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 TreasureCoastFl:


I think the faulty levies breaking and N.O. being below sea level contributed to the damage that Katrina did. Katrina hitting a different area, which actually she did (Mississippi, right?) didn't cause as much damage indirectly as she did in N.O.


Katrina only wiped out nearly every building on the MS Coastline, leaving most of them with nothing but a slab. That's a stretch of coast line some 60-70 miles long.
Member Since: July 15, 2006 Posts: 17 Comments: 10156
Quoting TreasureCoastFl:


I think the faulty levies breaking and N.O. being below sea level contributed to the damage that Katrina did. Katrina hitting a different area, which actually she did (Mississippi, right?) didn't cause as much damage indirectly as she did in N.O.



i think the same thing... but i try n keep it to myself :)
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WOW!!

112.5 knots* (~ 129.4 mph*)
Category Three Hurricane

hahahaha
Member Since: September 6, 2007 Posts: 0 Comments: 5695
Quoting Grothar:


Might be ready to make the WNW turn.
I don't know, I thought it would be on that heading by now. Lets see 8AM it was at 15.4N and at 11AM it was at 15.6N, if it's not north of that last point then it is still moving westward.
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Quoting SFLWeatherman:
Bernie Rayno It may be going to S FL
Link


But that's InAccuweather. I would believe my dog's forecast before I would believe them.
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Quoting Bluestorm5:
Is recon plane going into Isaac or landing at St. Croix?



That second blob that has fired up during the last few hours over the Turks and Caicos islands sure looks interesting. Might be able to see how conditions further north of Isaac are panning out and how in the short term they may influence steering patterns.
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Quoting aquak9:
Katrina hitting a different area, which actually she did (Mississippi, right?) didn't cause as much damage indirectly as she did in N.O.

googlemap waveland, ms. Look at the slabs.

Those were people's HOMES.


Yikes. I didn't mean to downplay the damage in Mississippi. I just meant that people seem to focus on N.O. when talk of Katrina gets mentioned and I think the faulty levees played a huge part in that mess.
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Quoting nrtiwlnvragn:


It could be an upper air mission. HRD is showing a C130 flight in tandem with the G-IV this afternoon.




Hmm, thanks nrti. Did not realize C-130's that Sure hope they will at least do a couple center fixes while out there.
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About an hour until we start getting the 12Z ECMWF. I personally expect a slight shift eastward, which should put it in a fairly impressive agreement with the 12Z GFS. Starting to look like an easter GoM storm.
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614. wpb
12gfs along north coast of cuba
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Quoting floridaboy14:
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



Some bits are flat, some aren't. Gustav went over the mountainous extreme western tip of Cuba and its eye wall collapsed. Otherwise, it could have been a cat 4 at landfall.
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Quoting GTcooliebai:
Convection seems to be waning but expanding in size also note the dip in the GOM trying to eat away at the Ridge.

..GT what do you think will happen around our area?
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Bernie Rayno It may be going to S FL
Link
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One of the most beautiful storm I've tracked... Igor
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Quoting GTcooliebai:
For the 2PM advisory Isaac's forward speed down to 10 mph. any takers?


Might be ready to make the WNW turn.
Member Since: July 17, 2009 Posts: 63 Comments: 23725
Quoting LargoFl:
Tampa Bay 7-day


yea I hope people on the west coast of FL are not letting their guard down with this west shift; Isaac is huge, so we will still likely feel a lot of impacts from this storm and that is even if the track stays west; which IMO is 50/50 best at this point
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Quoting TomballTXPride:

I'm with you.


Of course you are
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Katrina hitting a different area, which actually she did (Mississippi, right?) didn't cause as much damage indirectly as she did in N.O.

googlemap waveland, ms. Look at the slabs.

Those were people's HOMES.
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Quoting Chiggy:
Anyone see a "center" roughly at 66.5W/15N? Thx
If there is one that extends that far south it will probably be very broad as the last center fix was at 15.6N.
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Quoting LoveThemCanes:


sorry if a stupid question, but couldn't this occur then with the Typhoons? How far do the two storms need to be to begin the dance?


Could happen but not this time...

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Quoting Chiggy:
Anyone see a "center" roughly at 66.5W/15N? Thx


yeah but maybe a bit further S though umm maybe like near 14.8N
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Mid and low level becoming slightly better stacked, I think, and at least half a degree S of NHC official, no surprise there.

Venezuelan radar




Not much detail there.


Way SW of official.


same




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Gustav 2008

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those of us here in milton/pensacola area are deffinatly watching the storm thanks for you guys continued updates.



"SKY"
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Quoting Hurricanes101:


steering currents do not stay constant, I think we are already starting to see the WNW movement now
Actually the sterring currents have been fairly steady for 5 days or so witha decided wsw direction at mid-level and w at high level.This is the first sign of a westerly mid-level flow and it may stay that way for a day or more before a wnw/nw track starts. IMO!!
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Quoting bocahurricane:


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


Boca, don't put your guard down yet. As we all know, the East side of the storm can have a lot of severe weather in it. It is possible that Isaac could slow down if it does move to the west coast. Isaac should stay a large system regardless of its intensity. Many models are still showing the possibility of very intense weather on the Southeast Coast of Florida.
Member Since: July 17, 2009 Posts: 63 Comments: 23725
so, where i live, is squirrel central... but when i took the dogs out about 5 mins ago, i didn't even see a single one. not even a bird singing. im on the east coast, and i know im probably am just being crazy, but im just saying......
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Tampa Bay 7-day
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Quoting HoustonTxGal:



Largest Atlantic hurricanes by gale diameter

Rank Storm Season Diameter
(mi) (km)
1 Igor 2010 920 1,480
2 Olga 2001 863 1,389
3 Lili 1996 806 1,296
4 Karl 2004 777 1,250
5 Helene 2006 748 1,204
6 Irene 1999 719 1,157
7 Gabrielle 1989 690 1,111
8 Florence 2006 690 1,111
9 Wilma 2005 662 1,065
10 Keith 1988 633 1,018
11. Grace 1991 633 1,018






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lots of surf action @ pr SE coast

Link
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592. wpb
Quoting GetReal:


HWRF starting to run....
link
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For the 2PM advisory Isaac's forward speed down to 10 mph. any takers?
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Hmmm...

HPC

ALSO OF INTEREST WILL BE AN UPPER LEVEL TROUGH AXIS EXTENDING FROM
THE EASTERN GULF UP THROUGH THE EASTERN U.S. THIS TROUGH WAS
JUXTAPOSED WITH AN OLD AND BROAD FRONTAL ZONE RESIDING IN THE
SOUTHEAST STATES. SATELLITE LOOPS SEEM TO SUPPORT THE MODEL
FORECASTS THAT FORM A WAVE ALONG THIS FRONT...AND ALLOW A
VORTICITY MAXIMUM TO LIFT UP THE EAST COAST TOWARD THE MID
ATLANTIC BY SATURDAY EVENING. THE MODELS HAVE BEEN SIMILAR IN
HANDLING THIS RELATIVELY WEAK VORTICITY MAXIMUM. THE GFS WAS VERY
CONSISTENT FROM ITS 06Z TO 12Z RUN...AND IS PREFERRED AS IT IS
SLOWER TO LIFT THE FEATURE NORTHWARD BENEATH SHORTWAVE RIDGING
OVER THE OHIO VALLEY. IN THE WAKE OF THIS FEATURE...A WEAK TROUGH
AXIS MAY REMAIN ACROSS NORTHERN FLORIDA AND THE EASTERN
GULF...WHICH COULD HAVE SOME IMPACT ON THE EVENTUAL TRACK OF ISAAC
IN THE MEDIUM RANGE.
Member Since: August 24, 2010 Posts: 0 Comments: 459
Quoting TomballTXPride:

My guess is more people are probably familiar with Katrina given how notorious it has become. I couldn't name a single person who doesn't know what she was or what she did.

But yes, Alex and IKE were larger, to name a few. In the wind field diameter category, that is.


I think the faulty levies breaking and N.O. being below sea level contributed to the damage that Katrina did. Katrina hitting a different area, which actually she did (Mississippi, right?) didn't cause as much damage indirectly as she did in N.O.
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With the naming of Joyce today, we are tied with 2005 for names. Tropical Depression 12 formed on this date in 2005, but wasn't named Katrina until the 24th. We obviously haven't had storms as intense as the ones in 2005, but we are keeping up name-wise.

10-3-0
Member Since: July 15, 2006 Posts: 17 Comments: 10156
hey anyone has a Sattelite pic of when Gustav was in the same location please post it
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Anyone see a "center" roughly at 66.5W/15N? Thx
Member Since: June 26, 2012 Posts: 0 Comments: 297
if isaac keeps pushing west, the odds of it stalling over the panhandle increase with every hour the steering trough lifts out
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Quoting AussieStorm:
I hope I don't wake up to find TS Isaac is Hurricane Isaac.


same thing happened yesterday but
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Convection seems to be waning but expanding in size also note the dip in the GOM trying to eat away at the Ridge.

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Anyone on here tell me what D-Value is?
Member Since: September 6, 2007 Posts: 0 Comments: 5695

Still a bursting convective pattern with waning convection strength currently.

VERY disorganized mess of a TS right now.
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Quoting AllStar17:


Hopefully to Isaac...I don't think they'd be gathering observations if they are only going to land in St. Croix. Why even bother?

`they may need fuel
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Quoting Felix2007:

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.


sorry if a stupid question, but couldn't this occur then with the Typhoons? How far do the two storms need to be to begin the dance?
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Quoting midgulfmom:
kinda like my washing machine when it's overloaded to one side....see Moms have real life scientific applicable experience.

lol yeah I guess
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Quoting TomballTXPride:

My guess is more people are probably familiar with Katrina given how notorious it has become. I couldn't name a single person who doesn't know what she was or what she did.

But yes, Alex and IKE were larger, to name a few. In the wind field diameter category, that is.


2008 produced both the largest Atlantic tropical cyclone on record up to that time (Ike, I think Alex may have been bigger) and the smallest (Marco).
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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.