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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waiting to hear what Max Mayfield say at 5pm on Channel 10 news. He's my weather god! I do as Max says!
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Quoting cutlerbay32:


The news media in MIA has been saying that it "can't hurt" to be prepared and, as they show empty grocery store shelves formerly filled with bottled water, say that it is better to have the water than not just because it is hurricane season. They gently advise us to buy supplies but nothing more than that. They do not say they are being conservative- they say to wait another day or so because what will happen after the storm interacts with Cuba will tell us a lot. They did say we ought to think about filling prescriptions and that if someone has to call their doctor for a refill, they should do it now while there is that extra day or two to play with. Also said to stock up on pet food. All good suggestions for anyone on a vulnerable coast anytime during the season.


that is the perfect thing to say.. we don't want panic but we want people to be prepared.
Thanks for posting that here.

I am in Broward County.
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I'm not sure you guys are getting the whole thing Re: HPC

THE MODEL CHOICE THIS PERIOD WAS PARTIALLY CONSTRAINED BY THE LATEST NATIONAL HURRICANE CENTER (NHC) FORECAST FOR ISAAC, WHICH RESEMBLED THE 12Z UKMET THROUGH THURSDAY MORNING. A 00Z GFS/00Z ECMWF COMPROMISE WAS USED THEREAFTER, WITH INPUT RECEIVED FROM NHC REGARDING TROPICAL SYSTEMS AT 17Z. THE 06Z/12Z GFS AND 12Z CANADIAN SOLUTIONS HAD TO BE THROWN OUT BY DEFAULT. THIS LED TO REASONABLE CONTINUITY WITH THE MID-MORNING PRESSURES.

The last NHC track is similar to the UKMET, and for consistency purposes they had to show a track similar to the UKMET. Obviously the GFS and CMC are further east and could not be considered when it came to fronts and pressure.

At least thats what I got out of it.
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1707. barbamz
Quoting weatherconch:
Link

Heres a cool view if you have a big monitor.


True. The most breathtaking one.
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Looking at the satellite presentation this afternoon, Isaac doesn't look as organized as few hours ago??, any comments on this observation?.
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Quoting RetiredPWB:
TWC Mike Seidel is doing remotes from Cuba...That's a first. Very cool IMO.
I agree! If I could go there too... I'm so damn close!
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If Isaac stays on it's current heading it's going to spend very little time over land...
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1703. LargoFl
Quoting stormchaser19:
Isaac on the coast of DR


boy we are going to see alot of that here
Member Since: August 6, 2011 Posts: 4 Comments: 39690
Look at all the convection gathering north of Cuba a sure sign that is where Issac is heading or may even get pulled into at some point over the next 36 hours. Watch this area north of eastern Cuba for Issac to end up there over the next day or so.


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1701. FOREX
Quoting hurricanejunky:


Considering they claim to be using a "ECMWF compromise", I assume they mean a little east of the ECMWF, I wouldn't think New Orleans would be in the cone. A little too far west IMHO. Not trying to claim I know more than the NHC, just making some observations in hopes someone might be able to clarify. Not sure that has happened yet. Thanks anyways though.


I'm trying to look at it this way. Le Bron James is the EURO and Dwayne Wade is the GFS. Both are awesome players. Miami makes the finals and decides that Wade is good enough and they let LeBron sit and rest a few games. That would be stupid. Time will tell I guess.
Member Since: August 17, 2011 Posts: 0 Comments: 2335
Quoting Jedkins01:
The NHC isn't going to swing it's forecast track way east just because the GFS has shifted well east. They are discounting it because they plan to wait and see how additional runs from the model turn out, as well as to see how runs from the other models turn out. The overall consensus has shifted a little further to the east this afternoon, so I expect the NHC to adjust it a bit more east at the 5 PM advisory or maybe by tonight if the trend continues. They do that for a reason, because if they flip flopped their track back and forth all the time that makes them unrealistic and unreliable. But of course contentious individuals never stop to think about that.
We're definitely going to get a lot of weather from this track Jed... should be just the right amount of excitement without causing a lot of damage. The convention will be screwed though which I am ok with. I was getting upset about their preventing protesting bureaucracy anyway
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1699. HarryMc
Quoting emcf30:


That is a very cool tool. A friend of mine text me a bit ago with that link. Loading the 300 frame animation now. Thanks for sharing


I agree. That has to be the neatest loop I've seen in a long time
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and the east trend begins, climatology wants this to ride the east coast of FL, something to still be considered, IMO
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Latest on Recon Info:
994 MB central Pressure
16.9N 71.7W
65 Mph Surface Winds
80 Mph Flight Level Winds
Member Since: October 3, 2010 Posts: 40 Comments: 4129
1696. LargoFl
I would imagine, they would order evacs in all the beachside communities if he comes up the coast huh.....Pinellas County has five evacuation zones:
•A (Red) - Potential surge is 4 to 8 feet.
•B (Orange) - Potential surge is 8 to 14 feet.
•C (Yellow) - Potential surge is 14 to 19 feet.
•D (Green) - Potential surge is 19 to 26 feet.
•E (Purple) - Potential surge is 26 to 29 feet.

If you live in any of the beach communities (along Gulf Boulevard or across the bridges), you are in zone A.
Member Since: August 6, 2011 Posts: 4 Comments: 39690
Quoting nrtiwlnvragn:


Don't know about considerable, they want to avoid the "windshield wiper" affect. I would think a move eastward, at least for South Florida will occur.
At this point, a 75 mile shift is "considerable" in my eyes hahaa. Your point is valid, but there's a difference between avoiding the "windshield wiper" effect and giving people a false sense of complacancy.
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1694. Grothar
Quoting redwagon:

You'd think they could have smoothed that track line out; cyclones don't make 90o turns.


Oh, sometimes they do.
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Quoting GoWVU:


Press thanks for taking the time to answer. I am supposed to go on a trip leaving Wed.


that'd be a good day to get outta town
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Isaac on the coast of DR


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Quoting wunderkidcayman:


that is true but how much of it belongs to us a lot less than an county would have

people just put there money down here and sometimes even we don't know about it

but no I think he ment by Hurricanes yes Grad Cayman is like in the top 5 to get hit by hurricanes (a few times we were ranked as #1) and that is also why quite a bit of storm they and we say coming to Cayman and a good amount of them do end up here



pokin' rib is one thing but constantly pestering me and name calling and total disrespect is another

here too moderate NE winds



last I recalled it was the TVCN that NHC follows


You weather geeks have more acronyms than we had in the army. :)
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Quoting Levi32:
Holy cow! GOES-14 brought out of storage and running 1-min data until October, currently focused on Isaac!

1-min super rapid scan visible loop


Very nice find! Thanks Levi
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1689. GoWVU
Quoting presslord:


well...it's likely to be pretty nasty for us....but not Godawful...


Press thanks for taking the time to answer. I am supposed to go on a trip leaving Wed.
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1688. Grothar
I expect a significant shift to the East with all the models at the next advisory.
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1687. emcf30
Quoting Levi32:
Holy cow! GOES-14 brought out of storage and running 1-min data until October, currently focused on Isaac!

1-min super rapid scan visible loop


That is a very cool tool. A friend of mine text me a bit ago with that link. Loading the 300 frame animation now. Thanks for sharing
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Torrential tropical rain here today in sfl.
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Quoting GoWVU:
I am trying to digest all of the chatter on this blog and watch the weater channel. So it looks like the East Coast/South Carolina should get some rain and not really worry about the real nasty stuff?


well...it's likely to be pretty nasty for us....but not Godawful...
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1684. guygee
Quoting ncstorm:

Floyd..was supposed to hit florida..
No it was not, except in Guv Jebby's mind.
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there is no eye yet...........so why keep saying there is one.
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Quoting jrweatherman:
There is one thing for sure about Isaac. It is NOT going WEST! 305 degree heading is not West.


Where is that west compass when you need it?

BTW based on the distance line projection I did on google earth, Isaac is moving at 16 mph.
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Quoting RTSplayer:


Because about half of those models are crap anyway, and the most reliable model, the Euro, is not on that graphic (for legal reasons,) and it takes the storm much farther west.


Moreover, the consensus output of any one model is not set in stone, that is just the line representing the highest probability calculated by that model's members.

Even the GFS is not one center line. It's lots of members that are all over, though on this particular run the GFS members are closer to it's own consensus than on the two previous runs, still on the previous runs even the GFS had members going far to the west, even outside the cone.



Considering they claim to be using a "ECMWF compromise", I assume they mean a little east of the ECMWF, I wouldn't think New Orleans would be in the cone. A little too far west IMHO. Not trying to claim I know more than the NHC, just making some observations in hopes someone might be able to clarify. Not sure that has happened yet. Thanks anyways though.
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TWC Mike Seidel is doing remotes from Cuba...That's a first. Very cool IMO.
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Hey Levi........Your Tropical Tidbits was excellent as usual. Thank You.
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1678. Grothar
Quoting Levi32:
Holy cow! GOES-14 brought out of storage and running 1-min data until October, currently focused on Isaac!

1-min super rapid scan visible loop


Hey, Levi, with this "unexpected" :) shift. Would you say there is a possibility this could be a much stronger system if it approached the Bahamas and Florida? I know you don't like to guess.
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Quoting hurricanejunky:
None of these models go any further west then the FL/AL border. Not sure why the cone is that far west now...



It's because the EURO is the top ranked model and it is still the farthest west.
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Quoting StormTracker2K:


Miami what is your thinking of the models taking this to southern FL while the NHC is much further south than the guidance? What is the feeling there in MIA? Is the media properly informing people are are they being conservative as the mets in Orlando are?



The news media in MIA has been saying that it "can't hurt" to be prepared and, as they show empty grocery store shelves formerly filled with bottled water, say that it is better to have the water than not just because it is hurricane season. They gently advise us to buy supplies but nothing more than that. They do not say they are being conservative- they say to wait another day or so because what will happen after the storm interacts with Cuba will tell us a lot. They did say we ought to think about filling prescriptions and that if someone has to call their doctor for a refill, they should do it now while there is that extra day or two to play with. Also said to stock up on pet food. All good suggestions for anyone on a vulnerable coast anytime during the season.
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Quoting Bluestorm5:


lots of white in there
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Quoting ProgressivePulse:
Isaac doesn't want to go over those mountains unless he has to. Path of least resistance is through the passage. Interested to see the motion once he gets there.
These systems sometimes have a mind of their own and can create their own mini-environments around a larger environment. Also in terms of landmass the friction usually draws them in.
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1672. CJ5
Quoting ProgressivePulse:
Isaac doesn't want to go over those mountains unless he has to. Path of least resistance is through the passage. Interested to see the motion once he gets there.


Correct. He will begin to slow down, then at the right time start a zig zag motion through the Windward Passage and out into the Atlanatic. That is what I would do If I were him.
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Quoting Joshfsu123:



now that's pretty awesome.


Hope the duct tape holds up for a week or two.
Member Since: May 31, 2007 Posts: 0 Comments: 1204
1670. Seastep
Quoting MiamiHurricanes09:
NHC losing their marbles if there isn't a considerble eastward shift in the forecast cone.


I don't think it would be considerable.

A nudge works and is probably what they'll do.
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img src="http://www.cabaretecool.com:8080/cam_1.jpg?un iq=0.25012637581676245Caribbean getting choppy in the D.R.
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Quoting CaicosRetiredSailor:


not really....

There is a lot more American money in the Caymans....

; )


that is true but how much of it belongs to us a lot less than an county would have

people just put there money down here and sometimes even we don't know about it

but no I think he ment by Hurricanes yes Grad Cayman is like in the top 5 to get hit by hurricanes (a few times we were ranked as #1) and that is also why quite a bit of storm they and we say coming to Cayman and a good amount of them do end up here

Quoting hulakai:
Hey WKC, those folks are just pokin ya in the ribs. Just laugh (like levi) and they will go away. Keep watchin and expressin yer opinion and you'll learn as ya go along.

I'm 60 and been watchin fer a long time and I still learn something in here every day!

Could be one day, like doc and NHC folks will value your opinion over their own.

Meanwhile, wind is freshening here in Broward from NE



pokin' rib is one thing but constantly pestering me and name calling and total disrespect is another

here too moderate NE winds

Quoting CybrTeddy:
The most significant thing about the 18z model run suite (for me) was the fact that the model consensus now is now the TVCA is, like we mentioned, only showing Isaac briefly making landfall with Cuba instead of traversing half the length of the island as the NHC has it doing. The TVCA for those who don't know much about the models, is the mean or average of all the model runs. You will often find that the NHC follows usually pretty close to the TVCA.


last I recalled it was the TVCN that NHC follows
Member Since: June 13, 2009 Posts: 2 Comments: 12180
Latest Euro Ensembles (12z) at the Gulf landfall (120hrs).

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Quoting Grothar:

You'd think they could have smoothed that track line out; cyclones don't make 90o turns.
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nice TWC video where Brian Norcross and Knabb talk inside the NHC Hurricane Hurricane Operations room
check it out here!!!
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Quoting jrweatherman:
There is one thing for sure about Isaac. It is NOT going WEST! 305 degree heading is not West.

True, but 305 has more westward movement than north movement!
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Quoting nrtiwlnvragn:


Don't know about considerable, they want to avoid the "windshield wiper" affect. I would think a move eastward, at least for South Florida will occur.


I think so too.
Member Since: August 24, 2010 Posts: 0 Comments: 249
Quoting jrweatherman:
There is one thing for sure about Isaac. It is NOT going WEST! 305 degree heading is not West.


It is definitely moving NW now..
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1661. GoWVU
I am trying to digest all of the chatter on this blog and watch the weater channel. So it looks like the East Coast/South Carolina should get some rain and not really worry about the real nasty stuff?
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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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