Isaac is strengthening

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

Share this Blog
51
+

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

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: 811 - 761

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 | 36 | 37Blog Index

Hippo-thetically, if it's shifting to the east, would Mobile AL be affected?
Member Since: Posts: Comments:
Finally. Got Google Earth to work...
Member Since: October 3, 2010 Posts: 40 Comments: 4129
Interested to see what recon finds, one could say the center is just off the coast of DR ATM.
Member Since: August 19, 2005 Posts: 5 Comments: 4863
Quoting JasonRE:


When is he projected to be off of the islands and begin meandering into the GOM? Thanks for the heads-up JBird


Looks like Sunday night per:
http://icons-ak.wunderground.com/data/images/at20 1209_5day.gif
Member Since: Posts: Comments:
Quoting CybrTeddy:


I can already tell you the main problem it would have.

12z GFS continues 5 days out from where he posted that...
Brings "Kirk" out to sea as it clips PR. and DR. Makes it a Hurricane.

12z GFS also shows Leslie, and Michael by September 9th.
Member Since: October 3, 2010 Posts: 40 Comments: 4129
806. ARiot
gut feeling, going with ECMWF on this one, yeah, yeah, I know.

just a gut feeling this time. can't explain it :-)
Member Since: Posts: Comments:
805. wpb
recon on the way
Member Since: May 28, 2011 Posts: 0 Comments: 572
Why on Earth would anyone repost someone using bad language?!?!?!?! It just confounds me...
Member Since: Posts: Comments:
Quoting FOREX:


With the highest respect for this blog, I won't even respond to that. Have a great day though.


I rather like to visit chocolate-munching pike-bearing banker country. However..Levi seems to like the CMC 12Z. the Euro will be interesting.
Member Since: Posts: Comments:
Quoting CybrTeddy:


I can already tell you the main problem it would have.


Not good instability in the central atlntic and in the carribean
Member Since: Posts: Comments:
Big shift east on the 12Z HWRF.

Member Since: Posts: Comments:
Quoting CaicosRetiredSailor:



13:50 GMT


hmm pretty much online with 16.3N and elongated W-E

still waiting for RECON to get in
Member Since: Posts: Comments:
Link

If you look at last few frames, appears storm may be working storms into its COC?
Member Since: October 5, 2007 Posts: 0 Comments: 64
Quoting GTcooliebai:
SHIPS and HWRF bring Isaac up to Cat. 2:



Big shift in the SHIPS. It wasn't forecasting more than a strong TS for the last couple of days.
Member Since: Posts: Comments:
Quoting scott39:
I will be back. Im going to the store to stock up on humble pie.


Bottom shelf of the freezer, last door on the left. (I know because I eat a lot of it.)
Member Since: Posts: Comments:
HwRF has shifted considerably to the EAST now. Models consensus is for a FL west coast rider now.

Member Since: Posts: Comments:
Yeah, no more politics! ..... Let's talk religion! :)
Member Since: Posts: Comments:
SHIPS and HWRF bring Isaac up to Cat. 2:

Member Since: August 31, 2009 Posts: 0 Comments: 5628
Get in the Nuke Shelters! It's a tropical riot!
Member Since: Posts: Comments:
I will be back. Im going to the store to stock up on humble pie.
Member Since: Posts: Comments:
Quoting BahaHurican:
Ya'll do realize the Haitians BEAT the French, right? I don't think the French [or most of the rest of Europe, FWIW] ever forgave the upstarts.

BTW, Haiti's recent troubles are related to a political system where dictators and their cronies were able to keep the masses poor. No large middle class there, and international companies were comfortable taking advantage of the extremely low wage policies allowed there. The basic result: no development of infrastructure; no mass education; poor health care. And can anybody understand how difficult keep trees on hillsides are there when both economic conditions and "custom" has made cutting down of trees for burning the "national" standard?

I've really oversimplified the the situation in a lot of ways, but it does at least give an idea of the challenges they face.


A good post.
Member Since: Posts: Comments:
the answer to that is yes RECON is flying
Member Since: Posts: Comments:
Quoting wunderkidcayman:
is RECON in the air yet
yes
Member Since: Posts: Comments:
Quoting CaicosRetiredSailor:



13:50 GMT


Yep, he's intensifying.

I don't know strength, but I would think that this will parallel the west coast of the Florida Peninsula.

Isn't Tampa especially vulnerable to Storm Surge because of the bay? That a weaker storm will cause higher storm surge there than it would elsewhere?
Member Since: Posts: Comments:
Quoting stormchaser19:
GFS showing isaac part 2?


I can already tell you the main problem it would have.
Member Since: Posts: Comments:
Quoting WxGeekVA:
Going to make a new forecast... After the 12Z Euro comes out!


When will this be?

Thanks
Member Since: Posts: Comments:
HWRF seems determined to recreate Katrina
Member Since: Posts: Comments:
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.


RFID is a really, really BAD idea at this stage of the technology, it is far too easily hacked.

RFID

That being said, it has nothing to do with TS Isaac, which I hope makes landfall as a weak tropical storm and brings rain to the areas which desperately need it.
Member Since: Posts: Comments:
Quoting Levi32:
Good afternoon.

Blog update:

Tropical Tidbit for Friday, August 24th, with Video


Thanks you inadvertly answered my question about the high in the GOM central and potential landfall in MS.
With your prediction/assesment I can expect piling of water not too high and some wind.
Member Since: Posts: Comments:
Until it fires convection OVER the center and works out the dry air, Isaac won't strengthen anymore (may weaken a little bit).

Expect some slight organization tonight before it makes landfall in Haiti. But again, needs a CDO over the center if possible.
Member Since: Posts: Comments:
2pm advisory should be out in 30min
Member Since: July 14, 2009 Posts: 0 Comments: 2990
Quoting Bluestorm5:
Note to myself: DO NOT EVER POST A SINGLE SENTENCE OF POLITICS AGAIN...

Anyway, Recon is in the air.


Good plan, especially if you are going attack my countries generosity. Not to mention this is a weather blog ;)
Member Since: Posts: Comments:
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.


It will be close.
Member Since: Posts: Comments:
Quoting SouthTXWX:


I read the cold water riptide is from Nova Scotia, source?


The waters of our coast are way higher than average. 22C onshore, 120miles offshore, we're looking at 27C!
Member Since: Posts: Comments:
Quoting wunderkidcayman:
is RECON in the air yet
yeap
Member Since: July 14, 2009 Posts: 0 Comments: 2990
Quoting tramp96:


The United States may not be perfect but we are generous
and caring. The main reason we can be is because of free enterprise
AMEN!!!
Member Since: Posts: Comments:
is RECON in the air yet
Member Since: Posts: Comments:



13:50 GMT
Member Since: Posts: Comments:
Going to make a new forecast... After the 12Z Euro comes out!
Member Since: Posts: Comments:
bad.time.to.come.to.florida...bring.a.poncho
Member Since: September 11, 2010 Posts: 0 Comments: 4018
Quoting rattnroll:
I am a hardocre conservative and I wont even talk politics, its Isaac time!!!! oh, and football time, but Isaac first


me 2!
Member Since: Posts: Comments:
GFS showing isaac part 2?
Member Since: Posts: Comments:
Quoting Hurrihistory:
Sunday evening into Monday afternoon the lower Florida Keys could get blasted with 60 to 80 MPH wind gusts. Folks living in that area should get prepared now!
Not to down play 60 - 80 mph winds, we get squalls that come through at that speed. Our experience with hurricanes is long and we have built our homes to withstand quite a lot. And we have been getting ready since yesterday. Blasting winds are more at 125mph on up. And yes, I have experienced them.
Member Since: Posts: Comments:
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.


Do you honestly not see the problem here? No network is safe from hacking, and solar flares would literally cause money to disappear.

Come to think of it, I can't remember you talking about weather that much. Your ideas there are completely loony.

Back to Isaac. It appears to have gotten its organization together (mostly). So, doesn't that mean strengthening has a green light?
Member Since: Posts: Comments:
Quoting GeoffreyWPB:
Levi...are you trying to start a riot in here????



It's my goal in life, you know?
Member Since: November 24, 2005 Posts: 628 Comments: 26455
Note to myself: DO NOT EVER POST A SINGLE SENTENCE OF POLITICS AGAIN...

Anyway, Recon is in the air.
Member Since: Posts: Comments:
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: Posts: Comments:

Viewing: 811 - 761

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 | 36 | 37Blog Index

Top of Page

About JeffMasters

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