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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Quoting WxGeekVA:

It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans.




will you this STOP WITH THAT its getinng annoying
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1460. JLPR2
Well I'll see you all later! Don't kill yourselves while I'm gone. xD

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Quoting stormpetrol:


Did someone say it was ?


that is what I don't get nobody did

I know I did not say it and you did not either I think he may be crazy or something
Member Since: June 13, 2009 Posts: 2 Comments: 12038
This is the worst case scenario for FL as the NHC again follows the Euro while a storm comes to FL and people get complacent as the local mets say we are in the clear. Very Very bad reasoning here.

NHC will have no choice but to adjust the track to hug the SW FL coast either at 5pm or 11pm.


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Current motion could also be a little deceiving as the convection just wrapped around the center.

Member Since: August 19, 2005 Posts: 5 Comments: 5405
Quoting HCW:
that's pretty good agreement for this far out


Just like Levi said models curving out.
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1455. Bielle
Quoting presslord:
oh, good Lord...the concept of 'right' goes two ways...yes...he has a 'right' to his opinion....and others have a 'right' to mock it...


The important point being, no matter what you may have heard elsewhere, that, while all may be entitled to an opinion (not my view, by the way) not all opinions are equally valuable. Some are even a waste of good air.
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The 12z GFDL solution is reasonable IMO. Clips S FL first:



Then brings it through the Gulf to the panhandle:

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Here's my latest track forecast. Similar to the one I made three days ago for the short term. Midpoints aren't drawn, but I still think South Florida or just west of there over the Keys. From there I expect it to enter the Gulf and then make landfall around the central Florida Panhandle. The track consensus is a little west of there at the moment, although I am pretty inline with the consensus. Anyway, I like the strong consistency among the GFS ensembles and the track shown by the 12z UKMET (especially the curve back to the north, rather than a due NW heading). Canadian likely too far east, while the ECMWF is likely too far west, and also don't think Isaac will continue on that NW heading for so long.

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.
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Interestingly, the AF C-130J in the storm isn't following the standard X flight path. Instead, having crossed northeast-to-southwest, it started back straight east, but is now slowly curving up to the northeast.

To me, it looks as if it's cheating over, trying to squeeze in another center pass in time to feed the data back, to be used in the 5pm update, if an upgrade turns out to be necessary.
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Quoting jrweatherman:
Repeat after me:
It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans.
LOL!!!!! excellent!!!!!!, believe me this bashing of the NHC track has been going on all night long,I was checking at the blog all night from time to time and the same comments over and over!!!!ridiculous!!!!!!.
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Some convection firing on the NW side in the last couple frames over Hispaniola
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Quoting gulfbreeze:
The H/center has it moving N/W looks more like a WNW to me. Could he be bumping the Mtr. Range?



It will move erratically till it makes it to the Atl.
Member Since: August 19, 2005 Posts: 5 Comments: 5405
1445. FOREX
Quoting OBXNCWEATHER:


literally just lmao....



lol. I don't get it.
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Quoting stormpetrol:


Did someone say it was ?


Wunderkid.... need I say more?
Member Since: September 2, 2006 Posts: 110 Comments: 6877
The H/center has it moving N/W looks more like a WNW to me. Could he be bumping the Mtr. Range?
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1442. HCW
that's pretty good agreement for this far out

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Quoting gustavcane:
THE 06Z/12Z GFS AND 12Z CANADIAN SOLUTIONS HAD TO
BE THROWN OUT BY DEFAULT.

That may be why Jim Cantore 
is on the central gulf coast and not in or near florida.



LOL! he'll be there with a slight breeze and sunny skies then as Issac is not going there.

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1439. auburn (Mod)
Quoting presslord:


for many a tent would be a giant step up...for tens of thousands it's more like a filthy bedsheet strung up on some sticks...


Its around 400.000 living like this I believe?
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I think that Cantore showed up on the Gulf Coast means that he is expecting it to hit here...some would say that where he goes the hurricanes do not. Others believe that he is pretty good at going where the cane will land :)

Now, this is a really newb question here - but - if the hurricane has the majority of it's "punch" in the NE quadrant, and it "skirts" the SWFL coast with the eye just to the west, doesnt that mean that the storm will be able to strengthen while riding the coast, thus bring more intense conditions to those areas to the cane's east?

Thanks in advance.
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Not too often you see the UKMET even showing such a large and potent system. Often it is the most conservative of the bunch. Granted, it is only showing a 991 mb cyclone but.. you get the picture.
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Quoting presslord:


that's kind like being "the prettiest girl in Accounting"


literally just lmao....
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wunderkidcayman
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Per Recon-
60-65 Mph TS
995 MB Pressure.
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1433. pottery
Quoting presslord:


that's kind like being "the prettiest girl in Accounting"

LOLOL
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Thought the blog could use a bit of humor (sorry if has been posted before, I have not seen it here)



On a more serious note...to those in the potential path get prepared and be safe. Back to the shadows.
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Here's a fun fact, We did not use Joyce in 2006, therefore, on August 23rd, we surpassed the amount of tropical cyclones produced in 2006. Impressive for a El- Nino year
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Quoting interstatelover7165:
Yay! The first anybody said i was right!


I didn't think Hurricane because of eastern Cuba, but then I looked and I saw why what you said.
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Quoting auburn:


good advice..and be sure you have a WX Radio..


Yes, a weather radio is a must!
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Quoting ncstorm:


they threw out the GFS with Debby too and we all know how that ended..
I have a feeling in the end the GFS will be right, it was right with Debby, Ernesto, and Gordon. So far it has done well this year.
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THE 06Z/12Z GFS AND 12Z CANADIAN SOLUTIONS HAD TO
BE THROWN OUT BY DEFAULT.

That may be why Jim Cantore 
is on the central gulf coast and not in or near florida.

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Quoting MAweatherboy1:

Generally yes, this happens with a lot of storms that get near Hispaniola... The effects vary though, sometimes they are significant and sometimes barely noticeable.


Thanks!
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1425. FOREX
Quoting jrweatherman:
Repeat after me:
It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans.


lmao
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Quoting FOREX:


The two Hurricane experts on TWC just said the center is moving WNW. go figure.


that's kind like being "the prettiest girl in Accounting"
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Quoting WxGeekVA:
Pretty easy to see where the center is on RGB...

i like how well this loop shows outer band vortices, mainly south of Puerto Rico.. it does seem the center is becoming more focused.
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Quoting JasonRE:
When is this thing supposed to break free of the islands and officially enter the GOM? Once it does enter the GOM, would warmer waters and less land have any effect on the path? Lastly, is there ANY chance of this thing still moving West and ending up where the EURO model places it?

Thank you


Per NHC, very early Monday AM.
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Quoting jrweatherman:
Repeat after me:
It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans. It is not going to the Caymans.


Did someone say it was ?
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Quoting ncstorm:


they threw out the GFS with Debby too and we all know how that ended..


This is getting ridiculous already. THe NHC and HPC are going to get burned again. They never learn throw the GFS out when it's been the best performing model!
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Quoting emcf30:


Good luck to both you and Levi.



1980 Alumni here. Loved that school



strengthening storm

The visible seems to show more than other sats are showing but the storm is slowly getting it's act together. I wouldn't be surprised with some interruption due to land but this storm means business. Everyone in it's path need to pay attention to what happens. I live an hour just north east of the landfall on the panhandle so I too am watching it.
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oh, good Lord...the concept of 'right' goes two ways...yes...he has a 'right' to his opinion....and others have a 'right' to mock it...
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1417. FOREX
Quoting JasonRE:
When is this thing supposed to break free of the islands and officially enter the GOM? Once it does enter the GOM, would warmer waters and less land have any effect on the path? Lastly, is there ANY chance of this thing still moving West and ending up where the EURO model places it?

Thank you


The two Hurricane experts on TWC just said the center is moving WNW. go figure.
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1416. JLPR2
With El Nino weaker, the GFS is showing an active start to September, with Kirk, Leslie, Michael and Nadine.



If that does materialize this blog will go haywire, 4 storms at the same time?
Overload... xD
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Quoting gustavcane:
THE 06Z/12Z GFS AND 12Z CANADIAN SOLUTIONS HAD TO
BE THROWN OUT BY DEFAULT.
 

there you have it folks.


nah.

i'll bet the NHC doesn't say that at 5pm when their discussion comes out.

i'll also bet they move the track closer to S. FL.
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1414. auburn (Mod)
Quoting HoustonTxGal:
It boggles my mind that people that are in the cone, or near the cone have to ask if they should get supplies in case it does come their way... WELL DUH!!

anyone that could POTENTIALLY be effected by this storm should prepare. If it hits, you are ready, if it does not hit, you are ready for the next one. For years I have kept what my daughter calls "DOOMSDAY BOXES".

Containers full of items in case of a hurricane. I have been through many storms and have never once been in need of anything. If you wait till the last minute, you will have long ;ines and everything picked over and gone... PREPARE EARLY AND BE AHEAD OF THE GAME.


good advice..and be sure you have a WX Radio..
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Quoting emcf30:


Good luck to both you and Levi.



1980 Alumni here. Loved that school



thank you!
Member Since: August 21, 2008 Posts: 0 Comments: 7451
Quoting MiamiHurricanes09:
The 12z has a hurricane making landfall right over my house in about 2 and a half days...that's interesting lol.



Where are you? Miami Lakes area here.
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Quoting chum8888:


Weather newbie here. With Issac's close proximity to the South Coast of Haiti, would Adiabatic winds coming from the north off the mountains impact the left side of the storm thus inhibiting its ability to organize? Sorry if this is a dumb question.

Generally yes, this happens with a lot of storms that get near Hispaniola... The effects vary though, sometimes they are significant and sometimes barely noticeable.
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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.