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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Yesterday's 12Z EURO: "Yeah, I should probably nudge east a bit.

00Z EURO: "Yeah those other guys are probably on to something. East we go."

Today's 12Z: "Nah, screw that, I'm going to Texas."
Member Since: August 10, 2010 Posts: 2 Comments: 1971
1123. LargoFl
Quoting RetiredPWB:

yes ive been to that site, my house is 45 feet above sea level, im not worried about storm surge, more about wind damage etc, thanks
Member Since: August 6, 2011 Posts: 4 Comments: 42045
I swear, if this blog had smell-o-vision I'd release laughing gas...
lighten up
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1121. WxLogic
:) who knows may be the NAM is correct.
Member Since: August 14, 2008 Posts: 4 Comments: 5038
Quoting StormTracker2K:
12Z Euro is taking issac into Houston,TX. Very weird run here.



That's all she wrote. just kidding
Member Since: September 30, 2005 Posts: 0 Comments: 1606
Hello,

I live on St. Croix , USVI and this is the condition right now live from TS Isaac.

http://www.gotostcroix.com/live
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I highly doubt this system goes as far west as the Euro is showing
Member Since: March 10, 2010 Posts: 1 Comments: 7874
1117. Chiggy
Completely different Heights pattern in 5 days time compared with GFS! WTF...
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I fail to see where Issac turns that far west with that weakness.
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1115. Grothar
Quoting Levi32:


The one on the 22nd had more words.


So when your were talking about the trough coming down. You weren't being condescending, you were just explaining something descending? Now it makes sense.

Just some quick questions.

1. The people who defend you, obviously like you. Does it upset you that they attack other people?

2. Would you be happier if all of this stopped?

3. Do you hope that people understand you are just
trying to provide an explanation of conditions
for them to think about?

4.

Member Since: July 17, 2009 Posts: 71 Comments: 27208
Quoting Levi32:


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.

I understand, I just feel that it isn't really that different from the previous run. Of course, the 24 hour gap between frame complicates things, as I am extrapolating the storm motion between the long frame rates in my head.
Member Since: August 2, 2006 Posts: 47 Comments: 11709
Quoting mikatnight:
Wind Fields for Isaac
Last Updated On 8/23/2012 6:00:00 PM GMT



where is that strong WNW direction change i'm not seeing?
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I'm not going to buy into any of the computer models until all the computer models get the G-IV and all the hurricane hunter data inputted into them for tonight's runs.
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1111. Levi32
Quoting jeffs713:



Error 404: Sense of humor not found.


Error 406: Not Acceptable
Member Since: November 24, 2005 Posts: 635 Comments: 26700
Hello,

I live on St. Croix , USVI and this is the condition right now live from TS Isaac.

http://www.gotostcroix.com/live
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Quoting MississippiWx:


It was interesting to see the GFS shift ever further west on the 12z run earlier, trying to agree with Euro a little more. However, I'm still not buying it yet. The Euro must be seeing something that other models aren't, but the GFS could be picking up on it.

The NOAA flight could cause models to shift significantly west or east or just into more of a consensus after the 00z runs tonight.
Honestly, with the hesitation in the intensification, I'm leaning towards a slightly more westward track. The only thing that I'm skeptical about for a west track, which may ending up being a huge thing, is that the frictional convergence over the Greater Antilles my try to slingshot this thing off to the N/NE then back WNW. I don't believe the global models have the resolution to predict that. I think the HWRF may, and that may be why it is farther east. Either scenario is plausible for now. I just don't think the G-IV flight data will help the models' interactions with the Greater Antilles.
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1108. yqt1001


Strong typhoon making landfall now.
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Wind Fields for Isaac
Last Updated On 8/23/2012 6:00:00 PM GMT

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Still multiple low level vorticity centers occuring. The better one seems south of aircraft data and current stated coordinates or forecast points on satellite loops.
Member Since: September 30, 2005 Posts: 0 Comments: 1606
1105. Chiggy
12Z EURO un shows a more northern track in the beginning but it may even end up WEST of NOLA ,, waiting on the 168hr run
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12Z Euro is taking issac into Houston,TX. Very weird run here.

Member Since: October 26, 2011 Posts: 0 Comments: 2651
1103. LargoFl
Quoting Seaknight8:


No direct building damage from the winds, maybe, but a lot of secondary damage from those trees. Went through Fran 90 miles inland, and probably half the houses in my area were wearing blue tarps for weeks.
yes that is what i was thinking, surely there has to be some damage..thanks for the reply
Member Since: August 6, 2011 Posts: 4 Comments: 42045
1102. Matt74
Quoting ecupirate:
What is with all the bickering on here?
As the blog turns!
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um this is further west on the euro and um we got a strong hurricane ready to plow lousiana
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Past tropical climate change linked to ocean circulation
August 23, 2012

A new record of past temperature change in the tropical Atlantic Ocean's subsurface provides clues as to why the Earth's climate is so sensitive to ocean circulation patterns, according to climate scientists at Texas A&M University. Geological oceanographer Matthew Schmidt and two of his graduate students teamed up with Ping Chang, a physical oceanographer and climate modeler, to help uncover an important climate connection between the tropics and the high latitude North Atlantic. Their new findings are in the current issue of PNAS. The researchers used geochemical clues in fossils called foraminifera, tiny sea creatures with a hard shell, collected from a sediment core located off the northern coast of Venezuela, to generate a 22,000-year record of past ocean temperature and salinity changes in the upper 1,500 feet of water in the western tropical Atlantic.

They also conducted global climate model simulations under the past climate condition to interpret this new observational record in the context of changes in the strength of the global ocean conveyor-belt circulation. "What we found was that subsurface temperatures in the western tropical Atlantic rapidly warmed during cold periods in Earth's past," Schmidt explains. "Together with our new modeling experiments, we think this is evidence that when the global conveyor slowed down during cold periods in the past, warm subsurface waters that are normally trapped in the subtropical North Atlantic flowed southward and rapidly warmed the deep tropics. When the tropics warmed, it altered climate patterns around the globe." He notes that as an example, if ocean temperatures were to warm along the west coast of Africa, the monsoon rainfall in that region would be dramatically reduced, affecting millions of people living in sub-Saharan Africa.

The researchers also point out that the southward flow of ocean heat during cold periods in the North Atlantic also causes the band of rainfall in the tropics known as the Intertropical Convergence Zone to migrate southward, resulting in much drier conditions in northern South American countries and a wetter South Atlantic. "Evidence is mounting that the Earth's climate system has sensitive triggers that can cause abrupt and dramatic shifts in global climate," Schmidt said. "What we found in our subsurface reconstruction was that the onset of warmer temperatures, thought to reflect the opening of this 'gateway' mechanism, occurred in less than a few centuries. It also tells us that it might be a good idea to monitor subsurface temperatures in the western tropical Atlantic to assess how the strength of the ocean conveyor might be changing over the next few decades as Earth's climate continues to warm." "One way to prepare for future climate change is to increase our understanding of how it has operated in the recent past."

Journal reference: Proceedings of the National Academy of Sciences Provided by Texas A&M University

Read more at: http://phys.org/news/2012-08-tropical-climate-link ed-ocean-circulation.html
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1099. Torgen
Quoting caneswatch:


I find the lack of a sense of humor for you disturbing.


Some of us actually have to work during the day and can't keep up with the Degrassi Jr High stuff going on.
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1098. Dunkman
At 168 the Euro is hitting Lake Charles, LA. Let me just say I'm not buying it. I think the Euro is way overdoing the ridge in the east to push it that far west.
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1097. LargoFl
Quoting zoomiami:


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.
ty for your reply, this coming week is going to be a learning experience for me for sure
Member Since: August 6, 2011 Posts: 4 Comments: 42045
1096. Chiggy
12Z Euro at 144hrs, 970mb moving NW, perhaps even WEST of NOLA..
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Member Since: August 1, 2011 Posts: 28 Comments: 8075
Hey folks...just getting on. So what's it gonna be east or west?? Haven't seen to many models?? Has GFS still been moving a little west? What's the Euro saying?? Thanks in advance...and Taz...don't tell me to read thru 100 pages to get this info...lol...Thanks!!
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1093. DVG
Quoting Bluestorm5:
This recon is finding more organized Isaac, not a slop like last recon plane found.


Yeah. 15.5+- by almost 67 Seems to be moving just in a tad more n of w. Looks like some tstorms popping near what I think is the circulation on the right side. IMHO the sloppiness is over until land interaction.
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Quoting Chiggy:
CIMSS 500mb vorticity at 18Z, still not aligned...!!

It will get aligned, I'm thinking the North Coast of South America is interfering with that.
Member Since: August 31, 2009 Posts: 0 Comments: 5628
Quoting LargoFl:
what can i expect from a cat-1 hurricane?.................... Damage is mostly to trees and shrubbery, with no real building damage.




No direct building damage from the winds, maybe, but a lot of secondary damage from those trees. Went through Fran 90 miles inland, and probably half the houses in my area were wearing blue tarps for weeks.
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Hoping storm will be ripped apart by Haiti. To late for Haiti though!
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Quoting presslord:
it used to be that you could google "stick your website where the sun doesn't shine" and the whole story came up


Almost spit out my drink reading that lol
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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 guess you missed the sarcasm.
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1087. Torgen
Quoting Hurricanes101:


Gro was being sarcastic, he was joking with Levi


Well, I'm certainly glad to hear that. I was wondering if I were in some alternate reality, because that just didn't sound like Grothar. I'm just checking in while working and can't keep a scorecard to stay up to date with all the drama, though. I just want to know when I need to start boarding up, if I do. It's going to take a half hour to kill all the brown recluses nesting in my hurricane panels.
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Quoting SouthDadeFish:
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.


It was interesting to see the GFS shift ever further west on the 12z run earlier, trying to agree with Euro a little more. However, I'm still not buying it yet. The Euro must be seeing something that other models aren't, but the GFS could be picking up on it.

The NOAA flight could cause models to shift significantly west or east or just into more of a consensus after the 00z runs tonight.
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Well, that is significantly further west.



ECMWF 12Z @144 hours.
Member Since: August 2, 2006 Posts: 47 Comments: 11709
Quoting 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.)







Have you ever seen the Pinellas county storm surge web page???...interactive ....you click the level and it colors in how much of pinellas is underwater. If you are in Largo, you need to be prepared to leave.

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1083. Chiggy
CIMSS 500mb vorticity at 18Z, still not aligned...!!

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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.



Error 404: Sense of humor not found.
Member Since: August 3, 2008 Posts: 16 Comments: 5891
Not very impressive anymore on IR imagery. Getting kind of ragged:

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Quoting NovaScotianSurf:


If i had to guess, i'd probably say Cindy Day


She "used" to be a Met, hasn't actually practiced for years. She just uses the Environment Canada media weather site, like Peter. Not a huge fan of either
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1079. icmoore
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.


But there is a lot of bad sportsmanship here not surprising it seems to be a growing epidemic...
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1078. Dunkman
Isaac is really bombing out on the Euro at 144 as it closes in on NO.
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Quoting chevycanes:

you are quoting the 11am discussion and not the 2pm advisory where they don't do a discussion.

they clearly say wnw on the 2pm advisory.


That is what happens when you are dumb as a box of rocks that doesn't float. So I am going to sit over here in the bottom of the water and try not to make my self look foolish any more.
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looks like Isaac might finally be starting to intensify per recon..
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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 find the lack of a sense of humor for you disturbing.
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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: 8075

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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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