff is days away.
It's really not a big deal, but the idol-worshipping on here ad nauseum gets a little old.
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Amen! Better yet, fizzle out in the middle of the GOM. Pray for SHEAR!
Quoting 69Viking:


That's a fact.
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193. MTWX
Unless Isaac picks up a good deal of strength over the next 12 hours or so, I'm going to have to go with the following odds:

West Coast/ Panhandle of Florida from Cape Coral to Panama City

60%

Panama City to Mobile Bay

35%

West of Mobile Bay

5%
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Quoting angiest:
FWIW, hurricanealley.net's latest forecast track (NOT official):


Almost looks like the took the old Gustav track from 2008 and made it into a forecast cone. :P

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You too....
Headed out, gotta run to FWB, then back to Destin & need to pick up a few supplies. We've had so much rain I really don't want a cane... but got to get my rumpus in gear. TTYL

Quoting StormJunkie:


Thanks BF and great to see ya!

Added to the Quick Links page under General Tropical (purple).
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Quoting KEEPEROFTHEGATE:

Thanks keeper for posting the new runs.
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Quoting HurricaneDean07:
Also. According to Kermit's Recon data.... Isaac's Center fix has been jumping around a bit...
One center fix put it near 14 N. But it jumped north on the last fix-pass, Still interesting to see.

I'll wait for the HH RECON to fly in at lower height before look at NOAA's P-3

AF HH WC-130J RECON flies at 5,000 ft
NOAA's WP-3D RECON flies at 10,000 ft
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Quoting StormJunkie:


We are on opposite sides on this one MLC, not because of my vast knowledge (lol); but because I can not bring myself to go against the consistency of the consensus for days on end. Kudos on sticking to your guns. That said, I have a feeling that the G-IV mission will work all of that out for us.


:) I nearly changed my mind late evening when the western periphery of the high was only in the central gulf. However, it's now extended over to Houston and over the central gulf. A strong storm can push up against 1016mb, but not a weak one. Isaac's western movement can only give way, imo, to a gradual northwesterly movement if/when it gets its act together and strengthens. In the present, I'm expecting the cone to shift even further, even if ever so slightly, more westwards. I think the FL east coast is out of the woods and that Isaac will miss Hispaniola altogether.

I'm weird, but that's what I'm seeing! ;P
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187. wxmod
Dust and pollution in the Atlantic hurricane sector yesterday. MODIS

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Taiwan is about to get sucker punched. Most of it's infrastructure is located on the West side of the island and for good reason.

However T'aitung is going get some terrible conditions, they may get lucky if the cyclone can dive WSW and possibly just brush by rather than just plowing directly westward into the the city. T'aitung has a population of 230,000
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12z GFS 850mb.



Shows a death stroll along Cuba. Can't imagine a 850mb vort holding together well through that.
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Quoting pensacolastorm:


Those of us on the gulf who have been through storms before are only wishcasting for it to go elsewhere.


That's a fact.
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I am very appreciative and respect LEVI and his daily updates. He is very analytical. However he has been very consistent on his forecast for Isaac moving EAST of Florida. I certainly am interested to see if he sticks with his forecast in today's post and look forward to his daily updates.
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here we go again...
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Quoting DDR:
Most areas in North western Trinidad areas have received 4+inches of rain from 4-8am this morning.

12mm (0.5") in central, but we had strong SW winds around midnight for an hour or so.

Incredible lightening all around too.
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After looking at the steering pattern, I just don't see Isaac crossing 85W, but Tampa is a really good possibility, or the big bend. the trough/weakness should recurve Isaac once its near Tampa and move northeast towards the Carolinas.. Also I have the feeling Isaac may not cross Hispaniola, which would lead to a stronger storm.
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God does answer prayer,thank goodness Issac moved a little farther AWAY from Hatie,DR.
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Quoting angiest:
FWIW, hurricanealley.net's latest forecast track (NOT official):

Plausible solution.
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A preparatory recheck of the data used in the page89comment4431 mapping has revealed that NHC_ATCF has changed the original 23Aug.12pmGMT report to show that 23Aug.06amGMT's Position&MaxSusWinds were re-evaluated&altered from 15.5n63.5w to 15.3n63.5w and from 40knots to 35knots, respectively
Vectors and straightline projections will be corrected on the next (23Aug.6pmGMT) mapping.
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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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