Little change to Isaac, but intensification coming; Joyce forms

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

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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

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Quoting WDEmobmet:


Well I kind of understood that, and I think you answered me in the last of your comment, but I was more wondering why it would fly almost due north of the system trailing somewhat behind it in Longitude. I would think that it would sample air out ahead of its projected path as well. Thanks jeffs713


No problem. It flies well north of it, as the area in front of the storm isn't influencing the direction much. Tropical cyclones want to go poleward by nature. The only thing preventing Isaac from going poleward right now is the strength and extent of the ridge.
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Its probably about time for Isaac to drop his CDO and have another weak period of reorganization along with the next search for the center of circulation.
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Not sure what the discussion about Levi is. But the reality is that all mets in Puerto Rico have mentioned that this storm has been very difficult to forecast, so we can't say that Levi was wrong, so and so was right. It's just been an erratic storm.I will continue to read his very informative analysis.
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Quoting MississippiWx:
GFS has shifted way west, in line with 00z Euro.



I wonder what the ensemble spread is this time.
Member Since: August 26, 2006 Posts: 16 Comments: 4766
Quoting MississippiWx:
GFS has shifted way west, in line with 00z Euro.



Yuk. I don't like where that red blotch sits at 132 hours. Really don't like.
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319. CJ5
Yea, it is a little shift west. Not really surprising. Like I said earlier, the models will get more consistent as time goes by and more data and observations are known. I think Isaac is looking pretty good and should continue to get better as the days move on. The big test will be when a turn begins and what trajectory he takes over the land masses ahead. If he avoids the higher mountains he could emerge into the gulf well organized.

I too wish people would stop the darn bashing. But as mentioned, if you are going to put yourself out there you better have think skin. Heck, look how much bashing the NHC takes.
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Quoting lowerbamagirl:
Thanks Weathermanwannabe! Not panicing or try to panic others, just want to be prepared. I lost my house to the bank this year (like many other Americans), so am living in a doublewide about four miles from the gulf on the AL/FL line. For some reason, I thought shear could be predicted further out than that, and kept wondering why it wasn't being mentioned. Now I understand better.


You need to pay close attention to NHC and your local authorities for their direction...........Stay Safe.
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Stronger storm will move more north into the weakness...
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Okay, so what about the ventilation provided by the ULL that was in an earlier comment?
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Quoting Chiggy:
12Z GFS @ 126hrs, approaching AL/FL border.. WOW!
i must caution that even though it has shifted to the west these models have been shifting back and forth but generally has maintained consistency in a cross over the florida keys into the eastern gulf , so for us either way south florida will get alot of bad weather
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Quoting Relix:
Look for the center game!

http://www.ssd.noaa.gov/PS/TROP/floaters/09L/flas h-swir-long.html

16 65.5?

nah
I'll say 15N or maybe just below

Quoting moonlightcowboy:
COC may even be actually just south of 15n, but then again my vision isn't all that good anyways. ;P


yes I think you are right

Quoting Chiggy:

NOPE, 66W - 15(ish)N


yep or maybe abit S of 15N

Member Since: June 13, 2009 Posts: 2 Comments: 12716
HR 144 FINAL

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Quoting reedzone:


Actually I have the storm WEST of me.. Nice call on the wishcasting though, I'm going by steering pattern.
Just poking at ya, buddy. Don't take it too harshly. :)
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Quoting MississippiWx:
GFS has shifted way west, in line with 00z Euro.



It doesn't make sense to me when the weakness on the steering layers map show a turn NE if the storm gets near Tampas latitude. Not ENE to my house, but NE towards GA.
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Quoting angiest:


Where is the radar station? The worst weather appears to be on the opposite side of the storm from where it would be expected.


Not sure where the radar is located. The weather station I am quoting is on the small Island in the southern section of the eyewall.
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Thanks Weathermanwannabe! Not panicing or try to panic others, just want to be prepared. I lost my house to the bank this year (like many other Americans), so am living in a doublewide about four miles from the gulf on the AL/FL line. For some reason, I thought shear could be predicted further out than that, and kept wondering why it wasn't being mentioned. Now I understand better.
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Intensity forecasts are not reliable this far out, and
track forecasts are also unreliable at days 4-5, so
picking a landfall spot at this time is impossible.
Be careful what you post as there are alot of lurkers
here that may get unnecessarily unnerved. For them
I advise using this blog as a secondary source of information after Local Wx Offices and the NHC....
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Quoting MississippiWx:
GFS has shifted way west, in line with 00z Euro.

the trend is even farther west... i wonder how the models will behave when the HH give them the new data later today
Member Since: July 25, 2011 Posts: 0 Comments: 1102
Quoting lowerbamagirl:


Then that begs the question what is the sheer prediction over the next 48-96 hours in the gulf? I have searched through the last 7 or 8 pages and no one seems to be mentioning it.


The Doc said shear would be low for the next 5 days meaning it would be low when it entered the 88-90 degree water in the GOM.
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Quoting MississippiWx:
GFS has shifted way west, in line with 00z Euro.

And almost right down the euro ens mean from the Monday timeframe.
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PalmBeach: Regarding LEVI I find his posts informative, but if his forecasts for past 3 days is wrong, he is subject to critcism. Nothing personal,just a fact.Also,I still rank LEVI and KMAN as the best bloggers on this blog.
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I hope Isaac doesn't pull a Felix on us.
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300. MahFL
Quoting WDEmobmet:


Someone would really have to explain to me the reasoning behind such a planned course. Makes ZERO since to me


To check the strength of the ridge, if it's weaker the storm might go more north, if stronger, west....
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Quoting MTWX:


But his large size all in itself could impede intensification....


Could be as well.............Unfortunately, we do not know exactly what will happen intensity wise once he makes the Gulf (or not if he trends over Florida). Nervewracking when they approach the US from this angle and we try to figure which side of Florida, or, up the middle..........We will have to leave that to the NHC 3-day track come the weekend and see what happens.
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Quoting AussieStorm:
Tembin is plunging the pressure pretty quickly...
Observations>Current>East>Lanyu
08/23 23:00 988.5mb >>>> 08/23 23:45 981.2mb

Lanyu is currently in the Southern section of the eyewall. That little island off the SE Coast.



In fact the weather station at Lanyu, Orchid Island, Taiwan has stopped reporting. I suspect it's either lost power or it's been damaged.


Orchid Island (Yami language: Ponso no Tao or Pongso no Tao; Chinese: 蘭嶼; pinyin: Lán Yǔ; Pe̍h-ōe-jī: Lân-sū) is a 45 km² volcanic island off the southeastern coast of Taiwan Island and separated from the Batanes of the Philippines by the Bashi Channel of the Luzon Strait. It is governed as Lanyu Township of Taitung County.

The island is home to the Tao, an ethnic minority group who migrated to the island from the Batan Archipelago 800 years ago. The island is known to them as Ponso no Tao or Pongso no Tawo (island of the people) or Irala. Out of a total current population of 4,000, approximately 2,400 belong to the aboriginal Tao community and the remaining 1,600 are mainly Han Chinese. In neighboring Philippines the island is referred to as Botel Tobago.

The Lanyu nuclear waste storage facility was built in 1982. The plant receives nuclear waste from Taiwan's three nuclear power plants operated by state utility Taiwan Power Company (Taipower). About 100,000 barrels of nuclear waste from the nation’s three operational nuclear power plants have been stored at the Lanyu complex.[1] In 2002 and 2012, there were major protests from local residents, calling on Taipower to remove the nuclear waste from the island.[2]


Hmmmmmm....A nuclear dump and a major hurricane....
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Quoting 1900hurricane:

I suspect you are right. That is one nasty looking eyewall there. They should probably be getting the worst that they're going to get right now.

It just updated....

08/23 23:00 988.5mb >>>> 08/24 00:00 978.8mb 9.7mb drop in 1hr.

WOW!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
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Quoting seminolesfan:





Now I totally know why you call them the Reed runs!


Actually I have the storm WEST of me.. Nice call on the wishcasting though, I'm going by steering pattern.
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GFS has shifted way west, in line with 00z Euro.

Member Since: July 15, 2006 Posts: 17 Comments: 10284
294. wxmod
Tembin last night and population overlay. MODIS
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Quoting guygee:
Thanks for the correction SJ, my source was one run behind. Old news I guess.


No worries. Now if we could just fast forward to the 00z run with the G-IV data in them, I think we would all feel a little more confident.
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Quoting Chiggy:
12Z GFS @ 114 hrs the most Western of its run so far..


I really wanna see that shift left or right.

My house is smack dab in the bulls eye of the latest GFS ensemble. The good news is, this far out, Isaac probably will end up east or west of current predictions.
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Quoting AussieStorm:
Tembin is plunging the pressure pretty quickly...

Observations>Current>East>Lanyu

08/23 23:00 988.5mb >>>> 08/23 23:45 981.2mb

Lanyu is currently in the Southern section of the eyewall. That little island off the SE Coast.



In fact the weather station at Lanyu, Orchid Island, Taiwan has stopped reporting. I suspect it's either lost power or it's been damaged.


Where is the radar station? The worst weather appears to be on the opposite side of the storm from where it would be expected.
Member Since: August 26, 2006 Posts: 16 Comments: 4766
Quoting Relix:
Look for the center game!

http://www.ssd.noaa.gov/PS/TROP/floaters/09L/flas h-swir-long.html

16 65.5?

NOPE, 66W - 15(ish)N
Member Since: June 26, 2012 Posts: 0 Comments: 297
Quoting AussieStorm:
Tembin is plunging the pressure pretty quickly...
Observations>Current>East>Lanyu
08/23 23:00 988.5mb >>>> 08/23 23:45 981.2mb

Lanyu is currently in the Southern section of the eyewall. That little island off the SE Coast.



In fact the weather station at Lanyu, Orchid Island, Taiwan has stopped reporting. I suspect it's either lost power or it's been damaged.

I suspect you are right. That is one nasty looking eyewall there. They should probably be getting the worst that they're going to get right now.
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Quoting Chicklit:


There's always the 'crow' remarks on here when somebody misses a track. It's a tradition. Anyway, I look forward to more of his videos and hope that all the attention he's getting on here doesn't stop him from doing that.


If you are planning on being a professional Meteorologist, take the time to develop a thick skin. I know from experience...you will need it :)
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Quoting seminolesfan:
He probably thinks it will hit him from the west coast now. lol


Quoting seminolesfan:
Hmmm, *draws line from Tampa to NC/SC border*...

Yup, right over his house from the west coast...

LOL!



Now I totally know why you call them the Reed runs!
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In this run, it can be said that the GFS is coming into agreement with Eruo, for a change. Good for FL, bad for elsewhere.
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Quoting floridaboy14:
GFS significant shift to the west


compared to the 06Z yes, but still within the range it has been the last few days
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Quoting StormJunkie:


That's the 06z, 12z is actually left of that possible solution. ...
Thanks for the correction SJ, my source was one run behind. Old news I guess.
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Storm tracks change several times when its very far out which is why I put more faith in tracks that are about 5 days out and even that could change.
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Quoting lowerbamagirl:


Then that begs the question what is the sheer prediction over the next 48-96 hours in the gulf? I have searched through the last 7 or 8 pages and no one seems to be mentioning it.


Too early to tell what it will be that far out. The current chart (below) out to about 48 hours has it increasing out to about 5 knots but impossible to know that will be the case in 96 hours and not a factor if he develops an anti-cyclone.

Link

My comments related to possible intensification in the Gulf are not meant to panic anyone. NHC is the Official source but intensity issues are tough to nail down and Gulf storms can ramp up very quickly as we know if conditions gell at the right time.

Remember the rule of thumb; if the forecast is for a Cat 1, you should prepare for a Cat 2 and so on...
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280. MTWX
Quoting weathermanwannabe:
201. lowerbamagirl 11:57 AM EDT on August 23, 2012

If sheer is low when he emerges off of Cuba into the SE Gulf, and he regains hurricane strength near or after passing the Florida Keys, there should be no major impediment to intensification beyond Cat 1. He is so large, that he would probably continue to feed moisture in from the Gulf and Atlantic so land interaction may not be as huge of an issue until landfall somewhere along the Gulf Coast.


But his large size all in itself could impede intensification....
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COC may even be actually just south of 15n, but then again my vision isn't all that good anyways. ;P
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GFS significant shift to the west
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finally getting decent rain / wind bands in puerto rico! NICE! whoo-hooo!! :))))))

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

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