Little change to Isaac, but intensification coming; Joyce forms

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

Share this Blog
49
+

Tropical Storm Isaac is a large and impressive-looking storm on satellite images, but data from the Hurricane Hunters reveal that Isaac remains a minimal-strength tropical storm with 40 mph winds, as it heads westward across the Eastern Caribbean. An Air Force Reserve hurricane hunter aircraft which completed its mission into Isaac at 8 am EDT found top winds at the surface near 40 mph, and highest winds at their 5,000 foot flight level of 47 mph. A NOAA hurricane hunter aircraft flying at 10,000 feet has found top winds of 47 mph at that altitude. The Hurricane Hunters found a broad area of light winds with a central pressure of 1003 mb. The aircraft did not observe an eyewall trying to form, and recent microwave satellite images also show no signs of an eyewall forming. There does not appear to be much in the way of dry air near the core of Isaac, as seen on water vapor satellite loops, which is a big switch from what we've seen previously. Visible satellite loops show that Isaac has a much more symmetric circular cloud pattern, and has developed a Central Dense Overcast (CDO) of high cirrus clouds, the hallmark of an intensifying storm. These clouds have very cold cloud tops, indicating that the updrafts creating them are quite strong. An analysis of upper level winds from the University of Wisconsin CIMSS shows that an upper-level pattern of outflow supportive of significant strengthening has developed this morning, with an upper-level outflow channel now well-established to the north, and a new outflow channel opening to the south. Radar imagery from Puerto Rico shows some weak low-level spiral bands that are slowing intensifying and becoming more organized.


Figure 1. Morning radar image of Isaac taken from the Puerto Rico radar. Isaac's rain bands are weak, but are starting to take on a more spiraling shape.

Intensity forecast for Isaac
Isaac has consistently confounded predictions that it would intensify, but all the potential factors inhibiting intensification seem to have diminished to the point where intensification has to occur. Wind shear is low, 5 - 10 knots, and ocean temperatures are warm, 29°C, and these warm waters extend to great depth, giving the storm a high total heat content to work with. These factors, combined with the favorable upper-level outflow pattern and more symmetric cloud pattern, support intensification, and all of the intensity models except the HWRF model predict intensification of Isaac to a strong tropical storm or Category 1 hurricane by Friday afternoon. The latest 8 am EDT run of the SHIPS model predicts that wind shear will be light to moderate, 5 - 15 knots, for the next five days. The 11 am EDT wind probability forecast from NHC predicted a 34% chance that Isaac will become a hurricane by Friday afternoon, and a 6% chance it will be a Category 2 or stronger hurricane then. By Friday afternoon, Isaac will likely be close enough to Southwest Haiti that the inner core will be disrupted, and the storm will likely be a 45 - 55 mph tropical storm on Saturday and Sunday as it moves over Cuba. Once Isaac pops off the coast of Cuba into the Florida Straits, it will be over very warm waters of 31 - 32°C (88 - 90°F), wind shear will be light to moderate, and the upper-level wind pattern favorable for intensification, with low wind shear due to an upper-level anticyclone over the storm. It will probably take at least 24 hours with the storm's center over water for it to become a hurricane.

Impact of Isaac on the Islands
The south coast of Puerto Rico should see Isaac's heaviest rains and strongest winds beginning near 8 pm EDT tonight, with tropical storm-force winds of 40 - 45 mph potentially affecting the southwest portion of the island. The San Juan airport may be able to stay open during Isaac's passage, but with delays when spiral bands move overhead.

Heavy rains and tropical storm-force winds should arrive on the southern coast of the Dominican Republic late tonight, and the Santo Domingo airport will probably be closed on Friday. Rainfall amounts of 8 - 12 inches will likely affect the Dominican Republic Thursday through Saturday, creating dangerous flash floods and mudslides.

Isaac is potentially a very dangerous storm for Haiti, where 400,000 people still live outside underneath tarps in the wake of the 2010 earthquake. Heavy rains from Isaac will begin on Friday morning in Haiti, and last through Sunday. Rainfall amounts of 8 - 12 inches are possible, which will be capable of causing extreme flooding on the vegetation-denuded slopes of Haiti. It will be a major challenge to keep those Haitians living outside safe, if rainfall amounts of 5 - 10 inches occur.

Impact on Florida, Cuba, Jamaica, and the Bahamas
Florida, Cuba, Jamaica, and the Bahamas are all at risk of receiving flooding rains and high winds from Isaac. The latest set of 00Z (8 pm EDT) and 06Z (2 am EDT) model runs for Isaac are fairly unified for the coming three days, showing a west-northwestward track over Southwest Haiti and into Western Cuba. At the 4 - 5 day forecast period for Sunday and Monday, the models have come into better agreement, and have shifted west some. Our best-performing model, the ECMWF, has now shifted Isaac's path more to the east, but still is the westernmost of the models, predicting a landfall for Isaac near the Alabama/Florida border on Wednesday. While we do still have some models predicting a path up the east coast of Florida, model consensus now favors a path up the west coast of Florida through the Gulf of Mexico. The recent reformation of Isaac's center more to the south supports the idea that Isaac will take a track more to the west through the Gulf of Mexico. Since this now means a final landfall for Isaac in the Florida Panhandle is likely, the storm will probably have an extra day over water, increasing the odds that it will become a Category 2 or stronger hurricane before this final landfall. The NOAA jet is scheduled to fly into the storm this afternoon, to do a large-scale dropsonde mission to aid model forecasts. These missions can improve model forecasts by 10 - 20%, so the model runs that will be available early Friday morning should have increased reliability.

Impact on Tampa, Florida
The Republican National Convention begins on Monday in Tampa, Florida. The latest 11 am EDT wind probability forecast from NHC gives Tampa a 15% chance of receiving tropical storm-force winds and a 1% chance of receiving hurricane-force winds on Monday. The latest model tracks for Isaac suggests that the trough of low pressure pulling the storm to the north will not be strong enough to give Isaac a northeastward component of motion when it crosses Tampa's latitude. Thus, Isaac will have difficulty making a direct hit on Tampa without passing over a considerable amount of land first, making a multi-billion dollar hurricane disaster in Tampa very unlikely. I put the odds of a mass evacuation occurring during the convention at 1%; a limited evacuation of people in the Tampa Bay area living in mobile homes in low-lying areas is probably about 5 - 10 % likely. I have detailed information on Tampa's storm surge vulnerability in a post from last week.


Figure 2. Morning satellite image of Tropical Storm Joyce.

Tropical Storm Joyce forms in the Central Atlantic
The season's tenth named storm of the year, Tropical Storm Joyce, has formed in the Central Atlantic. Joyce's formation on August 23 puts 2012 in a tie for second place with 1995 for earliest formation date of the season's tenth storm. Only 2005 had an earlier appearance of the season's tenth storm, when Tropical Storm Jose formed at 2 pm EDT on August 22. None of the models show that Joyce will be a threat to the Lesser Antilles Islands, but it may be a storm that will affect Bermuda. It is possible that Joyce will complicate the track forecast for Isaac 4 - 5 days from now, when the storms may be close enough together to interact.

Jeff Masters

Reader Comments

Comments will take a few seconds to appear.

Post Your Comments

Please sign in to post comments.

or Join

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

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

Viewing: 1074 - 1024

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

Quoting Torgen:


Jesus Christ, people. Cut the Jr High drama out. If you don't like what someone says, ignore them, disagree with them but let's cut this shit out. It sounds like X Box Live in here with all the personal attacks.
He was joking with Levi...
Member Since: August 1, 2011 Posts: 28 Comments: 8007
what is very funny is from back during Katrina this very same blog (a majority) said that Katrina had no chance of coming close to NOLA.

Storms are great they are the most un predictable things on this planet
Member Since: Posts: Comments:
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


Depends on the type of storm: wind or water, and how long it stays over you.

Katrina: cat 1 -- moving medium -- 4-5 hours of lashing winds, tons of rain (which makes the rain go sideways and other strange directions)

Wilma: ??? min cat 2 when it hit? Not so much water, but an entire night of winds.

We don't flood that badly here in Dade County, only in certain low lying areas, so it the water is usually down within 24 hrs. Power outs -- different story.
Member Since: Posts: Comments:
Quoting FOREX:


And people that would leave their pets should not have pets in the first place.


A lot of it is complacency. Those who have to evacuate over and over (such as Keys) and the storm never hits them. Their attitude can be "I'll be back in a day." That's why I'd prefer forecasters err on the side of worst-case scenario. Complacency can be our worst enemy.
Member Since: Posts: Comments:
1070. scott39
Quoting Bluestorm5:
Euro at 120 HR:

Looks like its sticking to ITS GUNS!
Member Since: Posts: Comments:
1069. LargoFl
what can i expect from a cat-1 hurricane?....................CATEGORY 1 HURRICANE:
A tropical storm with winds of 39-73 mph becomes a hurricane when it's winds near the center reach 74 mph. The storm surge is generally 4-5 feet above normal. Damage is mostly to trees and shrubbery, with no real building damage. Average wind speed for a cat. 1 is 74-95mph. Minimum central pressure (980 mb.)


Member Since: August 6, 2011 Posts: 4 Comments: 38423
This recon is finding more organized Isaac, not a slop like last recon plane found.
Member Since: August 1, 2011 Posts: 28 Comments: 8007
it used to be that you could google "stick your website where the sun doesn't shine" and the whole story came up
Member Since: August 13, 2007 Posts: 0 Comments: 10490
Quoting MississippiWx:
The Euro just needs to come out and say it already:

"I hate Louisiana/Mississippi."


looks to me like she likes them..maybe wants to do some visiting! hope not!
Member Since: Posts: Comments:
Quoting Torgen:


Jesus Christ, people. Cut the Jr High drama out. If you don't like what someone says, ignore them, disagree with them but let's cut this shit out. It sounds like X Box Live in here with all the personal attacks.

I fail to see drama in Grothar's post. More like mocking those causing the drama, while lightening the mood a bit.
Member Since: Posts: Comments:
1064. emguy
Quoting reedzone:
It doesn't make sense for a storm to smash right through a ridge... the weakness is over Florida and that is where Isaac is going to most likely head to. Whether it be the East Coast or West Coast. It's not passing 85W, in my opinion.


I agree...Something is strange about this...
Member Since: Posts: Comments:
the models wil have a better handle once the new data is put into them. especially our 2 best ones
Member Since: Posts: Comments:
Quoting Torgen:


Jesus Christ, people. Cut the Jr High drama out. If you don't like what someone says, ignore them, disagree with them but let's cut this shit out. It sounds like X Box Live in here with all the personal attacks.


Gro was being sarcastic, he was joking with Levi
Member Since: Posts: Comments:
When you think about it, the Euro has been the model that was the most hesitant to strengthen this system over the past few days, and has turned out to have done a pretty good job so far. It would be impressive if it ended up getting the western track correct while all the other models were farther east.
Member Since: Posts: Comments:
Euro at 120 HR:

Member Since: August 1, 2011 Posts: 28 Comments: 8007
1059. HrDelta
Quoting thesweetlycool:


I miss StormW... He left because people on this blog think that it's a competition to forecast instead of a hobby... No one knows where the thing is going... It's called an educated guess! Just like sports... You can guess how the playoffs will shape up, but that's why they play the games.


Very few of us in the comments are professionals. We are just weather enthusiasts.

Speaking of which, Isaac has shrunk from last night, and I would say the PR radar is placing a center at 15.6

It might still have two centers, but is consolidating. Could the centers be doing a real small version of the Fujiwhara Interaction?
Member Since: Posts: Comments:
Quoting Seflhurricane:
back later , going to wait and see 00Z models to see what happens but the NHC will likely keep the same track at 5Pm to see those models
Tonight's runs will shed some light towards the steering this storm might take downstream.
Member Since: Posts: Comments:
1057. Levi32
Quoting 1900hurricane:

I'm going to have to disagree with you here. The 00Z shows the same NW movement across Hispaniola and into southern Cuba until he starts to bump up against the ridge to the north and begins going WNW. I pointed it out in post 922.


I'm not saying the long-range track is different lol. Just that it jumps into Hispaniola more in the short-range, which is quite significant for rainfall impacts there and the overall impact of the mountains on Isaac.
Member Since: November 24, 2005 Posts: 635 Comments: 26647
Quoting presslord:
he left because he told Jeff Masters to stick his website up his a**...and Jeff whacked him...and that's that...


The other narratives going on about why he left are SO much more dramatic. Why must you ruin the fun with things like "truth", "honesty", and "reality"? No fun at all!
Member Since: Posts: Comments:
Quoting Hurricanes4life:


Umm, I am from there too and I'd like to know who you are referring too... there is no model support for that.


If i had to guess, i'd probably say Cindy Day
Member Since: Posts: Comments:
1053. sdswwwe
The anti-cyclone moved ahead of the system, therefore creating wind shear for the system in the north-to-south direction. This is why all of the convection is blown off to the south.

I believe people are looking at this blob of convection and assuming that the CoC is near the center of it as would be the case in a hurricane. But considering this is a weak tropical storm being sheared, the true CoC is well above the mass of convection. The satellite photos can be very deceiving...
Member Since: Posts: Comments:
1052. Levi32
Quoting Grothar:


Hey, Levi. Which would you say was your most condescending blog? The one on the 21st or 22nd?


The one on the 22nd had more words.
Member Since: November 24, 2005 Posts: 635 Comments: 26647
1051. LargoFl
Quoting reedzone:
It doesn't make sense for a storm to smash right through a ridge... the weakness is over Florida and that is where Isaac is going to most likely head to. Whether it be the east Coast or West Coast. It's not passing 85W, in my opinion.
ty
Member Since: August 6, 2011 Posts: 4 Comments: 38423
Quoting Levi32:


The 48-hour forecast point is significantly farther northeast into Hispaniola than last night's run, which is the significant difference. Mountains pull it in then spit it back out more this run.

I'm going to have to disagree with you here. The 00Z shows the same NW movement across Hispaniola and into southern Cuba until he starts to bump up against the ridge to the north and begins going WNW. I pointed it out in post 922.
Member Since: Posts: Comments:
1049. scott39
I hate to see heads swell..its not attractive.
Member Since: Posts: Comments:
54 mph FLIGHT winds found... remember, this is flight winds, not surface.
Member Since: August 1, 2011 Posts: 28 Comments: 8007
Quoting weatherh98:


No school!


Easy there kid lol
Member Since: Posts: Comments:
back later , going to wait and see 00Z models to see what happens but the NHC will likely keep the same track at 5Pm to see those models
Member Since: Posts: Comments:
he left because he told Jeff Masters to stick his website up his a**...and Jeff whacked him...and that's that...
Member Since: August 13, 2007 Posts: 0 Comments: 10490
Quoting Elena85Vet: Getting tired of scanning over posts about Levi, pro or con

What ev's..

thx

If you are tired, maybe you should go have a nap, get some quiet time. Bye, tty tomorrow.
Member Since: Posts: Comments:
It doesn't make sense for a storm to smash right through a ridge... the weakness is over Florida and that is where Isaac is going to most likely head to. Whether it be the East Coast or West Coast. It's not passing 85W, in my opinion.
Member Since: Posts: Comments:
Quoting poknsnok:
NOLA storm for sure sorry FL doomers!


you are aware that is ONE of many forecast models right?

the rest of which still makes this a FL storm
Member Since: Posts: Comments:
1041. ncstorm
Quoting Grothar:


Hey, Levi. Which would you say was your most condescending blog? The one on the 21st or 22nd?


Oh gosh..Im cracking up on some of these comments..
Member Since: Posts: Comments:
Quoting MississippiWx:
The Euro just needs to come out and say it already:

"I hate Louisiana/Mississippi."


No school!
Member Since: Posts: Comments:
Quoting icmoore:


I'm not singling you or anybody out but Levy asked very nicely the other day not to make him the subject in Dr Masters' blog maybe we could respect that and my own observation is there are usually many more defenders than attackers. It seems a waste of time maybe?


Ok. I will stop simply because Levi's work speaks for itself and he doesn't need defending. He has support here and he knows it so I will let it go from now on. I just don't want him to become discouraged by people who either don't have a clue, are jealous/bitter he gets attention, or a combination of both. As I said earlier, I learn more from his videos than anywhere else, and I appreciate that he is willing to make his own forecast and reasoning and not simply follow a model or the NHC (because they can both be wrong, too).

The bottom line is everyone on this blog has an opinion and everyone should respect each others opinions. Disagreement is perfectly fine- in fact it is healthy and we can and should all learn from each other. But I would like to see those who disagree go in depth with their own reasoning- like Levi does.

Member Since: Posts: Comments:
The Euro just needs to come out and say it already:

"I hate Louisiana/Mississippi."
Member Since: July 15, 2006 Posts: 17 Comments: 10244
So it's looking more and more likely this will tangle with the mountains. Might not have a clear definitive track of where it goes until it emerges back over water.
Member Since: Posts: Comments:
1036. Thaale
Quoting FOREX:


How are you able to follow the European model step by step. Which website??thanks.

http://raleighwx.americanwx.com/models/ecmwf.html
Member Since: Posts: Comments:
Quoting HurricaneDean07:
Recon Found 45 Mph winds on eastern side...
Not surprised... might even see some 50 Mph winds.

They're also finding 45 kt flight level winds.
Member Since: Posts: Comments:
1033. LargoFl
What Can i expect from a Cat-2 hurricane?..........CATEGORY 2 HURRICANE:
Winds are from 96- 110 mph. Storm surge is generally 6-8 feet above normal. Some roofing material, door and window damage to buildings. Considerable damage to trees and shrubbery with some trees blown down. Considerable damage to signs, mobile homes and poorly constructed piers. Coastal and low lying escape routes may flood 2-4 hours before the arrival of the hurricane's center. Minimum central pressure (80-965 mb.)
Member Since: August 6, 2011 Posts: 4 Comments: 38423
1032. luigi18

Link
Member Since: Posts: Comments:
Quoting yonzabam:



They're probably kids who think it's a laugh to come on here and do some baiting. The same thing happened when a bunch of them ganged up on StormW a few years ago. He also gave in depth analyses with graphics.


I miss StormW... He left because people on this blog think that it's a competition to forecast instead of a hobby... No one knows where the thing is going... It's called an educated guess! Just like sports... You can guess how the playoffs will shape up, but that's why they play the games.
Member Since: Posts: Comments:
1030. Chiggy
Quoting Levi32:


The 48-hour forecast point is significantly farther northeast into Hispaniola than last night's run, which is the significant difference. Mountains pull it in then spit it back out more this run.


Have a look at the 120hrs...!! LOL
Member Since: June 26, 2012 Posts: 0 Comments: 297
Recon Found 45 Mph winds on eastern side...
Not surprised... might even see some 50 Mph winds.
Member Since: Posts: Comments:
1028. Levi32
Quoting FOREX:


How are you able to follow the European model step by step. Which website??thanks.


This is a good site for tracking the Euro.
Member Since: November 24, 2005 Posts: 635 Comments: 26647
120 hrs.

Member Since: Posts: Comments:
1026. Grothar
Quoting Levi32:
ECMWF showing jerky motions associated with the greater Antilles mountains.


Hey, Levi. Which would you say was your most condescending blog? The one on the 21st or 22nd?
Member Since: July 17, 2009 Posts: 71 Comments: 26117
Euro has Issac even further west than the 0Z run.
Member Since: October 26, 2011 Posts: 0 Comments: 2651
1024. ncstorm
12z GFS rain precip map-120 hours


240 hours


360 hours
Member Since: Posts: Comments:

Viewing: 1074 - 1024

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

Top of Page

About

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