Little change to Isaac, but intensification coming; Joyce forms

By: Dr. Jeff Masters , 3:13 PM GMT on August 23, 2012

Share this Blog
49
+

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

Reader Comments

Comments will take a few seconds to appear.

Post Your Comments

Please sign in to post comments.

or Join

Not only will you be able to leave comments on this blog, but you'll also have the ability to upload and share your photos in our Wunder Photos section.

Display: 0, 50, 100, 200 Sort: Newest First - Order Posted

Viewing: 374 - 324

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34 | 35 | 36Blog Index

My lifelong and best friend lives in Foley AL on the east side of Mobile Bay. I have been sending the info I get from here to her. She has her elderly mother living with her and until I brought the storm to her attention, she had no clue about it. She asked me to thank you for the great information and giving her time to plan if she needs to get out.



Member Since: Posts: Comments:
Quoting doabarrelroll:


I have no problem with him. He is good but everytime you try to counter him with a valid point he puts you down.


how can you say he is condescending and yet say you have no problem with him, you obviously do or else you would not have said something in the first place

I will take Levis' word over just about anyones' on this blog and certainly before yours (was that condescending enough for you?)
Member Since: Posts: Comments:
Quoting AussieStorm:


I would hate to be in the centre.

Oh, for sure. Any storm that gets symmetric like that is sure to be a "hell on earth" near the center.
Member Since: Posts: Comments:
Quoting hydrus:
I would not be surprised to see an eye by late tonight or early tomorrow.


I think were starring down the barrel of a developing hurricane. I think that once the hurricane hunter arrive they will find a much stronger Issac.
Member Since: Posts: Comments:
Quoting Chiggy:


Disagree on the WNW path right now.., no way!


All you have to do is look at the changing motion in the past few advisories from 260 degrees at 2AM to 275 degrees at 11 AM. Shows a general trend towards the WNW in time and that continues to be the case at this hour.

Quoting Seflhurricane:
how have you been . Great to see your analysis again


Good to see you and everyone else here again. Been busy with school and working through some health issues that are improving now.
Member Since: Posts: Comments:
Quoting doabarrelroll:

He does deserve it. He come on here and is often condescening. I have no problem with that but when he is wrong he doesnt apologize to those he talked down to. The other thing is people on here say "poor levi" as if he is still that 13 year old kid who came on here in 2007 hes 18/19 he is a man he can take the heat


I haven't seen condescension from him. He may not suffer idiots but I guarantee alot of people on here are that way.

In any case, wonder what the strength will be at the intermediate advisory. Not a morning person, and am a bit groggy.
Member Since: Posts: Comments:
Quoting doabarrelroll:

If you try to produce coutner aruements Levi puts you down. He was wrong here and way off on Debby. I applaud his efforts but he is not gospel and he should treat others with respect

A lot of people was off on Debby, even the NHC. Quit kicking Levi when he is not here to defend himself.
Member Since: Posts: Comments:
Quoting yonzabam:
Still no obvious northwards movement. Isaac has been moving west for 3 days, now. The NHC track forecast takes it through the middle of Haiti. Seem likely to you?


he may shot the gap between haiti and jamaica
Member Since: Posts: Comments:
Quoting doabarrelroll:

If you try to produce coutner aruements Levi puts you down. He was wrong here and way off on Debby. I applaud his efforts but he is not gospel and he should treat others with respect

I've never seen him disrespect someone. Correct them, yes. But not in a disrespectful manner. (heck, he corrects me when I ask him questions, but his intent is more to educate, not embarass or "call out")
Member Since: Posts: Comments:
Quoting hydrus:
I would not be surprised to see an eye by late tonight or early tomorrow.


Seems to me like Isaac has finally started turning around one main centre. Convection starting to look much more organised. Also, the lower and mid=level circulations are becoming more stacked. Still not perfect, but getting there.

850mb:



500mb:

Member Since: Posts: Comments:
Quoting jeffs713:

That isn't at the center. That is at a static location as the storm approaches... and not an entirely unexpected thing.


I would hate to be in the centre.
Member Since: Posts: Comments:
Still no obvious northwards movement. Isaac has been moving west for 3 days, now. The NHC track forecast takes it through the middle of Haiti. Seem likely to you?


Member Since: Posts: Comments:
Quoting 69Viking:


About 10 miles to my East, not good! But it's 6 days out, plenty of time to go to somebody elses house, NOT that I wish that on anyone! We need some shear in the GOM to keep this thing weak though we don't need the rain either, most of Florida is pretty saturated already.


I think some people wished for rain a bit too hard... At the start of the year, many people were wishing very hard for drought breaking rains...
Member Since: Posts: Comments:
Quoting MississippiWx:


At 117 hours, a ridge at 500mb is directly to the east of Isaac. It makes plenty of sense. I've been stating the past few days that if Joyce is strong enough, an area of ridging can bubble up between Isaac and Joyce which could shove Isaac farther to the west than originally thought. It looks like that could occur.

Exactly. With the Trof-ridge-trof pattern in the N atlantic the subtropical ridge will want to fill in under the base of that western trof since it has nowhere else to really exist.
Member Since: Posts: Comments:
Quoting doabarrelroll:

He does deserve it. He come on here and is often condescening. I have no problem with that but when he is wrong he doesnt apologize to those he talked down to. The other thing is people on here say "poor levi" as if he is still that 13 year old kid who came on here in 2007 hes 18/19 he is a man he can take the heat
Levi is one of the best people on here , we dont all agree or disagree with peoples opinions but thats what a blog is giving your opinion and sharing ideas/analysis not this back and forth bickering and complaining !!
Member Since: Posts: Comments:
357. emguy
GFS track record for Isaac has been thus so far...
- 00Z and 06Z have been the easternmost...
- 12Z and 18Z have been the westernmost...

Trust the saying, "There's your story and there is his story...and the truth rests somwhere in between".

Since the overall model envelope for GFS Operational has not really changed between the flip flops...it's a safe bet Isaac will go slightly west of the 00Z and 06Z runs, yet east of the 12Z and 18Z runs we've been seeing.
Member Since: May 21, 2008 Posts: 0 Comments: 626
Quoting Chiggy:
12Z GFS @ 126hrs, approaching AL/FL border.. WOW!


Alignment... And may still move further west...NHC is on top of this. European was on it all along.
Member Since: Posts: Comments:
Quoting doabarrelroll:

He does deserve it. He come on here and is often condescening. I have no problem with that but when he is wrong he doesnt apologize to those he talked down to. The other thing is people on here say "poor levi" as if he is still that 13 year old kid who came on here in 2007 hes 18/19 he is a man he can take the heat


What???!!! Levi is not condescending to anyone, I have watched him on here for years, he is in discussions with everyone else on here

just because he disagrees with someone on something, does not make him condescending
Member Since: Posts: Comments:
Quoting AussieStorm:
Lanyu, Orchid Island, Taiwan.

08/23 22:00 994.0mb >>>> 08/24 00:15 976.2mb.

17.8mb drop in 2hrs 15mins. WHAT THE!!!!!!!!!!!!!


That isn't at the center. That is at a static location as the storm approaches... and not an entirely unexpected thing.
Member Since: Posts: Comments:
Quoting NICycloneChaser:


Interesting that it doesn't strengthen the storm as much as previous, more easterly runs. That said, I wouldn't like to see a hurricane get that much space in the GoM.


The GFS seems to have picked up on the internal structure issues and only gradually strengthens Isaac until he reaches the Gulf.
Member Since: July 15, 2006 Posts: 17 Comments: 10160
Quoting Minnemike:


Hilarious Mike.
Member Since: Posts: Comments:
Quoting Joshfsu123:


Landfall near Destin on this run...


About 10 miles to my East, not good! But it's 6 days out, plenty of time to go to somebody elses house, NOT that I wish that on anyone! We need some shear in the GOM to keep this thing weak though we don't need the rain either, most of Florida is pretty saturated already.
Member Since: Posts: Comments:
Quoting coffeecrusader:
Are these the 12z GFS runs that have shifted west or are they out yet?
all images posted by me are the 12z gfs precip mslp runs out to 144 hr i go no further than that hour
Member Since: Posts: Comments:
GFS 90 hours




GFS 132 hours

Member Since: Posts: Comments:
Lanyu, Orchid Island, Taiwan.

08/23 22:00 994.0mb >>>> 08/24 00:15 976.2mb.

17.8mb drop in 2hrs 15mins. WHAT THE!!!!!!!!!!!!!

Member Since: Posts: Comments:
Quoting hydrus:
I would not be surprised to see an eye by late tonight or early tomorrow.

He still has plenty of work to do. Have to get that CDO over him, and wrapped around the COC. Right now, the mean circulation is roughly between the two spots of convection
Member Since: Posts: Comments:
(click to enlarge)



Member Since: July 14, 2009 Posts: 51 Comments: 1721
344. CJ5
Quoting Tropicsweatherpr:
There is the 12z GFS landfall.



Ouch, that looks to be around Destin. My favorite place, sad.
Member Since: Posts: Comments:
Quoting Joshfsu123:
Stronger storm will move more north into the weakness...


The weakness still has to be in the right place at the right time, and stay long enough. Or you can get a situation like happened with Ike or Betsy.

Betsy (one of the more extreme examples of a storm statrting to feel a weakness and then missing it):
Member Since: August 26, 2006 Posts: 16 Comments: 4766
Quoting Minnemike:
lOL, is that from the Love Boat?
Member Since: Posts: Comments:
Quoting MississippiWx:
GFS has shifted way west, in line with 00z Euro.



Interesting that it doesn't strengthen the storm as much as previous, more easterly runs. That said, I wouldn't like to see a hurricane get that much space in the GoM.
Member Since: Posts: Comments:
I would not be surprised to see an eye by late tonight or early tomorrow.
Member Since: Posts: Comments:
339. HCW
Models and Current NHC track

Member Since: Posts: Comments:
Hey all! Is the UKMET model any good? Thanks! :)
Member Since: Posts: Comments:
Quoting cchsweatherman:
It appears that the structure and organization of Tropical Storm Isaac is finally approving as a circulation center has become better defined and banding continues to develop on both the western and eastern sides of the storm. In addition, convection has become better organized around the center as deep convection has finally formed around the northeast quadrant of the storm and become far more symmetrical than this time yesterday.

Also of note is that the storm appears to making more of a WNW track over the past several hours at about what I estimate to be roughly 280 degrees. I believe that Tropical Storm Isaac will be taking a more WNW course throughout the day and eventually begin turning more NW in about 24 hours time as the western flank of the subtropical ridge should begin eroding at this time.
how have you been . Great to see your analysis again
Member Since: Posts: Comments:
Quoting 69Viking:

Thanks for answering...even thought I don't necessarily like the answer:)
Member Since: Posts: Comments:
Quoting cchsweatherman:
It appears that the structure and organization of Tropical Storm Isaac is finally approving as a circulation center has become better defined and banding continues to develop on both the western and eastern sides of the storm. In addition, convection has become better organized around the center as deep convection has finally formed around the northeast quadrant of the storm and become far more symmetrical than this time yesterday.

Also of note is that the storm appears to making more of a WNW track over the past several hours at about what I estimate to be roughly 280 degrees. I believe that Tropical Storm Isaac will be taking a more WNW course throughout the day and eventually begin turning more NW in about 24 hours time as the western flank of the subtropical ridge should begin eroding at this time.


Disagree on the WNW path right now.., no way!
Member Since: June 26, 2012 Posts: 0 Comments: 297
334. CJ5
Quoting AAPLTrader:
PalmBeach: Regarding LEVI I find his posts informative, but if his forecasts for past 3 days is wrong, he is subject to critcism. Nothing personal,just a fact.Also,I still rank LEVI and KMAN as the best bloggers on this blog.


This is about the 4th post about Levi from you. Enough already! If you have a serious problem with him then produce your facts to counter what he has said. If you have no facts but just feel the need to point out he appears wrong then stop. You add nothing to the blog.
Member Since: Posts: Comments:
It appears that the structure and organization of Tropical Storm Isaac is finally improving as a circulation center has become better defined and banding continues to develop on both the western and eastern sides of the storm. In addition, convection has become better organized around the center as deep convection has finally formed around the northeast quadrant of the storm and become far more symmetrical than this time yesterday.

Also of note is that the storm appears to making more of a WNW track over the past several hours at about what I estimate to be roughly 280 degrees. I believe that Tropical Storm Isaac will be taking a more WNW course throughout the day and eventually begin turning more NW in about 24 hours time as the western flank of the subtropical ridge should begin eroding at this time.
Member Since: Posts: Comments:
Quoting reedzone:


It doesn't make sense to me when the weakness on the steering layers map show a turn NE if the storm gets near Tampas latitude. Not ENE to my house, but NE towards GA.


At 117 hours, a ridge at 500mb is directly to the east of Isaac. It makes plenty of sense. I've been stating the past few days that if Joyce is strong enough, an area of ridging can bubble up between Isaac and Joyce which could shove Isaac farther to the west than originally thought. It looks like that could occur.

Member Since: July 15, 2006 Posts: 17 Comments: 10160
There is the 12z GFS landfall.

Member Since: Posts: Comments:
Quoting weathermanwannabe:


Could be as well.............Unfortunately, we do not know exactly what will happen intensity wise once he makes the Gulf (or not if he trends over Florida). Nervewracking when they approach the US from this angle and we try to figure which side of Florida, or, up the middle..........We will have to leave that to the NHC 3-day track come the weekend and see what happens.
Yep, I have all the trust in the world in the 3 day track. They usually nail that one. Sans Debby.
Member Since: Posts: Comments:
Last night, Kori looked at the soundings and noted that the ridge steering Isaac was stronger than expected. It looks like the models may be picking up on that data with their westward shifts. Hats of to Kori.
Member Since: August 2, 2006 Posts: 46 Comments: 11666
Quoting KEEPEROFTHEGATE:
HR 144 FINAL



Landfall near Destin on this run...
Member Since: Posts: Comments:
Are these the 12z GFS runs that have shifted west or are they out yet?
Member Since: Posts: Comments:
Idol worship? That's the first time I've defended him other than yesterday when he was being treated very rudely by one of our other very good bloggers. Chicklit wow he was wrong with the Debbie; along with everyone else in the world. Get the tar and feathers; immediately. If you think it's nauseating to hear people say they appreciate his hard work and that people think he's smart then that sounds like a you problem. You almost always post nothing but maps, at least he has something of value to add.
Member Since: Posts: Comments:
Quoting WDEmobmet:


Well I kind of understood that, and I think you answered me in the last of your comment, but I was more wondering why it would fly almost due north of the system trailing somewhat behind it in Longitude. I would think that it would sample air out ahead of its projected path as well. Thanks jeffs713


No problem. It flies well north of it, as the area in front of the storm isn't influencing the direction much. Tropical cyclones want to go poleward by nature. The only thing preventing Isaac from going poleward right now is the strength and extent of the ridge.
Member Since: Posts: Comments:

Viewing: 374 - 324

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34 | 35 | 36Blog Index

Top of Page

About

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

Local Weather

Mostly Cloudy
75 °F
Mostly Cloudy