Little change to Isaac, but intensification coming; Joyce forms

By: Dr. Jeff Masters , 3:13 PM GMT on August 23, 2012

Share this Blog
49
+

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

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: 1324 - 1274

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 | 36Blog Index

Quoting mikatnight:
Too bad Tropical Cyclones can't read this blog. If they did, they would surely give up and shoot themselves in the eye!


I wonder what Isaac's take on the ECMWF would be...
Member Since: September 6, 2007 Posts: 0 Comments: 6592
Quoting duajones78413:
With models trending west, is there a chance Isaac could end up in texas?


Yes. Euro showed it coming in TX/LA border.
Member Since: August 24, 2010 Posts: 0 Comments: 245
Quoting Hurricanes101:


It did with Debby

Then it really doesn't make sense that such a reliable model would perform so terribly twice in one year. Debby was its own case though, one of the hardest forecasts of all time. I still have quite a bit of faith in the Euro.
Member Since: Posts: Comments:
1321. hydrus
Quoting Grothar:
Making less sense to me.

And I dont like that. It would be better for Isaac to slam a few mountains, those tracks in my opinion would cause a higher dander threat..Sorry for my short pposts today..bury
Member Since: Posts: Comments:
1320. snotly
On satellite it almost looks like it has two mid level circulations and then on the Puerto Rico radar it looks like the lower level circulation is running out ahead of the convection to the northwest.
Member Since: Posts: Comments:
Quoting MississippiWx:


The center fix was at 15.6N.


That was well over an hour ago at around 1:51 PM EDT. Just been going through the most recent data coming in from the aircraft and it reflects a center further north around 15.9 or 16 N right now.
Member Since: Posts: Comments:
Quoting STXHurricanes2012:
Or the EURO playing like the GFS did against Debby when the GFS was the only one showing FL and the EURO showing TX! Could the other way around this time if the EURO is trying to do! LOL!!


EURO had been from Texas to Florida Panhandle and all points in between. The GFS has remained pretty much set on a track? With minor swings?
Member Since: Posts: Comments:
Quoting reedzone:
EURO is out to lunch this afternoon. A Hurricane cannot slam into a ridge, maybe a banana like ridge, but not the side of a ridge.. Should recurve near Florida. I'm holding off on the REED run until I see better data in the models tonight. Off to work.



It's easy to jump to that conclusion, but you can't forecast where a storm will be when it reaches point:X2 based on the current data now for the starting point:X0. Yes a westerly path right now into the Central gulf may seem like its plowing into a ridge instead of the weakness over Florida, but that's based on initial conditions. The models that bring it west believe the greatest weakness will be over the central gulf by then and ridging over Florida instead. The euro isn't showing it plowing through a ridge, if it was then you could throw it because that would be a major and obvious error. But it's not.


I don't want to be confrontational here, but just because you expected this storm to move into Florida doesn't mean it will, I know you know that's true, but sometimes you need to get back to the basics in order to have balanced perspective. The fact is Isaac has about the same change of hitting the Central gulf coast right now as hitting Florida/eastern gulf. Yes there really is that much uncertainty, and the recent model shifts prove that all the more.


However, the proof of why in reality is based on the intensity of Isaac. We don't even know if Issac will even survive right now, yet an eastern gulf landfall is entirely dependent on it reaching hurricane strength or at least a strong tropical storm by the time it impacts the islands. If Isaac stays weak it will continue to go further west because that is how tropical cyclones work. A shallower tropical cyclone will travel farther west, a deeper one will feel the pull to turn north more. That is the biggest variable alone. I don't know about you but I don't have the greatest confidence in Isaac intensifying. The mid level center is continuing to slide southwest and Issac is continuing to become more disorganized regardless of how favorable conditions are for it to strengthen.


Yes I too am very confused as to why Issac isn't organizing as all conventional understanding of meteorology tells you Isaac should at least be steadily strengthening by now if not quickly. However, the fact is, it's not. If Issac stays weak, the eastern gulf path will become the less likely scenario because a weaker storm will be much less likely to turn north into the eastern gulf. However if Issac does finally strengthen, and becomes a hurricane in the Caribbean, it will likely turn northwest, and I would expect models to shift back east. Models or computer systems and the output is attempting to find the most logical solution. Well a weaker storm that has been jogging wsw repeatedly will cause the models to respond west.

You might think they are "out to lunch" but examine the situation further and you'll find it makes more sense as to why they have.
Member Since: Posts: Comments:
Quoting MAweatherboy1:
Right now, the Euro lies well to the west of model consensus. However, the models are consistently shifting slightly to the west each cycle, so its possible they're slowly catching on to something the Euro has seen all along. It just doesn't make sense that such a reliable model would perform so terribly. I still think its a bit too far west, but don't be surprised to see models keep trending that way.


It did with Debby
Member Since: March 10, 2010 Posts: 1 Comments: 7816
AtHome,
You're only about an hour or so from me, so I'll include your area in my ten year Hiatus from hurricanes. Rita, Ike and Gustav were enough.
Member Since: Posts: Comments:
I think you are right. trough is not that weak and high will not be that strong.
Quoting STXHurricanes2012:
Don't think its breaking through a ridge I think the EURO has it right but I don't think the ridge is going to be that strong!
Member Since: Posts: Comments:
1313. wpb
nogaps 12z not much change
Member Since: Posts: Comments:
Right now, the Euro lies well to the west of model consensus. However, the models are consistently shifting slightly to the west each cycle, so its possible they're slowly catching on to something the Euro has seen all along. It just doesn't make sense that such a reliable model would perform so terribly. I still think its a bit too far west, but don't be surprised to see models keep trending that way.
Member Since: Posts: Comments:
Quoting nofailsafe:



A whole lotta "NOPE!"


Amen
Member Since: August 24, 2010 Posts: 0 Comments: 245
Getting tired of scanning over posts about Euro, pro or con

What ev's..

thx
Member Since: Posts: Comments:
Another storm, another round of dry air issues...

Member Since: August 2, 2006 Posts: 46 Comments: 11668
1308. TXCWC
Model tracks CONSENSUS starting to point nearly out of Florida now - a couple of ensembles verrrry far west as well -can't get the Gulf Stream up fast enough for me to get this track set.



Link
Member Since: Posts: Comments:
Too bad Tropical Cyclones can't read this blog. If they did, they would surely give up and shoot themselves in the eye!
Member Since: Posts: Comments:
Quoting Kowaliga:
Nice pull to the N....he roundin' the bend?



that spin that you see there S of PR just N of where tha box that says Flash Flood near 16.3N 66.4W is not the LLCOC according to recon that so far says it is SW of that location

RECON is making another pass
Member Since: Posts: Comments:
Quoting scott39:
I think its pretty obvious by now that the all of the models have been following the EURO for a few days. Its also obvious that the models are not calling for strong a hurricane until it gets in the GOM. This would make Isaac move more W and in line with the trending models to the West. I think its a far reach to think that Isaac will hit the East Coast of Fl. IMHO


Nothing is OBVIOUS at this point
Member Since: March 10, 2010 Posts: 1 Comments: 7816
Quoting StormTracker2K:
What the hell is wrong withe Euro. I mean really from one of the best performing models to one of the worst in one year.



Maybe it has some indegestion?
Member Since: Posts: Comments:
Quoting cchsweatherman:
Very interesting to note a whole batch of winds from the SE at 16.5 N and winds from the S at 16.1 N. Shows that the center is indeed right around 16 N and has been continuing to move towards the WNW throughout the day. Not sure where people continue to get this westward or even WSW motion from as the storm has been gradually gaining more latitude all day long.


The center fix was at 15.6N.
Member Since: July 15, 2006 Posts: 17 Comments: 10282
With models trending west, is there a chance Isaac could end up in texas?
Member Since: Posts: Comments:
1301. scott39
I think its pretty obvious by now that the all of the models have been following the EURO for a few days. Its also obvious that the models are not calling for a strong hurricane until it gets in the GOM. This would make Isaac move more W and in line with the trending models to the West. I think its a far reach to think that Isaac will hit the East Coast of Fl. IMHO
Member Since: Posts: Comments:
I don't think anyone can rule anyone's forecast right or wrong at this point. After the storm, we'll know who was right and who was wrong period.
Member Since: Posts: Comments:
1299. HrDelta
Quoting SouthTXWX:
Could we be talking about possibly tomorrow, about if the new Levees in New Orleans would be able to hold off a possible Cat 2-3 Isaac barreling down its throat?  Seems like anything is possible now.


With the new levee system? I think it very well can.

In fact, with the hardening of Miami after Andrew, and the fortification of New Orleans after Katrina, I think only New York City remains of original vulnerable three without protection.

Tampa, Norfolk/Virginia Beach, and Houston metro replace those two.
Member Since: Posts: Comments:
Quoting Saltydogbwi1:
passing very close to this buoy



Wow, when you observe those 25 mph sustained winds, you know a serious storm is moving through . This storm has taken its sweet time getting its act together. Starting to remind me of Ernesto '06, though Ernesto was a strong tropical storm by Isaac's current longitude.
Member Since: Posts: Comments:
Quoting LargoFl:
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

I lived in Palm Harbor and St Pete for 15 years, I remember watching Dennis Phillips on abc as Charlie moved up the coast and seeing it turn, and Phillips almost yelling on the air that it was turning. And I sat there and went WHEWWWWWWWWWWWWWWWWWW!!!!

That was scary stuff.


This is the problem with ppl watching the center and not the cone. The ppl in Punta Gorda thought that the storm was going to Tampa. Most thought Charlie was going to Tampa. When the actual turn took place the majority of the ppl in the direct path of the storm were prepared for a direct impact from a hurricane.
Member Since: Posts: Comments:
1296. Grothar
Making less sense to me.

Member Since: Posts: Comments:
Tembin has made landfall on Taiwan:

Member Since: Posts: Comments:
Quoting moonlightcowboy:



Good spot, thanks. What's the coordinates of the exposed llc?


In the vicinity of 16N 42W.
Member Since: July 15, 2006 Posts: 17 Comments: 10282
Quoting MississippiWx:
Joyce is actually pretty disorganized with the low center exposed to the SE of the convection.



so that means it'll go WEST
Member Since: Posts: Comments:
Can one of you guys tell me how close to landfall do you think all the models will come into agreement?
Member Since: Posts: Comments:
nice blowup over llc
Member Since: July 21, 2010 Posts: 0 Comments: 1176
Very interesting to note a whole batch of winds from the SE at 16.5 N and winds from the S at 16.1 N. Shows that the center is indeed right around 16 N and has been continuing to move towards the WNW throughout the day. Not sure where people continue to get this westward or even WSW motion from as the storm has been gradually gaining more latitude all day long.
Member Since: Posts: Comments:
Quoting MississippiWx:
Joyce is actually pretty disorganized with the low center exposed to the SE of the convection.




Good spot, thanks. What's the coordinates of the exposed llc, or whichever vortice this is?
Member Since: Posts: Comments:
1287. JLPR2
Quoting HurricaneHunterJoe:
It's so funny how some people dwell on the negative aspects of the storms structure and then the folks who point out all the positive stuff.


Mix it up and you get a pretty balanced opinion. xD
Member Since: Posts: Comments:
The NHC puts a lot of stock in the euro model. There is no doubt in my mind they will continue to shift their track even more west, possibly somewhere between MS and AL with the 5pm update. If Isaac ever decides to strengthen to even a 50+ TS, maybe the models will shift back east a bit. Right now, he's so weak that he is being pushed by lower level steering currents and won't feel the weakness enough for a NW movement.
Member Since: Posts: Comments:
How do you like the Euro?

Texas/Louisiana border.

Obviously the Euro doesn't believe in the NHC forecast cone, nor it's alleged center fix.
Member Since: Posts: Comments:
Quoting AtHomeInTX:


A lot Rita-ish



A whole lotta "NOPE!"
Member Since: Posts: Comments:
1283. icmoore
Quoting presslord:
These missions can improve model forecasts by 10 - 20%, so the model runs that will be available early Friday morning should have increased reliability.

Uh Mr. Press would that be early as in 2am, 5am, or 8am? :)
Member Since: Posts: Comments:
My forecast, NOT OFFICIAL
Member Since: Posts: Comments:
I know people are anxiously anticipating model runs with the data from the gulf stream included. It should also be noted that the NWS has begun 6 hourly radiosonde launches to better sample the environnment over the CONUS, so that information will also be extremely helpful for the models.
Member Since: Posts: Comments:
Joyce is actually pretty disorganized with the low center exposed to the SE of the convection.

Member Since: July 15, 2006 Posts: 17 Comments: 10282
1279. GetReal
Quoting MrNatural:
While everyone is wondering about the next computer runs, I am curious how much longer TS Isaac must go on its' westerly track before it becomes more of a GOM storm instead of a Florida storm.



More and more likely with each passing hour on a westerly track.
Member Since: July 4, 2005 Posts: 204 Comments: 8896
1278. Chiggy
12Z UKMET moving NW just east of NOLA..

Member Since: June 26, 2012 Posts: 0 Comments: 297
1277. K8eCane
Quoting gordydunnot:
I think there is model manipulation going on here. BP is trying to get their 20 billion back on model manipulation.I want an investigation I tell ya.


I have actually thought about that! Meanwhile IMHO...This whole blog is a HOOTENANNY!
Member Since: Posts: Comments:
Quoting MississippiWx:


We will all wait in enthusiastic anticipation.


LOL I just spit out my drink
Member Since: Posts: Comments:
Quoting AtHomeInTX:


A lot Rita-ish


No Gustav..please no! Lol! I'm remembering the weeks without electricity now..ahh memories
Member Since: Posts: Comments:

Quoting louisianaweatherguy:
WOW.... A MAJOR model shift to the west... come on guys after that LONNGGGG WSW jog we should have expected that.... If Isaac starts more NW I believe they'll shift back to the east... I HOPE LOL
The jog or center reformation had nothing to do with the EURO shift, since the 48 hour forecast is pretty much the same as before and in line with most/all of the other models. 
Member Since: Posts: Comments:

Viewing: 1324 - 1274

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 | 36Blog Index

Top of Page

About

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

Local Weather

Mostly Cloudy
67 °F
Mostly Cloudy