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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IMO, too many people on this blog are occupied with their feelings...
They take things personally, take any disagreement as a shot at them, and are more into being "right" than engaging in discussion...
If you are going to get your feelings hurt because your forecast was wrong, or someone told you something you didnt like, get over it, its the internet....
There is NO reason for all the drama and arguments and discussions about....nothing
Lets not make much ado about nothing, and instead focus on the storms at hand...blogging and commenting on WU is supposed to be an enjoyable experience....not a dogfight.

ok, rant over,back to weather
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Quoting tropicfreak:


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.


Yeah, remember Charley. Conditions are ripe in that area of the Florida Straits/GOM for RI. SST's are in the 88-92 degree range depending on where you sample. LOTS OF FUEL!
Member Since: August 28, 2006 Posts: 6 Comments: 2898
Quoting StormTracker2K:
My lord here comes Kirk to FL. Geesh! We may need a bigger boat here across FL. Also by the 12Z GFS stalls Issac over Tallahassee for several days.

Travel in pairs...

Dennis floyd 1999

Eye within 10 miles of each other 18-19 days apart
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Quoting connie1976:
Someone, anyone s the UKMET model any good? Just curious...thanks... :)

Connie, here is a link to Jeff Masters' post yesterday regarding models.

Below is a graph from Dr. Masters' post showing model performance in 2011. The best ones are the ECMWF and the GFS (the other two ones you see at the top aren't individual models but are a forecast and a model average).

The UKMET is in the second tier of models and last year performed okay at 48-hour predictions, but successively worse at longer-range time scales. Read his whole post, or at least the section on the models.

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469. Tygor
Honestly Levi has maybe done more for teaching us newbies the intricacies of tropical storm watching and forecasting than 95% of the users on the blog. Nobody expects everyone to be 100% correct, but I would expect that if someone is wrong they had a reason for believing what they forecasted. This is exactly what Levi does. He may not always be right, but he explains why he believes what he does and it makes sense. There's always a certain amount of extrapolation in dealing with storms...can't really blame someone for their extrapolation not necessarily being correct.
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Quoting 1900hurricane:

That would be the UKMET or British model, not the ECMWF or European model. Both from europe, but different models.

For what it's worth, the ECMWF does show a similar track though.


Sorry, got them confused... my bad
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Quoting Grothar:


Early models on some sites are the latest models. Late models are the previous ones.

To add to the confusion, Early models are the first ones and Late cycle models are the latest.

So basically... the early models are later than the previous late models, but the early models come out before the late models. And by the time everyone on the blog figures this out, there will be another run of the late and early models, which means the late models will be more current than the recent early models.
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My 10 yo daughter, who suffers through my hurricane rambling talk, every year, suggested that if an eye of a hurricane came directly over us, why not just drive around in it? Or keep up with the eye in our car.

I may give that a try someday, but don't worry, I'll leave her home, safe with her sane mother.
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Quoting StormTracker2K:
My lord here comes Kirk to FL. Geesh! We may need a bigger boat here across FL. Also by the 12Z GFS stalls Issac over Tallahassee for several days.



nope

GFS turns Kirk away around the 300 hour mark
Member Since: March 10, 2010 Posts: 1 Comments: 7685
Quoting 1900hurricane:
At the risk of sounding uncultured, who the heck does the random floating head on 09L's projected path belong to and why the heck does it keep getting posted?


His character was named Isaac on a show called the love boat.
Member Since: August 24, 2010 Posts: 0 Comments: 151
Kirk Approaching Fl from the East at 276hrs, also the remnants of Issac still hangs around on the Gulf coast..
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461. Kumo
Quoting Hurricanes101:


sadly it is how it works on here...you have respected bloggers, most who are studying to have a job in the field of meteorology or who already do...you have some of us that have a healthy interest in it and some really good knowledge and you have those who do not know squat and only come on here to point out who is wrong and cause drama.

Those in the 3rd category are of no use to this blog and therefore should be ignored and IMO should be banned from the blog due to their only purpose being to start drama.


It's too bad that the 3rd category types don't realize just how much time and effort they are wasting. Just imagine the kind of progress that could be made on this blog if they worked together with the other two active types.

Thank you to the folks that post interesting links, data and insightful comments. I have learned much over the past few weeks that I've been lurking around here. :)
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Quoting lottotexas:
Here we go again I & J repeat
That's not Joyce as she is long gone into the graveyard of the North Atlantic, actually that's Kirk and Leslie.
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Quoting HoustonTxGal:


EURO still go way west

That would be the UKMET or British model, not the ECMWF or European model. Both from europe, but different models.

For what it's worth, the ECMWF does show a similar track though.
Member Since: August 2, 2006 Posts: 46 Comments: 11667
Quoting 1900hurricane:
At the risk of sounding uncultured, who the heck does the random floating head on 09L's projected path belong to and why the heck does it keep getting posted?



i agree and it was even posted under another nik this time
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The Latest
(click to enlarge)


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Quoting doabarrelroll:


It was very clear what he did to me. It wasnt nice

me:hey look at the steering currents on Debby she cant go west. She will find the gap over Florida"

Him:"You mean the steering currents that change all the time..."

This didnt correct me or bring up a counter point it was insulting.


yeah he told me his daddy was stronger than mine! I'm insulted too........
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I dont know how much rain weve had here in Dixie Co. Fl over the past week, and the Suannee is already running high. If Isaac skirts the coast, Im gonna be up the creek with out a paddle..... Watching the blog very nervously.
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My lord here comes Kirk to FL. Geesh! We may need a bigger boat here across FL. Also by the 12Z GFS stalls Issac over Tallahassee for several days.

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Here we go again I & J repeat
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UK isn't nearly as bad as that chart implies. It had some issues last year that caused the bad verification score.
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Close up of TS Isaac:

Member Since: August 1, 2011 Posts: 28 Comments: 8009
Quoting A4Guy:
what is with the ATCF images not updating after the 12Z early cycle? Yesterday,they never updated after that, and today they are not updating either.

personally...i am very confused by the time designaitons. I know Z is "zulu time" - which is 4 hrs ahead of ET...but I can never figure out when the runs really update, and the diffs between the early and late runs. probably explained onthe NHC site, but I have been alittle lazy about looking. :)


Early models on some sites are the latest models. Late models are the previous ones.

To add to the confusion, Early models are the first ones and Late cycle models are the latest.
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.
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Quoting angiest:


A tropical storm sitting on top of you for a week can be more damaging than a hurricane.


Yep but per the models, this storm will be gone within 24 hours. This is not an extremely slow mover
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Quoting doabarrelroll:


It was very clear what he did to me. It wasnt nice

me:hey look at the steering currents on Debby she cant go west. She will find the gap over Florida"

Him:"You mean the steering currents that change all the time..."

This didnt correct me or bring up a counter point it was insulting.


THAT is the comment that pissed you off?

Thin skinned are you?

Geez and he was right, the steering was changing all the time with Debby, sorry most on this blog would not have taken that personally and the fact that you are causing this stir over that comment tells me more about you than it does about Levi.

Moving on, Isaac is the topic of debate
Member Since: March 10, 2010 Posts: 1 Comments: 7685
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OK a geography lesson for you all. Key West is about 175 miles SW of Miami if Isaac skirts the keys it will not be pretty here is SE FLA. or any part of Fla. for that matter.
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Quoting connie1976:
Someone, anyone s the UKMET model any good? Just curious...thanks... :)



It's the worst performer several days out, but gets better with shorter term predictions.



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The GFS actually shows a landfall at 988.1 HpA at 85Kts which is a CAT 2 100mph
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GFS 156 hrs. shows a sharp turn towards the ENE and then gets blocked by the high as it circles back around and dissipates over the Panhandle.

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Quoting thewindman:


Actually a strong Tropical storm in Cabo a few years back we were in the pool by the afternoon. 992mb is a tropical storm. Usually 987 or less is needed for a Hurricane so like I said a nice storm but just an inconvience rather than a dangerous storm


A tropical storm sitting on top of you for a week can be more damaging than a hurricane.
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At the risk of sounding uncultured, who the heck does the random floating head on 09L's projected path belong to and why the heck does it keep getting posted?
Member Since: August 2, 2006 Posts: 46 Comments: 11667
Quoting Seflhurricane:
whats your analysis for Southern Florida and the florida keys.


People in South Florida and especially the Florida Keys should remain vigilant about the storm. Even though the forecast track has shifted west some, people must remember that forecast tracks will shift many times before an eventual end game. In addition, with this being such a large storm, effects will be spread out over a large area as one can see in the GFS where in fact, the most rainfall and inclement weather would occur over the Keys and South Florida since those areas would be on the northeast side of the storm, if the forecast track holds. Finally, I'm going to wait until the G-IV plane gets out there this afternoon to investigate the upper atmospheric pattern upstream from Isaac before buying into the computer models more as that data could change the ballgame in terms of forecasting.
Member Since: April 14, 2007 Posts: 8 Comments: 5169
Isaac Landfall Outlook from Wthr Wonk: Between Panama City and Gulfport with greatest likelyhood being Pensacola with movement on a somewhat NE trajectory. Cat 3-5 but then weakening prior to landfall.
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Quoting 1900hurricane:

It's still good enough that the NHC uses it, but there are also more consistent options out there.



Thank you so much!!! :)
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The bottom line for me on Levi's issue:

The best way I can prove something wrong is by demonstrating it...
If I want to prove Levi, Dr. Masters, GFS is wrong, I would have to present something superior to what I'm criticizing...

So, who's going to step ahead and present us with that alternative?

(must be ready to be criticized)

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Quoting lowerbamagirl:


No problem. Nobody needs to panic yet but everyone along the Gulf coast needs to keep an eye on Isaac.
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Quoting HoustonTxGal:


EURO still go way west


Where do you see the EURO on this?
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Quoting HoustonTxGal:


EURO still go way west


That's UKMET, not Euro.
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432. TXCWC
IF Euro holds we may finally have agreement between it and GFS on final landfall location area - Mobil/Pensacola area

0Z EURO last night


12Z GFS today
Member Since: May 18, 2012 Posts: 0 Comments: 519
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Quoting StormTracker2K:


I have no problems with the track but Issac seems to be getting much stronger right now. I bet we have a hurricane at 11pm. Also wouldn't rule out a cat.2 100mph storm making landfall in Haiti.

Notice this big blob to the south now starting to wrap around Issac's center.


I'm holding off judgement on what Isaac appears to be doing until recon confirms. There are still likely multiple vort centers rotating around a common center.
Member Since: July 15, 2006 Posts: 17 Comments: 10247
429. A4Guy
what is with the ATCF images not updating after the 12Z early cycle? Yesterday,they never updated after that, and today they are not updating either.

personally...i am very confused by the time designaitons. I know Z is "zulu time" - which is 4 hrs ahead of ET...but I can never figure out when the runs really update, and the diffs between the early and late runs. probably explained onthe NHC site, but I have been alittle lazy about looking. :)
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Quoting jeffs713:

You must have very interesting thunderstorms.

You've never been through a hurricane, have you?


Actually a strong Tropical storm in Cabo a few years back we were in the pool by the afternoon. 992mb is a tropical storm. Usually 987 or less is needed for a Hurricane so like I said a nice storm but just an inconvience rather than a dangerous storm
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Super slow loop of Isaac:

Link

Member Since: August 1, 2011 Posts: 28 Comments: 8009
425. wxmod
from the blog "Isaac has consistently confounded predictions that it would intensify, "
A heavy wheel takes more energy to start spinning. Issac is full of Sahara mud. And; the dust around it keeps sun energy from hitting the water. Less sun, less lift.
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Quoting connie1976:
Someone, anyone s the UKMET model any good? Just curious...thanks... :)

It's still good enough that the NHC uses it, but there are also more consistent options out there.

Member Since: August 2, 2006 Posts: 46 Comments: 11667

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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.