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 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: 11666
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Quoting HoustonTxGal:


EURO still go way west


UKMET is not the Euro. WU isn't allowed to post tracks for the ECMWF.
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421. CJ5
Quoting bbart99Miss:
I have been reading this blog for years now and this is my first post. My question is what is the chance that Isaac moves even further west? My house sits about a 1/8 of a mile from the Gulf in Ocean Springs MS. What is chance that Isaac moves even further west and puts Mobile and South Miss on the bad side?


There is a good chance that COULD happen. It is too early to tell but I would check frequently. The path is not certain and no landfall predictions are even the radar yet.
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Going to borrow Levi's map from his site to illustrate a point. This is about a day old, but still validates my point. You can see Isaac's and Joyce's low pressure imprint on this map, with an area of red in between them. This is a 24 hour pressure change map and you can see where Isaac had been 24 hours before (the red spot). The map is not necessarily showing that a ridge had developed between the two storms, but is indicative that higher pressure exists between the storms. It's fairly obvious that outside of the two low pressure centers, higher pressure would exist. However, as both storms get stronger, the pressure difference between the centers of low pressure and the space between them is going to increase causing an area of even higher pressure relative to the storms. Also, the flow around the storms, as long as they are close enough and strong enough, would promote anticyclonic flow. Isaac would induce a southwest to northeast flow on his eastern flank, while Joyce would induce a northeast to southwest flow on her western flank. The result is an anticyclonic flow in between. It is certainly possible that this can occur as long as Isaac and Joyce stay relatively close and Joyce can find enough favorable conditions to strengthen into at least a strong tropical storm. We'll see.

Member Since: July 15, 2006 Posts: 17 Comments: 10160
yes
Quoting AussieStorm:

Yes, especially when he's not here to defend himself.
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Quoting Abacosurf:
If by providing you with correct information means putting you down than perhaps.

Let's move on please....

Quoting thewindman:


Agreed. 992mb is like a heavy summer thunderstorm the only difference is it will be raining for 4-5 hours versus 30 minutes


Having said that, the gfs isn't very good with intensity, euro has a cat 3 to a 4
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Quoting CJ5:


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.


This blogger is just stating a fact. Yes it looks like Levi was wrong at this time based on current forecast. Of course this can change. It's all good.
Maybe I'm missing something but I don't see where this blogger is being trollish towards Levi. In fact he mentions that Levi is one of the best bloggers on here.
That's whats wrong with kids now a days....y'all cant be told your wrong. Everyone gets a medal..no one loses... Well that's not real life and we all make mistakes. In real life sometimes you lose, things don't go as planned.
I am trusting that Levi will be able to handle this just fine!
That being said I enjoy your posts as well :-).

Signed,
Yes I'm a little crumugeny, this site does that to me at times...
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Quoting jeffs713:

Well, yes, and also no. Heaven because you aren't in the eyewall of a hurricane. Hell because you just went through the eyewall... and there is not a way out. You either have to go through the other side of the storm, or wait until it hits land.

Talk about being stuck in a bad situation, with no way out. (the best analogy I can think of is being in your car, with a jack-knifed 18-wheeler accident ahead of you... you can't go forward, but the guy behind you isn't stopping)

I'm waiting for that weather stations next update then going to bed.
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EURO still go way west
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413. CJ5
Quoting opal92nwf:

I live within 15 min. of Destin, (if traffic is good)


I'm jelly. Keep you eye out, just in case.
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Quoting thewindman:


Agreed. 992mb is like a heavy summer thunderstorm the only difference is it will be raining for 4-5 hours versus 30 minutes

You must have very interesting thunderstorms.

You've never been through a hurricane, have you?
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Quoting Seflhurricane:
NOT AT ALL


well keep it to yourself

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It is possible that Isaac could remain no stronger than a tropical storm over its entire track. There can still be significant flooding and coastal erosion effects from such s storm, but the wind damage would be limited. I am not forecasting one way or the other just pointing out that the some models seem to be trending towards a weaker storm overall.
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Quoting MississippiWx:


The GFS seems to have picked up on the internal structure issues and only gradually strengthens Isaac until he reaches the Gulf.


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.
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Quoting coffeecrusader:
Anyone have links to the 12z GFS? The ones I have are still showing the 06z. Also, when does the 12z ECMWF usually come out (1-2pm?). Thanks.


Here you go:

Link
Member Since: August 10, 2010 Posts: 2 Comments: 1971
Quoting AussieStorm:

to get to the center and then to get to the other side would be hell, but the centre would be like heaven after going through hell.

Well, yes, and also no. Heaven because you aren't in the eyewall of a hurricane. Hell because you just went through the eyewall... and there is not a way out. You either have to go through the other side of the storm, or wait until it hits land.

Talk about being stuck in a bad situation, with no way out. (the best analogy I can think of is being in your car, with a jack-knifed 18-wheeler accident ahead of you... you can't go forward, but the guy behind you isn't stopping)
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I have been reading this blog for years now and this is my first post. My question is what is the chance that Isaac moves even further west? My house sits about a 1/8 of a mile from the Gulf in Ocean Springs MS. What is chance that Isaac moves even further west and puts Mobile and South Miss on the bad side?
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Quoting jeffs713:

Not really for tropical systems. Decent as part of an overall package, but it doesn't handle most tropical systems well.


Thank you!! :) I was wondering why it was going a different way...
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Anyone have links to the 12z GFS? The ones I have are still showing the 06z. Also, when does the 12z ECMWF usually come out (1-2pm?). Thanks.
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ape- ya beat me to it
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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.
If by providing you with correct information means putting you down than perhaps.

Let's move on please....

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Quoting mcluvincane:
Very week storm at landfall per the gfs


Agreed. 992mb is like a heavy summer thunderstorm the only difference is it will be raining for 4-5 hours versus 30 minutes
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Quoting MississippiBoy2:
=Levi has taken a beaten,undeserved,all he is doing is trying to help ones that don't realy know.What should happen is that the ones that give their thoughts on a storm don't bash ones that give their thoughts that don't agree with theirs.We all need to help one another during the season.Just my thoughts.


Very true... Even Dr. Masters has to adjust his forecasts... An noone is going to critisize him for that... As a Met. he depends on daily analisys of models and human technology... and all models during the last 5 days have adjusted their forecasts...
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Quoting pottery:
I'm not so sure that Isaac is going to turn north anytime soon.
Not seeing that in the next 48hrs, myself.


Then would have better time/resources for strengthening?
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Quoting GeorgiaStormz:
Is anyone else here tired of this Levi discussion?
NOT AT ALL
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Quoting CJ5:


Ouch, that looks to be around Destin. My favorite place, sad.

I live within 15 min. of Destin, (if traffic is good)
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Quoting GeorgiaStormz:
Is anyone else here tired of this Levi discussion?


Absolutely. Good forecaster, but the world of meteorology doesn't revolve around him. Or at least it shouldn't. And I'm sure he'd agree with me there.
Member Since: August 10, 2010 Posts: 2 Comments: 1971
Quoting Tropicsweatherpr:
There is the 12z GFS landfall.



The only good news (for me) about this run: plenty of time to shift east or west.
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Quoting GeorgiaStormz:
Is anyone else here tired of this Levi discussion?

Yes, especially when he's not here to defend himself.
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Quoting cchsweatherman:


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.



Good to see you and everyone else here again. Been busy with school and working through some health issues that are improving now.
whats your analysis for Southern Florida and the florida keys.
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Quoting GeorgiaStormz:
Is anyone else here tired of this Levi discussion?


Count me out.
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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.



Joyce's ridge-building warm advection is to its east; you can see the ridge on the prog chart developing in that location. In fact, if Isaac gets strong enough, it will be responsible for ridge building to its east. The primary effect of that will be to deflect Joyce further to the north. So bottom line, its not Joyce shoving Isaac, its Isaac shoving Joyce.
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Very week storm at landfall per the gfs
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Quoting jeffs713:

Oh, for sure. Any storm that gets symmetric like that is sure to be a "hell on earth" near the center.

to get to the center and then to get to the other side would be hell, but the centre would be like heaven after going through hell.
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GFS shows 992mb at landfall. Pretty uneventful with 60 mph wind at most it appears based on that pressure. Biggest deal could be potential flooding but should be a lot less than this past June
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Quoting connie1976:
Hey all! Is the UKMET model any good? Thanks! :)

Not really for tropical systems. Decent as part of an overall package, but it doesn't handle most tropical systems well.
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Someone, anyone s the UKMET model any good? Just curious...thanks... :)
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Quoting MississippiWx:


The GFS seems to have picked up on the internal structure issues and only gradually strengthens Isaac until he reaches the Gulf.


Agreed. But even in the GoM it isn't strengthening Isaac as much as it has been. This run shows landfall at around 990mb, previous runs over the last 24 hours have shown 980 or less.
Member Since: August 10, 2010 Posts: 2 Comments: 1971
Quoting Tropicsweatherpr:
There is the 12z GFS landfall.


That is almost literally right over where I live...
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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.
i disagree he tries to explain how he got to that point but i have been here for years and have never seen him be condesending as you state but we have a tropical storm to discuss and the potential for a US landfall so lets move on !!!!!
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381. CJ5
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 don't take his counter arguments personally so I cannot comment on that. I also don't have any special relation to him or his forecasts, nor do I have with anyone else. That being said this constant bashing should stop, no matter who it is. It has driven off many good bloggers from this site over the years.
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380. wxmod
Quoting 954FtLCane:


Orchid Island (Yami language: Ponso no Tao or Pongso no Tao; Chinese: 蘭嶼; pinyin: Lán Yǔ; Pe̍h-ōe-jī: Lân-sū) is a 45 km² volcanic island off the southeastern coast of Taiwan Island and separated from the Batanes of the Philippines by the Bashi Channel of the Luzon Strait. It is governed as Lanyu Township of Taitung County.

The island is home to the Tao, an ethnic minority group who migrated to the island from the Batan Archipelago 800 years ago. The island is known to them as Ponso no Tao or Pongso no Tawo (island of the people) or Irala. Out of a total current population of 4,000, approximately 2,400 belong to the aboriginal Tao community and the remaining 1,600 are mainly Han Chinese. In neighboring Philippines the island is referred to as Botel Tobago.

The Lanyu nuclear waste storage facility was built in 1982. The plant receives nuclear waste from Taiwan's three nuclear power plants operated by state utility Taiwan Power Company (Taipower). About 100,000 barrels of nuclear waste from the nation’s three operational nuclear power plants have been stored at the Lanyu complex.[1] In 2002 and 2012, there were major protests from local residents, calling on Taipower to remove the nuclear waste from the island.[2]


Hmmmmmm....A nuclear dump and a major hurricane....


Great :<
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Doing good now
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This bowling ball we call Issac doesnt look like he's even trying to make that turn towards WNW... I could be wrong though.. Honestly folks in LA better keep 2 eyes on this one...
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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.

Floyd in 1999 had Gert off to his east. Created the same situation. I think it contributed to the landfall in NC after the Bahamas.
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Is anyone else here tired of this Levi discussion?
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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


Condescending?! Total bull. He is everything but that. Let's talk Isaac.
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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.



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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.