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 clwstmchasr:


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


This guy really wants a storm.
Member Since: October 26, 2011 Posts: 0 Comments: 2651
973. Relix
Quoting SouthTXWX:
Here is a zoom in of the alleged center, directly South of PR.  You can see the spin.




If that truly is the center its moving at like 305 degrees XD
Member Since: August 3, 2006 Posts: 0 Comments: 2639
971. FOREX
Quoting WindshearWillie:
A reminder to those who may need to evacuate:


TAKE YOUR PETS WITH YOU!


There was nothing worse than seeing pet cages in the homes and garages of the people of New Orleans containing skeletal remains. Think about being in a cage while storm surge slowly creeps up over your death trap and then remember it happens to pets in almost every storm.


Some people are stupid that way


And people that would leave their pets should not have pets in the first place.
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Kind of seeing what Levi described in his video, on the Euro. Haiti sends Isaac NW, but Cuba takes it back W. 
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969. MahFL
The G-IV is airborne.
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Quoting clwstmchasr:


They why did they put the 2:00 advisory at 16.0 with a heading of wnw?


Because recon wasn't in yet.

I was half-joking anyway, I very much suspect that it is moving WNW and it's still hard to tell where the dominant centre is, even with recon in.
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Quoting cheaterwon:


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

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


Isaac is still moving west per there words.


then why did they put WNW as the motion at 2pm?
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Still south of the guidance but further north than the 0Z run.

Member Since: October 26, 2011 Posts: 0 Comments: 2651
Quoting Relix:
WNW...

Feels so good to win that debate :p


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

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


Isaac is still moving west per there words.
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Quoting trey33:


I loaded up on roof caulk this am... got 4 tubes!!!


Hope you didn't forget the tarps if you think you'll need roof caulk, and wood strips and nails to nail the tarp down.
Member Since: August 22, 2009 Posts: 0 Comments: 3112
ECMWF 12Z @ 72 hours: looks pretty status quo to me.

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Here is a zoom in of the alleged center, directly South of PR.  You can see the spin.


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Quoting LargoFl:
I have to say something, I in my entire life, have been thru tropical storms yes, but i have never actually been in..a hurricane..not close anyway, closest was charley if i can remember right and that came in all the way down in sarasota..so..if i ask too many..what can we expect from issac questions..know why im asking them ok
Me neither, man. I just moved down here. It's exciting and scary at the same time.

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Member Since: July 4, 2005 Posts: 204 Comments: 8802
This is the average COC position of 4 sources...

Link



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Quoting LargoFl:
I have to say something, I in my entire life, have been thru tropical storms yes, but i have never actually been in..a hurricane..not close anyway, closest was charley if i can remember right and that came in all the way down in sarasota..so..if i ask too many..what can we expect from issac questions..know why im asking them ok
Punta Gorda not Sarasota :)
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Quoting StormTracker2K:
Euro is much further north this run.


Just watch this almost perfectly match the 12Z GFS...
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Convection has really dropped in all quarters last few hours. It's really struggling. Like suggested it must be ingesting dry air but I don’t really see it on WV.
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Quoting Levi32:
Will be very interesting to see exactly how far north the center is:



Levi. You do a great explaining everything on your Tropical Tidbits Video Presentation,to include all possibilities for public consumption.Keep up the excellent work!
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I hate it when NHC does that the LLCOC is not I repeat is not at 16N 66W RECON has pass through that already and saw nothing RECON is now heading toward the center
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Quoting LargoFl:
I have to say something, I in my entire life, have been thru tropical storms yes, but i have never actually been in..a hurricane..not close anyway, closest was charley if i can remember right and that came in all the way down in sarasota..so..if i ask too many..what can we expect from issac questions..know why im asking them ok


Prepare for the worst, hope for the best. Get out of Dodge if needed.
Member Since: August 22, 2009 Posts: 0 Comments: 3112
Euro is much further north this run.
Member Since: October 26, 2011 Posts: 0 Comments: 2651
Quoting LargoFl:
yes it would trey..we are in for an awful beginning of next week,wind, rain and stormy weather, local mets put the chance at 70%..monday morning it could be 100%


I loaded up on roof caulk this am... got 4 tubes!!!
Member Since: August 16, 2007 Posts: 0 Comments: 499
If the Center is at 16N then this is a more disorganized system then previously thought...just do not think it is that far north
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Quoting Bluestorm5:
Isaac is starting to get his act together...



Looks like more dry air problems to me...I thought the dry air issues were going away but obviously not.
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I have to say something, I in my entire life, have been thru tropical storms yes, but i have never actually been in..a hurricane..not close anyway, closest was charley if i can remember right and that came in all the way down in sarasota..so..if i ask too many..what can we expect from issac questions..know why im asking them ok
Member Since: August 6, 2011 Posts: 4 Comments: 33363
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Quoting Levi32:
12z GFS ensembles shifted west a bit.



I noticed ppl have been giving you a little bit of a hard time because of your forecase. Well, don't mind them at this point you could be right and your reasoning for your forecast is very logical, so I resppect it. At least you are honest enough to stick to your guns. Whether it proves right or not which is still a bit too early to tell you are the future of meteorology and IMO the future is bright because of ppl like you keep up the AWESOME job Levi
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Quoting clwstmchasr:
16.0N heading WNW. C'mon kid, tell the PHD's they are wrong.


15.6N, and we'll see about movement after the second fix...

;)
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Quoting StormHype:


That 16N is questionable. I can't see it farther N than 15.5N. Maybe they figure it doesn't matter at this point as it's so disorganized still.


you can see on satelitte presentation where the new converction is firing...its around 16N
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A reminder to those who may need to evacuate:


TAKE YOUR PETS WITH YOU!


There was nothing worse than seeing pet cages in the homes and garages of the people of New Orleans containing skeletal remains. Think about being in a cage while storm surge slowly creeps up over your death trap and then remember it happens to pets in almost every storm.


Some people are stupid that way
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Quoting RTSplayer:
Ok, what the hell is NHC smoking?


There's no way in hell the CoC is at 16N unless both the satellite and radar are broken...


So basically NHC is claiming the satellite is down-shifted at least a full degree, and the radar is just malfunctioning, right?


It is a tilted circulation still, its elongated from North to South I think you can see it on the RGB loops.

This circulation is stretched well over a degree in latitude giving the illusion that it could be further south.
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Quoting moonlightcowboy:


That's a fairly significant shift.
would not pay attention to that the 00Z models are going to be important with the g-IV info going into it
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Quoting StormHype:


That 16N is questionable. I can't see it farther N than 15.5N. Maybe they figure it doesn't matter at this point as it's so disorganized still.

Center Fix at 15.6 N.
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Quoting WDEmobmet:


I find it dangerous to "STICK TO YOUR GUNS" when people make decisions based on your his forecast
Dangerous???? Peoples decisions will be based off the NHC forecast not Levis. Levi is a student and enjoys teaching people about the weather and I have learned alot off of his videos. If there are some bloggers on here that listen only to Levi, then thats there right also. Like I said earlier the NHC is only official source, to get your tropical updates from.
Member Since: June 13, 2009 Posts: 0 Comments: 6706
I disagree with NHC and so does this.



Storm has done nothing but drift south all morning long..

1km resolution visible centered
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Quoting StormTracker2K:
Issac is very unpredictable. Center now 16N. I guess the NHC was a little quick to adjust the track left.



That 16N is questionable. I can't see it farther N than 15.5N. Maybe they figure it doesn't matter at this point as it's so disorganized still.
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Time: 17:52:30Z
Coordinates: 15.6167N 66.4833W
Acft. Static Air Press: 843.3 mb (~ 24.90 inHg)
Acft. Geopotential Hgt: 1,528 meters (~ 5,013 feet)
Extrap. Sfc. Press: 1004.1 mb (~ 29.65 inHg)
D-value: -
Flt. Lvl. Wind (30s): From 48° at 2 knots (From the NE at ~ 2.3 mph)
Air Temp: 18.0°C (~ 64.4°F)
Dew Pt: 18.0°C (~ 64.4°F)
Peak (10s) Flt. Lvl. Wind: 3 knots (~ 3.4 mph)
SFMR Peak (10s) Sfc. Wind: 13 knots* (~ 14.9 mph*)
SFMR Rain Rate: 1 mm/hr* (~ 0.04 in/hr*)

Probably the center, there is no WNW movement yet IMO.
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Quoting BarometerGirl:


The devastation that Katrina caused along the Gulf coast of Mississippi, especially near Biloxi, was staggering. The flooding in NOLA b/c of the levee breaks took the media focus completely away from the Miss. Gulf Coast, but the damage along Hwy 90 was equal to Camille.

I visited NO (the Lakeshore area and the Ninth Ward) and then traveled the coast on my honeymoon on the way to Florida, and the damage was even more shocking than in New Orleans. Everything was basically wiped out along the coastline to over a mile inland from the storm surge. The wind did the rest. Even along I-10 the billboards were twisted and many down, all the gas stations at exits with no roofs or completely wrecked. When we drove to the coast we were flabbergasted with what we saw-- the media was not covering any of it as they were all in New Orleans.

Hwy. 90 was still closed and undriveable, we spent and entire day driving down exits from I-10 south to the coast. Nothing was left but piles of devastation all along Hwy 90 from Waveland to Pascagoula. It looked like it had been bombed, or hit by a tsunami.

Link
Thanks.
Member Since: August 28, 2008 Posts: 0 Comments: 250
Quoting Levi32:
12z GFS ensembles shifted west a bit.



That's a fairly significant shift.
Member Since: July 9, 2006 Posts: 184 Comments: 29594
Quoting Levi32:
12z GFS ensembles shifted west a bit.

Levi..IF issac goes Up the west coast of florida..what do you guess at..the effects the Tampa area will get?..its only a guess im asking for ok
Member Since: August 6, 2011 Posts: 4 Comments: 33363
The LLC was always up just under 16N, but it looks like the 850MB center has now shifted north. Issac is stacked slightly better with each recon flight. Issac is currently tilted N to S roughly.
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Time: 17:52:30Z
Coordinates: 15.6167N 66.4833W
Acft. Static Air Press: 843.3 mb (~ 24.90 inHg)
Acft. Geopotential Hgt: 1,528 meters (~ 5,013 feet)
Extrap. Sfc. Press: 1004.1 mb (~ 29.65 inHg)
D-value: -
Flt. Lvl. Wind (30s): From 48° at 2 knots (From the NE at ~ 2.3 mph)
Air Temp: 18.0°C (~ 64.4°F)
Dew Pt: 18.0°C (~ 64.4°F)
Peak (10s) Flt. Lvl. Wind: 3 knots (~ 3.4 mph)
SFMR Peak (10s) Sfc. Wind: 13 knots* (~ 14.9 mph*)
SFMR Rain Rate: 1 mm/hr* (~ 0.04 in/hr*)
Member Since: August 1, 2011 Posts: 23 Comments: 7463
Quoting angiest:


How many of us have seen such a radical shift in one day?


Its going to Texas now?
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Quoting interstatelover7165:
I had an interesting thought recently- if tropical entities could talk, what do you think they would say?


"Ho Ho - this Blog amuses me - may just stick around a while longer"
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925. MahFL
Eye eye !!!
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Quoting Levi32:
Guess who shifted significantly northeast from last night's run, in the short-range at least:

You don't have to prove anything to these idiots.
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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.