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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1024. ncstorm
12z GFS rain precip map-120 hours


240 hours


360 hours
Member Since: Posts: Comments:
1023. Chiggy
12Z Euro at 120hrs, moving WNW/NW towards NOLA...!!
Member Since: June 26, 2012 Posts: 0 Comments: 297
1022. centex
Quoting Hurricanes101:


then why did they put WNW as the motion at 2pm?
Because they thought it was at 16N? Even so I'm kind of miffed by that also. Not being stacked and disorganized and mid and LL circulation dancing around.
Member Since: Posts: Comments:
1021. GetReal
Euro has Isaac on a track towards the N GOM coast.
Member Since: July 4, 2005 Posts: 204 Comments: 8898
1020. Levi32
Quoting 1900hurricane:
12Z ECMWF looks more or less continuous with the 00Z thus far. Looks like you could even overlay them like they were one model run.


The 48-hour forecast point is significantly farther northeast into Hispaniola than last night's run, which is the significant difference. Mountains pull it in then spit it back out more this run.
Member Since: November 24, 2005 Posts: 635 Comments: 26717
Quoting presslord:
Why in the world would anyone listen to the NHC when we have easy access here to any number of anonymous, dysfunctional bloggers without any qualifications or credentials whatsoever?!?!?!?!

Presslord... stop trying to think about that. You might hurt yourself trying to understand what is incomprehensible to logic.
Member Since: Posts: Comments:
Quoting clwstmchasr:


So the NHC is wrong and you are right. Your hired!
You do realize he is not the only one who said this so why do you single him out to tear to pieces ?

935. StormHype
That 16N is questionable. I can't see it farther N than 15.5N. Maybe they figure it doesn't matter at this point as it's so disorganized still.
936. RTSplayer
I disagree with NHC .Storm has done nothing but drift south all morning long..
948. louisianaboy444
If the Center is at 16N then this is a more disorganized system then previously thought...just do not think it is that far north







Member Since: Posts: Comments:
Today's 12Z Euro run is almost an exact update of yesterday's 12z run. Points for consistency I guess.
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Quoting FLWaterFront:


With all due respect, that is just hype.

There are still many possibilities and many variables in play, not least of which is the effect that tangling with all those high mountains in the Greater Antilles will have on Isaac, if he does indeed take that predicted path.

For example, any time spent over Hispaniola and/or Eastern Cuba, with the high mountains there, could well disrupt the circulation of this storm so much that it will not have time to reorganize significantly before reaching some point on the Florida peninsula. And IF that turns out to be what happens, then there is a good chance that most if not all of the areas in Florida that are affected will only see moderate tropical storm impacts, or less. And this has happened dozens of times in the past without causing significant loss of life or property damage.

Florida is quite likely to be affected by Isaac but it is far from certain just how or where exactly, as of yet. To say "Florida is in big trouble (either way) is premature at best.


Not at all! A track up the west coast of FL or just offshore in the Gulf would cause big problems for the whole FL Penisula as Issac's circulation is 600 miles wide. Flooding, tornadoes, high winds along the Gulf Coast, and storm surge flooding in Tampa as Issac slides by to the north. All spell trouble and that son you can take to the bank.
Member Since: Posts: Comments:
Quoting 12george1:
Why is this storm not strengthening?


Trade winds
Member Since: Posts: Comments:
1014. FOREX
Quoting Levi32:
ECMWF showing jerky motions associated with the greater Antilles mountains.


How are you able to follow the European model step by step. Which website??thanks.
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12Z ECMWF looks more or less continuous with the 00Z thus far. Looks like you could even overlay them like they were one model run.
Member Since: August 2, 2006 Posts: 47 Comments: 11771
1012. GetReal
120 HOURS
Member Since: July 4, 2005 Posts: 204 Comments: 8898
WEST
Member Since: Posts: Comments:
Quoting StormTracker2K:
Euro still going the south route.


Wow that ridge north of the storm..
Member Since: Posts: Comments:
1009. wpb
Quoting 12george1:
Why is this storm not strengthening?
been the case this year in this area
Member Since: May 28, 2011 Posts: 0 Comments: 573
1008. wn1995
Hurricane Hunters found 45 mph surface winds. Finally. haha
Member Since: Posts: Comments:
1007. BA
Hey everyone, since when did Levi become a professional forecaster with any sort of credentials or "weight" behind his opinion?

If you want that, you need to look elsewhere.

Otherwise, stop the whining and bashing just because people seem to like his forecasts more than your own. :)
Member Since: Posts: Comments:
Quoting Kowaliga:
Gaining some lat....finally....maybe...



looks like it still has multiple convec. centers
but look how fast the "main" one wraps around rain! at the end of the loop
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1005. wpb
Quoting Levi32:
ECMWF showing jerky motions associated with the greater Antilles mountains.
hmrf also
Member Since: May 28, 2011 Posts: 0 Comments: 573
Why is this storm not strengthening?
Member Since: Posts: Comments:
Here is a zoom in of the alleged center, directly South of PR.  You can see the spin.  Looks like the center is at 15.65N, 66.47W.  St Croix is in the upper right corner about 175 miles away.


Member Since: Posts: Comments:
It makes you wonder if Isaac is ever gonna get his act together. Other storms for some reason or another couldn't do it either. Maybe he will stay very little and just be a rain maker.

Sheri
Member Since: Posts: Comments:
Quoting 1900hurricane:

If that actually is the center (which I can't say that it is or isn't), the radar makes it appear that it is moving more north than west.


...guessin' its one of those crazy vorts.......(?)
Member Since: Posts: Comments:
1000. drs2008
Quoting CaneHunter031472:


I noticed ppl have been giving you a little bit of a hard time because of your forecase. Well, don't mind them at this point you could be right and your reasoning for your forecast is very logical, so I resppect it. At least you are honest enough to stick to your guns. Whether it proves right or not which is still a bit too early to tell you are the future of meteorology and IMO the future is bright because of ppl like you keep up the AWESOME job Levi
Quoting Levi32:
12z GFS ensembles shifted west a bit.

In my profession(medicine) we attempt to gather together as much data as we can and test our hypotheses. We come up with a diagnosis however we have a number of differential diagnoses.We chose the one with the greatest probability of being correct. It never ceases to amaze me how often a patient is shocked with the discovery that this is an inexact science. Please understand that predicting the weather is just as inprecise. Too many variables and unknowns.
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Quoting Elena85Vet:
Getting tired of scanning over posts about Levi, pro or con

What ev's..

thx

Didn't you know this blog is no longer about tropical weather it is here just to debate over Levi's forecast. It does get old and repetitive. I do appreciate your forecasts by the way Levi even if I don't agree all the time.
Member Since: Posts: Comments:
998. wpb
all models show winds under hurricane force the nhc had 12% chance of getting to hurricane cat 1 by fla keys think there correct
Member Since: May 28, 2011 Posts: 0 Comments: 573
What is with all the bickering on here?
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Quoting Levi32:
ECMWF showing jerky motions associated with the greater Antilles mountains.
How can you see jerky movements?
Member Since: June 13, 2009 Posts: 0 Comments: 6914
96 Hrs Euro. Doesn't seem to have changed substantially since the 00Z run.

Member Since: Posts: Comments:
994. Relix
Quoting presslord:
Why in the world would anyone listen to the NHC when we have easy access here to any number of anonymous, dysfunctional bloggers without any qualifications or credentials whatsoever?!?!?!?!


come on! Wunderkid is a prodigy! He can see hurricanes hitting the Caymans since before they are born in Africa!
Member Since: August 3, 2006 Posts: 0 Comments: 2741
Quoting LargoFl:
I have to say something, I in my entire life, have been thru tropical storms yes, but i have never actually been in..a hurricane..not close anyway, closest was charley if i can remember right and that came in all the way down in sarasota..so..if i ask too many..what can we expect from issac questions..know why im asking them ok


If you're 50 to 75 miles inland, it's usually not so bad, and actually a lot of fun.

They are awesome to watch, and go stand out in the middle of the wind and feel it's power.

I've been in at least 4 majors I can remember, not counting category 1s and Tropical storms.

Been in sustained hurricane force winds at least 3 times: Andrew, Katrina, Gustav.

Like I said, that's not counting cat 1s and dinky TS that everyone forgets...
Member Since: Posts: Comments:
Well, hello there Isaac.

The C-130J is moving through an extended area of ~40kt surface level winds, just south of east from the center of circulation. The 2pm advisory put maximum sustained winds at 40mph, and even that was something of an act of faith. This supports 45mph, and it's not even the best presentation on satellite or radar. Isaac might finally be pulling itself together.
Member Since: August 18, 2009 Posts: 0 Comments: 460
Euro still going the south route.
Member Since: Posts: Comments:
On visible, clouds going northwest on the west side of latest so called coordinates. lol
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guys,

isaac is not looking like a 12mph storm.
looks like it's never stopped racing.
Member Since: Posts: Comments:
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.



With all due respect, that is just hype.

There are still many possibilities and many variables in play, not least of which is the effect that tangling with all those high mountains in the Greater Antilles will have on Isaac, if he does indeed take that predicted path.

For example, any time spent over Hispaniola and/or Eastern Cuba, with the high mountains there, could well disrupt the circulation of this storm so much that it will not have time to reorganize significantly before reaching some point on the Florida peninsula. And IF that turns out to be what happens, then there is a good chance that most if not all of the areas in Florida that are affected will only see moderate tropical storm impacts, or less. And this has happened dozens of times in the past without causing significant loss of life or property damage.

Florida is quite likely to be affected by Isaac but it is far from certain just how or where exactly, as of yet. To say "Florida is in big trouble (either way) is premature at best.
Member Since: October 15, 2010 Posts: 0 Comments: 794
96 HOURS



W CUBA!
Member Since: July 4, 2005 Posts: 204 Comments: 8898
Quoting Kowaliga:
Gaining some lat....finally....maybe...


GOODI NFO IMPRESIVE WNW
Member Since: Posts: Comments:
Why in the world would anyone listen to the NHC when we have easy access here to any number of anonymous, dysfunctional bloggers without any qualifications or credentials whatsoever?!?!?!?!
Member Since: August 13, 2007 Posts: 0 Comments: 10492
Quoting Kowaliga:
Gaining some lat....finally....maybe...


If that actually is the center (which I can't say that it is or isn't), the radar makes it appear that it is moving more north than west.
Member Since: August 2, 2006 Posts: 47 Comments: 11771
Quoting CarolinaHurricanes87:


The point is that we want to hear why they disagree with his forecast. He gives reasoning for his forecast track... if they disagree, lets hear the reasoning for their forecast track. Playing follow the leader with NHC GFS or Euro does not count... Levi goes way more in depth and if they feel the need to criticize someone for their OPINION, they should at least explain why with their own reasoning.


I'm not singling you or anybody out but Levi asked very nicely the other day not to make him the subject in Dr Masters' blog maybe we could respect that and my own observation is there are usually many more defenders than attackers. It seems a waste of time maybe?
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Quoting clwstmchasr:


So the NHC is wrong and you are right. Your hired!

no hurricane hunter should be they flew over that area and nothing is there
Member Since: June 13, 2009 Posts: 2 Comments: 12728
Quoting cheaterwon:


Thats what they have posted but there own discussion states that it is currently moving west and they put that direction pretty much because the model guidance. which doesn't make since. Here is what they said.

THE OVERALL CIRCULATION OF ISAAC IS A LITTLE FARTHER SOUTH THAN 12
HR AGO. HOWEVER...IT SEEMS TO HAVE RESUMED A WESTWARD MOTION AT
ABOUT 13 KT. THE TRACK MODEL GUIDANCE IS IN GOOD AGREEMENT THAT
ISAAC SHOULD MOVE WEST-NORTHWESTWARD FOR THE NEXT 36-48 HR...


Isaac is still moving west per there words.

you are quoting the 11am discussion and not the 2pm advisory where they don't do a discussion.

they clearly say wnw on the 2pm advisory.
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ECMWF showing jerky motions associated with the greater Antilles mountains.
Member Since: November 24, 2005 Posts: 635 Comments: 26717
Be careful looking at loops as you can confuse rotating
vortexes and/or mid-level circ for the actual LLCoc
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Gaining some lat....finally....maybe...

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Preparing for a hurricane..what do i need to do?........here's a wonderful site.......Link
Member Since: August 6, 2011 Posts: 4 Comments: 43916
Quoting clwstmchasr:


So the NHC is wrong and you are right. Your hired!


This guy really wants a storm.
Member Since: Posts: Comments:

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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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