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: 1424 - 1374

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 Jedkins01:



Hey, this is a bit off topic, but I thought I'd just let you know, you do a great job here and you have a brilliant mind for meteorology, don't let envious and contentious people bother you...


agreed! 100%
Member Since: Posts: Comments:
Quoting angiest:


Throw in Humberto.


And Lili.
Member Since: Posts: Comments:
Quoting RitaEvac:
Remember everything has cruised the Caribbean this year from east to west. Remember from the beginning of season to now the ridges have been strong and have closed the door on things going north out to sea. Remember there is a reason storms during this time period on this map are going west.....



Yes.
Member Since: Posts: Comments:
Quoting Hurricanes305:


Hey man liked your Video update on Isaac last nite. I having a hard time figuring out where Isaac's LLC and MLC are. However looking at the vorticity it has align itself quite nice but still has work to do on the 500mb and 200mb. Should become better vertically stacked by late tonight.


Thanks. I used to have a blog on this site for many years but I have moved. I try not to talk too much on the main blog here because it can get alittle crazy to say the least at times. I dont know how Levi does it!..LOL If you want you can follow me on Youtube and subscribe to me just in case I dont put it in this blog. I dont always. Just look for weatherguy03 on You Tube.
Member Since: Posts: Comments:
HPC

EASTERN U.S. TROUGH PREFERENCE: 12Z GFS AND/OR 12Z ECMWF
CONFIDENCE: HIGH

VERY EARLY IN THE FORECAST...THE 12Z NAM BEGINS TO MOVE FAR
FORWARD AND TO THE RIGHT OF THE ENSEMBLE TRACK GUIDANCE FOR TS
ISAAC. ADDITIONALLY...THE NAM SHOWS SUBSTANTIAL STRENGTHENING OF
THE CYCLONE ON SATURDAY DESPITE ITS HAVING TRACKED DIRECTLY ACROSS
THE TALL PEAKS OF HISPANIOLA PER THE NAM FORECAST. NOTE THE
OFFICIAL TRACK FROM THE NATIONAL HURRICANE CENTER IS TOWARD THE
LOWER ELEVATIONS OF THE WEST/SOUTHWEST PORTION OF THAT
ISLAND...AND SLOWER THAN THE NAM. THE 12Z GFS AND CANADIAN ARE IN
VERY GOOD AGREEMENT WITH THE OFFICIAL NHC TRACK THROUGH THE SHORT
RANGE/THROUGH EARLY SUNDAY. THE 12Z UKMET IS SIMILAR IN
TRACK...ALTHOUGH IT MOVES THE CYCLONE MORE QUICKLY. THE 12Z ECMWF
TAKES A TRACK THAT IS SIMILAR IN SHAPE...BUT FALLS NOTICEABLY
FARTHER SOUTH AND WEST...MOVING ISAAC ALONG THE SOUTHERN COAST OF
CUBA. THE ECMWF SOLUTION IS WITHIN REASON...DEPENDING ON WHEN THE
CYCLONE BEGINS TO TURN NORTHWESTWARD...BUT THE MAJORITY OF
GUIDANCE IS STILL CLOSER TO THE OFFICIAL NHC TRACK.
Member Since: Posts: Comments:
Quoting Jedkins01:


Yes it does, in fact it has plenty enough tear at tropical system, not quite as high as Haiti, but still.


Excuse me, for some reason I read eastern Cuba on that comment, lol.
Member Since: Posts: Comments:
Quoting opal92nwf:

Texas/Louisiana (Western Gulf) has certainly had their share of storms in the past 5 years.


We haven't had anything of note since '08 (Gustav & Ike), just sayin'..........
Member Since: Posts: Comments:
1416. Chiggy
Quoting RitaEvac:
Remember everything has cruised the Caribbean this year from east to west. Remember from the beginning of season to now the ridges have been strong and have closed the door on things going north out to sea. Remember there is a reason storms during this time period on this map are going west.....


I posted this pic a few times earlier this morning showing rarity of FL strike...
Member Since: Posts: Comments:
Quoting ProgressivePulse:


Been the game all along IMO. The longer it takes to develop the more west it goes. Furthermore, impacts on FL, if any, will most likely not be realized until Isaac moves off the N coast of whatever mountain it's coming down.
Now the case more than ever. We won't have a good clue as to whether it'll impact eastern Florida directly until it emerges off of Haiti; as well as how intense it is when it emerges. Tomorrow night should unlock many answers.
Member Since: Posts: Comments:
Remember everything has cruised the Caribbean this year from east to west. Remember from the beginning of season to now the ridges have been strong and have closed the door on things going north out to sea. Remember there is a reason storms during this time period on this map are going west.....

Member Since: Posts: Comments:
Product: Air Force Vortex Message (URNT12 KNHC)
Transmitted: 23rd day of the month at 18:34Z
Aircraft: Air Force Aircraft (Last 3 digits of the tail number are 300)
Storm Number & Year: 09L in 2012
Storm Name: Isaac (flight in the North Atlantic basin)
Mission Number: 7
Observation Number: 09
A. Time of Center Fix: 23rd day of the month at 17:51:40Z
B. Center Fix Coordinates: 15°39'N 66°26'W (15.65N 66.4333W)
B. Center Fix Location: 193 miles (310 km) to the S (187°) from San Juan, Puerto Rico (USA).
C. Minimum Height at Standard Level: 1,459m (4,787ft) at 850mb
D. Estimated (by SFMR or visually) Maximum Surface Wind: 22kts (~ 25.3mph)
E
Member Since: Posts: Comments:
Quoting hurricanejunky:


Looks like the Bermuda high is forecast to be stronger.


if that were the case joyce would not be forecast to go over bermuda...come on..there is a weakness west of bermuda..almost all models see it
Member Since: Posts: Comments:
1411. scott39
Quoting 1900hurricane:

In places, although it is much less mountainous than Hispaniola.

thanks
Member Since: Posts: Comments:
Quoting Buhdog:
Sure seems to be running NW now.....this is going to be a fun few days...not.




?????????????
Member Since: Posts: Comments:
1409. TXCWC
Quoting Jedkins01:



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.


Excellent post! And pretty much sums up the fundamental issue in my view - THE CORE/INTENSITY ISSUES WITH ISAAC. Dr. M pretty much sumed it up yesterday on his blog - if Isaac does not reach hurricane status by the end of the day the eastern solution becomes much LESS likely.
Member Since: Posts: Comments:
Can we please discuss what's going on with Isaac right now? I want to know more about it. Like... is the storm stronger or weaker than a few hours ago.
Member Since: Posts: Comments:
Quoting scott39:
Does the central and W side of Cuba have mountains?
There are some mountains, but not really tall enough to any harm to a system, I use Charley as an example it held together as it crossed over the Western Tip of Cuba. For the most part it is relatively flat on the central and Western Tip of Cuba.


Member Since: Posts: Comments:
Quoting scott39:
Does the central and W side of Cuba have mountains?


Yes it does, in fact it has plenty enough tear at tropical system, not quite as high as Haiti, but still.
Member Since: Posts: Comments:
1405. wpb
Quoting 1900hurricane:

In places, although it is much less mountainous than Hispaniola.

Member Since: Posts: Comments:
1404. Chiggy
Latest Recon Flight, courtesy of Levi:
Member Since: Posts: Comments:
1403. scott39
Isaac has some work to do, and really dont think its going to do too much before land interaction...for the first time.
Member Since: Posts: Comments:
1402. wpb
the goes satelitte in rapit scan over tropical storm isaac must have a headachk
Member Since: Posts: Comments:
Quoting scott39:
Does the central and W side of Cuba have mountains?

In places, although it is much less mountainous than Hispaniola.

Member Since: Posts: Comments:
Remember everything has cruised the Caribbean this year from east to west. Remember from the beginning of season to now the ridges have been strong and have closed the door on things going north out to sea. Remember there is a reason storms during this time period on this map are going west.....

Member Since: Posts: Comments:
What is the current forward speed now?
Member Since: Posts: Comments:
1398. LargoFl
Member Since: Posts: Comments:
Recon isnt updating... :P
Member Since: Posts: Comments:
1396. Chiggy
CoC roughly at 15N-67.5W - this is just from satellite loops
Member Since: Posts: Comments:
Quoting 1900hurricane:

At this point, it seems highly unlikely. However, at more than five days out, it can't be completely discounted. In three days time, things will be a little more certain.

Was there any discussion today of that monster convective column we were watching 11p last night jump up and pounce on the SW side? 'Alien scud blob' I think was its name at the time.
Member Since: Posts: Comments:
1394. LargoFl
Member Since: Posts: Comments:
1393. scott39
Does the central and W side of Cuba have mountains?
Member Since: Posts: Comments:
Quoting HurrMichaelOrl:


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.


Isaac definitely not living up to the legacy of "I" storms...Ivan...Ike...Irene...Isabelle...
Member Since: Posts: Comments:
Quoting Charliesgirl:
When is recon going in.




there in now
Member Since: Posts: Comments:
Quoting Levi32:
12z GFDL with the east gulf crew now as well.




Hey, this is a bit off topic, but I thought I'd just let you know, you do a great job here and you have a brilliant mind for meteorology, don't let envious and contentious people bother you...
Member Since: Posts: Comments:
Again I think I said this already there is a reason why systems don't strengthen in the Eastern Caribbean and hence the name "Dead Zone."
Member Since: Posts: Comments:
1388. angiest
Quoting aislinnpaps:
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.


Throw in Humberto.
Member Since: Posts: Comments:
Quoting DVG:
My take on the slow speed of strengthening is that the competeing centers that previously existed created gaps in the circulation where dry air has entrained.

IMHO there is one center now. I see two thunderstorms braketing the circulation. One on the west, one on the east side. Over the next hours I think we'll see them extend and connect to create a CDO of the center.



It does appear to be consolidating a little south of NOAA forecast tracks.
Member Since: Posts: Comments:
Quoting stormtopz1:


thats and old map. the new models come out now for a texas/louisianna landfall.


No. Just... no.
Member Since: August 10, 2010 Posts: 2 Comments: 1970
When is recon going in?
Member Since: Posts: Comments:
Quoting MiamiHurricanes09:
Simply put, if Isaac strengthens, south Florida is screwed, if it remains weak, it should be a southern Keys/Florida Straights event.


Been the game all along IMO. The longer it takes to develop the more west it goes. Furthermore, impacts on FL, if any, will most likely not be realized until Isaac moves off the N coast of whatever mountain it's coming down.
Member Since: Posts: Comments:
Recon did find an uncontaminated wind barb of 50mph surface winds. We could see that be the new wind speed for the next advisory package, but a more reasonable speed would be 45mph, which is what recon has been finding a lot of.
Member Since: Posts: Comments:
Quoting weatherguy03:


Ahh, I have to give you grief, its fun!!!..LOL


Hey man liked your Video update on Isaac last nite. I having a hard time figuring out where Isaac's LLC and MLC are. However looking at the vorticity it has align itself quite nice but still has work to do on the 500mb and 200mb. Should become better vertically stacked by late tonight.
Member Since: Posts: Comments:
1381. scott39
Isaacs lack of organization is why the models are trending W. He is taking his time about becoming stacked. I look forward to the show tonight.
Member Since: Posts: Comments:
Quoting Grothar:
Making less sense to me.



Looks like the Bermuda high is forecast to be stronger.
Member Since: Posts: Comments:
My Latest Forecast.
Member Since: Posts: Comments:
1378. LargoFl
Member Since: Posts: Comments:
Quoting cchsweatherman:


Been noticing that all day long. You can see how the lower cloud motion off to the west is diving south and southwest further north than the analyzed center right now.



Yeah, everyone is getting ahead of themselves, we need to focus more on what's happening right now with Isaac before we talk about what's going to happen in the gulf in several days. Isaac is barely a tropical storm right now, and the way it's looking on satellite right now it could weaken to a depression or decouple into an open wave. I'm not saying it will because technically the environment supports at least steady strengthening, but it's doing anything but strengthening. In fact it looks worse right now than ever since it was named. A broad center with light winds is not a good sign if you're expecting an an organized inner core. It's acting more like a warmed cored system with a non-tropical structure right now.
Member Since: Posts: Comments:
1376. Chiggy
Quoting MiamiHurricanes09:
Simply put, if Isaac strengthens, south Florida is screwed, if it remains weak, it should be a southern Keys/Florida Straights event.


Reasonable me thinks...
Member Since: Posts: Comments:
Key west here...ya'll think I should get some groceries in? Any input appreciated,thanks.
Member Since: Posts: Comments:
At this point, I don't see Isaac becoming even a strong tropical storm before Haiti. It's just so... clumsy.
Member Since: Posts: Comments:

Viewing: 1424 - 1374

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 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.