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 sunlinepr:

That storm is massive, even by WPac standards.

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Tembin....Taiwan.... is going to get hammered...



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Quoting cchsweatherman:


That is a plane performing a dropsonde mission of the atmosphere around the storm. It's probably picking up those winds in the sheared thunderstorms just off the northern coast of the Dominican Republic from what I can tell.

I think this is the next recon plane actually, the G-IV plane departs at 130pm
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Quoting MississippiWx:
The fact that the GFS has Isaac stalling over the Panhandle sends a red flag to me that there must not be much of a trough/weakness to the north. Add in the shift to the west on the 12z run, I'm a little more concerned at a fairly strong hurricane headed to the Panhandle of FL. With a final landfall still 5+ days out, plenty of things can change.


HAHA.., I was just about to say that! Thx, There is a remnant of Issac on Gulf coast even at 300hrs (7 days after landfall...
Member Since: June 26, 2012 Posts: 0 Comments: 297
700-850mb



500-850mb


There is no doubt that Isaac is going to go much more further west, until it reaches the NW Caribbean.
Member Since: July 4, 2005 Posts: 204 Comments: 8802
Quoting AtHomeInTX:


His character was named Isaac on a show called the love boat.


OMG now I feel old. Another another note I just got back from BJ's where gas lines were 5 cars deep and water was flying off the shelf. I bought some extra D batteries but besides that it was just stocking up on stuff for my sons birthday party on Saturday. I think east south florida once again dodged another storm. I wish all of those in its path good luck. Now back to lurking
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Quoting jeffs713:

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.


EXACTLY,.... thanks for clearing that up. LOL
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517. TXCWC
Quoting WthrWonk:
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.


I agree with track - my thinking is Mobil to Pensacola area as EURO and GFS SEEM to have come into an agreement on this area - we shall see what Euro says in a couple of hours. Do not see CAT 5 or even 4 but CAT 3 I believe is a possibility. As EURO and SHIP has been showing.
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Quoting KEEPEROFTHEGATE:
Kind of interesting how we have 2 storms traveling together at the same time as West Pac.
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Quoting HoustonTxGal:
What is the distance between Isaac and Joyce? Anyone know?


1600 miles. Ish.
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Quoting AtHomeInTX:


His character was named Isaac on a show called the love boat.


A very annoying show....
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Joyce has made strides today as well.

Member Since: July 15, 2006 Posts: 17 Comments: 10156
Quoting MississippiWx:
The fact that the GFS has Isaac stalling over the Panhandle sends a red flag to me that there must not be much of a trough/weakness to the north. Add in the shift to the west on the 12z run, I'm a little more concerned at a fairly strong hurricane headed to the Panhandle of FL. With a final landfall still 5+ days out, plenty of things can change.
if it gets south of cuba that could be bad also. the ssts are warm and deep and western cuba is very flat and once it hits the bathtub hot gulf waters, bad things can happen
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Quoting LargoFl:
your right


People on the blog get nervous about NOLA and I understand that. But folks often forget that the poulation of Southern Florida has a million more people than the entire state of Louisiana and they are sandwhiched on a 12 mile wide stretch between the everglades and the Atlantic
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Bolaven the monster....

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Isaac is priming, gonna get a kick-start soon.. worry for some folks in the path :(
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Quoting AussieStorm:

1550miles


Thank you
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Quoting VAbeachhurricanes:
HH far from center but finding these winds?

45.3 knots (~ 52.0 mph)
Tropical Storm


That is a plane performing a dropsonde mission of the atmosphere around the storm. It's probably picking up those winds in the sheared thunderstorms just off the northern coast of the Dominican Republic from what I can tell.
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Quoting DocBen:
Are Isaac and Joyce close enough to interact with the tracks? Can't recall the name of the 'dance' but the one where they tend to go counterclockwise to each other. Would push joyce north and Isaac more west (keeping south)

It's called Fujiwhara Effect and no I don't think they're close enough, and Joyce is probably too small anyways to have an effect on huge Isaac.
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Quoting HoustonTxGal:
What is the distance between Isaac and Joyce? Anyone know?

1550miles
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Quoting 10Speed:
I'm going to be real surprised if Isaac ends up being where the NHC currently says it's going to be at the 8 PM. I'm becoming inclined to believe Isacc might even go a tad to the WSW for a bit.
It does seem if the whole system is lining up than there is no way the center can be north of 15 to 15.5 at this time...so a slight adjustment left may still be in the cards.
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Quoting Hurricanes101:


they are also still at 26,000 ft


Yeah thats SFMR with error correction
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The fact that the GFS has Isaac stalling over the Panhandle sends a red flag to me that there must not be much of a trough/weakness to the north. Add in the shift to the west on the 12z run, I'm a little more concerned at a fairly strong hurricane headed to the Panhandle of FL. With a final landfall still 5+ days out, plenty of things can change.
Member Since: July 15, 2006 Posts: 17 Comments: 10156
This says it all really....
Lanyu, Orchid Island, Taiwan.





Latest Obs.... 08/24 00:30 975.5mb


Keep an eye on this weather station, I will get the eye of Tembin.

Goodnight all. Get prepared if your in the cone or at least make a plan. I hope I don't wake up to find TS Isaac is Hurricane Isaac.
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Quoting ApeinaCrate:
i thought it was funny too ;)
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Quoting cchsweatherman:


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.


nice, looks like Isaac has slowed
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Quoting oracle28:


XTRP model is pointing to Central America. What a relief for us in the U.S.

We dodged a bullet again, thank goodness.



LOL i don't know if your serious or not... but that model only shows the current direction of the storm.
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Quoting Clearwater1:
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.


Good luck finding streets you can drive in.
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Quoting weaverwxman:
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.
your right
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What is the distance between Isaac and Joyce? Anyone know?
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Quoting VAbeachhurricanes:
HH far from center but finding these winds?

45.3 knots (~ 52.0 mph)
Tropical Storm


they are also still at 26,000 ft
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There is still a lot of uncertainty with Isaac. The models can easily change depending on the intensification of Isaac. Land interation and the lack of land interation can cause sizable model shifts. I wouldn't get caught up too much with what the models are saying right now because they change.
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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.

Wow, not another one to worry about. Geesh is right. Kirk to Scotty, "beam me up"
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Please let us all talk tropics! I left this site last summer because of the stupid bickering...came back this morning for the first time in over a year...same crap. See you later...
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At least some of the models are showing it's not gonna be a monster. That's a relief by it self. I don't understand why the wind wont be very strong but i guess there's to many obstacles in the way of it maturing. This is just a guess, I'm just reading.

sheri
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Are Isaac and Joyce close enough to interact with the tracks? Can't recall the name of the 'dance' but the one where they tend to go counterclockwise to each other. Would push joyce north and Isaac more west (keeping south)
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I know this is off topic, but could someone tell me how to change my picture that show up beside my name when i post a question. Thanks in advance.
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Quoting Clearwater1:
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.


Because you have to endure an eyewall to get into the center.

If you can endure the eyewall, then why worry about the rest of the storm?
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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?


lol, that's an 80's tv show character, Isaac the bartender from the Love Boat
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Quoting thewindman:


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


Oh I wasn't necessarily referring to this specific case, just in general. Until Allison, tropical storms weren't taken as seriously here. Now they are.
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HH far from center but finding these winds?

45.3 knots (~ 52.0 mph)
Tropical Storm
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Quoting lottotexas:
Here we go again I & J repeat


That's K, not J. Joyce is gone over the Atlantic by then. The storm approaching Florida is Kirk which it forms from the wave just off of Africa.
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Quoting jeffs713:

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.


which reminds me, I have to get to bed early tonight since I have to wake up early tomorrow, because Id rather be early to work, than late, because if I am late then I have to stay late and there goes my shot of starting my weekend early
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I'm going to be real surprised if Isaac ends up being where the NHC currently says it's going to be at the 8 PM. I'm becoming inclined to believe Isacc might even go a tad to the WSW for a bit.
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Quoting oracle28:


XTRP model is pointing to Mexico. What a relief for us in the U.S.

We dodged a bullet again, thank goodness.


Not sure if serious....
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Member Since: July 4, 2005 Posts: 204 Comments: 8802
Issac stalling over N FL would be catastrophic.
Member Since: October 26, 2011 Posts: 0 Comments: 2651
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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About JeffMasters

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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