Isaac is strengthening

By: Dr. Jeff Masters , 2:58 PM GMT on August 24, 2012

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Tropical Storm Isaac is strengthening. An Air Force Reserve hurricane hunter aircraft measured surface winds of 60 mph on the east side of the center, about 170 miles south of Santo Domingo in the Dominican Republic, at 8:40 am EDT this morning. Winds at the aircraft's flight level of 5,000 feet were hurricane force, 76 mph. The surface pressure remained fairly high, at 1000 mb. Tropical cyclones have a warm core, and the Hurricane Hunters typically find that a storm's lowest pressure is also where the warmest temperature are. However, this morning's flight found that Isaac was still disorganized, with the storm showing almost no evidence of a warm core. Isaac's warmest temperatures were displaced 75 miles to the west of where the lowest pressure was. There were no signs of an eyewall beginning to build. Infrared and visible satellite loops show that Isaac is somewhat asymmetric, with a large band of intense thunderstorms to the east, separated from the core region. This is interfering with both the storm's low-level inflow and upper-level outflow, but the band appears to be dying out. An analysis of upper level winds from the University of Wisconsin CIMSS shows an upper-level outflow channel well-established to the north, and an intermittent outflow channel to the south.


Figure 1. Evening shot of Tropical Storm Isaac taken on August 23, 2012, by the NOAA Hurricane Hunters.

Isaac's rains
Radar imagery from Puerto Rico shows that Isaac is dumping some very heavy rains to the south and east of the center. Ponce, Puerto Rico had a wind gust of 37 mph this morning as a heavy band of rain moved through, and radar-estimated rainfall amounts are in excess of 7 inches for the region just north of Ponce. Power outages to 2,000 homes have been reported in Puerto Rico this morning. NOAA buoy 42085 offshore from Ponce reported a wind gust of 54 mph near 9 am EDT this morning. Rainfall estimates from microwave satellite instruments suggest that Isaac's heaviest rains are to the south of the center, and that the Dominican Republic and Eastern Haiti will escape the worst of Isaac's rains. Haiti's southwest peninsula and Eastern Cuba should suffer the heaviest rains.


Figure 2. Radar-estimated precipitation from the Puerto Rico radar shows the region near Ponce has received up to 7" of rain as of 10 am EDT August 24, 2012.

Latest model runs for Isaac
The latest set of 00Z and 06Z (8 pm and 2 am EDT) model runs have come into better agreement, thanks to the dropsonde mission by the NOAA jet yesterday afternoon and evening. Isaac should move over Haiti's southwest peninsula and then eastern Cuba, then track along the spine of Cuba before popping off into the Florida Straits on Sunday. A trough of low pressure will then pull Isaac to the northwest, and then north, towards the Central Gulf Coast. Landfall locations range from Mississippi (06Z HWRF model run) to the Florida Panhandle south of Tallahassee (06Z GFDL model run.) It is possible that the trough of low pressure pulling Isaac to the north may not be strong enough to pull Isaac all the way to the northeast and out to sea, and the ECMWF model indicates that Isaac could stall out after landfall over the Tennessee Valley for several days.


Figure 3. Predicted 5-day rainfall total ending at 2 am EDT Wednesday August 29, from Tropical Storm Isaac. Graphics were generated from the 6Z (2 am EDT) August 24, 2012 run of the HWRF model. Image credit: Morris Bender, NOAA/Geophysical Fluid Dynamics Laboratory.

Intensity forecast for Isaac
Isaac has not intensified as much as predicted, and I think that the storm's very large size is partially responsible for that. It's tough to spin up as much atmosphere as Isaac is attempting to do very quickly. Conditions remain favorable for intensification today, with wind shear low, 5 - 10 knots, ocean temperatures warm, 29°C, and dry air mostly mixed out of the storm's core. The large band of intense thunderstorms to the east, separated from the core region, appears to be dying out now, which will help the storm grow more organized. The storm's structure has improved considerably between 9 am - 10 am EDT, with a fairly tight center forming, exposed to view, on the north edge of Isaac's heaviest thunderstorms. A curved band of heavy thunderstorms is now trying to wrap around this center to the northeast, and this band will bring very heavy rains to Haiti and the Dominican Republic this afternoon. I expect that the Hurricane Hunters will observe a partial eyewall in their vortex reports between 2 - 4 pm EDT this afternoon. The storm's large size and disorganized structure suggests that Isaac will be able to intensify only slowly today, and will have top winds of 70 - 75 mph before encountering Southwest Haiti and Eastern Cuba tonight and Saturday. Isaac will likely be a 50 - 60 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. The upper-level wind pattern favorable may be quite favorable for intensification, with low wind shear due to an upper-level anticyclone over the storm--though the models disagree on whether or not this anticyclone will set up directly over Isaac or not. It will probably take at least 24 hours with the storm's center over water for it to become a hurricane. It is possible that Isaac could be approaching Category 3 strength by the time it makes landfall on Tuesday on the Gulf Coast, as suggested by the latest 06Z run of the HWRF model.

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 17% chance of receiving tropical storm-force winds and a 1% chance of receiving hurricane-force winds on Monday. Tampa is in the NHC cone of uncertainty, though near the edge of it. At a minimum, Tampa will receive very heavy rains and wind gusts in excess of 40 mph. Isaac is going to be hard-pressed to bring hurricane-force winds to the city, though, since any path that takes it close to Tampa would keep the storm too close to land for significant intensification to occur. I put the odds of a mass evacuation being ordered for Tampa during the convention at 1%. I have detailed information on Tampa's storm surge vulnerability in a post from last week.

Invest 97L off the coast of Africa
A tropical wave that moved off the coast of Africa on Thursday has been designated Invest 97L by NHC this morning. The storm has a modest amount of spin and heavy thunderstorms, and is under moderate wind shear of 10 - 20 knots. In their 8 am EDT Tropical Weather Outlook, NHC gave 97L a 30% chance of developing by Sunday morning. The 8 am EDT SHIPS model forecast predicts that 97L will track west-northwest over the next few days, and encounter a region of high wind shear associated with an upper-level low on Monday and Tuesday. This low may be capable of tearing the storm apart, as happened to Tropical Storm Joyce. None of the models currently foresee that 97L will affect the Lesser Antilles Islands, but 97L may pass near Bermuda 7 - 8 days from now.



20th anniversary of Hurricane Andrew
Today, August 24, is the 20th anniversary of Hurricane Andrew, which hit South Florida as a Category 5 hurricane with 175 mph winds--one of only three Category 5 hurricanes ever to hit the U.S. With Isaac churning through the Caribbean this week, I didn't have time to prepare a special post on Andrew, but our Hurricane Andrew archive page has links to satellite and radar images, newspaper headlines, and 49 YouTube videos. Here's an additional link for an Andrew damage video shot by wunderblogger/storm chaser Mike Theiss, when he was 14 years old.

Jeff Masters

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761. CJ5
Things appear to be getting better for Isaac, but he still is unable to wrap convection all the way around. If he cannot do it before the mountains ahead, he will emerge a tattered mess.
Member Since: July 4, 2007 Posts: 0 Comments: 1755
If Isaac tracks up the spine of Fl, I will eat 2 vultures, 8 crows and a chocalate covered canary for dessert.
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Quoting opal92nwf:
I think this is a good example of what this might be able to do after moving over Cuba.


I know these projections are all opinions based on what EVERYONE sees and it's all different but why is yours possibly so far W compared to some saying this thing will hug the W coast of FL?

Just wondering, not questioning.
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Quoting cchsweatherman:


Lovely. I got another imposter on the blogs here. Not how he uses 2 s in the handle while mine is the original. Must be doing something right for people to want and impersonate me.

hmm I had one too
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Quoting slavicthunder:
Fuck off with the politics already.
I am a hardocre conservative and I wont even talk politics, its Isaac time!!!! oh, and football time, but Isaac first
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Quoting floridaboy14:
lots of strong storms bust through ridges. its unlikely but can happen so dont discount it


Only if the ridge is banana shaped, which means the high can split. Though a storm cannot bust through the corner of a developing ridge. It's impossible.
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Levi...are you trying to start a riot in here? :)

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Isaac is now getting dry air intrenchment from the W and NW as seen on the visible.


But, he is finally wrapping deep convection around his COC. Thats the something we havent seen yet.
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Quoting RTSplayer:


You can make digital currency that is still physical by having an RFID chip inside the coin with a matching serial number, and a authenticity code, and have coins of higher values, like dollar, five dollar, hundred dollar, etc.

For transactions, the coins would be scanned by the store clerk, in much the same way items are scanned now for purchase.

This system would track all legitimate wages and sales transactions automatically, so that fake tax loopholes and other evasions would no longer be possible.


Sounds like you wanna chip all of us. Mr. mark of the beast?? LOL
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Quoting SFLWeatherman:
From me at 8AM yesterday and that what i have for today two

From Levi today


Don't forget the REED run lol
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So much for the lull before the storm. Got some pretty good boomers going on right now in Loxahatchee.
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HWRF 72 hrs. 984 mb. turning wnw about 50 miles offshore Tampa Bay:

Member Since: August 31, 2009 Posts: 0 Comments: 5628
745. wpb
Quoting Levi32:
Good afternoon.

Blog update:

Tropical Tidbit for Friday, August 24th, with Video
ty
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Quoting reedzone:


EXCELLENT analysis!!! A storm cannot bust through a developing ridge, has to recurve off the corner of the weakening ridge. This will not cross 85W.
lots of strong storms bust through ridges. its unlikely but can happen so dont discount it
Member Since: July 25, 2011 Posts: 0 Comments: 1102
From me at 8AM yesterday and that what i have for today two

From Levi today
Member Since: May 23, 2012 Posts: 0 Comments: 4415
Quoting AegirsGal:
It is a troll baiting the less observant...its all hogwash..


Thank you, now i know to put him on ignore. Something was fishy about all that.
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Quoting SouthTXWX:
According to visible, does it not look like the center of Isaac is about to make landfall at the souther tip of the DR? sure looks like it to me.
its going to come close but its going to make landfall on the hatian peninsula
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Quoting SouthTXWX:


I read the cold water riptide is from Nova Scotia, source?
It is a troll baiting the less observant...its all hogwash..
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Until Isaac goes over Cuba....predicting a specific landfall is pointless.
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HWRF 66 hrs. 983 mb. hugging the West FL. coastline:

Member Since: August 31, 2009 Posts: 0 Comments: 5628
I wish that people would keep their political opinions to themselves... This is a weather blog.
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Quoting WDEmobmet:
Not to do a double post but I just got word from Navy Official at work that Jim Cantore is in Mobile,AL. Do not understand why

The local Chamber of Commerce in Mobile has hired Cantore as storm insurance. They saw some of the model runs yesterday, and wanted to be safe, so they brought Cantore in to eliminate even the slim possibility of landfall that far west.
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Quoting Levi32:
Good afternoon.

Blog update:

Tropical Tidbit for Friday, August 24th, with Video


EXCELLENT analysis!!! A storm cannot bust through a developing ridge, has to recurve off the corner of the weakening ridge. This will not cross 85W.
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According to visible, does it not look like the center of Isaac is about to make landfall at the souther tip of the DR? sure looks like it to me.
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Quoting SFLWeatherman:
Were is Levi??????
Yesterday seemed like abuse Levi day. He's probably taking a break. People were giving him cr*p because his individual forecast for Issac was on the east coast of Florida. Levi's not the only person thinking this way. Henry Margusity from accuweather is saying the same thing. It has something to do with a low pressure trough coming from the four corner states. According to this line of thinking, if this trough stays more south in the CONUS, Issac will go more east, despite the models, which don't show this. Who knows if this will or will not pan out. I say we should respect all people's individual opinions. Things aren't over until they are over. I've never seen a weather forecast that was perfect. Just the word forecast has an air of uncertainty. No met is always right. In the long run everyone is guessing to some degree.
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Quoting Seflhurricane:
what the hell is this ???


Please don't feed the trolls
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Quoting cchsweatherman:


Lovely. I got another imposter on the blogs here. Not how he uses 2 s in the handle while mine is the original. Must be doing something right for people to want and impersonate me.
thanks for the heads up, overlooked that little detail.
some folks.. seriously
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What is the HWRF model worth?
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Quoting will40:



very nice Levi you da man. young man but still da man lol


Lol
Member Since: November 24, 2005 Posts: 635 Comments: 26564
Not to do a double post but I just got word from Navy Official at work that Jim Cantore is in Mobile,AL. Do not understand why
Member Since: February 3, 2010 Posts: 0 Comments: 749
Quoting JBirdFireMedic:


Until Isaac is off the islands and model run off those coordinates and strength, I would say everyone from FL to TX/LA border needs to watch.


When is he projected to be off of the islands and begin meandering into the GOM? Thanks for the heads-up JBird
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Quoting leelee75k:
I'm in Western Broward, currently expecting that we will experience Tropical Storm conditions starting sometime Sunday afternoon. I've already bought the usual supplies (batteries, water, canned foods)I do it in June and just refresh everytime I go shopping till hurricane season is over. Today I picked up bread and fresh fruit, since I won't be making the decision regarding shutters and really cleaning up the yard (birdbaths, lawn chairs) till tomorrow. Don't want to deal with long lines if I have yard and house prepping to do. Btw shutters don't go up unless it's Cat 1 or higher.

I honestly don't think we will experience the worst, my concern is the possible tornados and flooding. I think Monday and even Tuesday will just be very nasty days in South Florida.

In Naples here, and I fully agree; that is pretty much how we are looking at it.
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The upper level's definitely on Isaac's side.
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eek! Torcon 6/10 for Central & South Florida and it might go up says the weather channel!!
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Quoting Seflhurricane:
what the hell is this ???

an imposter having a good laugh
Member Since: September 5, 2007 Posts: 0 Comments: 3481
Miami-Dade Office of Emergency Management urges preparedness for Tropical Strom Isaac

Link
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Quoting cchssweatherman:


Okay, after reviewing the data from the Gulfstream-IV along with my own personal instrumentation, I'm able to report my observations and my forecast for this system.  There are a few anomalies that the models don't seem to be picking up on, but which should seem rather obvious to the trained eye.  

First, there is a rather potent riptide traversing the coastline from Maine to just west of Florida, where a substantial area of cooler water is now present.  As my graphic indicates this will serve to weaken Isaac from a category 4 to 3 briefly; however, Isaac will quickly gain category 5 status due in part to the sudden change from cold to extremely warm temperatures as well as a large area of cumulus clouds south of Cuba.  These clouds act to “supercharge” storms due to their shape, which creates the perfect amount of turbulence needed to reach category 5.

The blocking low, along with an area of concern in the Eastern Pacific (though expected to enter the Gulf of Mexico as early as Sunday), will serve to turn Isaac sharply north in a “V” motion.  Shortly thereafter, the Saharan Air Layer over the Eastern Gulf/Texas will cause a slight weaking, albeit only to Category 4.  The Wind, along with the encroaching High over Texas, will cause Isaac to make several right angles, after which the blocking high over Florida will allow Isaac to move north towards the Louisiana coast.  Because this motion will occur rather slowly, the waters off the northern Gulf coast will have churned for quite some time, cooling them substantially.  As a result, combined with the perfect amount of Saharan Air Layer over Florida, shortly after landfall in Louisiana on September 13, when Isaac re-enters the Gulf after a brief eastward trajectory, Isaac will transition to a Noreaster (depicted by blue dots on my graphic).

This Noreaster status could potentially cause more problems for the northern Gulf coast than even Isaac’s landfall as a Category 4 hurricane.  Nor’Isaac is expected to produce substantial hail and snow, with Louisiana and Mississippi possibly experiencing blizzard-like conditions for upwards of a week.  Residents should prepare accordingly.  

In addition to Isaac, forecasters should note the additional two areas of concern I have highlighted.  I will update my forecast as additional information rolls into the instruments in my parents’ basement.  

CCHS signing off for now!


I read the cold water riptide is from Nova Scotia, source?
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Recon is away..
Member Since: July 8, 2005 Posts: 259 Comments: 23626
Quoting sar2401:


LOL! Great work. That's the most comprehensive personal forecast I've seen in the last week. :)
thats not hi9s forecast thats bogus and someone copied his logo/name
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Quoting cchssweatherman:


Okay, after reviewing the data from the Gulfstream-IV along with my own personal instrumentation, I'm able to report my observations and my forecast for this system.  There are a few anomalies that the models don't seem to be picking up on, but which should seem rather obvious to the trained eye.  

First, there is a rather potent riptide traversing the coastline from Maine to just west of Florida, where a substantial area of cooler water is now present.  As my graphic indicates this will serve to weaken Isaac from a category 4 to 3 briefly; however, Isaac will quickly gain category 5 status due in part to the sudden change from cold to extremely warm temperatures as well as a large area of cumulus clouds south of Cuba.  These clouds act to “supercharge” storms due to their shape, which creates the perfect amount of turbulence needed to reach category 5.

The blocking low, along with an area of concern in the Eastern Pacific (though expected to enter the Gulf of Mexico as early as Sunday), will serve to turn Isaac sharply north in a “V” motion.  Shortly thereafter, the Saharan Air Layer over the Eastern Gulf/Texas will cause a slight weaking, albeit only to Category 4.  The Wind, along with the encroaching High over Texas, will cause Isaac to make several right angles, after which the blocking high over Florida will allow Isaac to move north towards the Louisiana coast.  Because this motion will occur rather slowly, the waters off the northern Gulf coast will have churned for quite some time, cooling them substantially.  As a result, combined with the perfect amount of Saharan Air Layer over Florida, shortly after landfall in Louisiana on September 13, when Isaac re-enters the Gulf after a brief eastward trajectory, Isaac will transition to a Noreaster (depicted by blue dots on my graphic).

This Noreaster status could potentially cause more problems for the northern Gulf coast than even Isaac’s landfall as a Category 4 hurricane.  Nor’Isaac is expected to produce substantial hail and snow, with Louisiana and Mississippi possibly experiencing blizzard-like conditions for upwards of a week.  Residents should prepare accordingly.  

In addition to Isaac, forecasters should note the additional two areas of concern I have highlighted.  I will update my forecast as additional information rolls into the instruments in my parents’ basement.  

CCHS signing off for now!


You sure put alot of thought into that anaylsis.....
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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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